ZSM-5 type zeolites: Synthesis and use in gasphase reactions with ammonia

F.J. van der Gaag

ZSM-5 type zeolites: Synthesis and use in gasphase reactions with ammonia

ZSM-5"type zeolites: Synthesis and use in gasphase reactions with ammonia

Proefschrift

ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus, prof.dr. J.M. Dirken, in het openbaar te verdedigen ten overstaan van een commissie door het College van Dekanen daartoe aangewezen, op 14 december 1987 te 16.00 uur, door

Frederik Jan van der Gaag,

geboren te Delft scheikundig ingenieur,

TR diss ï 1595

Dit proefschrift is goedgekeurd door de promotor: prof.dr.ir. H. van Bekkum.

STELLINGEN

1. Thermische degradatie van polyvinylchloride (PVC) wordt tegengegaan door toevoegen van metaalzepen (bv. Ca-, Ba-, of Zn-stearaat). Gezien het werkingsmechanisme lijkt de benaming stabilisator voor verbetering vatbaar.

2. Het refereren naar artikelen door het overnemen van referenties zonder de literatuur zelf te lezen kan de nodige gevaren opleveren en ook tot kettingeffecten aanleiding geven. Zo leidt een klein verschil in paginanummers ertoe dat de MeAPO-molekulaire zeven niet als een recente vinding, doch als één van de oudst beschreven zeolieten gezien zouden moeten worden.

D.W. Breek, "Zeolite Molecular Sieves, structure, chemistry and use", J. Wiley & Sons, New York 1974, p. 27. A. Damour, Ann. Mines, 17, (1840), 191. A. Damour, Ann. Mines, 17, (1840), 202.

3. Het door Ohrui en medewerkers gegeven mechanisme voor de werking van galactose-oxidase is aan bedenking onderhevig.

H. Ohrui, Y. Nishida, H. Hori, H. Meguro, Abstr. 4th Eur. Carbohydr. Symp, Eds. F.W. Lichtenthaler, K.H. Neff, (1987), p. B 11.

4. De door Fukui en Tanaka voorgestelde racemisatie van (+)-menthol is chemisch niet eenvoudig uitvoerbaar.

S. Fukui, A. Tanaka, Enzyme Eng., 6, (1982), 191.

5. Het gebruik van elektronische apparatuur in een chemisch laboratorium vraagt om bijzondere maatregelen in verband met corrosieproblemen.

6. Gezien de ervaringen met de fonnosereactie dient bij het onderzoek naar een eerste stap bij de methanolconversie over ZSM-5 type zeolieten (de Methanol-to-Gasoline reactie) ook rekening gehouden te worden met autokatalyse via sporen Cz-verbindingen.

A. Butlerow, Justus Liebigs Ann. Chem., 120, (1861), 295. R. Breslow, Tetrahedron Lett. 1959, 22. R.F. Socha, A.H. Weiss, M.M. Sakharov, J. Catal., 67, (1981), 207. A.P.G. Kieboom, H. van Bekkum, Reel. Trav. Chim. Pays-Bas, 103. (1984), 1

7. Het gebruik van apparatuur voor de versnelde (foto-)degradatie van bv. kunststoffen (bv. "Weather-O-Meters") als model voor de natuurlijke veroudering heeft nog enkele duistere kanten.

8. Het Europarlement zou, naar voorbeeld van internationale wetenschappelijke congressen, het Engels als voertaal dienen aan te wijzen.

9. Het valt op dat de elementkleuren (waterstof, zuurstof en stikstof) van molekuuIraode11en en van gasflessen niet in harmonie met elkaar zijn.

10. De benaming "zelfklevende lijm" is enigermate misleidend; de Amerikaanse term "pressure sensitive adhesive" ("drukgevoelige lijm") is een betere omschrijving.

11. In octrooiliteratuur inzake zeolietsynthese wordt veelal ten onrechte niet expliciet vermeld of er al dan niet geroerd wordt tijdens de kristallisatie.

S.T. Wilson, B.M.T. Lok, E.M. Flanigen, Eur. Pat. EP 0.043.562 (1981). H.W. Grose, E.M. Flanigen, US Pat. 4.061.724 (1977).

F.J. van der Gaag 14 december 1987

To Sylvia.

CONTENTS

1. Introduction 1

History 1

Structure 5

Synthesis 8

Analysis 10

ZSM-5 special properties 13

Literature 16

2. Identification of ZSM-type and other 5-ring containing zeolites by i.r. spectroscopy 18

Introduction 18

Experimental 19

Results and discussion 19

References 24

3. Template variation in the synthesis of zeolite ZSM-5 26

Introduction 26

Experimental 27

Results and discussion 29

References 35

4. Isomorphous substitution in zeolite ZSM-5 37 Introduction 37

Experimental 38 Results and discussion 38

Conclusions 43 ' References 43

5. A note on the effect of the template on the acid features and the particle size of ZSM-5 zeolites 45

Introduction 45

Experimental 45

Results and discussion 47

Literature 49

6. Ammoxidation of toluene over modified ZSM-5 type

catalysts Introduction

Experimental Results and discussion

Literature

7. Reaction of Ethanol and Ammonia to Pyridines over Zeolite ZSM-5 Introduction

Experimental

Results

Discussion

Conclusions

References

8. Reaction of Ethanol and Ammonia to Pyridines over ZSM-5-Type Zeolites Introduction

Experimental Results

Discussion

Conclusions

References

50 50

51 53

60

61

61

62

63 68

70

70

72

72

73

73

76 78

78

9. The formation of 2,6-lutidine from acetone, methanol and ammonia over zeolite ZSM-5 79 Introduction 79 Experimental 80

Results and discussion 81

Mechanistic experiments and considerations 87

Literature 93

10. Exploratory work on silicon aluminum phosphate molecular sieves and related materials 94

Introduction 94

Experimental 98

Results and discussion 99

Conclusions 104

Literature 105

Summary 106

Samenvatting 108

Dankwoord 111

Curriculum vitae 112

I

I n t r o d u c t i o n 1 HISTORY

I N T R O D U C T I O N

HISTORY

The first zeolitic species, stilbite, was described in 1756 by Cronstedt [1]. This type of new materials, crystalline aluminosilicates, was named zeolites, due to its behaviour upon heating (see Figure 1). The crystals produced water vapor when heated in a blowpipe.

Figure 1: Zeolite powder appears to be boiling upon heating.

The next important event in zeolite science was the discovery of the reversible hydratation-dehydratation character of zeolites by Damour [2], almost a century later (1840). This property provided one of the more important uses of zeolites both in industry and in the laboratory, namely as a drying agent for liquids and gases.

= » 3 0 2 ■ . - i —■ ■ —ri -Ccttc experience réitérée sur Ie mémc échan-

ESSAIS tillon , et sur un autre morceau d'opale de Hon-grie pesiint o5r,3135 , m'a toujours présenté des

Sur quelques mmêrnux connus sous Ie nom resul ia Is ideittiques et qui ne me laissent aucun de .quartz résirüte; dou lcsur la propiiété que possècle 1'opale de pci-

ihe et d'absorber f'acilement une notablequanlité r-ar M. A. DAMOUR. d'eau.1

Figure 2: Extract form the original literature.

Some decades later another important property of zeolites, the cation exchange capacity, was discovered (Eichhorn, 1858). This property opened a new world of applications, ranging from the removal of cations from aqueous solutions (e.g. as Ca binder in washing powder or capture of radioactive ions by exchange) to the modification of the adsorptive and catalytic properties of the zeolite.

Introduction 2 HISTORY

In 1896 the idea was advanced that the structures of zeolites consist of open spongy frameworks. Friedel [3] observed that various liquids such as alcohol, benzene, chloroform and carbon disulfide were occluded by zeolites. Grandjean [4], who studied the adsorption of gases, observed that the zeolite chabazite adsorbs ammonia, air, hydrogen, carbon disulfide, hydrogen sulfide, iodine and bromine. However, vapors of acetone, diethyl ether and benzene were essentially not adsorbed. McBain suggested the expression molecular sieve to describe this phenomenon of selective adsorption. Barrer et al. performed much of the pioneering work on this property of zeolites [5]. The often encountered high selectivity of zeolite adsorbents is based on two principles: a) separations based upon size of the adsorbates in relation to the

zeolite's pore size. b) separations based on the different strength of adsorption due to

different polarizability of the adsorbates and/or different strength of cation coordination in relation to the zeolite's polarity and cations.

The number and available amounts of natural zeolites of consistent quality were limited. This has led to a search for synthetic zeolites, in which Barrer also played an important role. The search resulted in the large scale preparation of the zeolite types A and Y by the Union Carbide Corporation in the 1950's [6,7]. The almost unlimited availability of synthetic zeolites induced an

enormously increased effort in zeolite research. Soon zeolites were discovered as catalysts. Especially in acid-catalyzed reactions zeolites are powerful after exchange of the cations for ammonium, hydronium or rare earth (HE) ions. In 1959 the first industrial application of a zeolite catalyst was introduced by the Union Carbide Corporation with a zeolite Y isomerization catalyst [8]. Three years later the industrial use of zeolite catalysists really started off with the introduction of a rare earth-exchanged X zeolite as a cracking catalyst [9]. Newer

Introduction 3 HISTORY

developments are the dealuminated Y type zeolites, which share a high stability and high acid strength. Nowadays most cracking units use zeolite catalysts. Another field of fast growing interest is hydroisomerization. Here

straight-chain hydrocarbons are converted into their branched isomers. Zeolite catalysts containing Pt or Pd (e.g. Pt(0)-containing H-Mordenite in the Shell Hysomer process [10]) are ideal for the reaction. A further development of this process is the Shell-Union Carbide Total Isomerization Process (TIP, see Figure 3)[11], in • which linear hydrocarbons are isomerized in a first stage and then separated in a branched and a linear fraction over another zeolite (A-type) column. The linear hydrocarbons are recycled to the isomerization step. Here two applications of zeolites are used: as a catalyst and as a selective adsorbent. The increase in branched hydrocarbons is very important in view of the

use as gasoline, where a higher octane number is required. Branched hydrocarbons have a higher octane number than the linear isomers. A TIP plant can increase the octane number of the Cs, C6 fraction of gasoline by as much as 20 points, so the addition of lead can be reduced. This is important in those cases where an exhaust catalyst is used, since even small traces of lead deactivate the catalyst completely. In 1985 over 20 TIP plants were in operation.

H2 PURGE PLUS NORMALS

Figure 3: Flowsheet TIP process [11].

Introduction 4 HISTORY

A relatively recent important discovery in the zeolite field is the invention of the so-called "pentasil"-type zeolites, of which ZSM-5 [12](1972) is the bestknown member. The reaction for which ZSM-5 is most frequently cited is the MTG (Methanol-To-Gasoline) reaction which converts a methanol feed to a hydrocarbon fraction containing aliphatic as well as aromatics compounds (<= Cio) in the gasoline boiling range and with good gasoline properties. An installation using this process has recently been started up in New Zealand. Other important applications include catalytic dewaxing and p-xylene technology (see later).

Present consumption volumina of the various uses of zeolites are shown schematically in Figure 4.

subdivis ion c a t a l y s t s s u b d i v i s i o n c a t a l y s t s

a: detergent builders; b: catalysts; c: adsorbants; d: desiccants; e: new applications. Catalysts subdivided in: f: miscellaneous; g: aromatics processing; h: isomerization; i: hydrocracking;

j : catalytic cracking.

Figure 4: Use of synthetic zeolites in 1986 and 1990 (*1000 tons).

The latest inventions in the zeolite field include the A1PO-, SAPO-, MeAPO- and MeAPSO- molecular sieves [13,14]. These materials have a lattice consisting of Al and P tetrahedra (A1P0) with incorporation of secondary or tertiary ions like Si (SAPO), Co, Mg and/or Mn (MeAPO and MeAPSO sieves). This family of molecular sieves includes novel structures as well as pore structures which have an analogon in the families of zeolite molecular sieves.

This thesis deals mainly with pentasil-type zeolites, so in the following part of this introduction particularly properties of ZSM-5 will be discussed.

Introduction 5 HISTORY

STRUCTURE

Zeolites are crystalline aluminosilicates, which contain in their natural forms ions of Group IA and Group HA elements such as Na, K, Mg and Ca. The structure is composed of tetrahedra of an Al3+ or Si4+ ion surrounded by four 02- ions. The Al and Si atoms are referred to by the term "T-atoms" because of their tetrahedral coordination. Each 02" ion is shared between two neighbouring tetrahedra, so an average formula of TO2 results. In the case of a. Si tetrahedron this will give an electrically neutral unit, whereas an Al tetrahedron bears a negative charge. This charge has to be compensated to yield electrically neutral crystals. The zeolite contains cations to neutralise the charge on the Al tetrahedra. Thus, zeolites are represented by the general formula:

Mx/n [(Al02)x(Si02)y] .WH20

n is the valence of the charge balancing cation M, w is the number of water molecules per unit cell, and the sum of x and y are the total number of tetrahedra per unit cell. The Si/Al ratio (y/x) ranges from 1 to 5 for the classical zeolites. Pentasil type zeolites have a higher Si/Al ratio, e.g. 11 or higher for ZSM-5. The Si/Al ratio cannot be lower than 1. In that case the Loewenstein rule (no adjacent Al tetrahedra) will be violated.

It may be noted that lattice defects, e.g. hydroxyl nests in ZSM-5, may occur in as synthesized zeolites, as shown in recent investigations [15]. Other ions can also be incorporated as T-atom in a zeolite lattice;

phosphorus(V), germanium(IV), gallium(III) and boron(III) are well-known examples. A prerequisite is that the T-atoms (ions) can to. adopt a tetrahedral configuration in an oxidic lattice. In these cases the strict definition of a zeolite no longer applies: a zeolite should be an aluminosilicate. Samples containing other T-atoms than Si and Al will have to be described as, for instance, borosilicate molecular sieves.

Introduction 6 STRUCTURE

The alternative lattice ions can be incorporated during synthesis, but in recent years it has become clear that in principle all ions in a zeolite can be exchanged. Well-known are for instance dealumination procedures in which the Al ions are replaced by Si by treatment with SiCl4 vapour [16]. Von Ballmoos showed that the oxygen ions are also subject to exchange reactions using H2180 at 95°C [17]. Especially hydroxyl-oxygens show fast exchange; bridging (T-O-T) oxygens exchange 40 times slower.

The TO2 tetrahedra are the primary building units. In these units the differences between Al and Si are neglected. These primary building units are linked through the oxygen ions to form larger building blocks, the secondary building units (see Figure 5). Linking the secondary building

a O O SIR D4R

T,0„ 4-1 T.O„ 5-1 T„0» 4-«-

Figure 5: Building units in zeolite structures.

units together yields the smallest unit of the lattice bearing all properties of this lattice: the unit cell. The zeolite structure can be generated by translating the unit cell in the crystallographic directions. A unit cell of zeolite ZSM-5 is shown in Figure 6. The secondary building

(b) Figure 6: The ZSM-5 structure, view in the straight channel

(left, SBU and 5-ring chain).

Introduction 7 STRUCTURE

unit for ZSM-5 is the T12O20 block also shown in Figure 6. The ZSM-5 unit cell contains 96 T-atoms (with an observed maximum of 8 Al atoms (Si/Al>ll), cf. Chapter 3) and 192 O-atoms. The complete zeolite structure does not fill the complete space. It

contains cavities in the form of cages and channels. These pores will contain the adsorbed species when the zeolite is filled with an adsorbate. The intracrystalline space is substantial: a zeolite can have a void volume of up to 0.48 ml/ml (0.31 ml/g for H2O adsorption in CaA zeolite, [1], p.428). Zeolite ZSM-5 has a pore system as shown in Figure 7: it

Figure 7: Channel structure of ZSM-5.

consists of a system of intersecting straight and sinusoidal channels. For clarity, the channels in the schematic drawing in Figure 7 are drawn with a smaller diameter than actually is the case. In the photograph the channels are shown in the right scale. The void volume of this zeolite is 0.17 ml/g, so this zeolite has a higher structural density than for instance zeolite A. The channels in ZSM-5 have a diameter of 0.50 to 0.56 nm, leaving enough space to allow passage of aromatic nuclei like benzene, (p-)xylene and pyridine(s). Figure 8 shows a drawing of the top view of the intersections in the ZSM-5 structure. Note that many figures given in literature do not give the proper geometry. The diameter at the intersections is much larger, reaching in some directions 1 nm, thus allowing reactions to occur with intermediates or transition states with diameters larger than 0.6 nm.

Introduction 8 STRUCTURE

Figure 8: Top view of ZSM-5 channels showing large space at the intersections

SYNTHESIS

Several zeolites (analcime, mordenite and stilbite) occur naturally. Some natural zeolites have also been synthesized, important representatives being mordenite and X and Y (isostructural with the natural faujasite). Several zeolites which are industrially interesting (e.g. types A and ZSM-5) are synthetic without a natural counterpart. The synthesis of zeolites is usually performed under hydrothermal

conditions: a silica source, an alumina source and an exchangeable cation are dissolved in water and the crystallization of the zeolite is effected by heating the resulting gel (80-200°C) for a period of time. To obtain good dissolution of all chemicals a high pH is applied by adding a base (e.g. NaOH). The so-called "low-silica"-zeolites (A, X, Y) can be synthesized as described above. The synthesis of the "high-silica"-zeolites like ZSM-5 is more difficult: an organic structure-directing agent generally has to be added to obtain the desired product. For the synthesis of ZSM-5-type zeolites a range of "templates" has been reported (table 1, [18]). The effectivity of some of these templates is discussed in Chapter 3 of this thesis.

Introduction 9 SYNTHESIS

TABLE 1: Templates reported for the synthesis of zeolite ZSM-5. Tetrapropylammonium halide Tetraethylaramonium halide Tripropylamine Diprbpylamine Propylamine 1,6-diarainohexane 1,6-hexanediol 1,5-diaminopentane Ethanolamine Propanolamine Pentaerythritol

Methylquinuclidine Morpholine Ethylenediamine Diethylenetriamine Triethylenetetraamine Dipropylenetriamine Dihexamethylenetriamine Di-n-butylamine Ethanol Ethanol + ammonia Glycerol

The template is believed to play two roles in directing zeolite synthesis: firstly by promoting the formation of the desired building blocks in the gel [19], and secondly by acting as a hydrophobic pore filler to prevent dissolution and recrystallization of already formed crystals [20]. Several analysis methods show that in the as-synthesized sample the pores are almost completely filled with the template molecules (see Figure 9).

Spac* filling drawing of TPA' in flr»t i i i anta l lon * ho win o tha packing tn tha linuaoldai channal (van d*r Waal* radii uaad).

Figure 9: TPA in ZSM-5 (light atoms: zeolite lattice, dark atoms: TPA), from [22].

Some of the templates shown in Table 1 will be locked in the zeolite pores after synthesis. In these cases the as-synthesized zeolites have to be activated before application. Activation requires a high temperature treatment (e.g. 550°C) to decompose the organic species and to remove

Introduction 10 SYNTHESIS

water from the pores. In some cases the high temperature may damage the zeolite structure. Recently an alternative technique was developed in this laboratory by Maesen et al. [21] using a rf-plasma. Here the temperature is low (less than 100°C) and activation is effected by the combined action of low pressure and reactive plasma.

ANALYSIS

In zeolite science two types of analysis have to be distinguished: regarding the resulting crystal structure and as to the chemical composition. In most cases another separation can be made: between the as-synthesized and the activated (calcined) samples, as sometimes small lattice changes can be observed during calcination. Structural analysis. Structural analysis is performed by X-ray diffraction. This technique

gives direct information about the crystal structure of the sample. For zeolite samples it is usual to apply a powder technique, because synthetic zeolites generally are powders of 1-10 urn particle diameter. Special synthesis methods allow the preparation of large (>200 urn) crystals which can be analysed in more detail using a single crystal technique. Thus a recent X-ray structural analysis of as-synthesized ZSM-5 gives details on the lattice and on the location and conformation of the TPA template [22]. X-ray diffraction data give a way of determining the crystalline species present in a sample, but amorphous impurities cannot be detected. It should be stressed that X-ray diffraction techniques need a minimum crystal size to detect the structure. This size is in the order of 4 times the unit cell dimension (e.g. for ZSM-5 in the order of 8 nm) [23]. A compilation of computer-simulated X-ray diffraction powder patterns is given by Von Ballmoos [24]. The XBD pattern of ZSM-5 is shown in Figure 10.

Introduction 11 ANALYSIS

A second method, infrared spectroscopy, allows a quick identification of some zeolites. This analysis method is treated in detail later in this thesis. Infrared spectroscopy gives information about the occurrence of specific structures in the lattice. These structures are absent in amorphous phases, thus giving a way of estimating the amount of amorphous impurities. For infrared spectroscopy the minimum particle size needed for the detection of the zeolite structures is smaller than required in X-ray analysis. This technique has been used to show the presence of ZSM-5 type particles in an X-ray amorphous material [23]. A crystal size of a few unit cells (2-4 ■ nm) has been mentioned. The IR spectrum of ZSM-5 is shown in Figure 10.

Another method, MAS-NMR[25], allows to focus in principle on all nuclei having a magnetic moment in the zeolite. Frequently reported are the use of 13C-NMR to study the template or occluded organic species, the use of e.g. 23Na-NMR to study the exchangeable ions and the use of 27A1 and 29Si-NMR to study the T-atoms in the lattice. The last two techniques (27A1 and 29Si-NMR) allow an estimation of the chemical composition (Si/Al ratio) of the sample by integration of the peaks obtained for Si surrounded by 0 Al and 4 Si, by 1 Al and 3 Si and so on. A more accurate way of determining the Al content of the zeolite lattice is by . use of 27Al-nutation-MAS-NMR [26]. In this method tetrahedrally coordinated (lattice-) Al and octahedrally coordinated (extra-lattice-) Al can be distinguished. Combined with the results from the chemical analysis this yields an accurate Si/Al ratio. Detailed studies are reported by Fyfe et al. [27,28]. At high Si/Al ratios the 29Si NMR spectrum of ZSM-5 shows substantial fine structure for the Si(OAl) peak (see Figure 10). The observed multiplicity arises from crystallographically non-equivalent tetrahedral units of Si(OAl) silicons. This may be explained by assuming no less than 24 non-equivalent Si sites in the unit cell. X-ray diffraction shows either 12 (orthorombic structure) or 24 unique locations (monoclinic structure). Phase transition can be achieved by thermal

Introduction 12 ANALYSIS

treatment [29] or by adsorbing or desorbing e.g. ammonia.

XHD

NMR

UwlluUiu 30 28

— I — 40

SUOAI) (SI,A| ) =

Si (IAD/

60

~i 1 1 1 r -i 1 1 1 r

,J\ —i 1 i i 1 -i 1 1 1 1—

-80 - 90 -100 -110 -120 150 100 50 O -50 ppm from TMS ppm from AI(H 20) |*

—i 1 1 1 1 -80 -90-100 -110 -120

ppm Irom TMS ~i 1 1 1—T-150 100 50 0 - 5 0

ppm from AI(H20)J*

IR

Figure 10: XRD [24], IR and NMR [27] spectra of ZSM-5

T o obta in =~~~. inflation about"

materials .ie zeolite sample cheml exact

buüt ln r

our work two basic / o d s w e r e u s e d : A A S (atonlic md XRF (X-ray uorracence spectrometry). Predecomposition' jf tte-^sample- For AAS the sample is decoü hydrofluoric acid yie>'ins a s o l u t i o n u P o n which analysis is The XRF method y^ss discs prepared by decomposing the zeolite aï ni«h temperature'' l i t h i u m borate mixtures. The results obtained by both methods are co^arable. It will be clear that not all elements can be analysed by e a c h method: it will, for instance, be impossible to analyse for boron using the XRF method. C . . ZSM-5 SPECIAL PROPERTIES

Zeolite ZSM-5 is a special type of zeolite. It is a "high-silica"-zeolite, which gives it most of its special properties. Zeolite ZSM-5 is moderately hydrophilic to highly hydrophobic (depending on the Si/Al ratio), whereas zeolites like the types A, X and Y are very hydrophilic. The number and type of cations compensating the lattice charge are an important factor as to this property. Zeolite ZSM-5 has a very high temperature (>1000°C) and acid stability (down to pH=3). The last property makes it possible to obtain the hydrogen form directly by exchanging the zeolite in a dilute hydrochloric acid solution without large Al-losses. To convert the "low-silica"-zeolites to the hydrogen form they have to be exchanged with an ammonium salt solution and then calcined to decompose the ammonium ions.

The ZSM-5 structure allows the introduction of alternative T-atoms (B, Ga, Fe etc.) during synthesis. The structural properties of the zeolite remain unchanged, just the unit cell dimensions change slightly (see Figure 11 for the relation between cell dimensions and B content of a borosilicate sample [30]). The catalytic (especially the acidic)

H-ZSM-5 have a very aat the acid strength in

Al content of the sample. The Les where the Next Nearest Neighbour

Ps not an Al tetrahedron. For ZSM-5 this for all permissible Si/Al ratios (Si/Al > 11).

tie special pore structure (the channel diameter is the same as the diameter of an aromatic ring) this yields an

'combination of activity, selectivity and stability in numerous üatalytic reactions. Some examples are: the conversion of methanol [32] (and/or ethanol [33] or higher alcohols [34]) to a hydrocarbon fraction in the gasoline range or to ethene, the alkylation of toluene with methanol to form (p-)xylene[35], the disproportionation of toluene to benzene and (p-)xylene[35,36] and selective cracking paraffins [37].

Among these applications of zeolite ZSM-5 two are especially noteworthy: the (p-)xylene formation and the catalytic "dewaxing" of gas-, fuel- or lubricating oil. Both applications show the shape-selective properties of the catalyst. It has been mentioned that the channels of ZSM-5 allow the passage of

aromatic nuclei. Para-substituted benzenes like p-xylene will also pass

L

Introduction 14 ZSMT5 SPECIAL PROPERTIES

properties will be significantly modified. ThusA so-called T-atom

substitution during synthesis renders a powerful tool to tailor the

catalytic activity of a ZSM-5-type zeolite.,

5380 =< 5360 |5340 15320 | S 3 0 0 .= 5280 D 5260

5240

= 20.12 20.08 20.04

\ •< 20.00 ■ \ £ 19.96 - \ S 19.92

\ " 19.88 \ 19.84

\ 19.80

i

! ■

:

\

b

^ ^ -\ ^

O ^ O

^_&b t 1 \ 1 1

■ 13.34 c< / 13.32 „• (f 13.30

0 1 2 3 4 5 0 1 2 3 4 5 B/unii cell B/unit cell

Figure 11: Variation of (a) unit cell volume and (b) individual cell

parameters as function of boron content [30]. \

Due to the low aluminium content the acid sites in H-ZSM-5 have a very

high acid strength. Barthomeuf [31] shows that the acid strength in

zeolite-type materials is related to the Al content of the sample. The

acid strength is maximal for samples where the Next Nearest Neighbour

(NNN) of an Al tetrahedron is not an Al tetrahedron. For ZSM-5 this

condition is fulfilled for all permissible Si/Al ratios (Si/Al > 11).

Together with the special pore structure (the channel diameter is

approximately the same as the diameter of an aromatic ring) this yields an

unique combination of activity, selectivity and stability in numerous

catalytic reactions. Some examples are: the conversion of methanol [32]

(and/or ethanol [33] or higher alcohols [34]) to a hydrocarbon fraction in

the gasoline range or to ethene, the alkylation of toluene with methanol

to form (p-)xylene[35], the disproportionation of toluene to benzene and

(p-)xylene[35,36] and selective cracking paraffins [37].

Among these applications of zeolite ZSM-5 two are especially noteworthy:

the (p-)xylene formation and the catalytic "dewaxing" of gas-, fuel- or

lubricating oil. Both applications show the shape-selective properties of

the catalyst.

It has been mentioned that the channels of ZSM-5 allow the passage of

aromatic nuclei. Para-substituted benzenes like p-xylene will also pass

w ~Y

•

Introduction

Chemical composition.

ƒ /

1 ,

13 STRUCTURE

To obtain exact information about the fractions of the starting materials built in in the zeolite sample chemical analysis is required. In our work two basic methods were used: AAS (atomic absorption spectrometry) and XRF (X-ray fluorescence spectrometry). Both methods require a predecomposition of the sample. For AAS the sample is decomposed using

■ / hydrofluoric acid, yielding a solution upon which analysis is performed. The XRF method uses'glass discs prepared by decomposing the zeolite at high temperature/in lithium borate mixtures. The results obtained by both methods are comparable. It will be clear that not all elements can be analysed by, each method: it will, for instance, be impossible to analyse for boron using the XRF method.

ZSM-5 SPECIAL PROPERTIES

Zeolite ZSM-5 is a special type of zeolite. It is a "high-silica"-zeolite, which gives it most of its special properties. Zeolite ZSM-5 is moderately hydrophilic to highly hydrophobic (depending on the Si/Al ratio), whereas zeolites like the types A, X and Y are very hydrophilic. The number and type of cations compensating the lattice charge are an important factor as to this property. Zeolite ZSM-5 has a very high temperature (>1000°C) and acid stability (down to pH=3). The last property makes it possible to obtain the hydrogen form directly by exchanging the zeolite in a dilute hydrochloric acid solution without large Al-losses. To convert the "low-silica"-zeolites to the hydrogen form they have to be exchanged with an ammonium salt solution and then calcined to decompose the ammonium ions. The ZSM-5 structure allows the introduction of alternative T-atoms (B,

Ga, Fe etc.) during synthesis. The structural properties of the zeolite remain unchanged, just the unit cell dimensions change slightly (see Figure 11 for the. relation between cell dimensions and B content of a borosilicate sample [30]). The catalytic (especially the acidic)

Introduction 15 ZSM-5 SPECIAL PROPERTIES

easily, whereas the transport of e.g. o- and m-xylene will be slower. Passage of higher substituted aromatics (when formed at an intersection) is even more limited, so these will probably be converted before leaving the zeollte[38]. Therefore, alkylatipn. of toluene with methanol . and disproportionation of toluene will yield a xylenes mixture with a higher p-xylene content than the thermodynamic equilibrium. The catalytic dewaxing of heavy oil fractions is a (hydro-)cracking

process in which only the linear ("waxy") hydrocarbons are involved. Branched hydrocarbons are too large to enter the zeolite's pores. The products of a dewaxing unit are a fraction with a boiling range comparable to that of the feed fraction 'and a gasoline fraction. The pour point of the gas-, fuel- or lubricating oil will be lowered (e.g. for a lubricating oil from 7°C to -12°C and for a middle distillate ' from 32°C to -18°C [39]), which drastically improves the properties of these oils at low temperatures. Dewaxing of gas oil (diesel fuel) lowers the temperature at which "fogging" occurs. This phenomenon is encountered during the winter when the linear paraffins form clouds and plug the fuel lines of the car.

In this thesis the unique catalytic properties of ZSM-5 type zeolites will be demonstrated in two . new gas phase reactions, namely the conversion of ethanol and ammonia to pyridines (Chapters 7 and 8) and the ammoxidation of toluene to benzonitrile (Chapter 6). Further chapters describe the detection and analysis of ZSM-5 zeolites using infrared spectroscopy (Chapter 2) and experiments on the synthesis of zeolite ZSM-5 using a range of templates (Chapter 3) and a range of substituting T-atoms introduced during synthesis (Chapter 4). In Chapter 10 some data will be given on experiments with molecular ..' sieves from the SAPO- and MeAPO group, as these systems might offer the possibility of synthesizing materials with anion exchange properties (here the lattice has to carry a surplus of positive charge). It will be shown that the SAPC— type materials can be effectively used in the catalytic ammoxidation of toluene (cf. Chapter 6).

Introduction 16 LITERATURE

LITERATURE

1. D.W. Breck, "Zeolite Molecular Sieves, structure, chemistry and use", J. Wiley & Sons, New York 1974.

2. A. Damour, Ann. Mines, 17, (1840), 202. 3. G. Friedel, Bull. Soc. Fr. Mineral. Cristallogr., 19, (1896), 14, 96. 4. F. Grandjean, Compt. Rendu, 149, (1909), 866. 5. R.W. Barrer, "Zeolites and Clay Minerals as Sorbent and Molecular

Sieves", Academic Press, London 1978. 6. R.M. Milton, U.S. Patent 2.882.243 (1959). 7. R.M. Milton, U.S. Patent 2.882.244 (1959). 8. R.M. Milton, in "Molecular Sieves", Soc. Chem. Ind., London, (1968),

p.199. 9. C.J. Plank, E.J. Rosinski, W.P. Hawthorne, Ind. Eng. Chem., Prod. Res.

Dev., 3, (1964), 165. 10. H.W. Kouwenhoven, Mol. Sieves Int. Conf. 3rd, Adv. Chem. Ser., 1973,

(121), 529. 11. I.E. Maxwell, Proc. Shell Zeol. Catal. Conf., (1986), 2. 12. R.J. Argauer and G.R. Landolt, US Patent 3.702,886 (1972). 13. S.T. Wilson, B.M. Lok, CA. Messina, T.R. Cannan, E.M. Flanigen, ACS

Symp. Ser., 218, (1983), "Intrazeolite Chemistry", G.D. Stucky, F.G. Dwyer. Eds., p.79.

14. E.M. Flanigen, B.M. Lok, R.L. Patton, S.T. Wilson, Pure & Appl. Chem., 58, (10), (1986), 1351.

15. G. Boxhoorn, A.G.T.G. Kortbeek, G.R. Hays, N.C.M. Alma, Zeolites 1984, (4), 15.

16. J. Klinowski, J.M. Thomas, M.W. Anderson, CA. Fyfe, G.C. Gobbi, Zeolites 1983. (3), 5.

17. R. von Ballmoos, W.M. Meier, J. Phys. Chem., 1982, (86), 2698. 18. B.M. Lok, T.R. Cannan andC.A. Messina, Zeolites, 1983, (3), 282. 19. G. Boxhoorn, O. Sudmeijer, P.H.G. van Rasteren, J.C.S., Chem. Coramun.,

1983, 1416. 20. J. Keijsper, M. Mackay, J. v.d. Berg, A.G.T.G. Kortbeek, M.F.M. Post,

Prep. KNCV Katal. Symp., 1986, 39. 21. Th. L. Maesen, J.C.S., Chem. Commun., in press. 22. H. van Koningsveld, H. van Bekkum, J.C. Jansen, Acta Cryst., B43,

(1987), 127. 23. P.A. Jacobs, E.G. Derouane, J. Weitkamp, J.C.S., Chem. Commun.,

1981. 591. 24. R. von Ballmoos, "Collection of Simulated XRD Powder, Patterns for

Zeolites", Butterworth, Guildford, (1985). 25. J.M. Thomas, J. Klinowski, Adv. Catal., 33, (1985), 199-374. 26. A. Samoson, E. Lippmaa, G. Engelhardt, U. Lohse, H.G. Jerschkewitz,

Chem. Phys. Lett., 134. (1987), (6), 589. 27. C.A. Fyfe, G.C. Gobbi, G.J. Kennedy, J. Phys. Chem., 1984. (88),

3248.

Introduction 17 LITERATURE

28. C.A. Fyfe, G.C. Gobbi, J. Klinowski, J.M. Thomas, S. Ramdas, Nature, 296. (1982), 530.

29. H. van Koningsveld, J.C. Jansen, H. van Bekkum, Zeolites, in press. 30. B.L. Meyers, S.H. Ely, N.A. Kutz, J.A. Kaduk, E. van den Bossche, J.

Catal., 91, (1985), 352. 31. D. Barthomeuf, Mat. Chem'. Phys., 1987, (17), 49. 32. e.g. T. Mole, J.A. Whiteside, D. Seddon, J. Catal., 82, (1983), 261. 33. e.g. J.C. Oudejans, P.F. van den Oosterkamp, H. van Bekkum, Appl.

Catal., 3, (1982), 109. 34. e.g. O.A. Anunziata, O.A. Orio, E.R. Herrero, A.F. Lopez, C.F. Perez,

A.R. Suarez, Appl. Catal., 15, (1985), 235. 35. e.g. L.B. Young, S.A. Butter, W.W. Kaeding, J. Catal. , 76, (1982),

418. 36. e.g. N.R. Meshram, S.G. Hegde, S.B. Kulkarni, Zeolites 1986. (6), 37. e.g. R.B. Borade, S.G. Hegde, S.B. Kulkarni, P. Ratnasamy, Appl.

Catal., 13, (1984), 27. 38. I.E. Maxwell, J. Inclusion Phenom., 1986. 4, (1), 1-29. 39. S.P. Donnelly, J.R. Green, Oil Gas J., 1980. 78, (43), 77-81,84.

18

IDENTIFICATION OF ZSM-TYPE AND OTHER 5-RING CONTAINING ZEOLITES BY I.R. SPECTROSCOPY

J.C. Jansen, F.J. van der Gaag, and H. van Bekkum Laboratory of Organic Chemistry. Delft University of Technology, Julianalaan 136, 2628 BL Delft. The Netherlands

ABSTRACT

The mid i.r. spectra have been recorded of the pentasil family, of the mordenite group, of ZSM-39 and Melanophlogite, and of the structurally unknown ZSM-34 and ZSM-35. It is concluded that i.r. spectroscopy enables fast differentiation of ZSM-type zeolites.

INTRODUCTION

During a current investigation program on the synthesis of ZSM-type zeolites a fast method to achieve a first differentiation of products including both the identification and the estimated purity was required. For this purpose i.r. spectroscopy and X-ray powder diffraction (XRD) were selected. Occasionally also scanning electron microscopy (SEM) and X-ray fluorescence (XRF) were applied. For a more precise characterization of the known i.r. spectra of some

2-4 -1 ZSM-zeolites the mid infrared spectra (1500-400 cm ) of a series of five-membered ring containing zeolites were recorded including both synthetic and natural materials. In this paper we present i.r. data on the members of the pentasil family, i.e. Silicalite, ZSM-5, ZSM-11, and

9 Boralite; of the mordenite group , i.e. Mordenite, Ferrierite, Epistilbite, Dachiardite, and Bikitaite, of the clathrate group, i.e. ZSM-39 and the natural polymorph Melanophlogite, and of the structurally unknown zeolites ZSM-34 and ZSM-35. Especially the absorption bands near 1200 and 550 cm assigned by Jacobs et al. and Vedrine et al. to the presence of five-membered ring systems, were studied.

fi—R Based on the known crystal structures of most of the above mentioned zeolites it was attempted to acquire an empirically consistent assignment of the near 1200 and the 550 cm absorption bands.

19

For the determination of the estimated purity.of especially ZSM-5 the i.r. optical density ratio of the 550 and 450 cm • bands of the pentasil products

4 was examined since different values have'been published .

EXPERIMENTAL

Materials For the synthesis of ZSM-type zeolites Aerosil (type 200 Degussa) as the silica source was added to aqueous solutions of organic template. Subsequently an aqueous solution of sodium aluminate was added under vigorous stirring. The gel being formed almost instantaneously was heated at 453 K and stirred in 30 ml autoclaves for 48 h. The solid product was washed three times with distilled water and dried at 373 K for four hours. Subsequently the zeolites were heated at a rate of 1 K/min to 773 K and calcined at this temperature overnight. The natural zeolites, which were obtained from several mineral collections, were air dried.

Methods and apparatus The mid infrared spectra were recorded on a Perkin Elmer 521 spectrometer using the KBr pellet technique. To identify all zeolite samples used the X-ray powder diffraction data were obtained with a Type II Guinier de Wolff camera. Only zeolitic materials which were pure according to X-ray analysis were used in the present i.r. work. The silica alumina ratio of ZSM-5 was determined by XRF using a PW 1400 PHILIPS Röntgen spectrometer. The crystallinity and the particle size of the ZSM-species SEM was studied with a Jeol Jxa-50A electron microanalyser.

RESULTS AND DISCUSSION

o The members of the pentasil family together with the complete mordenite

g group , their origin and silica.alumina ratio are listed in Table 1. The common secondary building unit (SBU) in these zeolite types is the 5-1 unit giving five-membered rings of T-sites in the framework

5 ~ structures . The five-membered rings of the synthetic ZSM-39 and the natural polymorph Melanophlogite of the clathro group are part of the polyhedra building units as depicted in Figure 1. The crystal structures of ZSM-34 and ZSM-35 are unknown. In column four and five of Table 1 the space group of the structures is given and the number of 2-fold screw axes per unit cell able to generate chains of five-membered rings from a typical motif of

20

T-sites indicated by dots in Figure 2. The last column of Table 1 contains the type of typical five-membered ring blocks as presented in Figure 3 and the number of blocks per unit cell.

Tabl* 1 Chemical and structural data of zeolites containing Springs

Zeolite type and or igin Si/AI Space group 2, axes" Number ofc

chainsV2i

4 4 4 4 1 1

— I 1

5-ring° blocks/UC

8 A. 8 B 8 A, 8 B 8 A, 8 B 8 A. 8 B 8 8 8 8 4 3 4 B 4 C

Silicalite l ' ZSM-5 ' Boraltte' Z S M - 1 1 ' Mordenite (Fasatal, It.) ' Ferrierite (Vincenza, It.) Epistilbite IGanagawa, Jpn.t Dachiardite (Niigata, Jpn.) Bikitaite (Bikitaite, Hhod.) ZSM-39 ' Melanophlogi le (Girgent i , It.) ZSM-34 ' ZSM-35 '

X

17.4 13.9* 13.8» 5.0 5.0 3.0 4.0 2.0

X

x

13.4» 9.0'

5 5 5 5 5 5 5 5 5 n n u u

1 Pnma 1 Pnma 1 r^nrna 1 Mm2 1 Cmcm 1 Immm 1 C2/m 1 C2Jm 1 P2, a. Fd3m a. P67mm

u. u.

4 4 4 4 4 4

— 2 2 n.a n.a u. u.

'Secondary bui ld ing unit "Only the 2-fold screw axes wh ich arrange f ive-membered rings in to chains 'Number of f ive-membered r ings per 2! axis [Figure 2) "Number and types of f ive-ring blocks per unit cell as depicted in Figure 3 "Si/B ratio 'Synthesized in this laboratory "Atomic reactant ratio

Figure 1 Polyhedra building units of ZSM-39 la.c) and Melanophlogi te (a.b)

The most important i.r. data in the framework absorption region of the zeolite types are given in Table 2. As examples the spectra of ZSM-5, Epistilbite, Dachiardite, Bikitaite and ZSM-39 are shown in Figure 4. Especially the structure sensitive absorptions around 1200 and 550 cm are of interest to differentiate the zeolite types. The external asymmetric stretching vibration around 1225 cm is clearly present in the i.r. spectra of either the structures with four chains of five-membered rings arranged around a 2-fold screw axis as in the pentasil family or with one chain of five-merabered rings on the 2-fold screw axis as in the mordenite group, shown in Figure 2a and b^ respectively. Although the space group of the Epistilbite structure indicates the presence of 2-fold screw axes, in this structure no five-membered ring chains are generated. However, the presence

21

of pseudo-five-membered ring chains might be the cause of the shift of the near 1200 cm absorption band to 1175 cm In the Dachiardite structure the absorption band at 1210 cm could be caused by the presence of five-membered ring chains, containing 2-fold screw axes. A large shift compared to the other members of the mordenite group is seen in the spectrum of Bikitaite: though 2-fold screw axes are present the absorption band of the chains is found at 1105 cm . Perhaps this shift is due to the low silica alumina ratio No absorption was found near 1200 cm in the i.r. spectrum of ZSM-39 and Melanophlogite. According to the structure data no five-membered ring chains are present in these structures. In the unknown structure of ZSM-35 chains of five-membered rings are possible since the absorption at 1232 cm was demonstrated in the i.r. spectrum of the structure whereas the reverse is true for the also unknown ZSM-34.

Z.

Figure 2 (a) Four f ive-membered r ing chains arranged around 2-fold screw axis; mot i f of 12 f-sites is indicated by dots, (b) One f ive-membered r ing chain on 2-fold screw axis; moti f of 3 T-sites is indicated by dots

22

Table 2 l.r. data between 1500-400 cm"' of zeolites containing five rings

Zeolite types

Lit. data* Silicalite 1 ZSM-5 8oral i te Z S M - l l Mordenite Ferrierite Episti lbi le Dachiardite Bikitaite ZSM-39 Melanophlogi te ZSM-34 ZSM-35 Aerosi l

Asym. stretch'

External"

1150-1050 1225(shl 1225lshl 1228(sh) 1225lshl 1223(shl 1218lsh| 1175lshl I210lsh) 110S(sh)

— — — 1232(sh)

—

Internal

1250-950 10931s) 10931s! 10961s) 10931s) 1045UI 10601s) 10501s) 1050(s) 968{s)

10901s) 11181s) 1060(s) 1070(sl llOOIs)

Sym. stretch'

External

820-750 790(wl 790|wl 800lwl 790lwl 800|w) 7 8 0 M 7 9 5 M 775(w) 782lwl 790|w| 795(w> 7851ml 7 9 0 M 810(w)

Internal

720-650

— — — — 720(wl 6 9 5 M 690lw) 670lw) 6801m)

— — — — —

Double* " r i n g

650-500 5501m) S50(m) 550tml 5501ml 580. 5 6 0 M 5 6 3 M 563(wl 558lwl

— — — 635. 580. 550(wl 5901ml

—

TO' bend

500-420 4501s! 450lsl 4S0IS) 450lsl 4501s) 4551s) 455(s) 4401s) 4601s) 4601s) 465(S| 4651s) 4601s) 4681s!

'l.r. assignments according to Flanigen era/." bFive-membered ring block vibrations according to Jacobs et a/, and Vedrine ef at.3'

According to Jacobs et al. and Vedrine et al. the second structure sensitive absorption band in the pentasil structures at 550 cm is caused by double five-membered ring blocks of Type A as depicted in Figure 3. Type A is a 5-5 block containing two parallel faces of nearly planar five-membered rings. However, in the pentasil structures also five-membered ring blocks are present of Type B (Figure 3) which is a 5-3 block with four faces of puckered five-membered rings in the envelope mode. The absorption band at 550 cm in the pentasil structures is therefore tentatively assigned to the

Figure 3 Types of five-membered ring blocks; A, 5-5 block; B. 5-3 block; C, 5-3-1 block

presence of a combination of Type A and Type B blocks. For the mordenite group an absorption is observed near 560 cm which is in the range

3 4 reported ' for structures with Type B blocks. An exception is Bikitaite, which zeolite shows no absorption near 550 cm . Bikitaite does not contain five-membered ring blocks of Type A and B. A five-membered ring containing block present in the Bikitaite structure is depicted in Figure 3 and called a 5-3-1 block. The 5-3-1 block is a 5-3 block with one additional T-site resulting into two five-membered ring faces in the envelope mode and two six rings. Another difference between Bikataite and the other members of the mordenite group is the relatively strong absorption band at 680 cm in the

23

i.r. spectrum of Bikitaite. Absorptions near 550 cm were also absent in the i.r. spectra of ZSM-39 and Melanophlogite. This is in agreement with the absence of Type A and Type B like blocks in these structures. The weak absorptions at 635 cm , 580 cm and 550 cm in the spectrum of ZSM-34 are considered to be related to the presence of Type B blocks in the structure. The spectrum of the ZSM-35 structure is almost a pentasil-like spectrum except for the large shift of the 550 cm absorption band to 590 cm which could probably be related to the presence of Type A blocks in the structure. It can be concluded that the presence of the near 1200 and 550 cm i.r. bands is indeed related to five-membered ring chains and blocks, respectively. The frequency shift of the i.r. bands is depending upon the particular zeolite type. Thus fast differentiation of zeolites containing five-membered rings via i.r. spectra is of great importance.

.o a

1500 1000 500 v/crrr

Figure 4 I.r. spectra IKBr pellets) of ZSM-39 ( I I , Z S M - 5 (2). Dachiardiie (3). Epistilbue (4) and Bikitaite 15)

24

The influence of very small crystals, d < 2 pm, must be sorted out because of a bad solution of the structure sensitive bands near 1200 and 550 cm and the poor X-ray diffraction pattern. Furthermore, a remark can be made regarding the use of i.r. spec.troscopy in determining the purity of zeolite ZMS-5 samples. The most important impurity in the pentasils, amorphous silica, has an absorption band at 450 cm and

-1 4 does not show a band at 550 cm . Therefore, as earlier reported , the optical density ratio of the 550 and 450 cm bands could indicate if pure and well crystallized samples are present. Upon measuring physical mixtures of pure ZSM-5 and Aerosil we found this ratio to decrease linear with increasing amounts of amorphous silica present. According to earlier 2 3 investigators ' and our present findings the optical density ratio of the 550 and 450 cm bands is 0.8 for all pure pentasil samples (calcined at 823

4 K). This value contradicts the proposal of other workers that each pentasil member has a different ratio value. A constant ratio is consistent with the fact that all pentasil members (cf. Table 1) contain the same type and number of five-membered ring blocks per unit cell. It may be noted that the presence of organic template or adsorbed molecules influences the optical density ratio. Thus proper activation is required. In conclusion the i.r. technique allows an estimate of the purity of the pentasil samples and gives valuable information regarding the structure of five-membered ring containing zeolites.

ACKNOWLEÜEMENT

We wish to thank Mr. N.M. van de Pers and Mr. J.F. van Lent of the Laboratory of Metallurgy for making the Guinier de Wolff photographs and Mr. D.P. Nelemans of the same laboratory for the SEM photographs. Mr. G.F. Herlaar is thanked for discussions. We are grateful to Prof. K. Koopmans and Mr. Th.W. Verkroost of the Department of Mining Engineering for the X-ray analysis of ZSM-5 and to Mr. C. Blotwijk of the same department for supplying the specimen of Bikitaite and Melanophlogite. We thank Dr. L.P. van Reeuwijk of the ISRIC (the former International Soil Museum) for supplying the specimen of Epistilbite.

REFERENCES

1. Gaag, F.J. van der, Jansen, J.C., and Bekkum, H. van, Appl. Catal., il. (1985), 261.

25

2. Ballmoos, R. von, PhD Thesis, E.T.H. Zurich, 1981. 3. Jacobs, P.A., Beyer, H.K. , and Valyon, J. , Zeolites, 1981, .1, 161. 4. Coudurier, G. , Naccache, C., and Vedrine, J.C., J. Chem. Soc. Chem.

Comm.. 1982, 1413. 5. Meier, W.M. and Olson, D.H., 'Atlas of Zeolite Structure Types', Juris

Druck and Verlag AG, Zurich, 1978. 6. Schlenker, J.L., Dwyer, F.G., Jenkins, E.E., Rohrbaugh, W.J., Kokotailo,

G.T., and Meier, W.M., Nature, 1981, 224, 340. 7. Smith, J.V., Fifth Int. Conf. on Zeolites - Recent Prog. Rep. and Disc,

(Eds., Seriale, R. , Colella, C., and Aiello, R.), Heyden, London, 1981, 228.

8. Kokotailo, G.T. and Meier, W.M., Chem. Soc. Spec. Publ., 1980, 33, 133. 9. Breek, D.W., 'Zeolite Molecular Sieves: Structure, Chemistry and Use',

John Wiley and Sons, New York, 1974, 122. 10. Gramlich-Meier, R. and Meier, W.M., J. of Solid State Chemistry. 1982,

44, 41. 11. Flanigen, E.M., 'Zeolite Chemistry and Catalysis', (Ed. Rabo, J.A.),

Adv. Chem. Ser.. 1976, 171, Ch. 2.

26

TEMPLATE VARIATION IN THE SYNTHESIS OF ZEOLITE ZSM-5

F.J . VAN DER GAAG, J .C. JANSEN, and H. VAN BEKKUM

Laboratory of Organic Chemistry, De l f t Universi ty of Technology, .

Julianalaan 136, 2628 BL Oei f t , The Netherlands.

(received 25 February 1985, accepted 22 March 1985)

ABSTRACT

The a b i l i t y of several organic template molecules in the synthesis of ZSM-5 type zeol i tes was studied under standard condit ions of temperature and time using s ta r t ing Si/Al ra t ios ranging from 4 to » (19.2 to 0 A l / u c ) . 1,6-Hexane-d i o l , 1,6-hexanediamine, 1-propanol, 1-propanamine, pentaery th r i to l and t e t r a -propylammonium bromide (TPA-Br) were used as templates. The zeo l i tes obtained were analyzed by X-ray. d i f f r a c t i o n and. infrared spectroscopy for c r y s t a l l i n i t y and by X-ray fluorescence for chemical composition. Scanning e lect ron micro­graphs were made of selected samples.

The range of the s ta r t i ng Si/Al ra t ios giv ing pure ZSM-5 product increases ih ' : the fo l lowing template order: alcohols < amines < tet rapropyl ammonium bro­mide. Both 1,6-hexanediamine and TPA-Br give good resul ts for low s t a r t i n g Si /Al r a t i o s .

The observed maximum content of 8 Al/uc of ZSM-5 i s discussed in terms of special Al s i tes connecting s i l i c a l aye rs .

INTRODUCTION In general zeo l i te ZSM-5 is synthesized in a hydrothermal system conta in ing

an alumina source, a s i l i c a source and an organic template molecule. The t e t r a ­propyl ammonium ion (TPA) was the f i r s t organic molecule which was reported [1] to be capable of inducing ZSM-5 format ion. Later invest igat ions showed that the use of TPA allows the synthesis of ZSM-5 zeol i tes with a Si /Al r a t i o ranging from 11 to °° (which corresponds to 8 to 0 Al/uc) [ 2 ] .

Other organic molecules reported to induce ZSM-5 formation a re , for example, 1,6-hexanediol [3] and 1-propanol [ 4 ] . A review on the use of d i f f e ren t tem­plates in zeo l i te synthesis has recently been given by Lok et a l . [ 5 ] . Derouane and Gabelica and coworkers [6 ,7 ,8 ] invest igated the process of forming the ZSM-5 phase and the role of the a l k a l i metal cat ions, using the templates TPA-Br and tetrabutylammonium bromide.

ZSM-5 zeol i tes have a number of propert ies which are not dependent on the chemical composition, i . e . the Si/Al r a t i o of the sample, l i k e c rys ta l s t ruc ­t u re , pore size and pore volume, X-ray d i f f r a c t i o n pattern and re f rac t i ve index [ 9 ] . Many other propert ies of ZSM-5 do vary wi th the composit ion. In d i f f e r e n t appl icat ions of ZSM-5 cer ta in ranges of composition are, there fore , favoured or required. Ion exchange capacity, ca ta l y t i c a c t i v i t y and hydrophobici ty are examples of composition-dependent p roper t ies .

27

In our laboratory the e f fec t of varying Si/Al r a t i o on the e f f i c iency of

ZSM-type cata lys ts in e .g . ammoxidation [ 10J and aromatization [11] is under

i nves t i ga t i on .

In order to obtain knowledge of the templating potency of d i f f e ren t organic

molecules a series of ZSM-5 samples has been synthesized, s ta r t i ng out w i th

d i f f e ren t Si /Al ra t ios and d i f f e ren t organic template molecules. Standard con­

d i t ions [ 5 ] of temperature and react ion time were chosen. The organic molecules

used were: TPA-Br, 1,6-hexanediol, 1,6-hexanediamine, 1-propanol, 1-propan-

amine, and p e n t a e r y t h r i t o l , a te t rao l which resembles TPA as to s t r uc tu re . Two

s i l i c a sources, aerosi l and waterglass, were applied in th is study.

EXPERIMENTAL

The ZSM-5 samples were prepared according to the general d i rec t ions given by Casci et al . [ 3 ] .

The c r y s t a l l i z a t i o n was performed in stainless steel (type 316) autoclaves (35 ml volume) a i r t igh tened by a te f l on r ing and containing tef lon-coated mag­netic s t i r r e r bars. Nine autoclaves were placed in an e lec t ron i ca l l y cont ro l led heated aluminum carrousel equipped with magnetic s t i r r e r dr ives, as shown in Figure 1 .

Figure 1 . Stainless steel autoclave and alu.ninum carrousel used for ZSM-5 syn­thesis experiments.

28

Chemicals.

Reagents were: aerosi l s i l i c a (S1O2, Aerosi l 200, Degussa), sodium hydroxide

(NaOH.H20, Merck Suprapur), sodium aluminate (NaA102, 41 wt% Na20, 54 wt%

Al2°3» Riedel-de Haehn), 1,6-hexanediol (A ld r i ch ) , 1,6-hexanediamine (A ldr ich

and Merck), 1-propanol (Merck), 1-propanamine (Merck), tetrapropylammonium bro­

mide (A ld r i ch ) , pentaerythr i to l (BOH), waterglass (sodium s i l i c a t e s o l u t i o n ,

26.7 wU S1O2, 8.1 w t t Na20, Lamers & Indemans), su l f u r i c acid (96 wt% H2S04,

Lamers & Indemans) and aluminum su l fa te (Al2(S04)3.18H2O, .Merck).

Aerosil as s i l i c a source

Each autoclave was charged with 1.55 g (25.8 mmole) aerosi l suspended in 20 ml demineralized water. To th is suspension a solut ion containing sodium hydrox­ide , sodium aluminate and organic template was added under s t i r r i n g . The t o t a l amount of NaOH in the solut ion was kept a t 8.11 mmole. The amount of NaA102 was adjusted to obtain a range of Si /Al ra t i os in the g e l , which usual ly formed wi th in a few seconds. The amount of template was 8.57 mmole (1,6-hexanedio l , 1.013 g; 1,6-hexanediamine, 0.993 g; pen tae ry th r i t o l , 1.167 g ; 1-propanol, 0.515 g; 1-propanamine, 0.506 g; TPA-Br, 2.29 g ) . The molar composition of the gel (as oxides) was: 1.00 Si02 :0-0.14 Al203 :0.333 template:0.157'Na20:48.8 H20.

Waterglass as s i l i c a source

Each autoclave was charged with a mixture of 7.44 g (30.38 mmole S i0 2 . 2.18

mmole Na20) waterglass and 6.67 g demineralized water, to which a so lu t ion of

0.261 g (2.55 mmole) 96% su l fu r i c ac id , 11.76 mmole template (1,6-hexanediol ,

'.";', i . 3 9 ' g ; 1,6-hexanediamine, 1.37 g; pen tae ry th r i t o l , 1.60 g; 1-propanol, 0.707

g; 1-propanamine,; 0.695 g; TPA-Br, 3.13 g) and aluminum su l fa te in 10.67 ml

water was added under..-st i rr ing. The amount of aluminum sul fate was adjusted to

obtain, a range of Sï/Al ra t ios in the g e l , which usual ly formed w i t h i n a few ,. seconds. The molar composition of the gel (as oxides) was: 1.00 S i0 2 :0 -0 .11

Al203 :0.382 tempi ate :0 .208 Na20:31.7 H20 . ":

In both procedures the autoclaves were closed and s t i r r e d at 448 K for 44 hours. After coo l ing , the sol ids were co l lec ted by f i l t r a t i o n and washed three times with demineralized water. The samples were dried overnight at 373 K and analyzed by in f ra red spectroscopy ( IR )and X-ray d i f f r a c t i o n (XRD). A number of

' samples was analyzed as well by X-ray fluorescence (XRF) for chemical composi-: , t ion ,and by scanning electron micrography (SEM) for morphology. IR spectra were

recorded on. a Perkin-Elmer 521 spectrometer, using KBr p e l l e t s . XRD analyses were performed using an Enraf-Nonius Type I I Guinier-de Wolff camera and CuKa rad ia t i on . XRF analyses were made on a Phi l ips PW 1400 rbntgen spectrometer using l i t h ium borate glass pe l le ts containing the disclosed sample. SEM micro­graphs were made using a Jeol JXa-50A electron microanalyser.

29

RESULTS AND DISCUSSION

A number of samples which were pure ZSM-5 according to XRD and IR were submitted to XRF analyses. The analysis data are p lo t ted in Figure 2.

10 Al/uc (prod)

8

6

4

2

0 0 2 4 6 8 10

— Al/uc (gel)

Figure 2 . XRF analysis data, p lo t ted as Al/uc in synthesis gel vs . Al/uc in

ZSM-5 product, s i l i c a source waterglass: x: 1,6-hexanediamine; +: 1,6-hexane-

d i o l ; s i l i c a source Aeros i l : v : TPA-Br; o: 1,6-hexanediamine; • : 1,6-hexane-d i o l .

Figure'2 shows that the ra t i o (Al/uc product ) / (A l /uc gel) i s somewhat larger

than uni ty for a l l compositions except one. Thus i t can be concluded that a l u ­

minum is preferably incorporated in the so l i d mate r ia l . This is in agreement

with the resul ts of Romannikov et a l . [12] and Gabelica et al . [ 8 ] .

In the so l id s tate Al-NMR spectrum [13] recorded from a sample containing

7.46 Al/uc ( in the product, synthesis from Aerosi l and TPA) no signal of oc ta-29 hedral Al was observed. Furthermore from Si-NMR spectra of the same sample a

l a t t i c e Si/Al r a t i o of 13 (6.9 Al /uc) was est imated. I t can be concluded that a l l Al in the sample is incorporated in the zeo l i t e l a t t i c e .

SEM micrographs indicated the growth of larger crystals when using a synthe­s is mixture wi th a lower aluminum content, as shown in Figure 3. This has also been observed by Gabelica et al . [8] and Romannikov et al . [;12]. The l a t t e r authors suggest an increase in c r y s t a l l i z a t i o n rate with an increase of Si /Al r a t i o . When Aerosi l was used as s i l i c a source, the crystals were usual ly bet ter shaped compared to the c rys ta ls formed wi th waterglass as s i l i c a source. This is assumed to be caused by a lower rate of c rys ta l growth in the case of Aero­s i l .

30

t e m p l a t e : TPA aeros ï l

5«

S i / A l * 35

S i / A l ■ 174

S i / A l = oo

Figure 3. SFM micrographs showing the effect of variation in Si/Al rat io on crystal size.

31

The pur i ty of the samples was judged from the recorded IR spectra, espec ia l ­ly from the bands at 1220, 550 and 450 cm" 1 . The bands at 1220 and 550 cm"1 are s t ruc ture-sens i t ive peaks [14] a r is ing from 5-r ing chain and 5-r ing block v i ­brat ions, respect ive ly . The pur i ty of the sample can be estimated from the op­t i c a l density r a t i o of the 550 and 450 cm bands, which should be 0.8 for pure ZSM-5 [ 1 4 ] . X-ray diffractograms were also used for ZSM-crystall i n i t y est ima­t ion and i d e n t i f i c a t i o n of impur i t i es . Main impur i t ies were alpha quartz ( s i l i ­con-r ich formulat ions) , mordenite and natroalumite ( N a A ^ t S O ^ t O H ^ ) (a l um i ­num-rich formulat ions, waterglass method) and near-kenyaite ( c f . [ 3 ] ) . In F i ­gure 4 the estimated ZSM-5 pu r i t i es of the various products obtained are p l o t ­ted versus the calculated number of aluminum atoms per un i t ce l l [ 1 5 ] .

Figure 4 c lear ly shows that amines allow a wider range of Al/uc-values to be used to prepare ZSM-5 i n a pure state than the corresponding a lcoho ls . TPA pro ­vides the widest range of pure ZMS-5 products, ranging from 0 to 8 A l /uc . The small templates (propanol, propanamine) give better resul ts when a double molar amount of these templates is used. TPA allows the use of smaller amounts o f t h i s template, e . g . ha l f the molar amount (of the standard formulations given in the experimental sec t ion ) . The use of waterglass as s i l i c a source gives a higher c r y s t a l l i n i t y compared to Aerosil . Similar resul ts were obtained by Derouane, Gabelica and coworkers [ 6 ] , who determined the time for 100% ZSM-5 c r y s t a l l i n i t y for act ive s i l i c a to be approximately six times the time for wa­te rg lass . I t is obvious that waterglass gives a higher c r y s t a l l i z a t i o n r a t e .

The precise ro le of the organic template molecules in zeo l i t e synthesis i s s t i l l a matter of much dispute ( c f . [ 5 ] ) . The good performance of TPA as a tem­plate has been re lated by Boxhoorn et a l . to the in teract ion and reordering of i n i t i a l l y formed complex s i l i c a t e anions by the TPA cat ion [ 1 6 ] . Other elements in the TPA templating potency may be i t s charge and the e f f i c i e n t f i l l i n g of the zeo l i te l a t t i c e . When the pores of ZSM-5 are completely f i l l e d with TPA, the zeo l i te contains 4 TPA/uc. Addit ional counter charge can be in the form of sodium (higher number of Al /uc) or hydroxide ions (lower number of A l / u c ) . I t is obvious that a pos i t i ve l y charged species is the best complexant for an anion. Perhaps template act ion of non-charged organic molecules may also be r e ­la ted in f i r s t instance to in te rac t ion wi th the complex s i l i c a t e anions. In th is view amines are better templates because they easier form H-bond complexes wi th the Si-OH terminal groups of the s i l i c a t e anion, compared to a lcohols . In the synthesized zeo l i tes the neutral templates are expected to act as l igands for sodium ions s i tuated at c ross-sect ions. The resemblance of Na(template)4 t o TPA is clear then .

Figures 2 and 4 show a maximum aluminum content of approximately 8 A l / u c . This maximum number is also mentioned in the l i t e r a t u r e [ 2 ] . The exact c r y s t a l -lographic posi t ions of the aluminum Ions in the ZSM-5 l a t t i c e are s t i l l under discussion. F r i p la t et al . [17] conclude from non-empirical mechanical c a l c u l a ­t ions that the Al atoms w i l l be pre ferent ly located at pos i t ions T2 and T12

32

&

e synthesis of

ate [ 5 ] , the

^nge of app

.ia amines

4.

v'<u:.<**

^ W1 * > < c

A ^

49'

»*° fcV

^ ^- -ca t a l . , / ' and H. va

^ ' 9 8 3 (D. 01 s 536.

..i^Oosterkamp, and H. >

.el. Mast ikhin, S. Hocevar,

^.-ormed by Dr. N.C.M. Alma (Shell Rese ^uer Gaag, J .C. Jansen, and H. van Bekkun

titutipn in ZSM-5

he direct (two-step-)conversion of synthesis e-containing ZSM-5-type zeolites show a raction [5]. s the . synthesis and analysis of ZSM-5 type ther than Al and Si present in the synthesis

ized in sealed glass containers in an oven at ing for 2 weeks. Two methods were used: the,

uPont) as the silica source, and the second . In all experiments tetrapropylammoniuni bromide the template. The molar gel composition was: 20 TPA-Br; 1500 H2O when using Ludox, and 100 5 TPA-Br; 1950 H2O when using waterglass. The added in the form and the amount given in Table as performed,using X-ray diffraction and infrared olume was measured thermogravimetrically by the t ca. 40°C) in a calcined sample (550°C) of the ies of the samples were determined by NH3-TPD on subsequently calcined sample.

ntroduction, an as-synthesized T-atom substituted the non-Na and non-TPA cations incorporated in

e the following characteristics: tructure according to spectroscopie techniques,

kept in mind.that the T-atoms should fit in a rdination, whereas their size should not introduce lattice [10,11].

i 34

(a) '(b)

Figure 5. Possible Al posi t ions in ZSM-5 wi th a maximum of 8 A l /uc . (a) along

[010] ax i s , f ou r - r i ng posi t ions (T9, T10) shown, (b) along [100] ax i s , s ingle

T-s i te posi t ions (T3, T4) shown.

(posi t ions as denominated by Olson et a l . [ 1 8 ] ) . Two other sets of locat ions can be suggested based on crysta l lographic cons iderat ions. F i r s t l y , the alumi­num atoms could be located in the four-membered rings in the ZSM-5 st ructure (see Figure 5a) (posi t ions T9 and T10). Secondly, the aluminum atoms could be located in single posi t ions on both sides of the in tersect ions of the ZSM-5 channels (T3 and T4), as shown in Figure 5b. Both posi t ions can explain the ob­served maximum number of e ight aluminum atoms per un i t c e l l .

When zeo l i te ZSM-5 and the members of the mordenite group are compared, one can see that more or less corrugated s i x - r i ng sheets cons t i tu te major bu i ld ing elements in both groups of zeo l i tes [19, c f . 2 0 ] . For mordenite and f e r r i e r i t e the aluminum posit ions have been reported by Meier [ 21 ,22 ] : in the mordenite structure the s i l i c a sheets are interconnected by four-membered r ings of J-L si tes and in the f e r r i e r i t e s t ructure by six-membered rings with Si and Al a l / ternately posit ioned in both sub-un i ts . The interconnect ion between the sheets in the ZSM-5 st ructure is made by four four-membered r ings of T-si tes per^unit ce l l and eight s ingle T-si tes ( c f . Figure 5 ) .

The s t ruc ture-sens i t i ve analysis methods also reveal an increase in crystal -u n i t y with decreasing number of Al/uc (especial ly not iceable with samp.les pre-pared with TPA). Using XRD a decrease in XRD l inewidth was not iced. This may be explained by mentioning the p o s s i b i l i t y of a change in un i t ce l l parameters due to aluminum enrichment in the rim of the c r y s t a l s , which was detected by von/ Ball moos [ 2 3 ] . // I

33

Figure 4. Estimated ZSM-5 content of solids plotted vs. Al content of synthesis mixture, expressed as Al/uc of ZSM-5. (a) 1-propanol as template, (b) 1,6-hexa-nediol, (c) pentaerythritol, (d) 1-propanamine, (e) 1,6-hexanediamine, ( f) TPA-Br. Silica sources: Aerosil (v ), waterglass (0). Aerosil, amount of template doubled (X) (in a and d). Waterglass, half amount of template (X) (in f ) .

35

CONCLUSIONS I t is demonstrated that for the synthesis of ZSM-5, under condit ions recom­

mended for 1,6-hexanediol as template [ 5 ] , the pur i ty of the zeo l i t e product depends on the template used. The range of applicable s ta r t i ng s i l i ca /a lumina ra t ios increases going from alcohols via amines to TPA as a template. More spe­c i f i c a l l y the order i s : pentaerythr i to l < propanol < hexanediol < propanamine < hexanediamine < TPA.

Casci et al . [ 3 j claim a range of Si/Al ra t ios for 1,6-hexanediol from 10 to 100, preferably 20 to 60. Our invest igat ions show a narrower range, Si /Al = 15-25, of app l i ca t ion .

In general, i t can be said that in the synthesis of ZSM-5 with a high Si/Al r a t i o (low number of A l / u c ) , templates l i k e 1,6-hexanediamine or TPA should b e ' used to obtain a 100% c r y s t a l l i n e ZSM-5 product. Samples prepared using water-glass as s i l i c a source have a higher c r y s t a l l i n i t y than those prepared from Aerosi l . This is in accordance with the resul ts of Derouane, Gabelica and co-workers { 6 ] .

An unique locat ion of A l , e .g . in the four- r ings of ZSM-5, can account for the observed maximum of 8 Al per un i t ce l l and is in harmony wi th aluminum po­s i t i ons in zeol i tes of the mordenite group.

ACKNOWLEDGEMENTS

The authors would l i k e to thank Mr. J .F . van Lent and Mr. N.M. van der Pers

for the XRD analyses and Mr. D.P. Nelemans (a l l of the Laboratory of Meta l lur ­

gy) for the SEM micrographs. Prof . K. Koopmans and Mr. Th.W. Verkroost (Depart­

ment of Mining Engineering) are thanked for the XRF analyses. Dr. N.C.M. Alma

(Shell Research B.V., Amsterdam) is g ra te fu l l y thanked for the so l id state 27 Al-NMR analys is . Mr. G.F. Herlaar is thanked for discussions.

REFERENCES

1 R.J. Argauer and G.R. Landolt, US Patent 3.702.886. 2 See, for example, R. von Ballmoos, Ph.D. Thesis, ETH Zurich, 1981. 3 J . L . Casci, B.M. Lowe, and T.V. Whittam, Eur . Pat. Appl . 0.042.225. 4 T. Mole and J.A. Whiteside, J . Ca ta l . , 75 (1982) 284. 5 B.M. Lok, T.R. Cannan, and C .A. Messina, Zeo l i tes , 3 (1983) 282. 6 E.G. Derouane, S. Detremmerie, Z. Gabelica, and N. Blom, Appl . C a t a l . , 1

(1981) 201. 7 Z. Gabelica, E.G. Derouane, and N. Blom, Appl. Catal., 5 (1983) 109. 8 Z. Gabelica, N. Blom, and E.G. Derouane, Appl. Catal., 5 (1983) 227. 9 D.H. Olson, W.0. Haag, and R.M. Lago, J. Catal., 61 (1980) 390. 10 J.C. Oudejans, F.J. van der Gaag, and H. van Bekkum, in "Proc. Sixth

Intern. Conf. Zeolites", Reno 1983 (D. Olson and A. Bisio, Eds.), Butterworth, Guildford, 1984, p. 536.

11 J.C. Oudejans, P.F. van den Oosterkamp, and H. van Bekkum, Appl. Catal., 3 (1982) 109.

12 V.N. Romannikov, V.M. Mast ikhin, S. Hocevar, and B. Drza j , Zeo l i tes , 3 (1983) 311.

13 Analysis performed by Dr. N.C.M. Alma (Shell Research B.V., Amsterdam). 14 F.J. van der Gaag, J .C. Jansen, and H. van Bekkum, Zeo l i tes , 4 (1984) 369.

36

15 Calculated from Si/Al in the synthesis gel, assuming 96 T-atoms per unit cell .

16 G. Boxhoorn, 0. Sudmeijer, and P.H.G. van Kasteren, J. Chem. Soc, Chem. Commun., (1983) 1416.

17 J.G. Fripiat, F. Berger-André, J.M. André, and-E.G. Derouane, Zeolites, 3 (1983), 306.

18 D.H. Olson, G.T. Kokotailo, and S.L. Lawton, J. Phys. Chem., 85 (1981) 2238.

19 F.J. van der Gaag, J.C. Jansen, and H. van Bekkum, to be published. 20 E.M. Flanigen, J.M. Bennett, R.W. Grose, J.P. Cohen, R.L. Patton, R .M.

Kirchner, and J.V. Smith', Nature, 271 (1978) 512. 21 W.M. Meier, R. Meier, and V. Gramlich, Z. Kristallogr., 147 (1978) 329. 22 W.M. Meier, "Constituent sheets in the zeolite frameworks of the mordenite

group", p. 99, in "Natural Zeolites", (L.B. Sand and F.A. Mumpton, Eds.), Pergamon Press, 1978.

23 R. von Ballmoos and W.M. Meier, Nature, 289 (1981) 782.

Substitution in ZSM-5 37

IS0MORPHOÜS SUBSTITUTION IN ZBOLITB ZSM-5.

SUMMARY

ZSM-5 type zeolites were synthesized using synthesis mixtures containing various ions other than Na, Si and Al. Structural analysis of the products invariably confirmed the ZSM-5 structure, however it appears that incorporation into the lattice is limited to Al, Fe and Ti.

INTRODUCTION T-atom substitution is a versatile tool to tailor a zeolite's

properties. Especially catalytic activity can be altered by substitution. An example is the decrease of the acid strength of H-ZSM-5 upon incorporating B instead of Al. It is well known that zeolites can be synthesized using Si or Ge and Al, B or Ga as T-atoms. Numerous patents claim the use of T-atoms other than Si and Al in zeolite ZSM-5 synthesis [e.g. 1-5]. Recently more detailed studies on the substitution of T-atoms, concerning both catalytic activity and the location of the substituting ion, were published [6-12]. Some authors claim that almost any metal forming a badly soluble hydroxide can be incorporated into a zeolite lattice. However, lone et al. [10,11] have stressed that it is also necessary that these ions should prefer a tetrahedral coordination. This limits the range of suitable elements considerably with as best-known members B, Be, Al, Ga and Fe. Kustov et al. [12] have recently published a spectroscopie investigation of the Fe ions in ferrisilicate ZSM-5 samples. Only a part of the Fe is found to be incorporated in the lattice; the other part is present in extralattice locations.

Another characteristic property of a well-crystallized zeolite sample might be its colour. In the case of Fe built in the materials have been reported to be white [18], provided coloured counter-cations are absent. Some of these materials (especially the Fe-containing samples) may

38 Substitution in ZSM-5

be interesting in view of the direct (two-step-)conversiqn of synthesis gas into hydrocarbons, e.g. Fe-containing ZSM-5-type zeolites show a high selectivity to the C3+-fraction [5]. The present paper describes the . synthesis and analysis of ZSM-5 type

zeolites with various ions other than Al and Si present in the synthesis formulation.

EXPERIMENTAL All zeolites were synthesized in sealed glass containers in an oven at

100°C with occasional shaking for 2 weeks. Two methods were used: the first using Ludox HS-40 (DuPont) as the silica source, and the second using waterglass (Merck). In all experiments tetrapropylammonium bromide (TPA-Br) was applied as the template. The molar gel composition was: 100 Site; x Ta; 20 NaOH; 20 TPA-Br; 1500 H2O when using Ludox, and 100 Si02; x T2; 11.9 0H-; 19.5 TPA-Br; 1950 H2O when using waterglass. The secondary T-atom (T2) was added in the form and the amount given in Table 1. Structural analysis was performed using X-ray diffraction and infrared spectroscopy. The pore volume was measured thermogravimetrically by the adsorption of n-hexane (at ca. 40°C) in a calcined sample (550°C) of the zeolite. The acid properties of the.samples were determined by NH3-TPD on an ammonium-exchanged and subsequently calcined sample.

RESULTS AND DISCUSSION As mentioned in the introduction, an as-synthesized T-atom substituted

ZSM-5 type zeolite with the non-Na and non-TPA cations incorporated in the lattice, should have the following characteristics: 1) exhibit the ZSM-5 structure according to spectroscopie techniques, 2) colourless (white), Moreover it should be kept in mind.that the T-atoms should fit in a

tetrahedral oxygen coordination, whereas their size should not introduce too much strain in the lattice [10,11].

Substitution in ZSM-5 39

Table 1: Substituted ZSM-5 type zeol i tes , synthesis conditions and analytical data.

Ion

Hg I I Ca I I

Sr I I Hn I I Fe I I

Fe I I I

Co I I

Hi I I Cu I I

Zn I I Cr I I I V V

Te VI

added fors

MgCh Ca(0Hh

SrfNthh Hn(0Ach

FeS0«

Fe2(S0<b

CoSOt

NiS0«

CuCh

ZnSOi

Cr (N0i ) ï

NH1VO3

HzTeO*

coordi­

nation')

6

6

6

6,(4t,4s) 4t,(6)

4t,6

6,(4t)

6,(4s,4t)

Si/X

(gel) 45

19

45 45 24

45

45

18 d6,4t,(4s) 45 4t

6,(d4t)<) d6,(4t)

6,(4t)

37

45 45

45

Si-

source

Ludox

Ludox Ludox

Ludox

Ludox Ludox

Ludox

Ludox Ludox

Ludox Ludox

Ludox

Ludox

CO. ourk)

before/after calc

white white

white

white

white

white

brownish brownish

white

white

pink

green blueish white

green white

white

white

white

purple grey

brwn/bluc

white

yellow white

white

XRD result

(structure)

ZSM-5

ZSM-5

ZSM-5

ZSM-5

ZSH-5

ZSH-5

ZSH-5

ZSM-5

ZSM-5

ZSM-5

ZSM-5

ZSM-5

ZSH-5

IR pur i ty

(I) 102.6

83.3

82.3

94.6

92.0

85.4

93.8

93.3

91.9

80.0

91.6

93.1

83.4

n-hexane

ads (il/g) 0.140 ■ 0.124

0.131 0.134

0.151

0.138 0.114

0.153

0.128 0.142

0.142 0.147

0.136

hexane/IR

(•1/9) 0.136

0.148

0.159 0.142 0.164

0.162

0.122 0.164 0.139

0.178

0.155 0.158

0.163

Hn I I

Fe I I Fe I I I

Co I I Ni I I

Cu I I Zn I I

Hg I I Ti IV')

Zr IV V V

Hn(0Ach FeS0«

Fez(S0«)j

C0SO4

NiS0«

CuCh

ZnS0«

Hgh11)

Ti0S0«*H:0!

6 , (4 t ,4s )

4t,(6)

4t,6 6,(4t) 6,(4s,4t)

d6,4t,(4s)

4t 4t

4t Zr0ChtHz02 4 t , 6 , ) 7

NH«V0J d6,(4t)

45

45 45 45 45

45 45

45

45

45 45

HG HG

HG HG HG HG

HG

HG HG

HG

HG

brownish brownish

white white

pink green

blueish white

white

white

white white

white white purple beige

blue white

white

white white white

ZSH-5

ZSM-5

ZSH-5

ZSH-5

ZSH-5

ZSH-5

ZSH-5

ZSH-5

ZSH-5

ZSM-5

ZSH-5

82.0

77.9

76.4

80.5

69.8

83.4

73.5

95.0

74.0

86.9

92.0

0.138

0.132

0.136

0.140

0.128

0.155

0.108

0.151

0.149

0.127

0.144

0.168

0.170

0.178

0.174

0.134

0.186

0.138

0.159

0.201

0.146

0.157

"} preferred coordination nuuber: 4s=square planar, 4t=tetrahedral, 6-octahedral, a d prefix «eans distorted; between brackets: alternative non-preferred configurations. [15]

b) after calcination at 550°C. c) data for Cr ( l i t ) ; Cr(VI) w i l l accowodate 4t. d) Hgh hardly dissolved. «) zeolite crystall ization 2 days at 180°C.

The resul ts of the syntheses, including data on the above-mentioned

properties, are l i s ted in Table 1. The pore volume was measured to verify

whether or not pores are obstructed by ex t ra - l a t t i ce clusters of the

T-atom oxide or hydroxide. For a well-crystal l ized ZSM-5 sample a value of

40 Substitution in ZSM-5

0.18 ml/g has been accepted for the adsorption of n-hexane [13] at 40°C. The purity of the sample' can be estimated from the IR spectrum [14] as a convenient means of analysis. Table 1 also shows the hexane adsorption of the various materials normalized via IR purity to pure ZSM-5 (=hexane/IR). The data in Table 1 show that all syntheses yield a product with a ZSM-5

type structure. Infrared data show a substantial variation in zeolite crystallinity from 70-100*. Nevertheless, the ZSM-5 structure is also clearly evident in the samples of relatively low crystallinity. It should be noted that amorphous materials cannot be detected using routine X-ray diffraction, whereas the difference is clear in infrared spectra.

The amount of n-hexane adsorbed, normalized to a pure ZSM-5 together with the colour of the sample, can be used to judge whether the ion is properly incorporated into the lattice or not. A white sample with a normalized adsorption of more than 0.16 ml hexane/g (allowing 10% for experimental errors) is supposed to have the substituting ions incorporated in the lattice. This leaves the samples prepared from gels containing Fe(III), Fe(II) and Ti(IV), and -for Ludox as the silica source- Zn(II) and Te(VI). It may be noted that these ions will all fit in a tetrahedral coordination, except for Te(VI) which prefers an octahedral coordination. Coloured impurities however cannot be observed in this case, because Te salts (as well as Ti and Zn salts) are white. Ball et al.[9] use MAS-NMR to show that Zn is only partially incorporated in a Silicalite lattice.

The incorporation of the substituting ions in a zeolite lattice may have an analogon in the phosphates: it is well-known that the phosphates of B(III), Al(III), Ga(III), Fe(III), As(III) and Sb(III) show a structure resembling that of quartz. In addition to the present analyses chemical analytical data of the

ZSM-5 samples will be required in order to establish the presence of the T2 atoms quantitatively.

Substitution in ZSM-5 39

Table 1: Substituted ZSM-5 type z e o l i t e s , synthesis conditions and analyt ical data.

Ion

Hg I I Ca I I Sr I I Hn I I Fe I I Fe I I I Co I I Hi I I Cu I I Zn I I Cr I I I V V Te VI

added fore

MgCh Ca(0Hh SrlNOsh Mn(0Ac)2 FeS0« FezfSOOs CoSO» NiS0« CuCh ZnS0< Cr(N<h)j NH4VO3 HzTeOi

coordi­nation') 6 6 6 6,(4t,4s) U,(6) 4t,6 6,(4t) 6,(4s,4t)

Si/X

(gel) 45 19 45 45 24 45 45

18 d6,4t,(4s) 45 4t 6,(d4t)<) d6,(4t) 6,(4t)

37 45 45 45

Si-source Ludox Ludox Ludox Ludox Ludox Ludox Ludox Ludox Ludox Ludox Ludox Ludox Ludox

colour6) before/after calc white white white

white white white

brownish brownish white white pink green blueish white green white white

white white purple grey brwn/blue white yellow white white

XRD result (structure) ZSH-5 ZSM-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5

IR purity

(I) 102.6 83.3 82.3 94.6 92.0 85.4 93.8 93.3 91.9 80.0 91.6 93.1 83.4

n-hexane ads ( i l / g )

0.140 0.124 0.131 0.134 0.151 0.138 0.114 0.153 0.128 0.142 0.142 0.147 0.136

hexane/IR

(■1/9) 0.136 0.148 0.159 0.142 0.164 0.162 0.122 0.164 0.139 0.178 0.155 0.158 0.163

Hn I I Fe I I Fe I I I Co I I Mi I I Cu I I Zn I I Hg I I U IV') Zr IV V V

HnlOAch FeS04 Fe2(S0«b CoS0« HiS0« CuCh ZnS0« Hgl2d) Ti0S04+Hi02

6 , ( 4 t , 4 s ) 4 t , ( 6 ) 4 t ,6 6 , ( 4 t ) 6 , ( 4 s , 4 t ) d6 ,4 t , ( 4s ) 4t 4t 4t

ZrOCli+HzOz 4 t , 6 , ) 7 NHWO3 d6 , (4 t )

45 45 45 45 45 45 45 45 45 45 45

HG HG UG HG HG UG HG UG UG HG HG

brownish brownish white white pink green blueish white white white white white

white white purple beige blue white white white white white

ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5 ZSH-5

82.0 77.9 76.4 80.5 69.8 83.4 73.5 95.0 74.0 86.9 92.0

0.138 0.132 0.136 0.140 0.128 0.155 0.108 0.151 0.149 0.127 0.144

0.168 0.170 0.178 0:174 0.184 0.186 0.138 0.159 0.201 0.146 0.157

') preferred coordination nueber-. 4s=square planar, 4t=tetrahedral, 6;octahedral, a d prefix aeans distorted; between brackets: alternative non-preferred configurations. [15]

b) after calcination at 550°C. c) data for Cr(III); Cr(Vl) will accowodate 4t. ') Hgl2 hardly dissolved. ') zeolite crystallization 2 days at 180°C.

The resu l t s of the syntheses, including data on the above-mentioned

propert ies , are l i s t e d in Table 1. The pore volume was measured to verify

whether or not pores are obstructed by e x t r a - l a t t i c e c l u s t e r s of the

T-atom oxide or hydroxide. For a w e l l - c r y s t a l l i z e d ZSM-5 sample a value of

40 Substitution in ZSM-5

0.18 ml/g has been accepted for the adsorption of n-hexane [13] at 40°C. The purity of the sample' can be estimated from the IR spectrum [14] as a convenient means of analysis. Table 1 also shows the hexane adsorption of the various materials normalized via IR purity to pure ZSM-5 (=hexane/IR). The data in Table 1 show that all syntheses yield a product with a ZSM-5

type structure. Infrared data show a substantial variation in zeolite crystallinity from 70-100*. Nevertheless, the ZSM-5 structure is also clearly evident in the samples of relatively low crystallinity. It should be noted that amorphous materials cannot be detected using routine X-ray diffraction, whereas the difference is clear in infrared spectra. The amount of n-hexane adsorbed, normalized to a pure ZSM-5 together

with the colour of the sample, can be used to judge whether the ion is properly incorporated into the lattice or not. A white sample with a normalized adsorption of more than 0.16 ml hexane/g (allowing 10% for experimental errors) is supposed to have the substituting ions incorporated in the lattice. This leaves the samples prepared from gels containing Fe(III), Fe(II) and Ti(IV), and -for Ludox as the silica source- Zn(II) and Te(VI). It may be noted that these ions will all fit in a tetrahedral coordination, except for Te(VI) which prefers an octahedral coordination. Coloured impurities however cannot be observed in this case, because Te salts (as well as Ti and Zn salts) are white. Ball et al.[91 use MAS-NMR to show that Zn is only partially incorporated in a Silicalite lattice.

The incorporation of the substituting ions in a zeolite lattice may have an analogon in the phosphates: it is well-known that the phosphates of B(III), Al(III), Ga(III), Fe(III), As(III) and Sb(III) show a structure resembling that of quartz. In addition to the present analyses chemical analytical data of the

ZSM-5 samples will be required in order to establish the presence of the T2 atoms quantitatively.

Substitution in ZSM-5 41

Information about the acid properties can be obtained with temperature programmed desorption of ammonia from ammonium-exchanged and calcined ZSM-5 samples. During ion exchange of Cr-containing samples (using either NH4C1 or HC1 solutions as exchange reagents), the exchange solution turned yellow, indicating extraction of Cr from the sample. Repeated (3 times) ion exchange using a 0.5 M HC1 solution yields a green (Cr(III)) sample and an almost colourless exchange solution after the last exchange. Chemical analysis shows that only the first exchange results in a significant decrease in Cr content of the sample, indicating two types of Cr present in the as-synthesized material. Note that only the substituting elements with a 2+ or 3+ valency will yield cation exchange capacity and the possibility of generating acid properties. Boro-, chromo- and ferrisilicate (all ions having valency 3+) are reported to show acid properties [7,8], all with a lower acid strength than a corresponding [Al]-ZSM-5 sample. [Cr]-ZSM-5 samples used in the ammoxidation of toluene (see Chapter 6) show a good activity and selectivity. In these samples the zeolite pore system will still be accessible to the reactants.

TPD experiments on most of the samples of Table 1 show hardly any ammonia-desorption at temperatures above 350°C. The only samples with a measurable high-temperature desorption are the zeolites containing Fe(III) (Ludox, WG) and Mn(II) (Ludox), and, with a smaller desorption, Fe(II) (Ludox, WG). Figure 1 shows the NH3-TPD curves of a ferrisilicate and of an aluminosilicate ZSM-5 sample with a comparable hetero-atom content. The acid strength of the former zeolite is somewhat lower, as was also shown by other Workers by means of several analytical methods [12,16,17]. The sample containing Mn has a much lower acid strength, as evidenced by a lower desorption temperature (390°C compared to 440-480°C for Fe(III)). It should however be noted that the manganosilicate zeolite contains some non-zeolitic impurities, as judged from the brownish colour of the sample.

Substitution in ZSM-5

Figure 1: TPD curve of a ferrisilicate and an aluminosilicate ZSM-5 zeolite sample, a) [Fe(III)]-ZSM-5 (Ludox, Si/Fe=45); b) [Al]-ZSM-5 (Ludox, Si/Al=50).

The amount of substitution seems to be limited to a low T2 content (e.g. less than 2-4 T2/UC). Attempts to synthesize a ferrisilicate sample with a higher content (8 Fe/uc, Si/Fe=ll) yielded a brown sample. Mossbauer analysis [19] of this sample showed the presence of two types of Fe, which are assumed to be an extra-lattice-type and an incorporated type. Mossbauer measurements on samples with a lower Fe content proved impossible so far due to the low sensitivity without S7Fe enrichment.

Substitution in ZSM-5 43

CONCLUSIONS Crystalline ZSM-5-type zeolites can be synthesized from gels containing

various ions other than Al and Si. Only ions which may be tetrahedrally coordinated appear to be incorporated in the lattice. Temperature programmed desorption of ammonia shows that only the ferri-

silicate ZSM-5 sample exhibits acidic properties comparable to those of aluminosilicate ZSM-5 samples. The Ti(IV)silicate sample does not exhibit acidity, according to expectations. Other ions are expected to be present as impurities in the zeolite

channels or on the outer surface. These ions can usually be extracted using a HCl or a NH4CI solution, as described for the partial exchange of a Cr containing sample. However, addition of these ions to the synthesis gel can be used to influence the catalytic properties of the zeolite as extra-lattice entities, (cf. Chapters 6, 9 and 10)

LITERATURE

1. F.G. Dwyer, E.E. Jenkins, US Patent 3.941.871 (1976). 2. L.Marosi, J. Stabenow, M. Schwarzmann, Ger. Offen. 2.831.631 (1980). 3. M. Taramasso, G. Manara, V, Fattore, B. Notari, Ger. Offen. 2.924.915

(1980). 4. J.A. Hinnekamp, V.V. Walatka, Ger. Offen. 3.215.069 (1981). 5. J.K. Minderhoud, T. Huizinga, S.T. Sie, Eur. Patent 173.381 (1984),

CA 104, P209940s (1986). 6. R. Szostak, T.L. Thomas, J. Catal., 100, (1986), 555. 7. T. Inui, A. Miyamoto, H. Matsuda, H. Nagata, Y. Makino, K. Fukuda,

F. Okazumi, "Proc. VII Int. Zeol. Conf.", (Eds. Y. Murakami, A. Iijima, J.W. Ward), Tokyo 1986, p.859-866.

8. R.B. Borade, A.B. Halgeri, T.S.R. Prasada Rao, "Proc. VII Int. Zeol. Conf.", (Eds. Y. Murakami, A. Iijima, J.W. Ward), Tokyo 1986, p.851-858.

9. W.J. Ball, S.A.I. Barri, S. Cartlidge, B.M. Maunders, D.W. Walker, "Proc. VII Int. Zeol. Conf.", (Eds. Y. Murakami, A. Iijima, J.W. Ward), Tokyo 1986, p.951-956.

10. K.G. lone, L.A. Vostrikova, A.V. Petrova, V.M. Mastikhin, in: "Proc. VIII Int. Congr. Catal.", Berlin 1984, vol. IV, p.519.

11. K.G. lone, L.A. Vostrikova, V.M. Mastikhin, J. Mol. Catal., 31, (1985), 355.

12. L.M. Kustov, V.B. Kazansky, P. Ratnasamy, Zeolites 7, (1987), 79.

44 Substitution in ZSM-5

13. D.H. Olson, W.O. Haag, R.M. Lago, J. Catal., 61, (1980), 390. 14. J.C. Jansen, F.J. van der Gaag, H: van Bekkum, Zeolites, 4, (1984),

369. 15. F.A. Cotton, G. Wilkinson, "Advanced Inorganic Chemistry", J. Wiley &

Sons, New York, 1980. 16. W.J. Ball, J. Dwyer, A.A. Garforth, W.J. Smith, "Proc. VII Int. Zeol.

Conf.", (Eds. Y. Murakami, A. Iijima, J.W. Ward), Tokyo 1986, p.137-144.

17. C.T.-W. Chu, CD. Chang, J. Phys. Chem., 89, (1985), 1569. 18. R. Szostak, V. Nair, T.L. Thomas, J. Chem. Soc, Faraday Trans. I,

83, (1987), 487. 19. Measurements of Dr. A.M. v.d. Kraan, IRI, Delft, which are gratefully

acknowledged.

Morphology and acid site distribution of ZSM-5 zeolites. 45

A note on the effect of the template on the acid features and the particle size of ZSM-5 zeolites.

Abstract: A series of ZSM-5 zeolites was synthesized using different templates under fast crystallization

conditions using Aerosil and waterglass as the silica source. It seems that the more effective the template,

the smaller the crystals formed. It is concluded that a pronounced p state NH3-desorption is related to the

presence of imperfections in the zeolite crystals.

Introduction: Temperature Progammed Desorption (TPD) of volatile bases like ammonia is used to

characterize the acid sites of zeolites. Three desorption peaks are distinguished in the TPD of ammonia

from zeolite H-ZSM-5: the a, p and ypeak, with maxima at 400,500 and 775 K[1], respectively. The a state

peak is ascribed to the desorption of physisorbed NH3. The p and y state peaks are ascribed to Lewis and

Bransted acid sites, respectively.

Previous experiments[2] showed that the 'template strength' in forming (and stabilizing) ZSM-5 zeolite is

in the order: TPA > 1,6-hexanediamine > 1 -propanamine > 1,6-hexanediol > 1 -propanol > pentaerythritol.

SEM micrographs (Figure 1) indicate that the morphology changes in the same order from particles without

crystalline appearance to well-crystallized samples. Although only shown here for Aerosil as silica source,

similar micrographs are obtained for samples prepared using waterglass. This note will show that the results

obtained using NHg-TPD experiment bear a relation to the particle size of and the template used in the

preparation of the ZSM-5 crystals.

Experimental: ZSM-5 zeolites were synthesized using tetrapropylammonium bromide (TPA-Br),

1,6-hexanediamine, 1,6-hexanediol, pentaerythritol (PET), 1-propanamine and 1-propanol as template.

The zeolites will be referred to as ZSM-5 (TPA), ZSM-5 (hexanediamine) etc. Aerosil and waterglass were

used as silica source, and the corresponding Al sources were sodium aluminate and aluminum sulphate.

Synthesis was performed in stainless steel autoclaves for 48 hours at 180°C as described in earlier [2]. The

products were identified as pure ZSM-5 zeolites using X-ray diffraction and infrared spectroscopy. An

exception is the sample prepared from waterglass using PET as the template. Infrared spectroscopy,

showed this sample to contain some amorphous material. The. zeolites were calcined at 823 K and

ammonium exchanged using 2M NH4CI (10 ml/g) at 353 K for 1 hour. The zeolites were dried at 373 K

prior to further use. All zeolites had a charged Si/AI ratio of 35 (silica source Aerosil) or 45 (silica source

waterglass). AAS analysis of part of the samples (after dissolution in HF) showed that the chemical

composition of the product is close to as the composition of the synthesis mixture[2].

A sample of F-Silicalite [3] was included for comparison.

NH3-TPD spectra were measured on 100 mg samples of the NH4-ZSM-5 zeolites. Before recording the

spectrum the zeolite was heated to 873 K in the TPD apparatus under flowing nitrogen. The sample was

then cooled to ca 300 K and a flow of NH3 was adsorbed for half an hour. After displacement of the NH3

vapour with nitrogen the sample was heated at a rate of 10 K/min in flowing nitrogen. The rate of NH3

46 Morphology and acid site distribution of.ZSM-5 zeolites.

Figure 1: SEM micrographs showing the particle size of the zeolite samples (Aerosii used as silica

source).

Morphology and acid site distribution of ZSM-5 zeolites. 47

desorption was measured using a thermal conductivity detector. Peak areas (corresponding to amounts of

desorbed ammonia) were determined by cutting out and weighing the peaks. The homogeneity of the

paper was checked.

BET surfaces were determined on an Areameter using a single point method.

Results and discussion: Typical NH3 -TPD spectra of the zeolites are shown in Figure 2. Ratios

between the areas under the TPD peaks (and therefore relative amounts of desorbed NH3) are presented

as bar graphs in Figure 3, together with BET surface areas. In the TPD spectra of ZSM-5 (TPA) and ZSM-5

(hexanediamine) the a state desorption looks more pronounced than in the other spectra indicating a

relatively better crystallized pore system.

Figure 2: NH3-TPD spectra of ZSM-5-type zeolites. Templates used: a: TPA; b: 1,6-hexanediamine;

c: 1-propanamine; d: 1,6-hexanediol; e: 1-propanol; f: PET.

The. a/y ratio in Figure 3 is about the same for all templates in the Aerosil as well as the waterglass

experiments suggesting that pore volume variations and number of Bronsted sites go parallel (bearing in

mind a constant Al content). The ct/p ratio in the spectrum of ZSM-5(TPA) and to a lesser extend in the

spectrum of ZSM-5 (hexanediamine) are high compared to the spectra of the other templates. Apparently

there is less material causing (3 state desorption (e.g. extra-lattice Al, lattice imperfections, side products)

formed using the first two templates than when using the other templates.

Obviously, the same trend appears to be present considering the yp ratio in Figure 3. Consistent with the

48 Morphology and acid site distribution ot 2SM-5 zeolites.

above explanation is the higher BET area of ZSM-5 (TPA) compared to the BET areas of the other

templates. Low pore blocking and highly crystalline material creating the proper surface area is expected to

result from the high templating strenght of TPA in ZSM-5 crystallization.

Aerosi l

Y / f i 0-/Y <*■/$> BET area

Waterglass

Vr'fb a / Y C*/|S BET area

Figure 3: Bar graphs showing NH3-TPD and BET data for samples of ZSM-zeolites prepared using

different templates.

As shown in Figure 1 the crystal size and agglomeration of crystallites seems to depend upon the typical

template used in the synthesis mixture. As discussed the differences in the above mentioned particle size

influence the TPD spectra, as reflected in the variations in Figure 3. A strong template yields a faster

nucleation (and therefore smaller crystallites) and a better formed crystal structure (i.e. a better defined

TPD spectrum). In spite of the spheroid appearance of the crystals, the pore structure is better formed and

accessible to adsorbates.

It is concluded that:

-Using the template TPA, aluminum is more regularly incorporated as T-atom in the lattice system than with

the other templates studied.

-1,6-hexanediamine is the second to TPA in this respect.

-The other templates show more pronounced Lewis acid features according to the TPD spectra.

Morphology and acid site distribution of ZSM-5 zeolites. 49

-A well-formed pore system (according to TPD) corresponds to badly formed crystals (shown in SEM

micrographs) and vice versa, in the series studied.

-The present findings underline the necessity to establish of the quality of a zeolite sample using

a combination of techniques.

Literature:

1. N.Y. Topsee, K. Pedersen, E.G. Derouane, J. Catal., 70, (1981), 41.

2. F.J. van der Gaag, J.C. Jansen and H. van Bekkum, Appl. Catal., 17, (1985), 261.

3. E.M. Flanigen, R.L. Patton, US Patent 4.073.865, (1976).

50 Ammoxidation of toluene

A M M O X I D A T I O N O F T O L U E N E O V E R

M O D I F I E D Z S M - 5 T Y P E C A T A L Y S T S .

F .J . van der Gaag, G.F. Herlaar and H. van Bekkum, Laboratory of Organic Chemistry, Delf t Univers i ty of Technology, Ju l i ana laan 136, 2628 BL DELFT, The Netherlands.

ABSTRACT.

Toluene was ammoxidized over modified ZSM-5 type

zeolites as catalysts. Modification was performed by

(partial) T-atom substitution of Fe and Cr for Al in the

synthesis gel and by ion exchange. Especially zeolites

CuCrH-ZSM-5 and CuH-[Fe]-ZSM-5 proved to combine high

activity in the ammoxidation at 350° C with high

selectivity to benzonitrile.

INTRODUCTION.

Ammoxidation is a process converting hydrocarbons containing activated

methyl groups such as toluene, the xylenes and propene to the

corresponding nitriles. As for the synthesis of benzonitrile, several

studies have been published, envisaging the use of mixed oxides consisting

of vanadium, molybdenum and chromium [1,2]. Also catalysts with low

oxidation power such as solid acids like Si02-Al203, Zr02-Si02 and

TiÜ2-Si02 were found to possess ammoxidation activity [3]. For the

oxidation of toluene and related aromatics Jonson et al. [4] recently

have suggested a relation between an infrared vibration of oxidic

catalysts and the activity of the catalyst; high activity is reported for

CuO, Cr2Ü3 and Fe2Ü3 catalysts, which have an infrared vibration near 520

cm"1. Ohorodnik et al. [5] demonstrated that impregnation of a bismuth-

phosphomolybdate propene ammoxidation catalyst with an Fe solution

increases the activity. Deactivated catalysts can be restored to their

Ammoxidation of toluene 51

original activity by impregnation. In a previous paper [6] we reported on the ammoxidation activity of a

Cu-H exchanged ZSM-5 type zeolite catalyst in converting toluene into benzonitrile. When water was added to the feed, a significant increase in activity and selectivity was observed. Water is supposed to play a role either as a ligand to the Cu ion, in proton transport and/or as a decoking agent. Optimum selectivity to benzonitrile was observed at 350°C. In this paper we present data on the ammoxidation activity of a

series of exchanged and T-atom substituted ZSM-5-type catalysts. In particular the effect of Fe- and Cr-incorporation was studied, as these metals have been shown to enhance the ammoxidation activity of amorphous catalysts.

EXPERIMENTAL. Catalysts. Zeolite ZSM-5-type catalysts were synthesized according to the patent

literature [7-10]. Two procedures were used, one using Aerosil as the silica source and the other using waterglass. The first procedure comprised mixing an Aerosil (Degussa) suspension

with a solution containing sodium hydroxide, the secondary T-atom(s) source and the template TPA-Br, 1,6-hexanediol or 1,6-hexanediamine [11] (Janssen Chimica), followed by crystallization for 48 hours in a Teflon-coated autoclave at 180°C with stirring. The second method comprised mixing a waterglass solution with a solution

containing sulfuric acid, the secondary T-atom(s) source and TPA-Br, followed by a crystallization under the same conditions as for method 1. The secondary T-atom was supplied as sodium aluminate (Aerosil method,

Riedel-de Haehn), aluminum sulfate (waterglass method, Merck), chromium(III)sulfate (Merck) or ferrous sulfate (UCB). When the secondary T-atom is not Al, the zeolite is denoted [X]-ZSM-5, with X being the guest

52 Ammoxidation of toluene

T-atom. [Fe]- and [Al,Fe]-ZSM-5 were prepared using TPA-Br as the

template, 1,6-hexanediamine was used for [Cr]- and [Al,Cr]-ZSM-5.

In both procedures the synthesis product was filtered, washed and dried.

The ZSM-5-type structure was inspected by X-ray diffraction. The

as-synthesized samples were white and remained white during calcination at

550°C. An exception is [Cr]-ZSM-5, which was light-green after drying and

yellow after calcination, showing that part of the Cr is not incorporated

in the lattice. H-exchange was performed by exchanging the calcined

zeolite twice with a 0.5 M HC1 solution (100 ml/g of zeolite, 80°C, 0.5

hr). Under these conditions part of the Cr was leached out of the

[Cr]-zeolites, as evidenced by a yellow colour of the exchange solution

after filtration. The effect of Cr-extraction during H-exchange was .

monitored in a separate experiment. AAS analysis of [Cr,Al]-ZSM-5 samples

(see Table 2) show that the Cr content decreases from 0.88 Cr/uc

(Si/Cr=100) to 0.45 Cr/uc (Si/Cr=195) during the first exchange.

Subsequent exchanges do not cause a significant further decrease in Cr

content. The Al content of this sample was constant at 6.5 Al/uc

(Si/Al=13.6).

M"+-exchanged MH-ZSM-5 zeolites were prepared by exchanging H-ZSM-5

twice using a 0.05/n M solution, of the desired metal ion (100 ml/g of

zeolite, 80°C, 0.5 hr). AAS analyses of [Fe]-ZSM-5 and Cu-[Fe]-ZSM-5

samples showed Si/Fe=19 and a Cu content of the latter sample of 0.91 wtfc

Cu (17 % exchange),

The catalysts were dry pressed, crushed and sieved to obtain particles

of 1.4-2.0 mm diameter.

Apparatus and procedure.

The catalyst (usually 3 g) was placed in a fixed-bed continuous flow

glass microreactor. The reactor was placed in an electronically

controlled fluid-bed oven and heated to the reaction temperature. The

Ammoxidation of toluene 53

reaction mixture was then passed over the catalyst using air as the

carrier gas. Standard reaction conditions are as follows : molar

composition: toluene: ammonia: water: oxygen=l:2:6:4.7, WHSV(toluene)=

0.17 hr"1, reaction temperature 350°C. The product mixture was analyzed by

on-line gas chromatography, and, if necessary, components were identified

by GC/MS. The selectivity to benzonitrile and the toluene conversion are

almost constant after the first few hours of reaction. A typical

conversion versus time plot is given in Figure 1. The analytical data

reported in the following were obtained after a reaction time of

approximately 4 hours.

16 20 24 — t(hr)

FIGURE 1: Typical plots for toluene conversion ( ) and selectivity to benzonitrile ( ) vs. time-on-stream, Standard conditions, catalyst: CrH-ZSM-5(25).

RESULTS AND DISCUSSION.

The product mixture of the toluene ammoxidations usually contains

toluene, benzene, benzonitrile and carbon dioxide. Sometimes traces of

benzyl alcohol and benzaldehyde were observed. Hydrogen cyanide appears to

be absent (tested using a 'Draeger' detection tube).

The results for the ammoxidation of toluene over several M"*-exchanged

54 Ammoxidation of toluene

ZSM-5-type catalysts are summarized in Table 1. Highest activity is exhibited by CuH-ZSM-5, FeH-ZSM-5 and CrH-ZSM-5, whereas the highest selectivity to benzonitrile is shown by CuH-ZSM-5(25.7) and NiH-ZSM-5. The activity sequence agrees with the observations made by Jonson et al. [4] for the oxidation of toluene to benzaldehyde over oxidic catalysts. Here a very high activity is reported for CuO, Cr203 and Fe203 and a lower activity for NiO and ZnO. The oxidation activity is related by these authors to an 1R vibration near 520 cm"1 and with semi­conducting properties of the oxide. Both conditions are fulfilled in a ZSM-5-type zeolite.

TABLE 1: Ammoxidation results*> for M-exchanged ZSM-5-type catalysts.

Catalyst type Na-ZSM-5 H-ZSM-5 CuH-ZSM-5 CrH-ZSM-5 FeH-ZSM-5 NiH-ZSM-5 ZnH-ZSM-5 CuCrH-ZSM-5 CrCuH-ZSM-5 CuH-ZSM-5 CrH-ZSM-5 CuCrH-ZSM-5 CrCuH-ZSM-5

Si/Al (gel) 25.7 25.7 25.7 24.9 25.7 25.7 25.7 25.7 25.7 44.5 44.5 44.5 44.5

Conversion (wtX)

7.1 14.2 100 98.5 100 24.0 10.3 100 100 100 96.8 100 100

Selectivity (wt%) to benzonitrile benzene

52.6 60.5 78.0 45.7 1.9

80.5 28.9 92.3 84.4 29.5 92.3 57.2 73.6

39.9 38.1 18.7 52.4 93.0 17.8 67.4 3.2 14.0 65.1 6.3 38.3 22.9

CO2 7.5 1.4 3.3 1.9 5.1 1.7 3.7 4.5 1.6 5.4 1.4 4.5 3.5

*' Results after 4 hours on stream, conditions: 350°C, WHSV(toluene)= 0.17 hr"1, standard feed composition.

In our previous work [6] we showed CuH-ZSM-5 zeolite to be much more selective in the toluene ammoxidation than CuY catalysts. Fraenkel et al. [12] also show that Cu-ZSM-5 zeolites are much more active in ammoxidation (of methylnaphthalenes) than other Cu-exchanged zeolites. These authors conclude that the ZSM-5 outer surface structure is involved

Ammoxidation of toluene 55

in the catalytic process, as for methylnaphthalenes the reaction would

seem to be restricted to the outer surface of the zeolite because of the

molecular dimensions. It might be noted that ZSM-5 has a much stronger

infrared vibration near 520 cm-1 than most other zeolites. FeH-ZSM-5 has

a low selectivity for benzonitrile and produces mostly benzene. This can

be caused by problems during Fe-exchange of the zeolite. In this

procedure some ferric hydroxide precipitated, even though the exchange was

performed in an acidic solution under nitrogen. Incorporating Fe in the

zeolite under conditions where no ferric hydroxide precipitation can

occur might be an effective way of increasing the catalytic activity

without affecting selectivity. Chromium is especially selective when

present in a zeolite with a relatively high Si/Al ratio (selectivity

increases from 45.7* to 92.3% when the Si/Al ratio is increased from 24.9

to 44.5). It may be noted that treatment of a zeolite with a

chromium(III) solution is reported to cause, besides exchange, also

dealumination of the zeolite [13].

The doubly exchanged catalysts, and especially CrCuH-ZSM-5 (first

exchanged with Cu(II) and then with Cr(III)) are very active.

Selectivity (not only for the Cr exchanged samples) depends on the Si/Al

ratio, here with the higher ratios being less selective.

In another approach, Fe and Cr ions were introduced during synthesis

of the zeolites generally in the absence of Al. The results of

ammoxidation experiments with [Fe]-ZSM-5 and [Cr]-ZSM-5 catalysts are

shown in Table 2. These materials can contain some non-zeolitic material.

H-[Cr]-ZSM-5 and H-[Al,Cr]-ZSM-5 catalysts are indeed more active than

H-ZSM-5. However, these catalysts are less active than the best catalysts

in Table 1. H-exchange has a positive effect on the selectivity of the

chromium-containing ZSM-5 type catalysts, as can be seen from the

comparison between the ZSM-5 catalyst and the corresponding H-ZSM-5

56 Ammoxidation of toluene

material. In this case, the unexchanged material probably contains some occluded extra-lattice chromium, which causes a low ammoxidation activity and a high selectivity for benzene. During acid exchange the surplus

TABLE 2: Ammoxidation results*' for [X]-ZSM-5-type catalysts.

Catalyst type H-ZSM-5 H-[Al,Cr]-ZSM-E H-[Cr]-ZSM-5 H-[Cr]-ZSM-5 [Al,Cr]-ZSM-5 [Cr]-ZSM-5 H-[Fe]-ZSM-5 CuH-[Fe]-ZSM-5 CuH-[Fe]-ZSM-5 CuH-[Fe]-ZSM-5 CuH-[Fe]-ZSM-5

Si/Al (gel) 25.7 25 --25 ------

Si/X (gel) -80 88 88 80 88 45 45 45 45 45

* > Results after 4 hours on

Temperature <°C) 350 350 335 350 350 350 360 295 310 325 340

stream,

Conversion (wt*)

14.2 86.6 35.0 75.1 94.0 100 99.8 40.0 67.3 97.7 99.4

WHSV(toluene)=

Selective Lty benzonitrile 60.5 77.6 85.8 86.4 41.9 24.1 76.9 92.9 94.3 95.1 94.4

0.17 hr-1

(wt*) to benzene 38.1 20.4 9.8 12.3 53.2 71.3 12.3 1.9 1.8 2.8 1.5

CO2 1.4 2.0 4.4 1.3 4.9 4.6 10.8 5.2 3.9 2.1 4.1

, standard feed composition.

chromium is leached out of the zeolite, causing a somewhat lower total activity and a higher selectivity to benzonitrile.- During the ammoxidation reaction the colour of the [Cr]-ZSM-5 catalyst changed from yellow to light green, indicating a change from Cr(VI) to Cr(III). This is a sign that the remaining chromium is still not totally incorporated in the zeolite lattice. It is questionable whether Cr ions can be introduced' in the zeolite lattice. lone [10] states that only ions with a tetrahedral coordination (Al, B, Be, Ga and Fe) can be built in. The H-[Fe]̂ -ZSM-5 catalysts combine a very high activity and a high

selectivity to benzonitrile, especially when they are used in the CuH-exchanged modification. The latter catalyst possesses the highest selectivity to benzonitrile of all catalysts tested. This also indicates that FeH-ZSM-5 contains non-zeolitic Fe (oxide) particles instead of

Ammoxidation of toluene 57

exchanged Fe ions. Note that the results are obtained at even lower

temperatures compared to an experiment with a Cr-containing catalyst.

In Figure 2 conversion and selectivity are plotted versus reaction

temperature. The conversion increases with increasing temperature reaching

100* at 325°C, while selectivities stay almost constant.

295 310 325 3<0 360

FIGURE 2: Effect of reaction temperature on conversion & selectivities in the aimnoxidation of toluene over CuH-[Fe]-ZSM-5(45), WHSV(toluene)=0.17 h"1, standard feed composition; • conversion, x benzonitrile, + benzene, o CO2.

FIGURE 3:Selectivities. and conversion in toluene ammoxidation for [Fe,Al]-ZSM-5. zeolites vs. Fe content. Standard reaction conditions; • conversion, o benzonitrile, x benzene, + CO2.

58 Ammoxidation of toluene

The effect of the Fe content of the zeolites was examined using a series

of [Al,Fe]-ZSM-5 catalysts, synthesized according to both the Aerosil and

the waterglass method. The results for the waterglass-based catalysts are

shown in Figure 3. For the Aerosil-based catalysts a similar picture is

obtained.

The plots show that the toluene conversion increases with increasing Fe

content, whereas the changes in selectivities are not pronounced. This

shows that the Fe ions are catalytically active. In Chapter 4 evidence

is produced that Fe ions are built in in the zeolite lattice.

O—O—H / ■ Cu(l> — - -

■■'WO

Scheme lb

SCHEME 1: Possible reaction mechanisms.

Thus, the catalytic activity is found to increase with increasing Fe

content of the [Al,Fe]-ZSM-5 catalysts as well as upon Cu (or Cr)

exchange of the zeolite while in both cases the selectivity remains almost

constant. This suggests a mechanism in which both the exchanged ion (Cu,

C u ( l l ) NH,

Cu( l )

O—O" /

— C u ( l l ) / \

U NH,

H,C - @

Snhfmwa 1 a

o?- — cw '/MM/M'jd/// r ^ Zeoliet :

4 W A W M M m ^ Z e o l i e t wy/w.

H,0 ► N H ,

o-« — o-^ NH

777T?7Tr777777777777/ % Z e o l i e t : ^ ^ /y///////////////////

Ammoxidation of toluene 59

Cr) and the secondary T-atom can play a role. The present experiments do not allow the formulation of a detailed mechanism. However, the following considerations can be made. First, ammonia may be assumed to be present as NH4+ and NH3 in

equilibrium with (residual) Bronsted acid sites of the zeolite as well as liganded (as NHa and also - in view of the reaction temperature - as NH2-) to the Cu (or Cr) ions. Oudejans et al. [6] showed using EPR that copper is mainly present in Cu-ZSM-5 as single Cu(II) ions. For Cu it could not be shown that Cu(II) is reduced to Cu(I) under reaction conditions, but catalysts containing Cr show that reduction is indeed taking place by changing from yellow (Cr(VI)) to green (Cr(III)). Moreover, it is known that Cu(II) can be reduced to Cu(I) by NH3 [14]. This led Oudejans et al. to suggest a mechanism in which toluene enters into a (Rideal-like) reaction with 02" and NH2 ligands of a Cu(II) site in which hydrogen is transferred from toluene to oxygen with simultaneous C-N bond formation and electron uptake by the Cu (see Scheme la). . Here nitrogenated intermediates are formed.

Secondly, a mechanism can be formulated on the analogy of literature [16,17] on the ammoxidation over e.g. bismuth molybdate catalysts. In such a mechanism a hydrogen is abstracted from the methyl group of toluene, forming a benzylic species. This species may be transformed into benzonitrile as indicated schematically in Scheme lb. It can be imagined that the Fe and Cr ions incorporated in the zeolite lattice play a role in this mechanism. It may be noted that oxygenated species (benzyl alcohol, benzaldehyde) were detected in small amounts in the experiments. The present data do not allow the formulation of a more definite

mechanism of the ammoxidation of toluene over ZSM-5-type zeolitic catalysts.

60 Ammoxidation of toluene

LITERATURE.

1. J.J.J. den Ridder, Thesis, Delft University of Technology, 1981. 2. Y. Murakami, M. Niwa, T. Hattori, S. Osawa, I. Iguahi and H. Ando,

J. Catal., 49, (1977), 83. 3. M. Niwa, M. Sago, H. Ando and Y. Murakami, J. Catal., 69, (1981), 69. 4. B. Jonson, R. Larsson and B. Rebensdorf, J. Catal., 102, (1986), 29. 5. A. Ohorodnik, K. Sennewald, H. Erpenbach and H. Vierling, Ger. Offen.

2.104.223 (1972), Ger. Offen. 2.127.996 (1972), Ger. Offen. 2.127.997 (1972), Ger. Offen. 2.155.776 (1973), Ger. Offen. 2.155.777 (1973).

6. J. C. Oudejans, F.J. van der Gaag and H. van Bekkum, in "Proc. VI Int. Zeol. Conf.", Reno 1983, Publ. 1985, p.536.

7. L. Marosi, Ger. Offen. 2.831.630 (1982). 8. M.R. Klotz, US Patent 4.405.502, US Patent 4.405.504 (1983). 9. T. Inui, 0. Yamase, K. Fukuda, A. Itoh, J. Tarumoto, M. Morinaga, T.

Hagiwara and T. Takegami, in "Proc. VIII Int. Congr. Catal.", Berlin 1984, vol. Ill, p.569.

10. K.G. lone, L.A. Vostrikova, A.V. Petrova and V.M. Mastikhin, in "Proc. VIII Int. Congr. Catal.", Berlin 1984, vol. IV, p.519.

11. F.J. van der Gaag, J.C. Jansen and H. van Bekkum, Appl. Catal., 17, (1985), 261.

12. D. Fraenkel, B. Ittah and M. Levy, in "Poster Preprints VII Int. Zeol. Conf.", Tokyo 1986, p.271.

13. W.E. Garwood, N.Y. Chen and J.C. Bailar Jr., Inorg. Chera., 15, (5), (1985), 1044.

14. I.E. Maxwell and E. Drent, J. Catal., 41, (1976), 412. 15. S.L.T. Andersson, J. Catal., 98, (1986), 138. 16. J.D. Burrington, C.T. Kartisek, R.K. Grasselli, J. Org. Chem., 46,

61

REACTION'OF ETHANOL AND AMMONIA TO PYRIDINES OVER ZEOLITE ZSM-5

F.J. VAN DER GAAG, F. LOUTER, J.C. OUDEJANS1 and H. VAN BEKKUM Laboratory of Organic Chemistry, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands. Present address: Unilever Research Laboratory, Olivier van Noortlaan 120,

3133 AT Vlaardingen, The Netherlands.

(Received 2 December 1985, accepted 10 March 1986)

ABSTRACT Pyridine bases are formed by reacting ethanol and ammonia in the presence of

air in a.continuous flow microreactor over zeolite ZSM-5. Optimum selectivity to pyridine and optimal conversion are obtained using a HZSM-5 catalyst with Si/Al = 65 at temperatures between 600 and 650 K. Other catalysts i.e., Co-, Fe- or Cd-HZSM-5, HY, HMordenite or amorphous silica-alumina show lower selectivity and/or activity. When air as a vector gas is replaced by nitrogen, no pyridines are formed. For the ethanol-ammonia reaction to pyridines a mechanism is suggested. INTRODUCTION

Since the discovery of zeolite ZSM-5 numerous ZSM-catalyzed reactions have been studied. The conversion of methanol and ethanol to hydrocarbons [1-3], the alkylation of benzene [4], the isomerization of xylenes [5], the alkylation [6] and disproportionation of toluene [7] are the most frequently reported.

A relatively small number of recent papers deal with reactions catalyzed by zeolite ZSM-5 in which ammonia is one of the reactants [8-17]. The synthesis of amines from alcohols, ethers or olefins was reported in the patent literature [8,11,12,16]. Zeolites like ZSM-5, erionite and cl inoptilolite were found to increase the selectivity of the reaction of alcohols to primary amines.

Cu-H-exchanged ZSM-5 type zeolites were reported to be good catalysts in the ammoxidation of toluene [17]. The addition of water to the feed had a beneficial effect on the activity and selectivity.

The production of (methyl-)pyridines from acetaldehyde and ammonia over zeolite HZSM-5 was reported in the patent literature [9]. Depending on the cation of the zeolite the formation of acetonitrile was observed. Recently 2-methyl-pyridine was found to be the principal side product of phenol amination to aniline over zeolite ZSM-5 at high temperature (783 K) [13]. Aniline can also be converted to 2-methylpyridine under similar conditions [14,15]. The conversion is low and many byproducts are found.

From the data available it is clear that in the absence of oxygen in the reactant mixture zeolite ZSM-5 is able to catalyze the conversion of ethanol and ammonia to amines.

62

Here we present data on the reaction of ethanol and ammonia over zeolite ZSM-5 in the presence of oxygen. H+-exchanged as well as metal ion exchanged zeolites have been studied. For comparison also HY, HMordenite, and an amorphous silica-alumina have been included. The influence of some variables on the formation of N-containing compounds (particularly heteroaromatics) is shown and a mechanism is suggested.

EXPERIMENTAL Materials

Zeolite ZSM-5 was prepared as described in the literature [20] using tetra-propylammonium bromide as the organic template. Silicalite was prepared according to the patent literature [21] with NH.F added to the synthesis mixture. The zeolites'were calcined overnight at 823 K before further use. H -exchanged zeolites were prepared by ion exchange in 0.5 M HC1 at ca. 353 K for 0.5 h. (10 g zeolite per 1 solution), followed by thorough washing with water and repeating the pro­cedure. M( )-exchanged zeolites were prepared by ion exchange of HZSM-5 in a 0.05/n M solution of the desired ion under the conditions for H-exchange.

Zeolite HY was prepared by ion exchange of NaY (SK-40, Union Carbide) in an 0.1 M NH.C1 solution (10 g zeolite per 1 solution) for 1 day at room temperature, followed by calcination at 673 K.

Zeolite HMordenite (Zeolon 100H, Norton) and amorphous silica-alumina catalysts, HA-HPV and LA-LPV cracking catalysts (Ketjen), were used without exchange.

All catalysts were dry pressed, crushed and sieved to obtain a sieve fraction of particles of 1.4-2.0 mm.

Procedure The apparatus used in the catalytic experiments is essentially the same as

described by Oudejans [19]. The catalyst (3 g) was placed in a fixed-bed continuous flow glass reactor of

8 mm internal diameter. The reactor was placed in an electronically controlled fluid.bed oven. The carrier gas (usually air) was passed through two thermostatted saturators containing ethanol and an aqueous 0.5 M ammonia solution, respectively. The desired flows of the reactants were obtained by adjusting and controlling the temperature of the saturators and the two flows of the carrier gas. Standard conditions were chosen such that the molar ratio of the reactants was: NH-^C-Hj-OH: HgOiOg = 1:3:6:9. ' The.saturated gas streams were mixed and fed to the reactor at WHSV (ethanol) =

0.17ih.. . The gas mixture leaving the reactor was analyzed by online gas chromato-graphy using a 3 m 10% PEG on Chromosorb column with FID for organic components (temperature programmed operation) and a 1 m PORAPAK Q column with TCD for inorganic components (e.g., CO and C0„, isothermal operation). Peak integration was performed by a computer connected to the gas chromatographs. If necessary products were identified by GC-MS using a Varian 44 S mass spectrometer.

63

> Al/uc

FIGURE 1 Conversion and selectivity (wt%) plotted vs. Al atoms per unit cell in the ethanol-ammonia reaction over HZSM-5.^,0 conversion; | , Q selectivity to pyridine; V , A selectivity to ethene; reaction temperature: 613 K ( 0 , | , V . ) and 633 K ( O . D . A )•

RESULTS Several catalysts have been tested in the conversion of ethanol and ammonia

to pyridine bases. The results of these experiments will be presented and discussed in terms of the influence of single catalyst and reaction parameters on conversion and selectivity.

Effect of Si/Al ratio of ZSM-5 zeolites Data of experiments with HZSM-5 zeolites are presented in Table 1 and Figure 1.

Major products in the ethanol-ammonia reaction - in the presence of water and using air as the vector gas - are ethene, diethyl ether and pyridine. Other components in the product mixture include acetaldehyde, ethylamine, acetonitrile and toluene. Ethyl acetate and 3- and 4-picoline are generally present in amounts < 0.5%. Oxidation to carbon dioxide is substantial but in general lower than 20% (wt%) respectively 8.5% on carbon.

The data show that there is an optimum in pyridine selectivity at relatively high Si/Al ratios.

64

TABLE 1 Effect of Si/Al ratio in the ethanol-ammonia reaction3 over HZSM-5

Si/Al

12.3 12.3

Al/uc

7.2 7.2

Temp. /K

613 628

Conv. 1%

59.9 93.4

Selectivity / wt% ethene

51.4 72.6

diethyl ether

8.0 0.8

to:b acetal-dehyde

3.0 0.5

ethyl-amine

< 0.1 < 0.1

12.5 7.1 613 21.6 29.7 12.0 4.7 0.8 15.4 15.4 20.3

26.3 26.3 26.3

27.3 27.3

55.5 55.5 55.5 55.5C

131.1 131.1 131.1

» » 00

5.8 5.8 4.5 3.5 3.5 3.5 3.4 3.4 1.7 1.7 1.7 1.7 0.7 0.7 0.7 0 0 0

613 633 653 613 633 653 623 643 613 633 653 613 593 633 653 608 638 663

19.3 40.8 83.9

46.8 88.0 98.1

53.0 97.7

34.0 22.9 35.8 18.0

11.3 29.3 50.8

8.1 14.4 32.8

40.9 71.3 90.5

26.3 63.1 76.3

56.9 72.5

23.4 24.0 36.0 32.9

10.0 27.3 51.0

2.2 6.1 9.6

4.4 4.9 0.6 5.4 0.3 1.6 3.4

< 0.1

7.1 13.1 9.0 15.4

7.8 6.9 2.7 1.2 0.6 0.4

1.9 2.8

< 0.1

1.7 0.4

< 0.1

1.7 < 0.1

3.0 5.0 2.9 9.5 5.7 3.6 2.8 19.3 22.6 31.7

0.3 0.3

< 0.1

0.4 < 0.1 < 0.1

0.4 < 0.1

2.2 3.5 1.7

< 0.1

6.8 3.5 1.2 6.4 3.0 2.7

aMolar ratio NH3:C2H50H:H20:02 = 1:3:6:9, WHSV (ethanol) = 0.17 h"1. Composition of product mixture after 4 h on stream. c Experiment with 1% 0 in N- vector gas instead of air.

It is also observed that with increasing number of Al atoms per uc the con­version increases, as the number of acid sites increases. Zeolites with a high Al content show an increased selectivity to ethene.

In general, deactivation of the HZSM-5 catalysts is hardly observed under the conditions used; after an initial period of a few hours a steady state is reached, in which conversion and selectivity stay almost constant over a period of at least 48 hours.

65

a c e t o n i t r i l e toluene pyr id ine 2-p ico l ine CO

3.7

2.7

5.2

4.1

0.1

0.1

8.1

3.5 1.6

4.6

2.8

3.0

2.1 2.5

6.4

3.3 3.1

2.4

0.1

2.6 5.6

< 0 . 1

< 0 . 1

< 0 . 1

3.4

3.7

2.1

< 0 . 1

2.1 0.4

< 0 . 1

< 0 . 1

< 0.1

< 0.1 < 0.1

4.4

< 0.1 < 0.1

< 0.1

12.6

11.9 0.5

13.4

6.1

11.7

10.2

5.5

1.4

36.2

12.4 7.5

18.8

14.5

47.6 33.6

31.5

23.4

43.8

33.5

27.9

16.0 7.0 2.6

4.6

< 0.1

6.8

5.1 1.6

0.3

8.0

0.5 < 0.1

3.9 < 0.1

2.5

2.4

1.8

4.9

2.5

0.8 0.4

< 0.1

< 0.1 < 0.1

14.3

17.3

11.6

20.8

7.3 4.9

11.7

17.3 14.0

10.2

10.2

8.9

13.3

12.0

0.1

20.0

21.2

11.7

38.1 39.7

44.3

Ef fec t o f metal exchange in zeo l i t e ZSM-5 Table 2 shows the analysis data of c a t a l y t i c experiments performed with some

metal ion exchanged HZSM-5 zeo l i t es . In general , HZSM-5 cata lysts show bet ter conversion and/or s e l e c t i v i t y to pyr id ine than the MHZSM-5 z e o l i t e s . FeHZSM-5 shows a r e l a t i ve l y high a c t i v i t y for deep ox idat ion and therefore a low s e l e c t i v i t y to py r id ine . NaZSM-5 shows hardly any a c t i v i t y .

Inf luence of the type of S i -A l - ca ta l ys t

The resul ts of experiments w i th d i f f e r e n t types of zeo l i t e and w i th amorphous

cata lys ts are given in Table 3. A l l cata lysts in Table 3 are , more or l e ss , capable of forming pyridines from

TABLE 2 Ethanol-ammonia reaction using MHZSM-5 catalysts.

Catalyst

CdHZSM-5 FeHZSM-5 CoHZSM-5 CoHZSM-5

Si/Al

28.5 17.9 16.5 16.5

M/uc

0.11 0.38 0.25 0.25

Temp. /K

623 598 613 633

Conv. /%

39.7 75.2 19.9 46.7

Selectivities/wt% ethene

48.0 10.6 33.4 56.9

diethyl ether

7.5 5.3 17.1 7.8

to: acetal-dehyde

1.9 5.1 8.7 4.0

ethyl -amine

0.6 0.8 2.2 1.0

aceto-nitrile

2.1 13.8 2.2 3.0

pyridine

16.5 10.6 7.4 5.0

2-picol

4.1 < 0.1 3.7 1.9

ine 3/4-picoline

2.4 < 0.1 3.5 2.2

co2

16.8 53.7 18.4 18.2

05 05

TABLE 3 Other Si-Al catalyst types

Catalyst Si/Al Temp. Conv. Selectivities/wt% to: /K /% ethene diethyl acetal- ethyl- aceto- pyri- CO.

ether dehyde amine nitrile dine

HMordenite HMordenite HY HY HA-HPV LA-LPV

5 5 2.5 2.5 a b

598 623 598 623 613 613

56.6 97.2 34.1 86.2 43.7 44.1

88.8 87.4 49.2 61.7 16.3 36.6

1.6 0.4 4.8 2.7 2.1 6.5

< 0.1 0.6 4.0 0.6 1.5 2.2

< 0.1 < 0.1 0.7

< 0.1 41.7 7.5

1.5 1.6 6.4 8.3 4.4 8.5

< 0.1 < 0.1 2.0 1.6 1.7 6.2

a25 wfê A1 20 3 b13 wtS Al,0o

68

ethanol and ammonia in the presence of oxygen. Comparison of the catalysts shows that HZSM-5 is a superior catalyst in this reaction. In addition, HZSM-5 catalysts, especially Si-rich preparations (Si/Al > 23, Al/uc < 4) , show a low rate of coking, in contrast to other Si-Al catalysts, e.g., HY. With Al-rich HZSM-5 catalysts some coking is observed but the activity is hardly affected after 48 h on stream whereas other Si-Al catalysts deactivate.

Influence of reaction temperature From Table 1 the following effects of increasing reaction temperature can be

observed: (i) The conversion of ethanol increases. (ii) The selectivity of the reaction to pyridine bases decreases and the selecti­

vity to ethene (and C0?) increases. (iii) The selectivity within the group of pyridine bases shifts towards the un-

substituted product.

Effect of feed composition Oxygen content of the vector gas. On decreasing the oxygen content of the

carrier gas from 20 vol% (air) to ca. 1 vol% the yield of pyridine decreases. The yields of diethyl ether and substituted pyridines increase. When using nitrogen as a carrier gas a product mixture comprised mainly of ethene, diethyl ether and ethylamine is obtained. A decrease in oxygen content thus leads to a decrease in oxidized products (substituted pyridines are less dehydrogenated than pyridine itself).

Ammonia and water content. Obviously, when no ammonia is fed to the reactor no nitrogen-containing compounds can be formed. Moreover, in the absence of ammonia, ethanol is almost completely oxidized to C0 ? and H?0. Ammonia therefore inhibits deep oxidation reactions on HZSM-5 catalysts.

When no water is present in the feed the HZSM-5 catalyst deactivates and coke formation is observed. It may be concluded that water assists in preventing coke formation and keeping the zeolite surface clean.

DISCUSSION A comparison of the optimum reaction conditions reported here with the results

obtained in the conversion of ethanol without ammonia [3] shows that here a considerably higher temperature is required to obtain a good degree of conversion. Obviously this is caused by partial poisoning of the catalytically active (acid) sites by ammonia and the product bases. Nayak and Choudhary [22] found pyridine to be the most effective poison for HZSM-5 in the conversion of alcohols and olefins to aromatics. They also reported an increased rate of coking on pyridine poisoned HZSM-5 catalysts (Si/Al = 17), probably caused by the lack of strong acid sites. These sites remove coke by cracking reactions. We also find coke

69

formation on Alrrich zeolites, but not on Si-rich zeolites. Here cracking activity seems to be high enough to keep the catalyst surface clean.

Water has a positive effect on the selectivity and the stability of the catalyst. Water vapor can assist in desorbing the product bases from the catalyst. Also the rate of coke formation is decreased by addition of water vapor to the feed.

For the conversion of ethanol and ammonia to pyridines two mechanisms can be envisaged: one involving carbenium ions, oligomerization, amination, ring closure and aromatization and the other via dehydrogenation of ethanol to acetaldehyde, aldolization/retroaldolization, reaction with ammonia, cyclization and aromati­zation. Because the use Of ethene or propene as a feedstock instead of ethanol was found not to result in pyridine formation, the second mechanism is preferred. Some pathways are depicted in a simplified way in Scheme 1.

CH3CH2OH

NH,

O ,

non-ac id s i tes

NH, CH,CHO . „ ...—. 3 acid sites

Pyr idines

- p » CH3CH2NH2

—► CHf=CH 2

NH,

H* o2

U- CH3CN

CH,CH2OH || — CHjCOOH ► C H 3 C - 0 - C H 2 C H 3

——► C H 3 C H r O - C H 2 C H 3 H

SCHEME 1 Possible mechanism for reaction of C?H,-0H and NH, to pyridines.

The first step for the formation of pyridines from ethanol and ammonia is supposed to be the dehydrogenation of ethanol to acetaldehyde. Acetaldehyde and ammonia are then converted to pyridines. Both steps have been separately reported in the 1iterature.

Matsumura et al. [24] showed that acetaldehyde can be produced from ethanol over ZSM-5 zeolites containing little or no acid sites. Protonated ZSM-5 zeolites catalyze the dehydration of ethanol. In our experiments the acid sites are for the most part poisoned by NH3 and the product bases. The dehydrogenation reaction could be catalyzed by the resulting non-acidic sites though a detailed molecular picture is lacking. Matsumura et al. use an oxygen-free feed and a somewhat higher reaction temperature. Adding oxygen as a hydrogen acceptor to the feed might lower the reaction temperature needed. Shabtai et al. [25] found that type X zeolites

70

are able to catalyze the dehydrogenation of alcohols in the presence of aldehydes as hydrogen acceptor at temperatures between 373 and 453 K. Table 1 and Figure 1 show that zeolites with increasing Al content show a shift in selectivity from acetaldehyde to ethene. This can be explained in terms of an increasing number of proton sites being in equilibrium with pyridinium and ammonium sites.

Chang and Lang [9] described the conversion of acetaldehyde and ammonia to pyridines over HZSM-5. A higher reaction temperature (ca. 725 K) and feed rate (LHSV = 1) are used here under oxygen-free conditions.

Optimum selectivity to pyridines is found at an Al content where catalysis of acetaldehyde production and conversion to pyridines is balanced. At this point .the number of acidic sites has to be high enough to assure enough activity for pyridine formation and low enough to assure ethanol dehydrogenation over non-acidic sites. At increasing temperature the rate of the former reaction increases more than the rate of the dehydrogenation (possibly caused by a lower fraction of acidic sites poisoned by N-compounds). As a result, optimum selectivity to pyridines is found at a higher Si/Al ratio at higher temperatures.

Further reactions on the zeolite catalysts comprise: (i) conversion to ethene and diethyl ether over the acid sites. (ii) ammoxidation of ethanol or acetaldehyde to acetonitrile. (iii) oxidation to acetic acid, followed by esterification to ethyl acetate. (iv) total oxidation of reactants or products to carbon dioxide and water.

CONCLUSIONS Pyridine bases can be produced from ethanol and ammonia in the presence of

oxygen, using HZSM-5 catalysts. The presence of water in the feed mixture has a positive effect on selectivity, activity and stability of the catalyst, therefore direct processing of aqueous ethanol, as obtained by fermentation processes, is possible. For optimum conversion and selectivity to pyridines under standard flow and concentration conditions temperatures between 600 and 650 K and a HZSM-5 catalyst with Si/Al = 65 should be selected.

A mechanism starting with the partial oxidation of ethanol to acetaldehyde, followed by stepwise conversion to pyridine bases, is suggested.

REFERENCES 1 S.L. Meisel, J.P. McCullough, C.H. Lechthaler and P.B. Weisz, Chem. Techn., ' 6 (1976) 86. 2 C D . Chang and A.J. Silvestri, J. Catal., 47 (1976) 249. 3 J.C. Oudejans, P.F. van den Oosterkamp and H. van Bekkum, Appl. Catal., 3

(1982) 109. 4 e.g. K.H.' Chandawar, S.B. Kulkarni and P. Ratnasamy, Appl. Catal., 4 (1982) 287. 5 US Patents 3,751,504 (1975); 3,751,506 (1975); 3,755,483 (1975); 4,159,282

(1979); 4,159,283 (1979). 6 P.J. Lewis and F.G. Dwyer, Oil Gas Journal, 75 (1977) 55. 7 P.B. Weisz in "Stud. Surf. Sci. Catal., 7, New Horizons in Catalysis", eds.

T. Seyama and K. Tanabe (Elsevier, Amsterdam and Kodanska Ltd., Tokyo, 1981) p.3.

!

71

8 W.W. Kaeding, US Patent 4,082,805 (1982). 9 C D . Chang and W.H. Lang, US Patent 4,220,783 (1980). 10 R. Bicker and R. Erckel, Eur. Patent 0,046,897 (1981). 11 Neth. Patent 82.01523 (1981). 12 H.S. Fales and J.O.H. Peterson, Eur. Patent 0,039,918 (1981). 13 C D . Chang and P.D. Perkins, Zeolites, 3 (1983) 298. 14 C D . Chang and P.D. Perkins, US Patent 4,388,461 (1983). 15 C D . Chang and P.D. Perkins, Eur. Patent 0,082,613 (1983). 16 M. Deeba and W.J. Ambs, Eur. Patent 0,077,016 (1983). 17 J.C. Oudejans, F.J. van der Gaag and H. van Bekkum, in "Proc. Sixth Intern.

Conf. Zeolites", Reno 1983, eds. D. Olson and A. Bisio (Butterworth, Guildford, 1984), p.536.

18 J.C. Oudejans and H. van Bekkum, Neth. Patent Application 82.02884 (1983). 19 J.C. Oudejans, Thesis, Delft University of. Technology (1984). 20 F.J. van der Gaag, J.C.Jansen and H. van Bekkum, Appl. Catal., 17 (1985) 261. 21 E.M. Flanigen and R.L. Patton, US Patent 4,073,865 (1978). 22 V.S. Nayak and V.R. Choudhary, Appl. Catal., 9 (1984) 251. 23 R.M. Dessau and R.B. LaPierre, J. Catal., 78 (1982) 136. 24 Y. Matsumura, K. Hashimoto, S. Watanabe and S. Yoshida, Chem. Lett., 1 (1981)

121. 25 J. Shabtai, R. Lazar and E. Biron, J. Mol. Catal., 27 (1984) 35.

72

Reaction of Ethanol and Ammonia to Pyridine over ZSM-5-Type Zeolites

F.J. van der Gaag, F. Louter, and H. van Bekkum Laboratory of Organic Chemistry, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands

Reaction of ethanol and ammonia in the presence of air and water over ZSM-5-type catalysts affords pyridine as one of the major products. Other products include ethene, diethyl ether, ethylamine, acetonitrile and carbon dioxide. Data are presented for zeolite H-ZSM-5, for H-Boralite and for iron-containing H-ZSM-5 zeolites. For H-Boralite and H-ZSM-5 the pyridine selectivity is found to depend on the Si/B and Si/Al ratio, respectively. Increasing the iron content of H-ZSM-5 (Fe) systems leads to higher activity whereas the effect on the selectivity is relatively small.

Other variables studied include reaction temperature and space velocity. A mechanism for the ethanol-ammonia reaction to pyridines is suggested.

INTRODUCTION Numerous ZSM-catalyzed reactions have been reported since the discovery of

zeolite ZSM-5. The conversion of ethanol and methanol to hydrocarbons [1-3], the alkylation of benzene [4], the isomerization of xylenes [5], and the alkylation (6) and disproportionation of toluene [7] are the most frequently studied.

ZSM-catalyzed reactions in which ammonia is one of the reactants have received less attention [8-18] so far. The synthesis of amines from alcohols, ethers or olefins was reported in the patent literature [8,11,12,16]. The selectivity of the reaction of alcohols to primary amines was found to be increased by using zeolites like ZSM-5, erionite and clinoptilolite as' the catalysts.

Cu-H-ZSM-5 proved to be a good catalyst for the ammoxidation.of toluene [17]. The addition of water to the feed had a beneficial effect on the activity and stability. .

The production of (methyl-)pyridines from acetaldehyde and ammonia over zeolite ZSM-5 was reported in the patent literature [9]. Depending on the cation of the zeolite acetonitrile formation was observed. Recently high temperature (783 K) phenol amination to aniline over zeolite ZSM-5 was reported [13] and was found to yield 2-methylpyridine as the principal side product. Conversion of aniline under similar conditions also yielded 2-methylpyridine [14,15]. The conversion is low and many by-products are found.

From the data available it is clear that in the absence of oxygen in the reactant mixture zeolite ZSM-5 is able to catalyze the conversion of ethanol and ammonia to amines.

We have shown recently [18] that in the presence of oxygen zeolite ZSM-5 catalyses the reaction of ethanol and ammonia to pyridines. Here we present data on the reaction of ethanol and ammonia over some T-atom substituted ZSM-5-type zeolite catalysts, together with additional data for the reaction over H-ZSM-5. Water was used as a component of the reaction mixture in view of earlier observed beneficial action and in view of the option of direct processing of aqueous ethanol as obtained by fermentation. The influence of the degree of T-atom sub­stitution, the space velocity and the reaction temperature has been studied. A mechanism is discussed.

73

EXPERIMENTAL 1. Materials

All zeolites have been prepared as described for ZSM-5 in the literature [19]. Tetrapropylaminoniura bromide was used as the organic template. For Boralite, Aerosil was used as the silica source and sodium aluminate was substituted by a mixture of boric acid and sodium hydroxide. For Fe-containing ZSM-5 zeolite {II-ZSM-5 (Fe)) either Aerosil or waterglass was used as the silica source and iron(II)sulfate was added to the synthesis mixture. The Fe-containing zeolites are completely white, so it can be concluded that iron is built in on T-atom sites. Silicalite was prepared according to the patent literature [20], with NHHF added to the synthesis mixture. H-ZSM-5 and H-ZSM-5 (Fe)' were analyzed by AAS.

The 2eolites were calcined overnight at 823 K before further use. H -exchange was performed by ion exchange in 0.5 M HCl at ca. 353 K for 30 minutes (10 g zeolite per 1 solution), followed by thorough washing with water and repeating the procedure. All catalysts were dry pressed, crushed and sieved to obtain a sieve fraction of particles of 1.4-2.0 mm.

2. Procedure The apparatus used in the catalytic experiments is essentially the same as

described by Oudejans [21]. The catalyst (1-3 g) was placed in a fixed-bed continuous flow microreactor.

The reactor was placed in an electronically controlled fluid bed oven. Ammonia and ethanol were fed to the reactor by bubbling air through thermostatted saturators. Standard molar reactant composition was: NH3:C2H5OH:H£0:02 = 1:3:6:9.

The gas mixture leaving the reactor was analyzed by online gas chromatography using a 3 m 10% PEG on Chromosorb column with FID for organic components (temperature programmed operation) and a i m PORAPAK Q column with TCD for inorganic components (e.g. CO and C02l isothermal operation). Peak integration was performed by a computer connected to he gas chromatographs. If necessary products were identified by GC-MS using a Varian 44S mass spectrometer.

RESULTS The results of the experiments on the conversion of ethanol and ammonia to

pyridines will be presented in terms of single catalyst or reaction parameters on conversion and selectivity.

1. Effect of Si/B ratio of Boralite zeolites Data of experiments with H-Boralite zeolites are presented in Table 1 and

Figures 1 and 2. After 3 hours an essentially constant selectivity together with a

Table 1. Effect of Si/B ratio in the ethanol-ammonia reaction over H-Boralite. Si/B

10.5 10.5 10.5

21 21

42 42 12 42

04 01 01

"

B/uc

e e a 4.4 4.4

2.2 2.2 2.2 2.2

1.1 1.1 1.1

0 0 0

temp. K

613 633 653

613 633

613 633 653 673

617 613 663

608 638 663

conv. X

20.1 50.0 98.2

13.5 30.2

11.8 24.1 43.1 80.8

9.9 30.4 46.9

0.1 14.1 32.0

ethene

8.5 12.6 22.6

1.7 2.5

13.6 16.7 27.3 36.0

2.5 4.4 10.9

2.2 6.1 9.6

diethyl ether

2.1 0.8

< 0.1

0.9 0.4

7.7 4.5 2.6 0.3

1.0 0.5 0.4

1.2 0.6 0.4

S e 1 e c acetal-dehyde

12.2 8.3 1.2

6.8 1.9

8.8 5.9 2.9 2.2-

15.8 6.3 1 8

19.3 22.6 31.7

t 1 V i ethyl-amine

11.6 14.5

< 0.1

11.1 10.4

7.6 5.8 3.6 0.5

16.1 23.8 19.0

6.4 3.0 2.7

t i e s aceto-nitrile

11.2 11.9 3.9

16.7 22.8

3.1 3.4 4.a 7.2

0.2 15.5 15.2

< 0.1 2.6 5.6

t o (wt toluene

0.4 1.1

12.6

< 0.1 < 0.1

< 0.1 < 0.1 < 0.1 < 0.1

5.7 < 0.1 3.5

12.6 11.9 0.5

pyri-dine

21.7 31.3 17.1

31.5 34.9

46.2 48.0 42.7 39.8

16.0 20.6 21.1

16.0 7.0 2.6

2-pico-line

< < < <

< < < < < < <

1.0 0.1 0.1

0.1 0.1

1.7 0.9 0.3 0.1

0.1 0.1 0.1

0.1 0.1 0.1

C0C

29.7 16.8 16.9

27.9 26.9

11.3 12.9 14.9 13.2

26.6 21.5 23.0

38.1 39.7 44.4

£ Molar ratio NH,:C,ll,0H: H(0:0, = 1:3:6:9, W1ISV (ethanol) s 0.17 h-Rcoctant composition of synthesis mixture. Composition if product mixture after 4 hrs on stream.

74

600 625 650 675 temp, K

Fig. 1. Conversion and selectivity (wt X) plotted vs. B atoms per unit cell (conversion: x, +; selectivity to pyridine: •, x, •, A: 613 K,

o; to C0„: k, A; +, o, A: 633 K).

Fig. 2. Temperature effect on ethanol-aramonia reaction over H-Boralite (2.2 B/uc, conversion: +; selectivities: x, ethene; •, acetonitrile; o, pyridine; A, C0„).

slowly decreasing activity was observed. Major products in the ethanol-amraonia reaction - in the presence of water and oxygen (air) - are ethene, ethylamine, acetonitrile and pyridine. Other components in the product mixture include acetaldehyde, diethyl ether and toluene. Ethyl acetate and methylpyridines are generally present in amounts < 0.5%. Oxidation to carbon dioxide is substantial but in general less than 30 wt % resp. 15* on carbon and distinctly lower -than observed for Silicalite. For Boralite zeolites, the picture is very much like ZSM-5 zeolites: with increasing number of B atoms per unit cell the conversion increases, as the number of acid sites increases. The data show that there is an optimum in pyridine selectivity at relatively high Si/B ratios (ca. 42). We have reported similar results for H-ZSM-5 catalysts [18] with an optimum at Si/Al = 65.

Caution has to be taken with respect to B-rich zeolites: here B-containing compounds were detected in the product mixture. This causes the catalyst composition to change.

2. Effect of Fe content of Fe-containing ZSM-5-type catalysts Table 2 shows the effect of the Fe content of the ferro-alumino-silicate ZSM-5

catalysts. The conversion increases with increasing Fe content. It is noteworthy that the deep oxidation does not increase with higher Fe content of the zeolite system. For the other selectivities the picture is more complex. There are dif­ferences between catalysts prepared with waterglass and with Aerosil as the silica source. NH3-TPD experiments also show differences between the two types of catalyst: The maximum of the "c"-peak (desorption near 750 K) of the ammonia-desorption is 20-30 K higher for samples prepared from waterglass compared to samples prepared from Aerosil. Waterglass as a silica source therefore appears to yield zeolites which, after H -exchange, have acid sites with a somewhat higher acid strength than Aerosil-prepared samples. From Table 2 it then seems that the H-ZSM-5 (Fe) zeolites with the more moderate acid properties give a higher selectivity for pyridine.

Figure 3 gives plots of the conversion and selectivities of the reaction of

75

Table 2. Effect of Si/Fe ratio in the ethanol-animonia reaction over H-ZSM-5 (Fe), temperature 615 K.

S i l i c a s c u r c e

WC HC WC

AE AE AE

h f*01"1-

si/r*

170 571

1200

109 1010

-r a t i o KK i t i u n o f

c WC ï w e t e r a l u » »

S l / A l

43 40 40

71 UO 71

:C,H.OII product , AE =

Te/uc

0 . 5 5 0 . 1 6 O.OU

0 . 5 0 0 . 0 0 0 . 0 0

11,0:0 , n iKture

A e r o e i l .

conv .

* 3 0 . 8 14 .7 1 1 . 4

2 8 . 5 1 3 . 3 7 . 7

1 : 3 : 6 : 0 , a f t e r 4 h

e t h c n e

1 2 . 0 8 . 4 8 . 9

8 .B 1 7 . 0 1 1 . 6

d i e t h y l e t h e r

8 . 6 5 . 1 9 . 3

5 . 6 8 . 0

1 7 . 2

MISV ( e l h a n o l ) > re on a r e n * .

S • 1 e c e c e t e l -dchj-de

0 . 2 2 . 3 2 . 0

< 0 . 1 0 . 6 3 . 3

0 . 1 7 h - ' .

1 v 1 e t h y l -e n l n e

1 5 . 4 1.4 1 . 0

0 . 6 3 . 4 2 . 6

1 e • e t h y l

a c e t a t e

3 . 2 2 . 8 6 . 2

2 . 5 4 . 0 4 . 0

t o <"t a c e t o -n i t

10 5 4

12 4 3

r i l e

3 9 2

2 2 □

«>b p y i -d i n e .

2 5 . 5 3 8 . 2 2 0 . 8

4 8 . 1 2 6 . 3 3 7 . 8

2 - p i c B -U n e

3 . 2 1 0 . 1 B . 9

1 .4 1 0 . 4 7 . 5

CO

21 22 24

20 23 13

6 2 3

7 C 0

O 5 10 15 ' 20 t(hr)

Fig. 3. Plot of the conversion and selectivities vs. runtime for the ethanol-animonia reaction (catalyst: H-ZSM-5 (Fe), Si/Fe = 189; Si/Al = 71, Aerosil (+, conversion; selectivities: •, ethene; *, ether; x, CH3CN; o, pyridine; a, coz).

ethanol and ammonia over a H-ZSM-5 catalyst (Si/Al = 71, Si/Fe = 189, Aerosil) versus the time-on-stream. After approximately 4 hours a steady state is reached. Most catalysts used in this study give a similar picture.

76

3. Effect of space velocity with H-ZSM-5 zeolite This effect has been studied with an aluminosilicate H-ZSM-5 catalyst, with

Si/Al = 55.5. This catalyst showed the best pyridine selectivity and a fair conversion in the comparison between aluminosilicate catalysts [18]. Results are shown in Table 3.

Table 3. Effect of space velocity in the ethanol-ammonia reaction . HIlSVb conv. S e l e c t i v i t l o s t o (wt *) h-' X ethene diethyl ecetal- ethyl- ethyl eceto- pyri- 2-pico- 4-pico- C0t

0.17 0.35 0.67 1.00

12.8 6 . 4 3 . 7 2 . 9

6 . 4 5 . 5 7 . 3 6 . 0

ether

7 . 4 12.8 IS.2 20.8

dehyde

3 . 2 6 . 3 6 . 3 9 . 8

eroine

1.7 3 . 1 4 . 2 4 . 4

acetate

5 . 7 6 . 8 7 . 6 6 . 1

n i t r i l e

4 . 0 3 . 8

< 0.1 < 0.1

dine

44.5 36.4 33.5 33.2

l ine

9 . 2 7 . 7 5 . 9 6 . 6

l i ne

2 . 8 < 0.1 < 0.1 < 0.1

15.2 17.7 16.9 13.2

° neaotor temperature 615 K..H-2SM-5 catalyst (Si/Al = 55.5). WHSV aa I ethanol/(e.catalyst.hr).

As could be expected, the conversion decreases with increasing space velocity. The changes in selectivities are an indication for possible mechanistic pathways. The selectivity for acetaldehyde and ethylamine increase with increasing space velocity, whereas the selectivity for acetonitrile decreases, indicating that acetaldehyde and ethylamine are first formed during reaction, whereas this is not the case for acetronitrile. Diethyl ether is another initial product, whereas pyridine obviously is formed later.

Applying the high WHSV a series of experiments was performed at different reaction temperatures. The results are given in Table 4. The space velocity was kept constant at a value of 1.0 h—l. At the high temperature the product mixture simplifies and consists almost entirely of ethene and pyridine. Deep oxidation is relatively low.

Table 1. Effect of reaction temperature on the ethanol-ammonia reaction to pyridines

Temp. K

615 615 670 693

Conv.

* 2 . 9 7 . 7

1 9 . 1 6 1 . 2

e t h e n e

6 . 0 1 2 . 9 2 8 . 8 5 5 . 5

d i e t h y l e t h e r

2 0 . 8 1 6 . 5

9 . 7 0 . 9

S e 1 e c a c e t a l ­dehyde

9 . 8 8 . 9 5 . 7 0 . 4

t i v i e t h y l ­amine

4 . 4 1.7 0 .4 0 . 3

t i e s e t h y l

a c e t a t e

6.1 4 . 5 1.2 0 . 3

t o (wt X) a c e t o ­n i t r i l e

< 0 . 1 3 . 0 2 . 0 2 . 5

p y r i ­d i n e

3 3 . 2 3 2 . 3 3 5 . 8 3 0 . 2

2 - p i c o -l i n e

6 . 6 4 . 1 3 . 4 0 . 9

CO t

1 3 . 2 1 6 . 3 1 3 . 2

8 . 9

H-ZSM-5 catalyst, Si/Al = 55.5.

DISCUSSION As shown earlier [18], a comparison of the reaction conditions for the etha­

nol-ammonia reaction to pyridines and the conversion of ethanol without ammonia [3] shows that for the former reaction a considerably higher temperature is needed to obtain a fair degree of conversion. This is obviously caused by (partial) poisoning of catalytically active (acid) sites by ammonia or the product bases. Nayak and Choudhary [22] reported pyridine to be the most effective poison for H-ZSM-5 in the reaction of olefins and alcohols to aromatics. They also found an increased rate of coking on pyridine-poisoned catalysts (Si/Al = 17), probably caused by the lack of strong acid sites. These sites are said to remove coke by cracking reactions. On low Si/B zeolites we also detect coke formation, together with loss of boron from the catalyst whereas on Si-rich zeolites hardly any coke is formed. Relatively high acid sites density appears to promote coking in the present reaction.

For the ethanol-ammonia reaction to pyridines two mechanisms can be envisaged: one involving carbenium ions, oligomerization, amination, ring closure and aromatization [23] and the other via dehydrogenation of ethanol to acetaldehyde, aldolization/retroaldolization, reaction with ammonia, cyclization and aromatiza­tion. Because experiments substituting ethene or propene for ethanol as a feed­stock under the present conditions show no pyridine formation, the second mechanism is preferred. High temperature reaction (693 K) at WHSV =1.0 h-1 yields

77

more ethene and more or l e s s the same percentage of pyr id ine than lower tempera­ture r e a c t i o n s . This i s a l so in favonr of mechanism 2.,Some pathways a re dep ic ted in a s impl i f ied way in Scheme 1.

O NH, or CH.CHjNH, CH CH OH * CHjCHO —— > Pyndlne

non- acid sites .

H '

H*

^ CH.CH-NH

■> CH.COOH

3 ï 2 non-acid sites C H J C - O - C H J C H ,

Scheme 1. Possible mechanism for reaction of C2H50H and NH3 to pyridines.

The first step for the formation of pyridines is supposed to be the dehydrogena-tion of ethanol to acetaldehyde or the amination of ethanol to ethylamine. Acetal-dehyde and ethylamine and/or ammonia are then converted to pyridines. Both reac­tion steps have been separately reported in the literature.

Matsumara et al. [24] showed that ZSM-5 zeolites containing little or no acid sites are able to catalyze the reaction of ethanol to acetaldehyde. They suspect Fe impurities in the zeolite to catalyze this reaction. The dehydration of ethanol is catalyzed by protonated ZSM-5 zeolites. In the ethanol-ammonia reaction the acid sites are at least partiallly poisoned by NH3 and the product bases. The dehydrogensition reaction can be catalyzed by the resulting non-acidic sites though a detailed molecular picture is lacking. Matsumura et al. use an oxygen-free feed and a somewhat higher reaction temperature. The reaction temperature needed might be lowered by the presence of oxygen as a hydrogen acceptor. Isomorphous substitution of Fe for Si in the zeolite lattice seems to have the same effect: ferro-alumino-silicate zeolites are more active than iron-free catalysts.

Table 1 shows that zeolites with increasing B content (except for the 8 B/uc sample) show a shift in selectivity from acetaldehyde to ethene. This can be explained by assuming that an increasing number of acid sites is in equilibrium with ammonia- and pyridine-poisoned sites.

Chang and Lang [9j showed that acetaldehyde and ammonia can be converted to pyridines over H-ZSM-5 catalysts. The reaction is performed under oxygen-free conditions at 723 K- and LHSV = 1. Our experiments showed that from an oxygen-containing feed pyridines can be formed at 693 K (WHSV = 1 h - 1 ) .

Optimum selectivity to pyridines will be found at an acid sites content where catalysis of acetaldehyde production and -consumption to pyridines is balanced. This explains why iron-containing catalysts are more active: the rate of acetaldehyde production is higher (catalyzed by Fe) so the rate of pyridine forma­tion can be increased. Comparing two catalysts from Table 2 (H-ZSM-5 containing 0.55 Fe/uc, prepared from waterglass and H-ZSM-5 containing 0.50 Fe/uc, prepared from Aerosil) illustrates again that a catalyst with a higher number of strong acid sites (the former catalyst) has a lower selectivity for pyridine (25.53») than a zeolite with less and milder acidic sites (selectivity = 48.151).

Further reactions on the zeolites comprise: (i) conversion of ethanol to ethene and diethyl ether over acid sites (ii) anunoxidation of ethanol or acetaldehyde to acetonitrile (iii) oxidation to acetic acid, followed by esterification to ethyl acetate (iv) amination of ethanol to ethylamine over acid sites (v) oxidation of ethylamine to acetonitrile (vi) total oxidation of reactants or products to carbon dioxide and water.

78

CONCLUSION Pyridine bases can be produced from ethanol and ammonia in the presence of

oxygen using H-ZSM-5 type catalysts. ZSM-5 zeolites with partial or complete isomorphous substitution of B or Fe for Al in the zeolite lattice also are catalytically active in the pyridine forming reaction. Using boron the performance of the catalyst is somewhat less than an aluminosilicate H-ZSM-5 catalyst, whereas incorporation of small amounts of iron increases the conversion without bringing about large changes in selectivity. The yield of pyridine can be increased by increasing both reaction temperature and space velocity. At WHSV = 1.0 h-1 and 693 K a product mixture consisting chiefly of ethene and pyridine (and carbon dioxide) is formed.

A mechanism starting with partial oxidation of ethanol to acetaldehyde, followed by stepwise conversion to pyridine bases, can be suggested.

ACKNOWLEDGEMENTS The authors would like to thank Mr. J.P. Koot (Laboratory of Analytical

Chemistry) for the AAS analyses and Mr. J.F. van Lent and Mr. N.M. van der Pers (Laboratory of Metallurgy) for the XRD analyses of the used zeolites. Dr. H.W. Kouwenhoven is thanked for valuable discussions.

REFERENCES 1. S.L. Meisel, J.P. McCullough, C.H. Lechthaler, andP.D. Weisz, Chem. Techn.,

6, 86 (1976). 2. C D . Chang and A.J. Silvestri, J. Catal. , 47, 249 (1976). 3. J.C. Oudejans, P.F. van den Oosterkamp, and H. van Bekkum, Appl. Catal., 3,

109 (1982). 4. e.g. K.H. Chandawar, S.B. Kulkarni, and P. Ratnasamy, Appl. Catal., 4, 287

(1982). 5. US Patents 3,751,504 (1975); 3,751,506 (1975); 3,755,483 (1975); 4,159,282

(1979); 4,159,283 (1979). 6. P.J. Lewis and F.G. Dwyer, Oil Gas Journal, 75, 55 (1977). 7. P.B. Weisz, in "Stud. Surf. Sci. Catal., 7, New Horizons in Catalysis", eds.

T. Seyama and K. Tanabe (Elsevier, Amsterdam, and Kodanska Ltd., Tokyo, 1981). R. W.W. Kaeding, US Patent 4,082,805 (1982). 9. C D . Chang and W.H. Lang, US Patent 4,220,783 (1980).

10. I!. Bicker and R. Erckel, Eur. Patent 0,046,897 (1981). 11. Neth. Patent 82.01523 (1981). 12. H.S. Fales and J.O.H. Peterson, Eur. Patent 0,039,918 (1981). 13. C D . Chang and P.D. Perkins, Zeolites, 3, 298 (1983). 14. C D . Chang and P.D. Perkins, US Patent 4,388,461 (1983). 15. C D . Chang ami P.D. Perkins, Eur. Patent 0,082,613 (1983). 16. M. Deeba and W.J. Arabs, Eur. Patent 0,077,016 (1983). 17. J.C. Oudejans, F.J. van der Gaag, and H. van Bekkum, in "Proc. Sixth Intern.

Conf. Zeolites", Reno 1983, eds. D. Olson and A. Bisio (Butterworth, Guildford, 1984), p. 536.

18. F.J. van der Gaag, F. Louter, J.C. Oudejans, and H. van Bekkum, Appl. Catal., in press.

19. F.J. van der Gaag, J.C. Jansen, and H. van Bekkum, Appl. Catal., 17, 261 (1985).

20. E.M. Flanigen and R.L. Patton, US Patent 4,073,865 (1978). 21. J.C. Oudejans, Thesis, Delft University of Technology (1984). 22. V.S. Nayak and V.R. Choudhary, Appl. Catal., 9, 251 (1984). 23. R.M. Dessau and R.B. LaPierre, J. Catal., 78, 136 (1982). 24. Y. Matsumura, K. Hashimoto, S. Watanabe, and S. Yoshida, Chem. Lett., 1981.

(1), 121.

Formation of 2,6-lutidine 79

THE FORMATION OF 2.6-LUTIDINE FROM ACETONE,

METHANOL AND AMMONIA OVER ZEOLITB ZSM-5.

F.J. van der Gaag, R.J.O. Adriaansens and H. van Bekkum, Delft University of Technology, Laboratory of Organic Chemistry, Julianalaan 136, 2628 BL DELFT, The Netherlands.

and P.C. van Geem, DSM Research BV., P.O.Box 18, 6160 MD Geleen, The Netherlands.

ABSTRACT

2,6-Lutidine is formed from acetone, methanol and ammonia

over ZSM-5 type zeolitic catalysts. Selectivity to

2,6-lutidine is found to be highest at relatively high Si/Al

ratios. At the higher Si/Al ratios a lower steady state

adsorption of lutidine (0.6 lutidine/Al) is present under

reaction conditions. A mechanism is discussed taking into

account an experiment with 13C-labeled methanol.

INTRODUCTION.

2,6-Dimethylpyridine (2,6-lutidine) is the starting chemical for the

manufacture of several industrially interesting products. A number of

syntheses of 2,6-lutidine have been reported. Most promising thusfar is

the direct methylation of 2-methylpyridine (2-picoline) with methanol.

Thus, 2-picoline and excess methanol are fed over a Ni-containing catalyst

at a temperature of 260°C [1,2]. Similarly, pyridine can be alkylated over

Raney-Ni, Raney-Co, Raney-Cu or Raney-Fe at 200°C [3]. Good initial

conversion and selectivity are obtained, however catalyst deactivation is

severe. Another route is the synthesis from acetone, ammonia and

formaldehyde:

2 (CH3)2 CO ♦ CH20 ♦ NH3 — f O l + 2 H 2 ° + H2

80 Formation of 2,6-lutidine

Patent literature [4,5,6] claims the use of promoted amorphous

silica-alumina catalysts, together with high temperatures (resp.

350-550°C, 420°C and 450°C) and high space velocities. Yields ranging from

29 to 483> are reported, starting from reaction mixtures containing an

excess of ammonia (molar ratio ammonia/ acetone is 2.7-2.8).

In this paper we report on the synthesis of 2,6-lutidine over a

crystalline aluminosilicate catalyst, zeolite ZSM-5. Reaction of ethanol,

ammonia and air to pyridines over zeolite ZSM-5 showed the dehydrogenation

ability of this catalyst [7]. These properties prompted us to attempt

lutidine synthesis from acetone, ammonia and methanol as a potential

formaldehyde precursor. The effects of a variation in Si/Al ratio of the

ZSM-5-zeolite and some other reaction parameters were studied. For

comparison Mordenite and H-Y were included.

EXPERIMENTAL.

Catalysts,

Zeolite H-ZSM-5 and Silicalite were synthesized according to a procedure

adapted from the patent literature [8,9). The procedure comprised mixing

an Aerosil (Degussa) suspension with a solution of sodium hydroxide, the

template, tetrapropylammonium bromide (TPA-Br) [8] (Chemische Fabriek

Zaltbommel, the Netherlands) and sodium aluminate (Riedel-de Haehn),

followed by crystallization for 48 hours in a teflon-coated autoclave at

180°C under stirring [9]. Finally, the product is filtered and washed. The

molar gel composition was SiCte: NaOH: TPABr: H20= 1:0.35:0.165:47.8. The

Si/Al ratio of the gel was varied from 12.7 to infinity (Silicalite). The

zeolites are denoted ZSM-5(X), with X is the Si/Al ratio in the

synthesis mixture. The actual Si/Al ratio of the zeolites is shown in

Table 1. Zeolite compositions were analyzed by AAS. After drying and

calcination (550°C, overnight) all ZSM-5 type zeolites were exchanged

twice using a 0.5 M HCl solution (100 ml/g, 80°C, 0.5 hr). This procedure

is known to yield an exchange degree of over 95*.

Formation of 2,6-lutidine 81

H-Mordenite (large pore: Zeolon 900H, Norton, and small pore: Alite 150.

(Na-form), Soc. Chim. de la Grande Paroisse) and zeolite Y (Na-LZY-5Z,

Union Carbide Corporation, Linde Division) were commercial zeolites.

Small pore Mordenite was converted to the H-form by repeated exchange with

1 M NlfcNOs (80°C), followed by calcination under shallow bed conditions at

420°C. Benzene adsorption showed that ,the . zeolite still possessed small

pore properties. H-Y was obtained by exchanging Na-Y with an 1M NH4NO3

solution at 80°C, followed by calcination. Analysis showed 8435 exchange of

the sodium ions.

The catalysts had a particle size of 0.3-0.5 mm, obtained by dry

pressing, crushing and sieving of the zeolites. 13C-labeled methanol (99* 13C) was obtained from Aldrich.

Procedures.

The catalyst (1-2 g) was introduced in a fixed bed continuous flow

stainless steel microreactor (internal diameter 4 mm, length 120, mm) and

heated to the reaction temperature (usually 450°C). The reactants were

then pumped into the reactor by means of two HPLC . pumps (Gilson model

302). No carrier gas was used. The condensed products (18°C) of the

reaction were analyzed by GC, and, if necessary, by GC-MS.

Adsorption/TPD experiments with 2,6-lutidine were carried out in a

GC-type apparatus according to Choudhary and Akolekar [12].

RESULTS AND DISCUSSION.

The reaction of acetone, ammonia and methanol (or formaldehyde).

generally leads to a product mixture with a rather complex composition.

The reaction products comprise: 2,6-lutidine, 2,4-lutidine, 2-picoline,

collidine (trimethylpyridine), a tetramethylpyridine, methylcyclohexenone,

mesityl oxide, 4-methyl-4-penten-2-one, butanone, acetonitrile, toluidines

and some other benzene derivatives. The ratio of 2,4-lutidine to

2,6-lutidine formed is always less than 0.05. Gases like ethene, propene,

82 Formation of 2,6-lutidine

butene and trimethylamine are also produced.

Some initial experiments were performed with the reaction of acetone,

formaldehyde, ammonia and water over H-ZSM-5 (Si/Al=96) and H-Y (molar

feed composition: acetone: formaldehyde: ammonia: water = 1.0: 1.0: 2.0:

5.5, (formaldehyde as 1,3,5-trioxane), WHSV(acetone)= 0.30 h~l.

Formaldehyde is fed as trioxane - which compound decomposes at reaction

conditions to formaldehyde - to avoid condensation reaction of

formaldehyde and ammonia before entering the reactor. In

these experiments catalyst activity as well as lutidine selectivity were

found to decrease relatively rapidly, especially in the case of H-Y as the

catalyst.

Activity and selectivity were found to increase upon replacing

formaldehyde by methanol in the subsequent experiments. Reaction

conditions were: feed composition (molar ratio): acetone: methanol:

ammonia: water = 1.0:1.0:0.4:2.8, WHSV(acetone)= 0.97 h"1, temperature

350°C.

The influence of the aluminum content of the zeolite catalyst was

determined by analysis of the condensed products of the first 7 hours of

reaction. The results are shown in Table 1.

Sometimes the condensate of 7-22 hours was also analyzed for comparison,

generally showing some gradual decrease of catalyst performance.

Silicalite does not catalyze the formation of 2,6-lutidine, showing that

lutidine formation requires the presence of acid sites. The conversion of

both methanol and acetone increases with increasing Al content of the

ZSM-5 zeolite, whereas the reverse is true for the selectivity to

2,6-lutidine. The ZSM-5 type pore system also plays a role, as can be seen

from the comparison with H-Mordenite and H-Y.

Formation of 2,6-lutidine 83

TABLE 1: Effect of zeolite type and composition on conversion and on 2,6-lutidine selectivity.

Catalyst Si/Al Conversion b)(*) Selectivity c> Amount of product a> acetone methanol to 2,6-lutidine(%) condensed d> (%)

Silicalite >2000 28.3 42.0 0.0 70.8 H-ZSM-5(96) 89.9 62.8 84.7 12.9 . 84.0 H-ZSM-5(23) 14.6 78.5 86.2 8.9 67.0 H-ZSM-5(12.7) 11.1 92.4 96.4 6.2 46.1 H-Mord (LP) 5.85 31.0 62.2 3.4 75.6 H-Mord (SP) 5.56 46.8 48.7 0.5 67.1 . H-Y 2.05 96.7 97.6 1.1 37.1

Reaction conditions: 350°C, WHSV(acetone)=0.97 h"1 , molar feed composition: acetone: methanol: ammonia: water=1.0: 1.0: 0.4: 2.8.

a) The number between brackets denotes the gel Si/Al ratio. b> Conversion reactant X=(l-(moles X condensed)/(moles X fed))*100& O ( 2*moles 2,6-lutidine condensed )*100%

(moles acetone fed*conversion acetone) d> (weight of condensate)/(weight of feed)*100&

Table 1 shows that H-Mordenite (small pore) hardly gives rise to the formation of 2,6-lutidine. This can be understood because the pores in this zeolite are too small to allow formation and passage of the product 2,6-lutidine. The product of the experiment with zeolite H-Y as a catalyst contains a large amount of volatile products, resulting in a low product recovery. Methanol is probably converted into dimethyl ether, which is not condensed under the conditions used. A plot of the 2,6-lutidine selectivity versus aluminum content is shown in Figure 1.

In order to get a picture of the zeolite pore filling with 2,6-lutidine (and other basic products formed) under reaction conditions some adsorption and desorption experiments were carried out. TPD experiments show that 2,6-lutidine desorbs from the weak acid sites of the H-ZSM-5 catalysts below 350°C. Desorption from Bronsted acid sites was not observed at temperatures up to 500°C. This desorption can be expected at approximately 700°C.

84 Formation of 2,6-lutidine

•/• s e l e c t i v i t y 2-6 lutidine

i + HZSM5I96)

\ + H Z S M 5 < 2 3 >

+ HZSM5 (12-7) \ \ \

+ HMord LP

HY ' +

30 Al

40

CM

FIGURE 1: 2,6-Lutidine selectivity plotted vs Al content.

TABLE 2: 2,6-Lutidine adsorption on H-ZSM-5 catalysts at 325°C

catalyst catalyst weight (mg)

H-ZSM-5(12.7) 404.1 H-ZSM-5(23) 420.9 H-ZSM-5(218) 459.2

calculated adsorbed lutidine/Al pore 2,6-lutidine volume (wl) volume («1) 68.7 30 0.526 71.5 20 0.589 77.7 2.5 0.619

Zeolite pore volume was calculated from the weight (170 ;ul/g).

Adsorption experiments of 2,6-lutidine on H-ZSM-5 at 325°C show an adsorption of ca. 0.6 lutidine molecule per Al atom in the zeolite lattice (see Table 2). Apparently a part of the acid sites is not strong enough to keep the lutidine adsorbed at 325°C. This is in agreement with the results of Datka and Tuznik [10], who show, by IR spectroscopie measurements, that there are two kinds of Bronsted acid sites for pyridine adsorption. The strong acid sites which account for about 60* of the Al atoms, still

Formation of 2,6-lutidine 85

adsorb pyridine at a temperature of 325°C [10].

Silicalite has been omitted in Figure 1. The graph shows a

relationship between the aluminum content (the number of acid sites) of

the zeolite and the selectivity to 2,6-lutidine. In the synthesis of

pyridine from ethanol and ammonia over zeolite ZSM-5 a similar effect has

been observed: a relatively high Si/Al ratio is advantageous for the

selectivity and the stability of the catalyst [7,11]. The behaviour of

H-Mordenite (large pore) and HY in the lutidine synthesis might indicate

that other factors such as the zeolite structure have a strong influence

on the reaction sequence.

The influence of the reaction temperature on the selectivity and

conversion was determined using H-ZSM-5(96) as the catalyst, which zeolite

showed the highest selectivity to 2,6-lutidine in the zeolite screening.

The results are shown in Table 3.

TABIE 3: Influence of temperature on conversion and selectivity

Temperature (°C) Conversion a>(&) Selectivity b>(Ss) Amount of product acetone methanol to 2,6-lutidine condensed (3S)C)

' 400 33.0 31.5 16.0 85.2 450 66.8 84.7 12.9 84.0 500 93.1 77.7 15.6 76.2

Reaction conditions: WHSV(acetone)=0.97 h~l, molar feed composition: acetone: methanol: ammonia: water=1.0: 1.0: 0.4: 2.8, H-ZSM-5(96) catalyst.

a> Conversion reactant X=(l-(moles X condensed)/(moles X fed))*100% b> Selectivity=( 2*moles 2,6-lutidine condensed )*100S

(moles acetone fed*conversion acetone) c> *condensed=(weight of condensate)/(weight of feed)*100%

As expected, the conversion increases with increasing reaction tempe­

rature. At 400°C the numerous byproducts (like methylcyclohexenone and

mesityl oxide) are present in small amounts only. The condensate of the

reaction at 500°C consists of two phases, an aqueous phase and an organic

phase. The organic phase contains, besides 23* (w/w) 2,6-lutidine as

the main component, more than 75 other components, generally each in

86 Formation of 2,6-lutidine

concentrations of less than IX. The aqueous phase contains over 30 compounds, among which'2.63> (w/w) 2,6-lutidine. At a higher reaction temperature (i) more low-molecular weight products

and (ii) more non-hydrophilic products are formed. Considering the almost constant selectivity and the increasing conversion with increasing temperature, it appears that the 2,6-lutidine yield goes up with temperature.

The influence of the space velocity was investigated using H-ZSM-5(96) as a catalyst and a reaction temperature of 450°C. Data are given (Table 4) for the condensate of the first 7 hours of reaction, and for the condensate'of 7-22 hours (between brackets).

TABLE 4: Influence of WHSV on conversion and selectivity

WHSV (h~l) Conversion a>(X) Selectivity b>(X) Amount of product acetone acetone methanol to 2,6-lutidine condensed (X)c>

0.243 94.3(62.2) 86.7(70.0) 10.9(23.7) 58.2(71.0) 0.969 62.8(50.6) 84.7(69.0) 12.9(11.3) 84.0(88.1) 1.938 48.4 69.4 11.4 82.0

Conditions: molar feed composition: acetone: methanol: ammonia: water= 1.0:1.0:0.4:2.8, H-ZSM~5(96) catalyst, 450°C.

a) Conversion reactant X=(l-(moles X condensed)/(moles X fed))*100% b) Selectivity=( 2*moles 2,6-lutidine condensed )*100%

(moles acetone fed*conversion acetone) c> *Condensed=(weight of condensate)/(weight of feed)*100%

The conversion increases with decreasing space velocity. The selectivity to 2,6-lutidine is more or less constant. In general, conversion decreases with increasing time-on-stream.

The influence of the reactant composition was examined by varying the acetone/methanol ratio and the ammonia/acetone ratio in some experiments using H-ZSM-5 (96) as the catalyst at 450°C. The results, shown in Table 5, suggest that the selectivity to 2,6-lutidine based on acetone converted

Formation of 2,6-lutidine 87

is hardly affected by the acetone/methanol ra t io .

TABLE 5: Influence of reactant composition on conversion and select ivi ty.3>

molar feed coiposition conversion"(I) selectivity tocl HHSV" A«ount of product acetorie:»ethanol:anonia:water acetone aethanol 2,6-lutidine (overall) condensed'1 (I)

1 4 0.41 2.78 60.3 86.8 14.3 5.94 73.2 1 1 0.41 2.78 62.8 84.7 12.9 2.69 84.0 1 0.5 0.67 4.57 35.5 34.7 15.9 5.11 82.3 1 1 1.64 11.11 36.0 53.5 21.6 5.31 56.9

•> H-ZSM-5(96) catalyst, 450°C, results for the first 7 hours of reaction. " NHSV h"1, HHSV(acetone) constant at 0.97 /hr. c ' Conversion reactant X=(l-(»oles X condensedj/Uoles X fed))*1002 <i) Selectivity;) 2*moles 2,6-lutidine condensed )*100I

(soles acetone fed*conversion acetone) e i ICondensed:(weight of condensate)/(weight of feed)*100I

The stoichiometric ammonia/acetone ra t io to form 2,6-lutidine is 0.5.

Increasing the ammonia/acetone ra t io to 1.64 resul ts in an increase in

select ivi ty to 2,6-lut idine. The positive influence of an excess of

ammonia may be due to improved trapping of reactive carbonyl

intermediates (cf. mechanistic considerations) by ammonia, thus inducing

higher lutidine se lec t iv i ty .

Mechanistic experiments and considerations.

To investigate the way methanol is built in in 2,6-lutidine an

experiment with 13C-labeled methanol was carried out. The reaction

conditions were: catalyst H-ZSM-5 (96), WHSV(acetone)= 0.30 h"1, molar

reactant composition: acetone: 13C-methanol: ammonia: water= 2.0: 1.0:

4.0: 13.7, reaction temperature: 450°C. The condensed products were

fractionated and the fraction containing 2,6-lutidine was analyzed with

GC/MS. Apart from labeled 2,6-lutidine (l*i3C), 2,4-lutidine (1*13C) and

trimethylpyridine (2*13C) were also detected. Purification by preparative

gas chromatography yielded pure 13C-labeled 2,6-lutidine, which was

analyzed by 13C-NMR. The 13C (from the 13C-methanol) appeared to be

88 Formation of 2,6-lutidine

present at the 4-position exclusively. Thus the reaction can be formulated

as: C H 3 0 H , r<^CN

^o NH3 o^x A N ^

The by-product 2-picoline nay be formed by demethylation of 2,6-lutidine

and therefore it is likely that the labeled l3C-atom is built in here too

at the 4-position. The 2,4-lutidine observed is probably formed by ring

closure of mesityl oxide or 4-methyl-3-penten-2-one, which has been

detected in the product mixture. Then the labeled carbon atom is expected

at the 6-position.

The trimethylpyridine, which is labeled twice in the 13C-methanbl

experiment is either formed by methylation of a dimethylpyridine with

methanol or by reaction of two molecules methyl ethyl ketone (or methyl

vinyl ketone) with ammonia. In either case, there is one labeled atom

present at the 4-position in the ring and one in a methyl group.

As to the mechanism of this condensation/aromatization the labeling

result leaves three possible routes for the formation of 2,6-lutidine from

acetone, methanol and ammonia.

Mechanism I involves the formation of methyl vinyl ketone either by

condensation of acetone and methanol followed by a dehydrogenation or

directly from acetone and formaldehyde, where formaldehyde is formed by

dehydrogenation of methanol. As to the latter reaction recent work has

shown methanol to be readily dehydrogenated over a Silicalite catalyst

under similar conditions [13]. Methyl vinyl ketone reacts in further

steps with another acetone molecule and ammonia followed by H-transfer

processes to form 2,6-lutidine.

MECHANISM I.

Formation of 2,6-lutidine 89

\ = 0 ♦ CH3OH

V = 0 ♦ CH20

O N

- 2 H ,

H2Q

-H20

■ H ,

O

-NH,

A , 2H2o

> 0

vo o

In an attempt to get more insight into a role of methyl vinyl ketone

we performed some explorative experiments on the reaction of methanol...and

/. 1 80 -

60 -

40 ■

20 -

0

3

/

1

2 1 4 »

product recovered •/

'

conversion methanol

^^\conversion acetone

selectivities: mesityl oxide :metnyi ethyl keton

1 1 6 8

runtime (hr)

100 -i

8 0 -

6 0 -

4 0

20 -

conversion methanol

conversion acetone

mesityl oxide - toluene xylene

I 4 6 8

-»- runtime (hr)

.methyl ethyl ketone

FIGURE 2: Conversions and selectivities for the conversion of acetone and methanol. WHSV(acetone) = 1.14 h"1 , molar ratio acetone/methanol=l. A: CaX catalyst, 300°C; B: H-ZSM-5(96) catalyst, 450°C.

90 Formation of 2,6-lutidine

acetone. When performing this reaction over zeolite ZSM-5 at 450°C a

complex mixture of relatively high molecular weight products was

obtained including, as expected, aromatic compounds. Some methyl ethyl

ketone (< 5 X) was found to be present in the product mixture. To prevent

the product undergoing consecutive reactions on a highly active (ZSM-5)

catalyst we used in a second experiment zeolite Ca-X while lowering the

reaction temperature to 300°C. The other reaction conditions were:

WHSV(acetone)=l.15 h"1, molar reactant composition: acetone: methanol =

1:1. The results are shown in Figure 2.

Though a Ca-X zeolite catalyst is much less active than H-ZSM-5 numerous

products were formed, mostly in low concentrations. Mesityl oxide,

methylcyclohexenone and methyl ethyl ketone were present in measurable

quantities. Methyl vinyl ketone was mot found, indicating that this

product is either very reactive or no real intermediate. The first

possibility is the most likely considering the dehydrogenating properties

of ZSM-5 catalysts [7,11].

The first step in the mechanism can also be the formation of methyl

vinyl ketone (MVK) directly from reaction between formaldehyde and

acetone. Addition of acetone in a fast Michael-reaction then will lead to

2,6-heptadione. Ring closure with ammonia, dehydration and dehydrogenation

yields 2,6-lutidine. This reaction is reported to yield 2,6-lutidine [14].

To verify this mechanism, methyl vinyl ketone was reacted with acetone

and ammonia under the present conditions (catalyst: H-ZSM-5(96), 450°C,

WHSV(total feed)=1.97 h'1, MVK: acetone: ammonia: water= 1:2.2:5.5:35.7).

Indeed, 2,6-lutidine is formed though selectivity is rather low, i.e.

6*. Presumably the high concentration of methyl vinyl ketone causes side

Formation of 2,6-lutidine 91

reactions, which do not take place when methyl vinyl ketone is formed in

situ from methanol and acetone.

MECHANISM II

>°

O

NH, H ,0

-2H ,

\ MH *y°r I l*CH3OH

+ CH20 H 20

<S y*^

A N'

Another mechanism (II) starts with formation of acetonimine which can

react in a fast reaction with acetone to yield a Schiff's base. Reaction

with methanol or formaldehyde then gives the triene product which might

undergo intramolecular ring closure with subsequent zeolite-catalyzed

dehydrogenation to 2,6-lutidine.

A third mechanism (III) starts again with reaction of acetone and

methanol or acetone and formaldehyde to yield methyl ethyl ketone or

methyl vinyl ketone, respectively. Again, formaldehyde is probably

formed by dehydrogenation of methanol over the catalyst [13]. Condensation

of this product with ammonia and then with acetone gives a diene system,

which upon ring closure and dehydrogenation will yield 2,6-lutidine.

92 Formation of 2,6-lutidine

MECHANISM I I I '

\ "H2° ( *NH3 C ' ^ ° ( \

J^~Xx —!

Except for methyl ethyl ketone none of the above-mentioned reaction

intermediates were found in the product mixture, which means that the

intermediates are either very reactive under reaction conditions or do not

exist.

The present data do not allow us to draw any conclusions about the

validity of the mechanisms, so additional work is required to

discriminate between them.

ACKNOWLEDGEMENT.

We thank DSM Research BV. for financial and technical support, and Mr.

L.H.W. Jansen for his technical assistance in performing the experiments.

We are also grateful to Dr. H. W. Kouwenhoven for valuable discussions.

Formation of 2,6-lutidine 93

LITERATURE.

1. 2. 3. 4. 5. 6. 7.

8. 9.

10. 11.

12. 13. 14.

US Patent 3.354.165 (1967); US Patent 3.334.101 (1967). H. Kashiwagi, S. Enomoto, J. Chem. Soc. Japan, 1980, (4), 551. Japan Patent 79.24.878 (1979). Japan Patent 72.22.579 (1972). Japan Patent 72.31.935 (1972). Japan Patent 72.46.070 (1972). F.J. van der Gaag, F. Louter, J.C. Oudejans and H. van Bekkum, Appl. Catal., 26, (1982), 191. US Patent 3.702.886 (1972). Eur. Patent 0.042.225 (1981). J. Datka and E. Tuznik, J. Catal. F.J. van der Gaag, F. Louter and H.

43. in: "Proc. VII Int.

102, (1986), van Bekkum,

Zeol. Conf.", Tokyo 1986, Eds. Y. Murakami, A. Iijima, J.W. Ward, p.763. V.R. Choudhary and D.B. Akolekar, J. Catal., 103, (1987), 115. Y. Matsumura, K. Hashimoto and S. Yoshida, J.Catal., 100, (1986), 392. L.I. Verachchagin and I.L. Kotlyarevskii,Isvest. Akad. Nauk. SSSR, Otdel Khira. Nauk, 1960, 1632, CA 55, 8404 i.

94 SAPO- molecular sieves

Exploratory work on Bilicon aluminum phosphate

molecular sieves and related materials.

INTRODUCTION

Aluminum phosphate molecular sieves (AlPO's) are a new class of

inorganic microporous materials [1,2]. These materials, which were

discovered by Flanigen et al.f 1], have structures much like those of

the alumino-silicate zeolites. The crystal structure is composed of AIO4

and PO4 tetrahedra, with a molar ratio of approximately 1. The lattice of

an aluminum phosphate molecular sieve is therefore almost electrically

neutral, yielding hardly any ion exchange capacity and having a low

polarity. In fact, the polarity of the so-called AlPO-family lies between

the polarity of the low-silica zeolites (e.g. types A, X and Y) and that

of Silicalite, as judged by H2O adsorption.

As mentioned above, the structure of the AlPO's consists of AIO4- and

PO4-tetrahedra linked together via the oxygen ions. Each oxygen is thus

shared between two tetrahedra, yielding a net formula of TO2 (T

representing an Al or P atom). Because each type of tetrahedron bears a

charge (+1 for a PO4- and -1 for an AIO4 tetrahedron), Loewensteins rule

is expected to apply to both types of tetrahedra. Odd-membered rings of

T-atoms should consequently not occur in the structure of the

AlPO-zeolites. The family of AIPO4-molecular sieves comprises both novel

structures and structures with have an analogon in the families of

"classical" (aluminosilicate) zeolites. However, structures containing

odd-membered rings of T-atoms have indeed not been found. Figure 1 shows

some structures of AlPO-type molecular sieves.

SAPO- molecular sieves 95

Figure 1: Structures of zeolitic aluminophosphates: a: A1P0-5; b: AlPO-11; c: A1PO-17; and of two often encountered impurities: d: metavariscite and e: AIPO4.I.5H2O

The lattice of the aluminum phosphate molecular sieves is in theory

electrically neutral. When slight deviations from the ideal Al/P molar

ratio (0.8-1.2 instead of exactly 1.0) are used a charge could be

introduced in the lattice. In the case of an excess of Al tetrahedra the

lattice would bear a net negative charge, giving rise to cation exchange

96 SAPO- molecular sieves

properties. These properties are also found in the classical zeolites

where the lattice also bears a negative charge. Specially interesting

would be those materials where an excess of P tetrahedra is present.

Here the charge on the lattice would be positive, yielding anion

exchange properties. If it would be possible to synthesize these

materials, zeolite science would be allowed to enter the field of

base-catalysed reactions by using OH"-exchanged AlPOa-molecular sieves.

Presently the zeolite technology is limited to acid-catalysed reactions or

one has to rely on suppression of the acidic properties, e.g. by

Cs-exchange of a zeolite.

A further expansion of the family of AlPO-zeolites is the isomorphous

substitution in these materials. Substitution of Si in the lattice yields

the SAPO (Silicon, Aluminum, Phosphorus Oxide) molecular sieves [3].

Theoretically three types of substition are possible:

a: introduction of a Si tetrahedron on the position of Al,

b: introduction of a Si tetrahedron on the position of P, and

c: introduction of two Si tetrahedra on the position of one Al

and one P tetrahedron.

It will be clear that only types a and b will yield charge on the lattice,

a positive charge for type a and a negative charge for type b

substitution. In the case of type c the electrically neutral unit AIPO4

will be substituted by the neutral unit Si2Ü4. In this chapter it will be

shown that only substitution types b and c are found to occur.

Also other substitutions can be envisaged: there is no reason at all to

limit the . substitution to Si. Numerous other metal ions can be

incorporated. Reported examples include: Co, Mg, Mn etc.[4-6]. It is also

possible to perform double substitution, i.e. to incorporate for instance

both Si and Co [4,5], Samples synthesized in this manner are generally

described as MeAPC— or MeAPSO- molecular sieves. Patent literature claims

SAPO- molecular sieves 97

the possibility of introduction of up to 14 substituting metal ions [7],

alone or in combination with Si or other ions. It will be clear that this

gives even more ways of substitution. Experiments described in this

chapter will show that only those substitutions yielding an electrically

neutral or negatively charged lattice will occur.

It is noteworthy that the substituted AlPO-molecular sieves can be

envisaged to be derived from the parent material: all SAPO-, MeAPO- and

MeAPSO-structures are closely related to the corresponding AlPO-structure.

Using X-ray powder diffraction it is virtually impossible to distinguish

between a substituted and a non-substituted A1P0 structure.

Synthesis of A1P0 molecular sieves is effected by mixing a phosphorus

source (usually ortho-phosphoric acid), an aluminum source (usually an

active form of alumina, like pseudo-boehmite or gamma-alumina) and a

structure-directing agent (a template as described for the synthesis of

ZSM-5 type zeolites). The resulting gel is then heated in an autoclave for

a period of time (100-250°C for 1 to 30 days, depending on the desired

structure). A profound difference between the classical (Al/Si-) zeolites

and the AlPO-derived families is the synthesis. Whereas the classical

zeolites are usually synthesized in an alkaline medium, the synthesis

mixture of the AlPO-families has a low pH.

This chapter describes the synthesis of several samples of SAPO-, MeAPO-

and MeAPSO- molecular sieves, their analysis and their properties. One of

the most important properties is the basicity of the sample. This has been

tested using the alkylation of toluene with methanol as a probe reaction.

An acidic catalyst will cause alkylation to occur at the ring, yielding

xylenes and higher substituted benzenes. A basic catalyst will induce

side-chain alkylation, with ethylbenzene and styrene as the products. The

effect of the incorporation of T-atoms other than Si, Al and P is studied

using the ammoxidation of toluene as a test reaction. The activity and

selectivity of catalysts from the AlPO-families is compared to the

98 SAPO- molecular sieves

properties of ZSM-5 type catalysts'.

EXPERIMENTAL

A number of SAPO and MeAPSO molecular sieve samples were prepared,

following the examples described in patent literature [7-11]. A general

procedure consists of the mixing of the alumina source (pseudo

boehmitej Dispural, Condea) and the phosphate source (85* H3PO4, Merck),

followed by the addition of the sources of the substituting T-atoms'. After

thorough mixing the template is added and the mixture was autoclaved for

the desired time at 150 °C. Five closely related synthesis methods were

used, according to Hef 7-11.

The solid samples obtained were analysed using X-ray diffraction, atomic

absorption spectrometry and cólorimetry. The XRD powder data enabled to

detect the presence of A1PO-5 phases, as well as a non-microporous

aluminum phosphate hydrate and some boehmite and other members of the

AlPO-molecular sieve family.

The adsorption properties were determined using NH3-TPD and

thermogravimetric adsorption of water and cyclohexane. Toluene adsorption

was determined in a slightly different way, i.e. by the weight difference

between a dried (400°C) sample and a sample containing toluene adsorbed

in an desiccator filled with toluene vapour.

Some of the samples were tested in a reaction to determine their

catalytic activity. Two reactions were used: the alkylation of toluene

with methanol to investigate whether basic properties are present, and the

ammoxidation of toluene. In the first reaction the following conditions

were applied: WHSV(toluene)=0.17 hr_1 , molar reactant ratio: methanol:

toluenè= 1:1, reaction temperature 250°C. The second reaction provides the

possibility to compare the AlPO-family molecular sieves to the ZSM-5

family (see Chapter 5). Reaction conditions were: WHSV(toluene)-0.17 hr"1,

molar reactant ratio: toluene: ammonia: water= 1:2:6, reaction

SAPO- molecular s ieves 99

temperature: 350°C.

RESULTS AND DISCUSSION

As mentioned above, molecular s i eves of the A1PO- (and re lated) famil ies

can be synthesized by mixing an alumina source, a phosphate source and a

template. The members of the re lated famil ies are obtained by adding the

extra component to the ge l . Here the samples were synthesized by preparing

Table 1: Synthesis conditions for the z e o l i t e cata lys t samples.

Saeple No. Synth Tiae Sources1»' for Tea- Sel «olar ra t io (P205=1.00) XRD t y p e " (hr) Ai P Si Metal plate AI2O3 S1O2 Metal Tenplate r e su l t 0 '

SAPO-5 SAPO-5 SAPO-5 SAPO-5 SAPO-5 SAPO-5 SAPO-5 SAPO-5 SAPO-5 SAPO-5 SAPO-5

1 2 3 4 5 6 7 8 9 10 11

Hg-APSO-5 12 Hg-APSO-5 13 Hg-APSO-5 14 Hg-APSO-5 15 Hg-APSO-5 16 Hg-APSO-5 Hn-APSO-5 Hn-APSO-5

17 18 19

Ti-APSO-5 20 li-APSO-5 21 Ho-APSO-5 22 Ho-APSO-5 23

8 8 8 9 8 8 8 8 8 8 8 10 10 10 10 10 10 11 11 7 7 11 11

120 120 120 64 16 25 40 46 111 135 159 48 72 48 72 48 72 115 140 68 93 90 164

8oeh Boeh Boeh Bpeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh Boeh

PA PA PA PA PA PA PA PA PA PA PA PA PA PA PA PA PA PA PA PA PA PA PA

Aeros Aeros Aeros Aeros Aeros Aeros Aeros Aeros Aeros Aeros Aeros ludox Ludox ludox Ludox Ludox Ludox Ludox Ludox Ludox Ludox Ludox Ludox

-----------Hg0Ac2 HgOAcz Hg0AC2 Hg0AC2 Hg0AC2 Hg0Ac2 HnOAc2 Hn0AC2 TiOS04 Ti0SO« Na?Ho0. NaiHo0<

EtsN EtsN Et3N EtsN EtsN EtsN EtiN EtsN EtsN EtsN EtsN PnN PnN TPA0H TPA0H PnN PnN PnN PnN PnN PnN PnN PnN

1.05 0.94 0.96 1.00 0.94 0.94 0.94 0.94 0.94 0.94 0.94 1.00 1.00 1.00 1.00 2.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00

0.04 0.06 0.04 0.04 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.22 0.22 0.67 0.67 1.33 0.67 0.22 0.22 0.22 0.22 0.22 0.22

-----------0,22 0.22 0.22 0.22 0.44 0.22 0.22 0.22 0.22 0.22 0.22 0.22

1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.0 1.0 1.0 1.0 3.0 1.5 1.0 1.0 1.0 1.0 1.0 1.0

5,H H 5,H 34,H 5,tr B 5 5 5 5 5,B 5,B 36,5 36,5 5,36 5,36 tr 36,tr 5 tr 36,tr 5 tr 5,tr 36 --5,tr H --

" Literature reference miibers. k ' Sources: Boeh: Pseudo-boehiite; PA: ortho-phosphoric acid; Aeros: Aerosil; Ludox: Ludox HS40. c ' S tructures: 5: AlP0-5-type; 34: AlPO-34-type; 36: AlPO-36-type; B: Boehiite; H: A1P04.X H2O; t r - t r ace .

100 SAPO- molecular sieves

a gel with the molar compositions shown in Table 1 and transferring this

gel to Teflon-lined autoclaves. Crystallization was performed at 150°C

during the time shown in Table 1.

All samples were filtered or centrifuged, washed and dried after

synthesis.

It should be noted that the particle size of the • AlPO-type samples is

usually very small. This can be judged from the fact that filtration of

the samples is slow and that a part of the solids pass the filter paper.

A crystal size of 1-10 jum (as is often encountered in the classical

alumino-silicate molecular sieves synthesis) will allow much faster

filtration. A better separation method for the AlPO-zeolites is

centrifugation. A cake is formed which allows easy decantation of the

supernatant liquid. Washing is performed by adding water, stirring the

sample and repeating the centrifugation procedure.

The catalysts were then subjected to an activation (550°C) and an

exchange-procedure (0.05 M NH4CI solution for samples 1-3, 0.05 M HC1

solution for samples 4-23; 10 ml/g of molecular sieve (80°C, 0.5 h). For

ammoxidation experiments Cr- and Cu- exchanged samples were obtained by

exchange with 0.017 M Cr(N03)3 or 0.025 M Cu(N03)z solutions (80°C, 0.5 h)

after H-exchange) to enhance catalytic activity. The crystal structure of

the samples was analysed using X-ray diffraction. The results are

summarised in Table 1. The resulting chemical composition of the samples

was determined using colorimetry (P content) and AAS or ICP (Al, Si and Me

content).

The acid sites distribution of the samples was determined by means of

NHa-TPD, whereas the adsorption characteristics were investigated using

the adsorption of water and cyclohexane in a thermogravimetric experiment.

The pore diameter of SAPO-5 samples is large enough to allow the

adsorption of cyclohexane[3]. All analytical results are shown in Table 2.

SAPO- molecular s i eves 101

Table 2: Results of the analyses on the cata lyst samples.

Saaple No. Product «olar r a t i o " NHs-TPD results*' Adsorbed atounts (wtZ)

AI2O3 SiOz Hetal a b c peaks water cyclohexane toluene

14.8 3.3 12.7

16.4 3.2 6.6

12.1 - 12.0

4.9 15.3 14.7 16.1

11.4 - 14.2

13.0 6.7 11.1

H-SAP0-5 CrH-SAPO-5 H-SAPO-5 CuH-SAPO-5 H-SAPO-5 CuH-SAPO-5 H-SAPO-5 H-SAPO-5 CuH-SAPO-5 SAPO-5 SAPO-5 H-Hg-APSO-5 Hg-APSO-5 H-Hg-APSO-5 Hg-APSO-5 Hg-APSO-5 Hg-APSO-5 Hn-APSO-5 Hn-APSO-5 Ti-APSO-5 H-Ti-APSO-5 H-Ho-APSO-5

1 la 2 2a 3 3a 4 5 5a 7 8 12 13 14 15 16 17 18 19 20 21 22

1.44

1.33

1.69

1.06

1.69 1.69 1.10 1.08 1.46 1.46 2.25 1.15 1.17 1.50 1.57 1.18 1.24

0.00

0.00

0.08

0.06

0.17 0.17 1.10 1.08 0.51 0.51 1.42 0.56 0.19 0.26 0.22 0.18 0.14

-

-

-

-

--0.22 0.22 0.29 0.29 0.42 0.26 0.05 0.05 0.05 0.05 0.14

520 380

374

527 506

319

575

234

390 33

112 -75 -

140 -

104 168 123

112 -

82 -

37 -

48 -- -

7.6 6.6 10.1 5.6

a> PzOs-1.00 b) TPD results as peak area (arbitrary units) for 100 ag sasple.

The adsorption experiments show that in a most cases where XRD indicates

a microporous structure the pore volume (as determined by the adsorbed

amounts) corresponds to the pore volumes mentioned in the patent

literature. These data lead to the conclusion that the prepared molecular

sieve samples do not contain much amorphous impurities, as in that case a

much smaller adsorption was to be expected.

As shown in Table 2 the SAPO molecular sieves show only weak acid sites

in the NH3-TPD-experiments. Desorption of ammonia at temperatures above

300°C was only detected for the SAPO-5 sample number 4. Elemental

102 SAPC— molecular sieves

analysis suggest however that all samples should posses cation exchange

properties, because all SAPO samples have a Al/P ratio which is higher

than unity. Sample number 4 also contains a significant amount of Si, so

this may cause the acidity evidenced by the high-temperature ammonia

desorption. Comparison of samples 1 and la (respectively H-SAPO-5 and

CrH-SAPO-5) shows that Cr-exchange reduces the total amount of adsorbed

ammonia to approximately 70%. It can therefore be assumed that about 30%

of the hydronium ions was replaced by Cr.

The SAPO molecular sieves were tested as a catalyst in the alkylation of

toluene with methanol (conditions are given in the experimental

section). A H-ZSM-5 type catalyst tested for comparison yielded almost

complete conversion to xylene and higher methylated benzenes (up to

hexamethylbenzene). The SAPO catalysts should, if synthesis of a sample

with a surplus of P was achieved, yield a product mixture containing

ethylbenzene and/or styrene. The only products that were detected were

xylene and some gaseous products. The conversion is always low (less than

5%). Both the TPD data and the catalytic experiments suggest that the

SAPO zeolites contain no strong acid sites, responsible for either a

high-temperature ammonia desorption or toluene (ring) alkylation activity.

Chemical analysis shows that no anion exchange properties can be expected,

as the samples contain an excess of Al tetrahedra giving the lattice a

negative charge.

The ammoxidation activity was determined in a reaction setup as

described in Chapter 6. The exchange of the catalysts was described above;

note that a M-H-exchanged catalyst underwent a H-exchange procedure

followed by a M-exchange. The results of the ammoxidation experiments are

shown in Table 3. A Cu-H-ZSM-5 catalyst (Si/Al=25.7) is added for

comparison [see Chapter 6]. Using SAPO-type catalysts gives rise to a

SAPO- molecular sieves 103

product mixture consisting mostly of benzene, benzonitrile and some gaseous products. No products with a higher boiling point were detected.

Table 3: Results of ammoxidation experiments3> with SAPO-type catalysts.

Sample Catalyst Conversion Selectivity (wt*) no. type (wtX) benzonitrile benzene CO2

-1 la lb 2a 3a 4 5a 12 14 21 22

Cu-H-ZSM-5 H-SAPO-5 Cr-H-SAPO-5 Cu-H-SAPO-5 Cu-H-SAPO-5 Cu-H-SAPO-5 H-SAPO-34 Cu-H-SAPO-5 H-MgAPSO-36 H-MgAPSO-5 H-TiAPSO-5 H-MoAPSO-5

100 5 65 5 70 45 5 60 0 5 -5 0

78.0 75 90 95 0 60 45 90 0 55 85 0

18.7 5 5 -10 5 5 5 -15 5 -

3 20 5 -20 35 20 5

0 0 -

a> Molar ratio toluene:NHa:H20=1:2:6, WHSV(toluene)=0.17 h"1, 350°C.

Table 3 shows that the performance of the AlPO-family of molecular sieves in the ammoxidation of toluene is comparable to ZSM-5 type zeolites, especially when a Cu- or Cr-exchanged SAPO-5 catalyst is used. Catalysts number la and 5a (respectively a CrH-SAPO-5 and CuH-SAPO-5 sample) combine a good conversion and a high selectivity to benzonitrile and are certainly comparable to corresponding ZSM-5-type catalysts. However, the samples from the AlPO-family are somewhat more vulnerable to deactivation due to pore blockage, because they have a unidimensional pore system. Note that the H-MoAPSO-5 catalyst (sample no. 22) is inactive. XRD

analysis (see Table 1) showed that this sample was amorphous. It was tested anyway, because amorphous molybdate catalysts are known to show ammoxidation activity. The present commercial catalysts consist of

104 SAPO- molecular sieves

bismuth-molybdenum-phoshate systems, sometimes promoted by treatment with Fe solutions [12]. Sample 22 therefore appears to contain Mo in an inactive form.

CONCLUSIONS Molecular sieves belonging to the AlPO-family (A1PO, SAPO, MeAPO and

MeAPSO sieves) can be synthesised according to the procedures.given in patent literature. In this work the results of elemental analyses and catalytic performance (in the alkylation of toluene) suggest that the structure dóes not allow the synthesis of samples with a positive charge on the lattice, i.e. with anion exchange properties. Syntheses starting with a gel containing a surplus of phosphorus will yield either a non-microporous product or a microporous product with a neutral or negative lattice (as judged by chemical analysis of the sample).

Adsorption properties of the samples show that the pores allow entrance and passage of e.g. water, cyclohexane and toluene. NH3-TPD shows that SAPO-type molecular sieves do not contain strong acid

sites, as judged from the absence of ammonia desorption at a temperature above 300° C. The ammoxidation experiments show that, in addition to the

application in some reactions mentioned in patent literature [4,5,7], the SAPOs studied can be used in the ammoxidation of toluene. Results are indeed comparable to the activity and selectivity of ZSM-5 type catalysts. Since the reaction was cursory explored even better results may be obtained after adjustment of the reaction conditions for the special properties of the A1PO type catalysts.

ACKNOWLEDGEMENT Mr. M.L. van Wijk is thanked for the performance of - the synthetic,

catalytic and adsorption experiments. Mr. J.P. Koot (Laboratory of

SAPO- molecular sieves 105

Analytical Chemistry) and Mr. J.F. van Lent (Laboratory of Materials Science) are thanked for performing AAS analyses and the X-ray powder diffraction on the zeolite samples, respectively.

LITERATURE 1. S.T. Wilson, B.M. Lok, C.A. Messina, T.R. Cannan, E.M. Flanigen, ACS

Symp. Ser., 218, (1983), "Intrazeolite Chemistry", G.D. Stucky, F.G. Dwyer, Eds., p.79.

2. S.T. Wilson, B.M. Lok, E.M. Flanigen, Eur. Pat. EP. 0.043.562, (1982). 3. B.M. Lok, C.A. Messina, R.L. Patton, R.T. Gajek, T.R. Cannan, E.M.

Flanigen, J. Am. Chem. Soc., 1984, (106), 6092. 4. E.M. Flanigen, B.M.T. Lok, B.K. Marcus, C.A. Messina, S.T. Wilson,

Eur. Pat. EP. 0.158.977 (1985). 5. B.M.T. Lok, B.K. Marcus, C.A. Messina, R.L. Patton, S.T. Wilson, E.M.

Flanigen, Eur. Pat. EP. 0.158.349 (1985). 6. E.M. Flanigen, B.M. Lok, R.L. Patton, S.T. Wilson, Pure Appl. Chem.,

58, (10), (1986), 1351. 7. B.M.T. Lok, B.K. Marcus, L.D. Vail, E.M. Flanigen, R.L. Patton, S.T.

Wilson, Eur. Pat. EP. 0.159.624 (1985). 8. S.T. Wilson, B.M. Lok, E.M. Flanigen, US Pat. 4.310.440 (1980). 9. E.G. Derouane, Eur. Pat. EP. 0.174.122 (1986). 10. B.M.T. Lok, L.D. Vail, E.M. Flanigen, Eur. Pat. EP. 0.158.348 (1985). 11. B.M.T. Lok, B.K. Marcus, E.M. Flanigen, Eur. Pat. EP. 0.161.490 (1985). 12. A. Ohorodnik, K. Sennewald, H. Erpenbach, H. Vierling, e.g. Ger.

Offen. 2.155.777 (1973).

106

S U M M A R Y .

In this thesis the synthesis of ZSM-5 type zeolites, the analysis of these zeolites and their use in gasphase reactions with ammonia are described. A last chapter describes experiments involving SAPO-type materials.

Chapter 1 describes the history of zeolite science and some general properties of zeolites. Moreover, a more detailed description is given for ZSM-5 type zeolites, which is used mainly in this thesis. Chapter 2 describes the use of infrared spectroscopy as a versatile

method for the identification of zeolites. Spectra are given for a number of 5-ring containing zeolites. It is shown that impurities in a sample give clear differences in the infrared spectrum. Thus, infrared spectroscopy can be used for the estimation of the purity of a ZSM-5 type zeolite sample. In Chapter 3 the effectivity of a number of templates in the synthesis

is described. The determination of the purity of the obtained samples is performed using both infrared spectroscopy and X-ray diffraction. It is shown that TPA gives the best results as a template, followed by 1,6-hexanediamine. Chapter 4 describes the synthesis of ZSM-5 type zeolites where T-atoms

other than Si and Al are substituted in the framework. It is shown that only a few ions (e.g. Fe, Ti) are built in in the framework; other ions seem to be present in other locations. The zeolites synthesized according to procedures described in Chapters 3 and 4 are used as catalysts in other parts of this thesis (Chapters 6-9). In chapter 5 the acid properties of ZSM-5 samples are compared using

temperature programmed desorption of ammonia. It is shown that the samples (all pure according to other analyses) have different acid properties,

Summary 107

depending on the template used during synthesis. This shows that

characterization of zeolite samples should be performed using as much

analysis techniques as possible.

Chapter 6 describes the use of modified ZSM-5 type zeolites in the

ammoxidation of toluene. The use of unmodified (i.e. only exchanged

samples) was described earlier. Here the use of zeolites modified by

isomorphous substitution (cf. Chapter 4) is reported. The incorporation of

Cr or Fe during synthesis of the catalyst improves the performance in the

reaction. Double exchange (with both Cu and Cr ions) also yields very

active catalysts.

In chapters 7 and 8 the conversion of ethanol and ammonia to pyridines

is described. Chapter 7 describes the use of unmodified ZSM-5 type

catalysts, whereas chapter 8 shows the effect of several modifications.

Good catalytic performance is obtained at temperatures of 300-400°C and a

feed composition which may be obtained by evaporation of a fermentation

mixtures. At high temperature and high space velocity product mixtures can

be obtained consisting almost exclusively of pyridine and ethene, thus

allowing easy separation of the product pyridine.

Chapter 9 describes the conversion of acetone, methanol and ammonia to

2,6-lutidine. It is shown (by 1 3C incorporation) that methanol is built

in at the 4-position of 2,6-lutidine. The reaction conditions were not

extensively optimized, so conversion and selectivity obtained were not as

high as obtained for the pyridine formation as described in the previous

chapters.

Last but not least chapter 10 describes exploratory experiments on

another type of zeolites, i.e. SAPO-type materials. Several samples were

prepared and analyzed. The SAPO-type zeolites were used in toluene

ammoxidation to allow comparison with ZSM-5 zeolites. It is shown that

SAPO molecular sieves can be effectively synthesized and used as a

catalyst.

108

S a m e n v a t t i n g .

In dit proefschrift wordt beschreven hoe zeolieten van het ZSM-5 type

kunnen worden gesynthetiseerd en hoe de producten kunnen worden

geanalyseerd. Tevens wordt het gebruik van deze zeolieten in gasfase­

reacties met ammonia beschreven. In een laatste hoofdstuk worden

enige synthese- en katalyse-experimenten met SAPO-molekulaire zeven

beschreven.

Hoofdstuk 1 beschrijft de geschiedenis van de zeoliet-wetenschap en

enige algemene eigenschappen van zeolieten. De zeolieten van het ZSM-5

type, die in dit proefschrift meestal gebruikt zijn, worden wat

uitgebreider beschreven.

Hoofdstuk 2 beschrijft het gebruik van infrarood spectroscopie als een

handige methode voor de identificatie van zeolieten. Van een aantal

zeolieten (waarvan de struktuur vijfringen bevat) wordt het infra-

roodspectrum gegeven. De aanwezigheid van onzuiverheden in een zeoliet­

monster veroorzaakt een duidelijke afwijking in het infraroodspectrum,

zodat deze techniek gebruikt kan worden om de zuiverheid van een ZSM-5

monster te schatten.

In hoofdstuk 3 wordt de effectiviteit van een aantal templates in de

synthese van zeoliet ZSM-5 beschreven. Voor de bepaling van de zuiverheid

wordt gebruik gemaakt van infraroodspectroscopie en Rontgendiffractie. Het

blijkt dat TPA de beste resultaten geeft in de synthese van zeoliet ZSM-5,

met 1,6-hexaandiamine als tweede.

In hoofdstuk 4 wordt een onderzoek naar de isomorfe substitutie in het

ZSM-5 rooster beschreven. Hierbij worden de Si of Al ionen uit het rooster

vervangen door andere ionen. Slechts enkele ionen (bv. Fe en Ti) blijken

ingebouwd te worden; andere ionen zijn op andere plaatsen in het zeoliet

aanwezig. In volgende hoofdstukken wordt het gebruik van zeoliet-

Samenvatting 109

monsters, die bereid zijn volgens de methoden die beschreven zijn in de

hoofdstukken 3 en 4, beschreven.

In hoofdstuk 5 worden de zure eigenschappen van ZSM-5 monsters, die

bereid zijn met verschillende templates, vergeleken. Het blijkt dat de

monsters (allen volgens andere analysemethoden zuiver) duidelijk

-verschillende zure eigenschappen hebben. Hieruit blijkt dat voor een

volledige karakterisering van een zeoliet zo veel mogelijk verschillende

technieken gebruikt moeten worden.

Hoofdstuk 6 beschrijft het gebruik van gemodificeerde ZSM-5 zeolieten

als katalysator in de ammoxidatie van tolueen. Het inbouwen van Cr en Fe

tijdens de synthese blijkt de katalytische eigenschappen te verbeteren.

Dubbele wisseling (met zowel Cu- als Cr-oplossingen) geeft ook actievere

katalysatoren.

In hoofdstuk 7 en 8 wordt de omzetting van ethanol en ammonia naar

pyridines beschreven. Hoofdstuk 7 beschrijft het gebruik van omge-

modificeerde ZSM-5 zeolieten. Dit wordt in hoofdstuk 8 uitgebreid met de

invloed van diverse modificaties. Bij temperaturen van 300-400°C wordt een

goede omzetting en selektiviteit bereikt, uitgaande van een reactorvoeding

zoals die verkregen zou kunnen worden door ethanol te verdampen uit een

fennentatiemengsel. Bij hoge temperatuur en reactanten-doorzet kan een

produktmengsel verkregen worden dat vrijwel alleen bestaat uit etheen en

pyridine, zodat gemakkelijk een zuivere pyridinefase verkregen kan worden.

Hoofdstuk 9 beschrijft de omzetting van aceton, methanol en ammonia naar

2,6-lutidine. Aan de hand van een experiment met 13C-methanol in de

voeding is aangetoond dat methanol op de 4-positie in 2,6-lutidine wordt

ingebouwd. Bij deze omzetting is minder aandacht besteed aan de

optimalisatie van de reactieomstandigheden, zodat conversie en

selektiviteit niet zo hoog zijn als in de vorige hoofdstukken voor de daar

beschreven reacties.

Als laatste wordt in hoofdstuk 10 enig onderzoek naar de eigenschappen

110 Samenvatting

van een ander type zeoliet, namelijk de SAPO-familie, beschreven. Een

aantal monsters werd bereid en gebruikt in de ammoxidatie van tolueen (dit

om deze molekuïaire zeven te kunnen vergelijken met de ZSM-5 zeolieten).

Het blijkt dat de SAPO-familie molekuïaire ' zeven goed gesynthetiseerd en

als katalysator gebruikt kan worden.

111

Dankwoord.

Hier wil ik iedereen bedanken die heeft bijgedragen aan de totstand- koming van dit proefschrift. Tijdens het onderzoek ben ik steeds met plezier bezig geweest. Dit is grotendeels te danken aan de goede samenwerking met het personeel van de Vakgroep Organische Chemie en aan de gezellige sfeer in de vakgroep, en met name de Zeolietgroep.

Ik dank mijn promotor, prof. dr. ir. H. van Bekkum voor de enthousiaste wijze waarop hij mijn onderzoek heeft begeleid, in de juiste mengeling van sturen en vrijlaten.

De afstudeerders Frans Louter, Bert Herlaar, Roel Adriaansens en Maurice Smits en Michel van Wijk (stagiar) ben ik erkentelijk voor hun bijdragen aan dit proefschrift. Ook alle studenten die in de zeolietgroep een practicum of project hebben gelopen wil ik bedanken voor de samenwerking. Ik dank ook de Rö'ntgendiffractie-service van de afdeling Materiaalkunde (J.F. van Lent en N.M. van der Pers) voorde snelle service.

Mijn collega's Rob Ie Fêbre, Koos Jansen en later ook Theo Maesen en Patrick Voogd dank ik voor de prettige sfeer en de vele discussies (ook over niet-chemische onderwerpen).

Mieke van der Kooy dank ik voor het vele en snelle (type-)werk en Wim Jongeleen voor alle fraaie tekeningen en posters die hij gemaakt heeft.

Ernst Wurtz dank ik voor de snelle en uitstekende wijze waarop hij voor de meest onzinnige vragen en problemen mijnerzijds een oplossing vond. Ik dank ook de instrumentmakerijen voor de glansrijke wijze waarop opdrachten werden uitgevoerd. Loek van Leeuwen dank ik voor de hulp bij GC-problemen.

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Curriculum Vitae.

Fred van der Gaag werd geboren op 14 maart 1959 in Delft. In 1977 behaalde hij het diploma VWO-B op het Christelijk Lyceum Delft. Vervolgens studeerde hij in 1982 af als ingenieur bij de Afdeling der Scheikundige Technologie van de TH Delft.

In april 1983 trad hij als wetenschappelijk assistent in dienst van de TH en begon, in aansluiting op zijn afstudeerwerk, aan een promotieonderzoek onder leiding van prof. dr. ir. H. van Bekkum bij de vakgroep Organische Chemie.

Sinds juli 1987 is hij als researchmedewerker werkzaam bij Fasson (Nederland) B.V. te Leiden.