Indian Journal of ChemistryVol. 28A, January 1989, pp. 19-22

Decomposition of Isopropyl Alcohol on Oxidised IntermetallicCompound LaNi 5

M P SRIDHAR KUMAR. B VISWANATHAN. C S SWAMY* & V SRINIVASANDepartment of Chemistry. Indian Institute of Technology. Madras 600 036

Received I December 19R7; accepted 28 March 1988

The catalyst formed by oxidation of LaNi, is found to have higher specific activity and lower activation energyfor the decomposition of isopropyl alcohol when compared with the corresponding conventionally prepared sup-ported metal catalyst. Both the catalysts lead to the formation of condensation products like n'lesityl oxide. isobutylmethyl ketone and diisobutyl ketone in addition to acetone. A probable mechanistic route for the formation of thecondensation products is proposed. The condensation ability of these supported catalysts is attributed to the basicnature of La:O,.

Intermetallic compounds (RM,), especially LaNi 5'

have been explored as catalysts for hydrogenationof CO I, ethylene? and other unsaturated hydrocar-bons ', as well as for syngas conversion". Luengo etal.5 have examined LnM 2 systems (Ln = rare earthelement; M = transition metal) for CO hydrogena-tion and proposed that oxide supported metal sys-tems can be prepared from these intermetallicsemploying suitable activation procedures. Wang etal", extending this proposal examined the LaCo 5

system and showed that the active catalyst display-ed the general features of the model catalyst, Co-supported on La203. In view of these observationsand in continuation of our studies on intermetalliccompounds of the ABs-type as catalysts 7, we haveexamined the catalytic properties of LaNis undervarying . experimental and activation conditions,towards decomposition of isopropyl alcohol (IPA).Reproducibility and consistent results could beobtained only when the system was oxidised.However, in other experimental procedureswherein the identity of the intermetallic phasecould be retained, reproducible results could notbe generated. In view of this it was felt desirableto compare the activity of the intermetallics withthat of a conventionally prepared (by impregna-tion/precipitation) supported metal system for thedecomposition of IPA. Both these systemspromoted in addition to dehydrogenation of IPA,condensation reactions leading to the formation ofcarbonyl compounds. In this paper particular at-tention has been paid to delineate the mechanisticdetails of the carbonyl condensation reaction onthis supported catalyst system.

Materials and MethodsThe intermetallic compound LaNi:; (Ergenics

Corporation, USA) was converted into a support-ed metal system by oxidising at 573 K in a flow ofoxygen for 20 hr and reducing in a flow of purifi-ed hydrogen gas at 673 K for 8 hr. This was de-signated as CAT-A.

The metal supported catalyst (CAT-B), i.e. 10%Ni/La.O, was prepared 'by impregnating LaZ03(Indian Rare Earths, 99.99% purity) with an aque-ous solution of nickel nitrate (AR) at 333 K. Thecatalyst was dried in an oven at 393 K for 10 hr,calcined in air at 598 K for 4 hr and reduced inpurified hydrogen at 673 K for 8 hr ..

The catalytic properties were studied in an all-glass continuous flow reactor. The liquid productswere analysed by gas chromatography.

Results and DiscussionConversion-time plots for the decomposition of

IPA on CAT-A and CAT-B are given in Figs 1 and2 respectively. The values of the energy of activa-tion calculated from the linear Arrhenius plots forthe decomposition of IPA on these two catalystsare found to be 27.2 and 51.5 kl/rnol respectively.The extent of conversions are much higher forCAT-A which is in agreement with the activationenergies calculated.

In view of the fact that these systems promoteda number of side reactions involving dehydrogena-tion product acetone, a series of experiments werecarried out using IPA alone. as reactant or acetoneand IPA or acetone and hydrogen as reactants andthe data generated on the product distribution forthese two catalysts are given in Tables 1 and 2 re-spectively. It is seen that apart from the conven-tional dehydrogenation product, namely, acetonethree other products, viz. isobutyl methyl ketone(IMK), diisobutyl ketone (DIK), and mesityl oxide

19

INDIAN J CHEM, JANUARY 1989

473K 473K

12 2.0

E N453K<,

~c:0 453K

c: 1.6.~ 0

•• 'in> ~c0 8 §!.2u

C C~ 433K II

uII 8.0.8a.II II(5 (5:!: 398K :!:

4 O.

Contact time, sec

2 3 Fig. 2-Conversion-time plots for decomposition of IPA on,··Contact time sec CAT-B

Fig. I-Conversion-time plots for decomposition of IPA onCAT-A

Table 1- Product Distribution for Decomposition of IPA on CAT-AReaction Feed Contact Mole % of the liquid collected

temp. time(K) (see) IPA Acetone IMK MO DIK

473 IPA 2.4 31.8 40.2 15.5 5.2 7.31.4 36.7 38.7 13.6 4.6 6.40.9 38.8 43.0 10.2 3.5 4.50.5 58.0 38.8 1.6 <I <I

453 IPA 2.5 48.8 40.2 6.5 1.7 2.81.5 51.5 43.2 2.9 < 1 1.50.9 53.1 44.1 1.8 <I0.5 63.8 36.2

413 Acetone + H, 71.3 22.7 4.0 2.0·(1:1)

31}3 -do- 78.0 20.0 1.0 <I37x -do- 80.9 19.1

Table 2-Product Distribution for Decomposition of IPA on CAT-BReaction Feed Contact Mole % of the liquid collected

temp. time(K) (see) IPA Acetone IMK MO DIK

473 IPA 2.4 45.8 22.5 16.9 4.6 10.21.4 50.2 30.2 10.8 2.5 6.30.9 65.3 25.1 6.4 2.2 1.00.5 79.2 18.8 2.0

453 IPA 2.5 60.7 26.5 6.8 3.3 2.61.5 66.4 26.6 3.1 1.2 2.70.9 77.2 20.7 2.1 trace trace0.5 89.4 10.6

433 IPA 3.9 66.2 28.1 3.5 2.2 trace2.6 72.1 22.9 2.8 2.2 trace1.6 81.5 16.9 <I

413 Acetone + H, (I: I) 42.2 41.8 9.7 4.0 2.3396 -do- 46.1 46.6 7.3 trace trace373 -do- 43.7 50.6 5.0 0.73.:1x -do- 22.4 74.9 2.7

20

SRIDHAR KUMAR et al.: DECOMPOSITION OF ISOPROPYL ALCOHOL ON LaNi,

(MO) were formed on both the catalysts and theextent of formation of these products (maximumof about 25%) follows more or less the same or-der. It is clear that the behaviour of CAT-A gener-ated from the intermetallic compound is more orless similar to that of the conventional supportedcatalysts, i.e. CAT-B. These results are in confirm-ity with the observations recorded by Chin et al.8and Wang et al.6 for CO hydrogenation on sup-ported metal catalysts prepared by the partial oxi-dation of the AB 5 type intermetallics.

The formation of other condensation productslike IMK, DIK and MO in the decomposition ofIPA has been reported on a number of mixed ox-ide systems? as well as on oxides 10of Mg, Ca, Srand Ba and on Raney CU11l2. On nickel supportedon alumina, the formation of mesitylene by thecondensation of three acetone molecules has beenreported during the reaction of IPA at 673 K13. Inview of these reports, it was considered worth-while to investigate the mechanistic aspects ofthese condensation reactions in some detail on thenickel supported on La 203 catalyst as well as thecatalyst generated from the intermetallic com-pound.

It was observed that when acetone alone wasused as the reactant in the feed no condensationproducts were obtained, while condensation pro-ducts were obtained when the feed was IPA orIPA and acetone or acetone and hydrogen (seeTables 1 and 2). Even though MO is produced bythe condensation of two acetone molecules (referScheme 1), this reaction is obviously not promotedin the absence of IPA or hydrogen in the feed.This could be because the catalyst does not a pri-ori possess acidic sites which can promote the de-hydration of acetone. This is also substantiated bythe observation that dehydration of IPA was notobserved when IPA alone was used as the feed.Hence, the possible reaction sequence for the for-mation of the condensation products can be pro-posed as shown in Scheme 1.

Aldol condensation is normally promoted byeither acids or bases through the formation of acarbocation or a carbanion. Since the initial stepsin these reactions involve either a 'proton additionor a proton abstraction by OH -, it is a prerequi-site that the catalyst should contain such centreswhere either of the two functions is promoted.Even though the generally activated catalyst maycontain acidic and basic sites of Lewis acid-baseconcept, the generation of OH - type species aswell as the availability of labile protonic species isfeasible only when either hydrogen is present or

"

l,

~ H..C 0C _~o-J " a

Hl/ 'CH;--- /CaCH-C-CH

H)C

~silyl oxide (MO)

'"'''~I-¥H)C" ~ /CH)

Cc CH- C-cH ~C·

~C/ "CHJPh",~

l'PAor H2

H)C" ~ /CHJCH- CH2-C -CH2 -CH

H)C/ \CH)

Oisobulyl ketone (01 K )

SCHEME'

prior dehydrogenation reaction (in this case dehy-drogenation of IPA) is possible. Once such type ofsites are generated in situ then subsequent hydrog-enation for the formation of IMK or dehydration!hydrogenation for the formation of DIK is auto-matically ensured. The validity of this mechanismis also reflected by the fact that the concentrationsof DIK and MIK are higher than that of MO,since subsequent hydrogenation!(dehydration!hydrogenation) reation can be expected to be fastas compared to the initial dehydration reaction.This condensation ability of these supportedcatalysts can be attributed to the basic nature ofLa203. It is therefore natural to expect a similarcondensation activity with other supported metalsystems containing basic supports.

Acknowledgement

The authors thank the CSIR, New Delhi for theaward of a fellowship to one of them (MPS).

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INDIAN J CHEM, JANUARY 1989

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