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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
• Catalyst wt. = 150mg
• solvent = methanol
• Reactant = 1.2g
• H2 Pressure = 10bar
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
Catalyst Conversion Selectivity%
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
• Catalyst wt. = 75mg
• solvent = methanol
• Reactant = 1.2g
• H2 Pressure = 10bar
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
• solvent = methanol
• Reactant = 1.2g
• H2 Pressure = 10bar
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
Catalyst Conversion Selectivity%
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
Catalyst Conversion Selectivity%
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.
Catalyst Conversion Selectivity%
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
• Temperature = 1200c
• Catalyst wt. = 150mg
• solvent = methanol
• Reactant = 1.2g
• H2 Pressure = 10bar
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.
Catalyst Conversion Selectivity%
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
• Temperature = 1000c
• Catalyst wt. = 20mg
• 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
Catalyst Conversion Selectivity%
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.
• H2 Pressure = 10bar
• solvent = methanol
• 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.
Catalyst Conversion Selectivity%
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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