Selectivity of gold catalysts for selective hydrogenation of cinnamaldehyde

Article abstract of DOI:10.14233/ajchem.2013.14864

Gold nanoparticles (A_uNP_s), SiO₂ and TiO₂ supported A_uNP_s prepared by colloid deposition method and A_u/TiO₂ prepared by depositionprecipitation method (A_u/TiO₂-DP) were used for the liquid-phase selective hydrogenation of cinnamaldehyde. The catalysts were characterized by HRTEM, H₂-TPR and XPS. Results showed that A _uNP_s, A_uNP_s/SiO₂ and AuNPs/TiO₂ in dried form selectively hydrogenated the C=C bond, whereas AuNPs/TiO₂ treated in H₂ and Au/TiO₂-DP preferentially hydrogenated the conjugated C=O bond. From our data, high selectivity toward cinnamyl acohol could be mainly attributed to an electron transfer from the reduced support to gold, which creates more electron-enriched gold particles, favouring C=O hydrogenation.

Full text of DOI:10.14233/ajchem.2013.14864

Asian Journal of Chemistry; Vol. 25, No. 15 (2013), 8617-8620
http://dx.doi.org/10.14233/ajchem.2013.14864
Selectivity of Gold Catalysts for Selective Hydrogenation of Cinnamaldehyde
1,*
1
2
YINGXIN LIU , YIMING LUO and ZUOJUN WEI
1College of Pharmaceutical Science, Zhejiang University of Technology, Hangzhou 310032, Zhejiang, P.R. China
2Institute of Pharmaceutical Engineering, Department of Chemical and Biochemical Engineering, Zhejiang University, Hangzhou 310027,
Zhejiang, P.R. China
*Corresponding author: Fax: +86 571 88320064; Tel: +86 571 88320064; E-mail: yxliu@zjut.edu.cn
(Received: 23 November 2012;
Accepted: 26 August 2013)
AJC-14010
Gold nanoparticles (AuNPs), SiO2 and TiO2 supportedAuNPs prepared by colloid deposition method andAu/TiO2 prepared by deposition-
precipitation method (Au/TiO2-DP) were used for the liquid-phase selective hydrogenation of cinnamaldehyde. The catalysts were
characterized by HRTEM, H2-TPR and XPS. Results showed that AuNPs, AuNPs/SiO2 and AuNPs/TiO2 in dried form selectively hydro-
genated the C=C bond, whereas AuNPs/TiO2 treated in H2 and Au/TiO2-DP preferentially hydrogenated the conjugated C=O bond. From
our data, high selectivity toward cinnamyl acohol could be mainly attributed to an electron transfer from the reduced support to gold,
which creates more electron-enriched gold particles, favouring C=O hydrogenation.
Key Words: Gold catalyst, Cinnamaldehyde, Selective hydrogenation, Cinnamyl acohol.
Chen et al.9,10 found a correlation between the gold states
INTRODUCTION
(Au3+/Au0) of MgxAlO hydrotalcite supported gold catalysts
The selective hydrogenation of α,β-unsaturated aldehydes
and the catalytic performance. The activity and selectivity to
to the corresponding unsaturated alcohols, an important
unsaturated alcohols increase with increasing theAu3+/Au0 ratio
procedure in the synthesis of fine chemicals and pharmaceu-
of the catalysts.
ticals, is a difficult task, since thermodynamics favours C=C
Some have proposed that the selectivity of gold catalysts
hydrogenation over the conjugated C=O bond1-3. Most of the
towards unsaturated alcohols is strongly influenced by the
nature of the support. Reducible oxides (TiO2, ZrO2, Fe2O3,
classical heterogeneous hydrogenation catalysts (Pt, Pd, Ru,
Ni, etc.) show no or low selectivity toward C=O hydrogena-
etc.) supported gold catalysts selectively hydrogenate the C=O
bond, while inert oxides (such as SiO2 and Al2O3) supported
tion3. In recent years, it has been found that supported gold
catalysts show remarkable selectivity toward unsaturated
gold catalysts show no or low selectivity toward C=O hydro-
alcohols in the hydrogenation of α,β-unsaturated compounds4-27
.
genation11-16. For example, Bailie and Hutchings11 found that
the selectivity toward crotyl alcohol in crotonaldehyde hydro-
genation is greater than 50 % over Au/ZrO2 and Au/ZnO,
whereas it is zero overAu/SiO2. Milone et al.14,15 reported that
the activity and selectivity of FeOOH, γ-Fe2O3 and α-Fe2O3
supported gold to unsaturated alcohols increase with increasing
the reducibility of the support in the hydrogenation of
benzalacetone and cinnamaldehyde. They argued that active
and selective sites are formed by electron-enriched gold
particles formed through an electron transfer from the reduced
support to gold. Claus et al.12 reported that the presence of
electron-enriched gold particles favours C=O adsorption in
the hydrogenation of α,β-unsaturated aldehydes.
Many researchers have investigated the factors affecting on
the selectivity of gold catalysts to unsaturated alcohols and
given different opinions.
Bailie et al.4 proposed that active and selective sites for
but-2-enal hydrogenation on Au/ZnO catalysts are associated
with the presence of large gold particles. Claus et al.5,6
reported that the selectivity ofAu/TiO2 andAu/ZrO2 to unsatu-
rated alcohols is favoured by face gold atoms in the larger
gold particles. Claus et al.7 identified that the edges of single
crystalline gold particles are active sites for C=O hydrogenation
through the decoration of gold particle faces by a second metal
indium. This conclusion is in contradiction to the earlier predic-
tions. Lenz et al.8 reported that the selectivity of iron oxides
modified alumina supported gold catalysts to unsaturated
alcohols is independent of the gold particle size and is related
to morphological aspects of gold particles.
The understanding of the main factors affecting on the
selectivity of gold catalysts is necessary for development
of tailor-made gold catalysts for the hydrogenation of α,β-

8618 Liu et al.
Asian J. Chem.
unsaturated compounds. The aim of the present work is to
gain a deeper insight into the role of the support in the selectivity
of gold catalysts in cinnamaldehyde hydrogenation, an important
reaction in the hydrogenation of α,β-unsaturated aldehydes,
by investigating the performances ofAu nanoparticles (AuNPs),
SiO2 and TiO2 supportedAuNPs prepared by colloid deposition
method and Au/TiO2 catalyst prepared by deposition-precipi-
tation method. Combined with the results of characterization
and activity/selectivity, the origin of the selectivity of gold cata-
lysts to cinnamyl alcohol was proposed.
steel autoclave equipped with magnetic stirring at 100 ºC and
2.0 MPa H2. The following conditions were applied over all
the supported gold catalysts: cinnamaldehyde 2.5 mL, isopro-
panol 50 mL, catalyst 0.5 g. Over AuNPs, the reaction was
carried out in 50 mL isopropanol using 0.5 mL cinnamaldehyde
and 0.125 mmol catalyst (molar cinnamaldehyde/Au = 30).
The reaction products were analyzed using a gas chromato-
graph equipped with a HP-5 capillary column and a flame
ionization detector.
RESULTS AND DISCUSSION
EXPERIMENTAL
The results of cinnamaldehyde hydrogenation over diffe-
rent gold catalysts are listed in Table-1. The catalytic activity
is expressed as the initial rate of cinnamaldehyde hydrogenation
per gram of gold. It can be seen that the activity of the gold
catalysts investigated was affected by the support and the
preparation method, following the order: AuNPs < AuNPs/
SiO2/reduced < AuNPs/SiO2/dried < AuNPs/TiO2/dried <Au/
TiO2-DP < AuNPs/TiO2/reduced.
Catalyst preparation: Gold nanoparticles were prepared
by the reduction ofAuCl41- ions using KBH4 (molar KBH4/Au
= 3:1) in water-isopropanol solutions containing a certain
amount of PVP (molar PVP/Au = 20:1) at 30 ºC under vigorous
stirring. After 1 h, a brown solution was obtained, indicating
the formation of gold colloid28.
Supported AuNPs were prepared by colloid deposition
method as follows: adding a desirable amount of SiO2 (Qingdao
Haiyang Chem, 400 m2 g-1) or TiO2 (prepared as in Ref.23, 60
m2 g-1) to the colloidal gold solution under stirring until total
adsorption (2 wt. % Au) occurred, indicated by decoloration
of the solution. The solids were separated, washed with deion-
ized water and dried in air at 100 ºC for 2 h. The as-prepared
catalysts were named as AuNPs/SiO2/dried and AuNPs/TiO2/
dried. A part of the two samples were then treated in hydrogen
flow at 200 ºC for 3 h and named as AuNPs/SiO2/reduced and
AuNPs/TiO2/reduced.
Table-1 showed that the gold catalysts investigated showed
remarkably different selectivity. Unsupported and inert SiO2
supported AuNPs in dried form as well as in reduced form
showed high selectivity toward hydrocinnamaldehyde (HCAL),
the product of C=C hydrogenation in cinnamaldehyde, with
lower than 7 % selectivity toward cinnamyl alcohol (COL),
the product of C=O hydrogenation. This result is in agree-
ment with that reported by Xu et al.30 in which SiO2 supported
gold nanoparticles prepared by colloid deposition method show
high selectivity to C=C hydrogenation in cinnamaldehyde. It
is worth noting that TiO2 supported AuNPs showed a signifi-
cant difference in selectivity before and after being treated in
H2 at 200 ºC for 3 h. AuNPs/TiO2/dried showed higher prefer-
ence for C=C hydrogenation over C=O, similar to the unsup-
ported and SiO2 supported AuNPs. However, AuNPs/TiO2/
reduced preferentially hydrogenated the C=O bond, similar
to Au/TiO2-DP. These results suggest that TiO2 by itself is not
sufficient to enhance C=O hydrogenation with respect to the
C=C bond in cinnamaldehyde hydrogenation and the catalytic
behaviour arises from a synergetic effect between gold and
TiO2.
Au/TiO2-DP catalyst was prepared by deposition-precipi-
tation method as in Ref.29. The gold content was measured by
an Elan DRC-e ICP-MS instrument of PE Inc. USA.
Catalyst characterization: High-resolution transmission
electron microscopy (HRTEM) analysis was performed on a
Tecnai G2 F30 S-Twin equipment. Hydrogen temperature-
programmed reduction (H2-TPR) of the catalyst was carried
out in a FINESORB-3010 chemical adsorption instrument,
heating the sample (0.1 g) from room temperature to 700 ºC
at a rate of 10 ºC min-1 under 20 H2/Ar (vol %) at a flow rate of
40 mL min-1. The effluent hydrogen concentration was detected
with a thermal conductivity detector (TCD). X-Ray photo-
electron spectroscopy (XPS) spectra were recorded on a Kratos
AXIS Ultra DLD instrument equipped with a monochromatic
AlKα X-ray excitation source (1486.6 eV).
Fig. 1 shows the TEM and STEM images of the catalysts.
The average particle sizes of gold are listed in Table-2. Different
particle sizes were obtained on the samples. For AuNPs [Fig.
1(a)], gold particles with an average size of 10.6 nm were
observed. After being supported on SiO2, the average size grew
to ca. 16 nm [Fig. 1(b)], significantly lager than the as-prepared
Catalytic activity test:The liquid phase selective hydroge-
nation of cinnamaldehyde was carried out in a 100 mL stainless
TABLE-1
CINNAMALDEHYDE HYDROGENATION OVER DIFFERENT GOLD CATALYSTSa
Activityc
Conversion
(%)
Selectivity (%)
Au
(wt %)
Catalyst
AuNPsb
-
(mmol ggold 1 min-1)
HCAL
63.8
42.2
53.8
43.3
21.4
23.0
HCOL
0.4
COL
1.6
100
2.0
2.0
2.0
2.0
1.9
0.526
0.960
0.715
3.455
4.077
3.741
98.8
14.5
10.8
52.2
61.6
53.7
AuNPs/SiO2/dried
AuNPs/SiO2/reduced
AuNPs/TiO2/dried
AuNPs/TiO2/reduced
Au/TiO2-DP
12.4
0
6.4
6.2
6.9
24.9
49.3
48.7
6.7
13.3
HCAL, hydrocinnamaldehyde; HCOL, hydrocinnamyl alcohol; COL, cinnamyl alcohol. aUnless otherwise specified, the reaction was carried out in
50 mL isopropanol using 2.5 mL cinnamaldehyde and 0.5 g catalyst under 2.0 MPa H2 and 100 ºC for 5 h. bThe reaction was carried out in 50 mL
isopropanol using 0.5 mL cinnamaldehyde and 0.125 mmol catalyst (molar cinnamaldehyde/Au = 30) under 2.0 MPa H2 and 100 ºC for 5 h. cThe
average rate for 5 h of reaction time.

Vol. 25, No. 15 (2013)
Selectivity of Gold Catalysts for Selective Hydrogenation of Cinnamaldehyde 8619
AuNPs in solution, indicating an agglomeration of gold parti-
cles during immobilization. Whereas TiO2 supported AuNPs
catalyst [Fig. 1(c)] showed smaller gold particles than unsup-
portedAuNPs. The smallest value of gold particles was found
for Au/TiO2-DP [Fig. 1(d)], with an average particle size of
3.9 nm. Combined with the results of cinnamaldehyde hydro-
genation (Table-1), it can be seen that small gold particle size
favours the activity of the gold catalysts for cinnamaldehyde
hydrogenation, whereas the selectivity of the gold catalysts
toward cinnamyl alcohol is not mainly dependent on the gold
particle size.
100
200
300
400
500
600
700
Temperature (oC)
Fig. 2. TPR profile of Au/TiO2-DP catalyst before reduction
Au nanoparticles
Au 4f7/2
Au 4f7/2
Au 4f5/2
Au 4f5/2
(a)
(b)
90
89
88
87
86
85
84
83
82
Binding Energy (eV)
Au 4f7/2
Au 4f5/2
AuNPs/TiO /reduced
2
(c)
(d)
Fig. 1. TEM and STEM images of gold catalysts: (a) AuNPs; (b) AuNPs/
SiO2/dried; (c) AuNPs/TiO2/dried; (d) Au/TiO2-DP
AuNPs/TiO /dried
TABLE-2
TEM AND XPS RESULTS OF THE GOLD CATALYSTS
2
d (nm)
TEM
BE (eV) Au
4f7/2
BE (eV) Au
4f5/2
Catalyst
AuNPs
10.6
83.8 (69 %)
85.1 (31 %)
–
87.4 (69 %)
88.6 (31 %)
–
90
89
88
87
86
85
84
83
82
81
80
Binding Energy (eV)
AuNPs/SiO2/dried
AuNPs/TiO2/dried
AuNPs/TiO2/reduced
Au/TiO2-DP
16.1
8.0
–
83.2 (100 %)
83.0 (100 %)
82.8 (100 %)
86.8 (100 %)
86.6 (100 %)
86.2 (100 %)
Au/TiO -DP
Au4f7/2
2
3.9
Au4f5/2
Fig. 2 shows the TPR profile of Au/TiO2-DP catalyst
before reduced in H2. The profile showed two overlapping
reduction peaks at higher temperature (500-600 ºC), which
was assigned to the partial reduction of TiO2 to TiO2-x31. Gene-
rally, TiO2 is difficult to be reduced. It has been reported that
the reduction temperature of TiO2 in H2 is at 1300 ºC32. Our
result indicates that the presence of gold enhances the reduci-
bility of Ti4+ species, which is in accordance with the literature31.
Fig. 3 shows the XPS spectra of Au 4f in AuNPs, AuNPs/
TiO2/dried,AuNPs/TiO2/reduced andAu/TiO2-DP. The corres-
ponding XPS data are summarized in Table-2. XPS data for
AuNPs revealed the presence of two different gold species,
96
94
92
90
88
86
84
82
80
78
76
Binding Energy (eV)
Fig. 3. XPS spectra of Au 4f in AuNPs, AuNPs/TiO2/dried, AuNPs/TiO2/
reduced and Au/TiO2-DP

8620 Liu et al.
Asian J. Chem.
Au0 (83.8 and 87.4 eV) andAuδ+ (85.1 and 88.6 eV)33. Whereas
forAuNPs/TiO2/dried,AuNPs/TiO2/reduced andAu/TiO2-DP,
only the Au 4f peaks assigned to metallic Au were detected.
Compared with the Au 4f binding energies (BEs) for AuNPs,
the three TiO2 supported gold catalysts showed lower BEs
corresponding to Au0. It should be noted that the treatment of
AuNPs/TiO2/dried sample in H2 (i.e.AuNPs/TiO2/reduced) led
to a significantly negative BEs shift of the Au 4f peaks. Au/
TiO2-DP showed the most negative shift compared withAuNPs
(1.0 eV for Au 4f7/2 and 1.2 eV forAu 4f5/2). The negative shift
ofAu 4f is due to an electron transfer from the reduced support
to gold, which lead to the increase in the electron density on
gold and can create more electron-enriched gold particles5.
Combined with the catalytic test results as shown in Table-1,
it can be proposed that the high selectivity of AuNPs/TiO2/
reduced and Au/TiO2-DP toward cinnamyl alcohol is mainly
attributed to the electron transfer from the reduced support to
gold. This is in agreement with the results reported by Milone
et al.14,15 in studying the hydrogenation of benzalacetone and
cinnamaldehyde over iron oxides supported gold catalysts.
4. J.E. Bailie, H.A. Abdullah, J.A. Anderson, C.H. Rochester, N.V.
Richardson, N. Hodge, J. G. Zhang, A. Burrows, C.J. Kiely and G.J.
Hutchings, Phys. Chem. Chem. Phys., 3, 4113 (2001).
5. S. Schimpf, M. Lucas, C. Mohr, U. Rodemerck,A. Brückner, J. Radnik,
H. Hofmeister and P. Claus, Catal. Today, 72, 63 (2002).
6. C. Mohr, H. Hofmeister and P. Claus, J. Catal., 213, 86 (2003).
7. C. Mohr, H. Hofmeister, J. Radnik and P. Claus, J. Am. Chem. Soc.,
125, 1905 (2003).
8. J. Lenz, B.C. Campo, M.Alvarez and M.A.Volpe, J. Catal., 267, 50 (2009).
9. K.J. You, C.T. Chang, B.J. Liaw, C.T. Huang and Y.Z. Chen, Appl.
Catal. A, 361, 65 (2009).
10. H.Y. Chen, C.T. Chang, S.J. Chiang, B.J. Liaw and Y.Z. Chen, Appl.
Catal. A, 381, 209 (2010).
11. J.E. Bailie and G.J. Hutchings, Chem. Commun., 2151 (1999).
12. N. Abudukelimu, H.J. Xi, S.J. Qing, Y.B. Ma, Z.X. Gao and W.J. Eli,
Asian J. Chem., 24, 5341 (2012).
13. C. Milone, R. Ingoglia, A. Pistone, G. Neri, F. Frusteri and S. Galvagno,
J. Catal., 222, 348 (2004).
14. C. Milone, R. Ingoglia, L. Schipilliti, C. Crisafulli, G. Neri and S. Galvagno,
J. Catal., 236, 80 (2005).
15. C. Milone, C. Crisafulli, R. Ingoglia, L. Schipilliti and S. Galvagno, Catal.
Today, 122, 341 (2007).
16. B.C. Campo, S. Ivanova, C. Gigola, C. Petit and M.A. Volpe, Catal.
Today, 133-135, 661 (2008).
17. P. Claus, Appl. Catal. A: Gen., 291, 222 (2005).
18. E. Bus, R. Prins and J.A. van Bokhoven, Catal. Commun., 8, 1397 (2007).
19. C. Milone, M.C. Trapani and S. Galvagno, Appl. Catal. A, 337, 163
(2008).
Conclusion
Our data showed that the selectivity of gold catalysts is
little dependent on the gold particle size, but is strongly af-
fected by the nature of the support in the liquid phase selec-
tive hydrogenation of cinnamaldehyde. Unsupported and in-
ert SiO2 supportedAuNPs as well asAuNPs/TiO2/dried selec-
tively hydrogenated the C=C bond. Whereas AuNPs/TiO2/re-
duced andAu/TiO2-DP exhibited good selectivity toward C=O
hydrogenation. Characterization results indicated an electron
transfer from the reduced TiO2 support to gold, which may be
the major factor for the enhanced selectivity toward cinnamyl
alcohol.
20. B. Campo, G. Santori, C. Petit and M. Volpe, Appl. Catal. A, 359, 79
(2009).
21. Q.Y. Yang, Y. Zhu, L. Tian, S.H. Xie, Y. Pei, H. Li, H.X. Li, M.H. Qiao
and K.N. Fan, Appl. Catal. A: Gen., 369, 67 (2009).
22. M.M. Wang, L. He, Y.M. Liu, Y. Cao, H.Y. He and K.N. Fan, Green.
Chem., 13, 602 (2011).
23. Y.X. Liu, L.F. Meng, Z.J. Wei and H.T. Shi, Chin. J. Catal., 32, 1269
(2011).
24. Y. Zhu, L. Tian, Z. Jiang, Y. Pei, S.H. Xie, M.H. Qiao and K.N. Fan, J.
Catal., 281, 106 (2011).
25. L.N. Protasova, E.V. Rebrov, H.E. Skelton, A.E.H. Wheatley and J.C.
Schouten, Appl. Catal. A, 399, 12 (2011).
26. E. Castillejos, E. Gallegos-Suarez, B. Bachiller-Baeza, R. Bacsa, P.
Serp, A. Guerrero-Ruiz and I. Rodriguez-Ramos, Catal. Commun., 22,
79 (2012).
ACKNOWLEDGEMENTS
27. M.S. Ide, B. Hao, M. Neurock and R.J. Davis, ACS Catal., 2, 671
(2012).
The authors gratefully acknowledged the financial support
provided by the National Natural Science Foundation of China
(No. 21106134 and 21276230) and Zhejiang Provincial Natural
Science Foundation of China (No.Y4100671 andY4090304).
28. M. Brust, D. Walker, D. Bethell, D.J. Schiffrin and R. Whyman, J.
Chem. Soc., Chem. Commun., 801 (1994).
29. Y.X. Liu, T.F. Xing, Z.J. Wei, X.N. Li and W. Yan, Catal. Commun.,
10, 2023 (2009).
30. H. Shi, N. Xu, D. Zhao and B.Q. Xu, Catal. Commun., 9, 1949 (2008).
31. K.M. Parida, N. Sahu, P. Mohapatra and M.S. Scurrell, J. Mol. Catal.
A: Chem., 319, 92 (2010).
REFERENCES
1. P. Gallezot and D. Richard, Catal. Rev. Sci. Eng., 40, 81 (1998).
2. P. Claus, Top. Catal., 5, 51 (1998).
32. M.A.R. Dewan, G.Q. Zhang and O. Ostrovski, Metall. Mater. Trans.
B, 40, 62 (2009).
33. E.D. Park and J.S. Lee, J. Catal., 186, 1 (1999).
3. P. Maki-Arvela, J. Hajek, T. Salmi and D.Y. Murzin, Appl. Catal. A,
292, 1 (2005).