Selective Hydrogenation of Cinnamaldehyde to COL

Project Report 3

Under the guidance of

Prof. Preeti Aghalayam

&

Dr. K.R.Krishnamurthy

National Centre for Catalysis Research

Indian Institute of Technology, Madras

Contents

• Summary of earlier work

• Further characterization of catalysts

• Calibration of GC

• Testing of Catalysts

• Initial conversion and selectivity trends.

• Optimization of different parameters of reaction.

• Future work

Summary of earlier work

� Reaction scheme

� Literature survey

� Problem for research

� Catalyst prepared

� Characterization (XRD, UV)

Reaction scheme

Fig.1 Reaction scheme of hydrogenation of Cinnamaldehyde to its products.

CAL=cinnamaldehyde, HCAL=hydrocinnamaldehyde, COL=cinnamyl alcohol,

HCOL=hydrocinnamyl alcohol.

The aim of the project is to selectively produce cinnamyl alcohol from cinnamyl aldehyde but

this reaction is thermodynamically not favorable which can be seen from Gibbs free energy

values depicted in the reaction scheme, so the challenge is to design a catalyst system which

would overcome thermodynamic barrier and facilitate the desired reaction.

Literature survey

According to literature the best catalyst known which give very good selectivity and conversion

is a platinum based bimetallic system whose details are given in Table 1.

----------------

Table.1 best catalyst known for selective hydrogenation of cinnamaldehyde to cinnamyl alcohol

The platinum based catalyst is a bimetallic system with Co, the nanoparticles are protected by

capping agent PVP.

Problem for research

As we see from Table 1 that Pt-Co/PVP is a very good catalyst for selective hydrogenation of

cinnamaldehyde but the TON is considerably low when compared to other noble metals like Ru,

Rh and Pd, so here lies a challenge to design a catalyst which can give good selectivity with high

TON. A comparison of selectivity conversion and TON is shown in Table 2, which reveals that

amongst Ir, Pt,, Ru, Rh, Pd, Palladium is having the highest TON of 6.7s-1

which is 600 times

greater than Pt, so we have chosen Pd noble metal to design a catalyst as the problem for our

research.

Table.2 comparison of selectivity conversion and TON of noble metals.

Catalyst prepared

Below listed catalysts were prepared and characterized by UV and XRD by the end of the

project evaluation 2

Shape controlled catalysts

• Tetrahedral Pd/Hydrotalcite

• Octahedral Pd/Hydrotalcite

• Spherical Pd/Hydrotalcite

TiO2 supported catalysts

• PVP-1.5% Pd/Ti02 P25

• PVP-1 % Pd/Ti02 P25

Further characterization of catalysts

The above listed catalysts were Characterized by TEM/HR-TEM, TG-DTA, XPS.

TEM/HR-TEM

Tetrahedral -Pd/Hydrotalcite

Figure.2 TEM of Tetrahedral -Pd/Hydrotalcite

Fig.2 shows the TEM images of Tetrahedral Pd/Hydrotalcite, the goal of preparing this catalyst

was to prepare tetrahedral shaped Pd crystallites, Fig.2 shows some Tetrahedral shaped Pd but

other shapes of Pd crystallites are also present, the reason to prepare tetrahedral Pd crystallite

was tetrahedral shaped crystallites exposes only (111) plane, exposure of a single plane gives

selectivity towards adsorption of a specific functional group which will give selectivity towards a

specific product.

Figure.3 EDAX of Tetrahedral Pd/Hydrotalcite.

Fig.3 shows the EDAX(energy dispersive X-ray spectroscopy) of Tetrahedral Pd/Hydrotalcite

which confirms the presence of Pd tetrahedral crystallites.

Fig.4 give the crystallite size distribution of Tetrahedral Pd/Hydrotalcite, the crystallite size is

centered around 25nm.

Fig.4 Crystallite size distribution of Tetrahedral Pd/Hydrotalcite

Octahedral Pd/Hydrotalcite

Fig.5 HR-TEM images of octahedral Pd/Hydrotalcite

Fig.5 depicts the HR-TEM images of octahedral Pd/Hydrotalcite, we can see octahedral

crystallites with other shaped crystallites of Pd nanoparticles. The goal of preparing octahedral

shaped particle was to expose specific planes, octahedral specifically exposes (111) and (110)

planes in comparison with tetrahedral which exposes only (111), it would be very interested to

see what might be the effect on the selectivity of products.

Fig.6 depicts the crystallite size distribution, the crystallites are centered around 22-28nm.

Fig.6 Crystallite size distribution of octahedral Pd/Hydrotalcite

Spherical Pd/Hydrotalcite

Figure 7 depicts the HR-TEM images of spherical Pd/Hydrotalcite, the images show mostly

spherical shaped Pd crystallites.

Figure.7 HR-TEM images of spherical Pd/Hydrtotalcite

In comparison with tetrahedral and octahedral, spherical shaped crystallites expose multi-

planes, and it would be interesting to see the variation in selectivity towards product formation.

Figure.8 Crystallite size distribution of spherical Pd/Hydrotalcite.

PVP 1.5% Pd/TiO2 P25

Figure.9 shows the TEM images of PVP1.5%Pd/TiO2-P25, which shows that the Pd nanoparticles

are impregnated on the Titania nanoparticles.

Fig.9 TEM images of 1.5%PVP Pd/TiO2 P25

Fig.10 depicts the EXDX of 1.5%PVP Pd/TiO2 P25 catalyst and we can clearly see the presence of

Pd, Ti, O.

Fig.10 EDAX of 1.5%PVP Pd/TiO2 P25

Fig.11 give the crystallite size distribution of 1.5%PVP Pd/TiO2 P25 which shows that crystallites

are centered around 3nm.

Fig.11 Crystallite size distribution of 1.5%PVP Pd/TiO2 P25

TG-DTA

PVP 1.5% Pd/TiO2 P25

Figure.12 TG-DTA of PVP1.5% Pd/TiO2 P25

The purpose of doing TG-DTA was to know till what temperature the catalyst is stable or do not

undergo any weight change, this information is essential to decide the reaction condition. In

this case we see significant weight loss at 270o C may be due to decomposition of organic

matter like ethylene glycol or PVP which means that we can conduct reaction below 250oC only,

reaction carried away above 270oC will lead to weight loss in catalyst which will lead to change

in basic design of catalyst. The endothermic peak at 270oC is due to PVP decomposition.

Octahedral Pd/Hydrtotalcite

Figure.12 depicts the TG-DTA of octahedral Pd/Hydrtotalcite, here we see three consecutive

weight losses between 200-400o c, the first loss is attributed to loss of interlayer water, second

weight loss is attributed to decomposition of interlayer carbonate anion and the third one is

attributed to dehydroxilation of OH groups. All these peaks are exothermic in nature. Fig.12

also helps us to fix the reaction temperature, the reaction temperature can be only below

200oC.

Figure.12 TG-DTA of octahedral Pd/Hydrtotalcite

XPS

Fig.13 is the full scan XPS of PVP1.5% Pd/TiO2 P25, which shows the presence of Pd, O,Ti,C.

Fig.13 XPS Full scan of PVP1.5% Pd/TiO2 P25

Figure.14 XPS of Pd 3d peak

Fig.13 gives the full scan of PVP1.5% Pd/TiO2 P25 showing the presence of Pd, Ti, O, c. Fig.14 is

the xps of Pd 3d which shows two peaks corresponding to 3d5/2 and 3d3/2 which are generated

because of spin-orbit coupling. The standard binding energies of the Pd 3d peaks and observed

values are given in table 3.

Standard BE(eV) Observed BE(eV)

Pd5/2 335 ± 0.2 335.22

Pd+2

340± 0.2 340.50

Table 1. Binding energies of Pd in PVP1.5% Pd/TiO2 P25

Figure.15 is the deconvoluted plot of figure.14, this plot gives information about the %surface

ratios of Pd in its oxidized and reduced form, this information is given in table 4.

Figure.15 Deconvolution of Pd 3d peak.

Table 4. % surface ratios of Pd and Pd+2

%Pd0 %Pd+2

54 46

Testing of Catalyst

Hydrogenation of cinnamaldehyde is carried in a parr reactor to test them performance of

catalyst and the obtained products are analyzed by GC with RTX-5 MS column. Before analyzing

products the GC has to be calibrated for the reactant and products of the reaction, Fig.16

depicts the chromatogram of the GC calibration.

Figure.16 chromatogram showing the calibrated peaks of reactant and products.

Initial reaction condition Reaction set 1

• Temperature = 120oc

• Catalyst wt. = 150mg

• Solvent = Methanol

• Reactant = 1.2g(9mmol)

• H2 Pressure = 10bar

Catalyst Conversion Selectivity%

HCAL HCOL COL

Tetra Pd/HT 100 78.9 20.8 0.3

Octa Pd/HT 100 78.3 21.5 0.2

1.5%Pd/TiO2

100 7.3 19.5 73.2

1% Pd/ TO2 100 1.2 13.2 85.6

Table.5 selectivity and conversion at 150mg,120oC.

( Tetra=tetrahedral, HT=hydrotalcite, Octa=Octahedral)

Table.5 depicts the selectivity and conversion of hydrotalcite supported catalysts and

titania supported catalyst under initial conditions chosen for reaction. Form table.5 it is

clearly evident that all catalyst systems are showing 100% conversion but only Titania

based catalyst are showing very good selectivity towards cinnamyl alcohol, whereas poor

selectivity is seen for hydrotalcite supported catalysts. Since all catalyst are showing 100%

conversion it means all the reactant has converted to reactant, but for the comparison of

catalyst systems it is important that we get some unreacted reactant. In order get

unreacted reactant we have to optimize the reaction conditions.

Figure .17 gives a graphical presentation of the activities of hydrotalcite and titania based

catalysts.

Figure.17 plot comparing selectivity of THT(Tetrahedral Pd/Hydrotalcite, OHT(octahedral

Pd/Hydrotalcite, 1.5% Pd/TiO2, 1% Pd/TiO2

THT OHT 1.5%Pd/Ti 1.0%Pd/Ti

0

20

40

60

80

Catalyst type

%S

ele

ctivity

Reaction set 2

Effect of Temperature

• Temperature = 100oc and 80

0c


• solvent = methanol

• Reactant = 1.2g


In this reaction set we have decreased the reaction temperature form 120

0C to 100 and 80

oC,

we want to see if by decreasing the temperature their might be decrease in conversion and we

might get some unreacted reactant, but we could not get any unreacted reactant, but the

selectivity at 100oC is much better than selectivity at 120

oC, the results of reaction set 2 are

presented in table6, form this data we can conclude that selectivity at 1000C is much better

than selectivity at 1200C. Figure.18 gives a graphical representation of the comparison of

selectivity of 1.5%Pd/TiO2 at 100 and 80oC.

Table.6 selectivity and conversion of 1.5%Pd/TiO2 at 100 and 80oC.

Figure.18 comparison of selectivity of 1.5% Pd/TiO2 at 100 and 80

oC.

110 105 100 95 90 85 80 75 70

0

20

40

60

80

Temperature

%S

ele

ctivity


HCAL HCOL COL

1.5%Pd/Tio2100

0

C 100 0.7 9.3 90

1.5%Pd/Tio280

0

C 100 1.2 15.8 82.6

Reaction set 3

Effect of Catalyst wt. • Temperature = 120

0c



• Reactant = 1.2g


Results of Reaction set 1 and 2 reveal that changing the temperature had not much effect

on the conversion and we could not get any reactant peak, so in this reaction we kept the

temperature at 120oC and decreased the catalyst wt to half of amount used in reaction set

1 which comes to 75mg. the result of this reaction is presented in table.7, even under these

conditions we were unable to get any reactant peak but the selectivity is retained.

Table7 selectivity and conversion of 1.5% Pd/TiO2 at 75mg, 120oC.

Reaction set 4

Change in catalyst wt. and temperature

• Temperature = 1000c

• Catalyst wt. = 40, 30, 20mg


• Reactant = 1.2g


Reaction sets 1,2 didn’t fetch us the desired unreacted reactant, so in reaction set 4 we

have decreased the catalyst wt. further down to 40,30,20 at a Temperature of 100oC. In this

reaction set we got unreacted reactant at 30mg catalyst wt with a conversion of 99.7 and

selectivity of 79.7, the trend has continued at 20mg wherein we got more unreacted

reactant, this signifies that at 30mg and 20mg the active Pd sites are not enough to bring


HCAL HCOL COL

1.5% Pd/ TiO2 100 3.9 7.1 89

about complete conversion. The selectivity is comparatively less at 30mg compared to

selectivity at 40mg. the results are presented in table 8 and figure.19.

.

Table.8 selectivity and conversion of 1.5% Pd/TiO2 at 40,30,20 at 100oC.

Figure.19 comparison of selectivity of 1.5% Pd/TiO2 at 40, 30, 20mg at 100oC

Reaction set 5

Effect of catalyst wt. at constant Temperature

In reaction set 4 we got some unreacted reactant as we were desiring, in this set of

reactions we wanted to see what will happen if we further reduce the temperature at

catalyst wt. used in reaction set 4. The results of reaction set is presented in table.9 and


HCAL HCOL COL UK

1.5%Pd/TiO2(40mg)

100 2.8 8 89.2 0

1.5%Pd/TiO2(30mg)

99.7 9.7 10.3 79.7 0.3

1.5%Pd/TiO2(20mg)

91 13.4 5.4 71.2 10

40 30 20

0

20

40

60

80

Se

lectivity%

Catalyst wt(mg)

figure.20, from these data it is evident that with decrease in temperature there is decrease

in conversion and selectivity, if we compare the results of reaction set 4 with 40mg, 100oC

and same conditions in reaction set 5 we observe that the selectivity is better at 40mg and

1000C, from this observation we can say that the optimum catalyst wt and optimum

temperature for 1.5% Pd/TiO2 catalyst are at 40mg and 100oC.


HCAL HCOL COL UK

1.5%Pd/TiO2(50mg)

100 12.6 8.6 78.8 0

1.5%Pd/TiO2(40mg)

98.7 7.6 6.4 84.7 1.3

1.5%Pd/TiO2(30mg)

89.7 21 5.7 66 7.3

Table.9 selectivity and conversion of 1.5% Pd/TiO2 at 50,40,30 at 75oC.

Figure.20 comparison of selectivity of 1.5% Pd/TiO2 at 50, 40, 30mg at 75oC

An interesting thing we can observe in sets 4 and 5 that whenever we are getting some

reactant peak we are getting an unknown peak around retention time 5.3. this unknown

20 30 40 50

0

20

40

60

80

Sele

ctivity%

Catalyst wt(mg)

peak is also visible in reaction mix prepared 15min before. Fig.21,22 shows the appearance

of this unknown peak.

Figure.21 chromatogram of reaction products of of1.5%Pd/TiO2(40mg,75

oC)

Unknown peak

Unknown peak

Figure.22 chromatogram recorded after 15min of preparation of reaction mix.

The unknown product appearing in the reaction product may be cinnamic acid which is

formed by the oxidation of cinnamaldehyde in presence of air or cinnamaldyde may also

form acetal with the solvent methanol, but the acetal of cinnamaldehyde is a vicinal alcohol

which is generally unstable but in the reaction mix the unknown product is persistent so the

unknown product may be cinnamic acid, even thermodynamically change in gibbs free

energy for cinnamaldehyde to cinnamic acid is -224kJ/mol whereas cinnamaldehyde to

cinnamaldehyde acetal is -92Kj/mol, since change in gibbs free energy for the formation of

cinnmic acid is more negative its formation is favored and cinnamic acid is stable, so most

probably unknown product is cinnamic acid.

Reaction set 6

Effect of calcination on catalyst performance




• Reactant = 1.2g


Till now all the reaction conducted were using as-synthesized catalysts, now in this reaction we

have used an calcined 1.5% Pd/TiO2 catalyst which was calcined at 300oC for 3h in N2

atmosphere, the results of this reaction are shown in Table.10 were very surprising, the same

catalyst which was not calcined was giving very good selectivity but calcined catalyst is giving

poor selectivity, rather selectivity for Hydrocinnamyl aldehyde has increased, the formation of

Hydrocinnamaldehdye takes place when cinnamaldehyde adsorbs through olefinic bond, when

a catalyst is calcined there is a chance that there may be change in increase in size of crystallite,

TEM results for Tetrahedral, octahedral and spherical shaped Pd/Hydrotalcite shown in fig.4,6,8

shows that the crystallites are in the range 20-30nm in case of tetrahedral and octahedral

Pd/Hydrotacite and 5-7nm in Spherical Pd/Hydrotalcite, these catalyst show poor selectivity for

cinnamyl alcohol, whereas Pd/TiO2 shows good selectivity in this catalyst crystallites are

centered around 3nm, , that means for good selectivity towards cinnamyl alcohol small

particles are favorable.


HCAL HCOL COL

Calcined 1.5% Pd/ TiO2 100 53.2 33.9 12.9

Table.10 effect of calcination on selectivity in 1.5% Pd/TiO2

Reaction set 7

Effect of solvent



• Reactant = 1.2g

• Solvent- isopropanol, AMW- (Ammonium accetate, methanol, water),

methanol.

• H2 pressure =10bar Till now we have used methanol as solvent for carrying out reaction, now we have

attempted to see the effect of solvent on selectivity and conversion, the other reason for

using other solvent is whether we can avoid formation of the unknown product, we have

tested the catalyst with isopropanol and a mixture of ammonium acetate, methanol and

water. The results are very surprising which are tabulated in table.11 and plotted in fig.23


HCAL HCOL COL UK

1.5% Pd/TiO2(isop)

42.6 58.5 17.4 5.6 18.5

1.5% PdTiO2AMW

14.8 81.1 7.2 2.4 3.5

1.5%Pd/TiO2meth

91 13.4 5.4 71.2 10

Table.11 effect of different solvents on selectivity and conversion in 1.5% Pd/TiO2

Isopropanol AMW Methanol

0

10

20

30

40

50

60

70

Solvant type

%S

ele

ctivity

figure.23 graphical representation of effect of solvent on selectivity towards cinnamyl

alcohol

The results are very surprising as the selectivity and conversion has decreased significantly

when we used isopropanol, AMW has shown much more drastic results with lowest

convection of 14.8, whereas methanol gives very good selectivity and conversion, the

probable reason for low conversion is due to low solubility of H2 in isopropanol and AMW,

water is known be have the lowest solubility for H2 hence AMW gives least conversion,

Solubility of H2 is necessary for H2 to reach catalyst surface and get adsorbed and

participate in reaction, when there is not enough H2 reaction conversion will come down

which is evident form the results.

Reaction set 8

Effect of catalyst wt.

• Temperature = 1000C

• Catalyst wt. = 40,20mg.



• Reactant=1.2g

We have optimized the parameters for the reaction as 40mg, 100oC , now we are trying to

compare catalyst 1.5% and 1% Pd/TiO2 to see which amongst is best. The results are shown

in table.12 and graphically represented in fig.24.


HCAL HCOL COL ACETAL

1% PdTiO2(40mg)

96.1 3.9 11.6 81.1 3.4

1% PdTiO2(20mg)

77.2 22.8 5.2 53.7 18.4

Table.12 selectivity and conversion of 1% Pd/TiO2 at 40mg, 100oC.

When we compare the results in table.8 and table.12 we can come to the conclusion that

1.5%Pd/TiO2 is better than 1% Pd/TiO2 , the possible reason for such a result could the

optimum loading of Pd in 1.5%Pd/TiO2 which avoids over hydrogenation or under

hydrogenation.

Conclusions • The optimum parameters for 1.5% and 1% Pd/TiO2 were determined as 40mg catalyst,

temperature = 100oC, P = 10bar.

• Among Hydrotalcite supported catalyst and Titania supported catalyst, Titania

supported catalyst systems are better for selective hydrogenation of cinnamaldehyde to

cinnamyl alcohol.

• Small Pd crystallite sized catalyst give good selectivity compared to larger crystallites.

• Out of 1% and 1.5% Pd/TiO2 , 1.5% is better in terms of selectivity and conversion.

• Methanol is most suitable solvent for better conversion and selectivity.

Future work

� Preparation of following catalysts, their characterization and testing of catalysts

� Determination of effect of support on selectivity and conversion

•

• Pd/TiO2(pure anatase phase)

• Pd/TiO2(pure rutile phase)

• Pd/TiO2(mesoporus)

• Bimetallic systems

• Pd-AU/TiO2 and Pd-Ag/TiO2

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Selective Hydrogenation of Cinnamaldehyde to COL