Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over Au Catalysts: Influence of the Oxide-Supports

Article abstract of DOI:10.1007/s10562-016-1901-8

Abstract: Uniform Au particles with a mean size of 1.9?nm were initially synthesized with polyvinyl alcohol (PVA) as protecting agent, and then deposited on MgO, Al₂O₃, TiO₂, Fe₂O₃, Co₃O₄, ZnO and In₂O₃. After calcinations at 300 °C in air to remove PVA, Au particles were highly dispersed and immobilized on all the supports, displaying narrow diameter distributions and almost identical mean sizes of 2.5–3.2?nm. The Au-oxides catalysts were further used to catalyze selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL). It was found that the selectivity of COL was tightly related to the acidity/basicity of the Au/oxides catalysts. The catalyst with only acidic sites such as the Au/Al₂O₃catalyst gave very low selectivity of COL of 15%. The catalysts with only basic sites such as Au/MgO catalyst displayed medium selectivity of COL of 52%. Interesting, the Au catalysts with both acidic and basic sites such as the Au/In₂O₃and Au/ZnO catalyts exhibited the highest selectivity of COL of around 86%. The synergistic cooperation of acidic sites and basic sites should be responsible for preferential adsorption and activation of the C=O group than C=C group in CAL, and then preferential hydrogenation of C=O to COL. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-016-1901-8

Catal Lett
DOI 10.1007/s10562-016-1901-8
Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol
over Au Catalysts: Inluence of the Oxide-Supports
Yifei Zhang1 · Shaohua Zhang1 · Xiaoli Pan1 · Ming Bao2 · Jiahui Huang1 ·
Wenjie Shen1
Received: 23 August 2016 / Accepted: 27 October 2016
© Springer Science+Business Media New York 2016
Abstract Uniform Au particles with a mean size of
1.9 nm were initially synthesized with polyvinyl alcohol
(PVA) as protecting agent, and then deposited on MgO,
Al2O3, TiO2, Fe2O3, Co3O4, ZnO and In2O3. After calci-
nations at 300°C in air to remove PVA, Au particles were
highly dispersed and immobilized on all the supports, dis-
playing narrow diameter distributions and almost identical
mean sizes of 2.5–3.2 nm. The Au-oxides catalysts were
further used to catalyze selective hydrogenation of cinna-
maldehyde (CAL) to cinnamyl alcohol (COL). It was found
that the selectivity of COL was tightly related to the acidity/
basicity of the Au/oxides catalysts. The catalyst with only
acidic sites such as the Au/Al2O3 catalyst gave very low
selectivity of COL of 15%. The catalysts with only basic
sites such as Au/MgO catalyst displayed medium selectiv-
ity of COL of 52%. Interesting, the Au catalysts with both
acidic and basic sites such as the Au/In2O3 and Au/ZnO
catalyts exhibited the highest selectivity of COL of around
86%. The synergistic cooperation of acidic sites and basic
sites should be responsible for preferential adsorption and
activation of the C=O group than C=C group in CAL, and
then preferential hydrogenation of C=O to COL.
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-016-1901-8) contains supplementary
material, which is available to authorized users.
* Ming Bao
mingbao@dlut.edu.cn
* Jiahui Huang
jiahuihuang@dicp.ac.cn
1
Gold Catalysis Research Center, State Key Laboratory
of Catalysis, Dalian Institute of Chemical Physics, Chinese
Academy of Sciences, 457 Zhongshan Road, Dalian 116023,
China
2
State Key Laboratory of Fine Chemicals, Dalian University
of Technology, No. 2 Linggong Road, Dalian 116024, China
Vol.:(0123456789)
1 3

Y. Zhang et al.
Graphical Abstract
as crotonaldehyde and cinnamaldehyde to corresponding α,
β-unsaturated alcohols with selectivities of more than 80%
[9]. In this respect, the selectivity of unsaturated alcohols is
intimately linked to the size of Au particles and the nature
of the oxide-support [5, 7, 11, 12].
Keywords Gold catalysis · Selective hydrogenation ·
Cinnamaldehyde · Cinnamyl alcohol · Acidity/basicity
1 Introduction
The efect of Au particle size on the selectivity of unsat-
urated alcohols has been extensively examined, but contro-
versial observations are frequently reported [5, 7, 11]. For
instance, the selectivity of acrolein hydrogenation to allyl
alcohol over Au/TiO2 and Au/ZrO2 catalysts increased with
enlarging the size of Au particles in the range of 1.1–5.3 nm
[7, 11], however, the selectivity of crotonaldehyde hydro-
genation to crotyl alcohol over the Au/TiO2 catalyst was
independent of the size of Au particles in the range of
1.7–8.7 nm, being 60–70% [5]. One possible reason might
be due to the wide size distribution of Au particles upon
dispersing on the oxide supports through conventional
preparation techniques such as deposition–precipitation,
co-precipitation and impregnation, from isolated Au atoms,
Au clusters (<2 nm), small particles (2–5 nm) to even large
particles (>5 nm) [13, 14]. On the other hand, the inves-
tigation on the efect of the oxide-support on the selectiv-
ity of unsaturated alcohols over Au catalysts has been less
examined. As the catalytic performance of Au catalysts is
very sensitive to the size of Au particles, the wide size dis-
tribution of Au particles would heavily shadow the efect of
the oxide-support on the selectivity of unsaturated alcohols.
The colloid-immobilization is a good method to pre-
pare the supported Au catalysts with narrow Au size
distribution because Au colloids with certain sizes are
pre-synthesized by virtue of the protection of suitable
Selective hydrogenation of α, β-unsaturated aldehydes to
α, β-unsaturated alcohols over heterogeneous catalysts has
attracted increasing attentions in recent years, because of
the wide application of the desired products in the syn-
thesis of value-added ine chemicals. Fundamentally, this
selective hydrogenation reaction has been viewed as one
of the most challenging reactions in heterogeneous cataly-
sis, primarily because of the diicult in selectivity control.
α, β-unsaturated aldehydes contain both C=C and C=O
groups, while the hydrogenation of C=C group occurs
preferentially than that of the C=O group, and moreover
the successive hydrogenation of α, β-unsaturated alcohols
to the fully saturated alcohols may also take place rapidly.
Supported Pd and Pt catalysts have been typically used to
catalyze selective hydrogenation of α, β-unsaturated alde-
hydes. However, saturated aldehydes and even alcohols
were produced as major product, rather than desired α,
β-unsaturated alcohols [1]. Gold catalysts have been dem-
onstrated to selectively hydrogenate the C=O group in α,
β-unsaturated aldehydes [2–12]. For example, Au/ZnO
catalysts were reported to be efective for crotonaldehyde
hydrogenation to crotonyl alcohol with a selectivity of 80%
[3, 4] and acrolein hydrogenation to allyl alcohol with a
selectivity of 63% [7, 8]. Au/CeO2 efectively catalyzed the
hydrogenation of diferent α, β-unsaturated aldehydes such
1 3

Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over Au Catalysts: Influence…
reagents such as thiols, poly(N-vinyl-2-pyrrolidone)
(PVP) and polyvinyl alcohol (PVA). Compared with thi-
ols and PVP, PVA is a better choice for Au NPs syn-
thesis because it can be decomposed at the relative
low temperature of 300 °C [15, 16]. Schüth et al. have
utilized the colloid-immoblization method to deposit
3.0 nm Au colloids protected by PVA on Al2O3, TiO2,
ZnO and ZrO2 [15] and 2.1 nm Au colloids protected
by PVA on FeOx [16], and the resulting Au catalysts
displayed the narrow size distribution of Au particles.
In this work, we used the colloid-immobilization strat-
egy to study the effect of oxide-support on the catalytic
performance of Au particles with uniform sizes in the
selective hydrogenation of CAL to COL. Gold particles
with a rather narrow diameter distribution were initially
synthesized with PVA as the protecting reagent, and
then dispersed on a series of oxides (MgO, Al2O3, TiO2,
Fe2O3, Co3O4, ZnO, and In2O3) with uniform sizes of
2.5–3.2 nm. A remarkable effect of the oxide-support
on the selectivity of CAL hydrogenation to COL was
observed. The ZnO- and In2O3-supported Au particles
offered the prominent selectivity of COL of 82–87%,
which is almost irrespective to the reaction temperature
and period.
2 Experimental
2.1 Catalyst Preparation
Chloroauric acid (HAuCl4·3H2O), polyvinyl alcohol
(Mw =16,000) and sodium borohydride (NaBH4) were
purchased from Acros Chemical Company. Metal oxides
MgO, Al2O3, TiO2 (P25), Fe2O3, Co3O4, ZnO, and In2O3
were purchased from Aladdin Chemical Company. Before
the use, metal oxides were calcined at 300°C in air.
Gold colloids were initially synthesized according to a
typical procedure using PVA as protecting agent, and then
the oxide-supported Au catalysts were prepared by a col-
loid-immobilization method [15, 16]. 20 mg HAuCl4 was
dissolved in 200 mL distilled water, and 4 mL 0.3 wt%
PVA aqueous solution was added (PVA /Au=1.2/1.0 in
weight ratio). After stirring at room temperature for 1.0 h,
5 mL 0.1 moL/L NaBH4 aqueous solution was promptly
added to the mixture, and Au3+ species were immediately
reduced into metallic Au species, and Au colloids were
formed. After further stirring at room temperature for 1.0 h,
1.0 g oxide-support was added to Au colloids solution
with an Au/support weight ratio of 1/100. The suspension
Fig. 1 TEM image of Au colloids (a) and HAADF-STEM images of Au/MgO (b), Au/Al2O3 (c), Au/TiO2 (d), Au/Fe2O3 (e), Au/Co3O4 (f), Au/
ZnO (g) and Au/In2O3 (h). The scale bar corresponds to 20 nm
1 3

Y. Zhang et al.
Table 1 Physical properties of
the Au catalysts
Au catalysts
Au/MgO Au/Al2O3 Au/TiO2 Au/Fe2O3 Au/Co3O4 Au/ZnO Au/In2O3
Au loading/wt.%
Au sizes/nm
0.77
0.82
0.50
0.71
0.81
0.89
0.83
3.2 0.7 2.5 0.5 2.9 0.5 2.6 0.5 3.0 0.6
2.5 0.5 2.7 0.5
BET surface area /m2/g−1 245.3
110.3
57.6
58.5
44.5
23.8
34.8
Table 2 Cinnamaldehyde
hydrogenation over the Au
catalysts
Catalyst
Temperature
(°C)
CAL conv.
(%)
Selectivity (%)
COL yield (%)
COL
HCAL
HCOL
Au/MgO
Au/Al2O3
Au/TiO2
Au/Fe2O3
Au/Co3O4
Au/ZnO
120
120
120
120
120
120
150
180
120
150
180
37
99
99
62
95
0
52
15
8
42
2
6
79
70
8
19
15
8
15
27
23
0
65
47
0
40
45
0
29
0
23
88
42
70
91
86
83
86
86
84
11
4
3
20
73
36
60
76
12
4
Au/In2O3
10
8
5
2
13
Reaction conditions 0.2 g Au catalyst and 1.6 mmoL CAL that was dissolved in 20 mL dioxane were added
into the autoclave, and then the reaction was performed under 1.0 MPa H2 pressure at the required tempera-
ture for 18 h
COL cinnamyl alcohol, HCAL hydrocinnamaldehyde, HCOL hydrocinnamyl alcohol
was further stirred overnight at room temperature so that
Au colloids could be completely deposited on the oxide-
support. The solid was collected by iltration, washed with
distilled water, dried under vacuum at room temperature
overnight, and inally calcined at 300°C in air for 1.0 h,
yielding the Au/oxides catalysts.
2.3 Catalytic Tests
The selective hydrogenation of CAL was conducted in a
50 mL stainless steel autoclave under stirring. Typically,
0.2 g Au catalyst and 1.6 mmoL CAL that was dissolved
in 20 mL dioxane were added into the autoclave. A small
amount of octane was used as inner standard. The autoclave
was purged with hydrogen for ive times, pressurized to
1.0 MPa at room temperature, and heated to 120°C under
stirring (600 rpm). After reaction for a certain period, the
products were analyzed by gas chromatography (GC, Agi-
lent 7890B) equipped with a lame ionization detector and
DB-1 capillary column (50 m×0.32 mm×0.25 μm). For
the Au/ZnO and Au/In2O3 catalysts, the reaction was fur-
ther tested at 150–180°C in order to examine the inluence
of reaction temperature on COL selectivity.
2.2 Characterizations
Transmission electron microscopy (TEM) was carried out
on a Hitachi 7700 microscope operated at 120 kV. High-
angle annular dark ield scanning transmission electron
microscopy (HAADF-STEM) was performed with a JEOL
JEM-2100F microscope operated at 200 kV. Gold load-
ings on the catalysts were analyzed by inductively cou-
pled plasma atomic absorption spectrometry (ICP-AAS,
Plasma-Spec-II). Infrared spectroscopy (IR) of Au catalysts
were recorded on a Bruker VEXTEX 70. BET surface area
was measured on ASAP 2020 instrument. Before the meas-
urement, the samples were degassed at 90°C for 1 h and
250°C for 6 h. Temperature-programmed reduction with
hydrogen (H2-TPR), desorption of CO2 (CO2-TPD), and
ammonia (NH3-TPD) were conducted with the same equip-
ment. The detailed operation procedures are available in the
Supporting Information.
2.4 Results and Discussion
Figure 1 shows TEM image of Au colloids and HAADF-
STEM images of Au/oxides catalysts. Gold colloids had a
mean diameter of 1.9 0.4 nm with a very narrow size dis-
tribution (Fig. S1). Upon dispersion on the oxide-supports
and thermal treatment at 300°C for removing the PVA
ligands (Fig. S2), Au particles were tightly immobilized
1 3

Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over Au Catalysts: Influence…
on the oxides. The mean diameters of Au particles over all
the six catalysts were almost identical, 2.5–3.2 nm, being
independent on the chemical nature of the oxide-support
(Table 1). It should be noted that the mean diameter of
supported Au particles was just slightly larger than that of
as-prepared Au colloids, indicating a minor aggregation
of Au colloids during the immobilization and calcination
processes. ICP analyses conirmed that the loadings of Au
were in the range of 0.71–0.89 wt.% (Table 1), whereas Au/
TiO2 was the only exception, which gave much lower Au
loading of 0.50 wt.%.
narrow size distributions (Fig. S1). Therefore, the inluence
of the size of Au particles on the selectivity of COL could
be simply ruled out, while the signiicant variations in COL
selectivity might be assigned to the diference in chemical
nature of the oxide-supports.
Since the reducibility of the oxide-support was reported
to remarkably alter the selectivity of unsaturated alco-
hols on Au catalyst [12], the redox properties of the Au/
Fe2O3 and Au/Co3O4 catalysts were investigated by H2-
TPR (Fig. 3). The Au/Fe2O3 catalyst showed two broad
Table 2 compares the performance of Au catalysts for
the hydrogenation of CAL. On the Au/Al2O3 and Au/TiO2
catalysts, the complete conversion of CAL was readily
achieved, but the main product was hydrocinnamyl alcohol
(HCOL) with a selectivity more than 70% and the selectiv-
ity towards COL was less than 20%. On the Au/MgO, Au/
Fe2O3 and Au/Co3O4 catalysts, the selective hydrogenation
of the C=O group in CAL became the major route, giving
the medium selectivity of COL in the range of 47–65%.
Interestingly, the selective hydrogenation of the C=O group
in CAL dominated the hydrogenation reaction over the Au/
In2O3 catalyst, providing the highest selectivity of COL of
86% with a CAL conversion of 42%. As further raising the
temperature to 150°C and then 180°C, the conversion of
CAL signiicantly increased to 71 and 91%, respectively,
but the selectivity of COL was kept unchanged, being
84–86%. Interestingly, the Au/ZnO catalyst showed a simi-
lar pattern to Au/In2O3. The only diference was that the
Au/ZnO catalyst required a relatively higher temperature to
initiate the reaction, but high selectivity of COL of about
86% was also achieved.
In order to elucidate unique properties of the Au/ZnO
and Au/In2O3 catalysts with extraordinary selectivity
towards COL, the reaction proiles over these two cata-
lysts were examined, as shown in Fig. 2. The conversion of
CAL was 17% at 3 h and gradually approached 88% at 18 h
over the Au/ZnO catalyst, while the selectivity of COL was
kept almost unchanged, which was in the range of 82–87%
(Fig. 2a). The conversion of CAL over Au/In2O3 increased
more rapidly than that over Au/ZnO with time on stream.
The conversion of CAL over Au/In2O3 attained 43% at 3 h
and 70% (the highest conversion of CAL) at 8 h, while the
selectivity of COL was also kept stable, irrespective of the
reaction time, which was in the range of 82–86% (Fig. 2b).
So far, supported Au catalysts have been popularly used
to catalyze selective hydrogenation of α, β-unsaturated
aldehydes [2–12]. It is generally believed that the selec-
tivity of unsaturated alcohols is closely linked to the size
of Au particles and the nature of the oxide-supports [5, 7,
11, 12]. HAADF-STEM observations on the Au catalysts
investigated here clearly identiied that Au particles had
almost identical mean diameters of 2.5–3.2 nm with very
Fig. 2 Hydrogenation of CAL on the Au/ZnO (a) and Au/In2O3 (b)
catalysts. 0.2 g Au catalyst and 1.6 mmoL CAL that was dissolved
in 20 mL dioxane were added into the autoclave, and then the reac-
tion was performed under 1.0 MPa H2 pressure at 180°C for Au/ZnO
and 150°C for Au/In2O3 for diferent period. COL cinnamyl alcohol,
HCAL hydrocinnamaldehyde, HCOL hydrocinnamyl alcohol
1 3

Y. Zhang et al.
Fig. 3 H2-TPR proiles of the Au/Fe2O3 and Au/Co3O4 catalysts
reduction peaks, and one low-temperature reduction peak
centered at 385°C was assigned to the reduction of Fe3+
species to Fe2+ species, while the broad reduction peak at
above 400°C was ascribed to the subsequent reduction of
FeO to metallic Fe [12]. The Au/Co3O4 catalyst displayed
one shoulder peak at about 330°C and one strong peak cen-
tered at 440°C. The former peak was ascribed to Co3O4
reduction to CoO and the latter peak was assigned to CoO
reduction to metallic Co [17]. As shown in Table 2, the Au/
Fe2O3 and Au/Co3O4 catalysts with typical reducible fea-
tures only displayed medium selectivities of 47 and 65% for
COL, which are still much lower than those obtained on the
Au/ZnO and Au/In2O3 catalysts. Therefore, the reducibility
of the oxide-supports might not be the main factor to deter-
mine the selectivity of COL in this work.
Fig. 4 NH3-TPD (a) and CO2-TPD (b) proiles of the Au catalysts.
The signals of NH3-TPD and CO2-TPD were recorded by TCD detec-
tor and mass spectroscopy, respectively
It has been reported that the introduction of Lewis acid
such as Fe and Sn cations to the Pt/SiO2 catalyst mark-
edly enhanced the selectivity of allyl alcohol in acrolein
hydrogenation [1]. Similarly, the introduction of Lewis
acid Mo, W, Nb, Fe and Re cations to Ir/SiO2 catalysts
was also conirmed to promote the selectivity of crotyl
alcohol during crotonaldehyde hydrogenation [18, 19].
It was presumed that metal cations on the oxide-support
adsorbed and activated the C=O group in the substrates
while noble metal particles dissociatively activated
hydrogen molecules and the resulting atomic hydrogen
species reacted with the activated C=O group to form
unsaturated alcohol. Accordingly, the acidity and basic-
ity of the Au/oxide catalysts in this work was analyzed by
NH3-TPD and CO2-TPD.
In Fig. 4a, the Au/MgO catalyst did not give desorption
peak of NH3, indicating the absence of acidic sites, while it
displayed two strong desorption peaks of CO2 in the tem-
perature range of 50–200 and 200–400°C in Fig. 4b. The
former peak was caused by the decomposition of bicarbo-
nates species formed by the reaction of CO2 and surface
hydroxyl groups, and the latter peak indicated the pres-
ence of the medium basicity caused by oxygen in Mg2+
and O2− pairs [20, 21]. In Fig. 4a, the Au/Al2O3 catalyst
exhibited two broad desorption peaks of NH3 in the tem-
perature range of 80–175 and 175–420°C, respectively,
similar to those present on Pt/Al2O3 during NH3-TPD
1 3

Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over Au Catalysts: Influence…
Scheme 1 A possible pathway of CAL hydrogenation on the Au/ZnO and Au/In2O3 catalysts. CAL cinnamaldehyde
analysis, indicating the presence of acidic sites with difer-
ent strength [22]. In Fig. 4b, the Au/Al2O3 catalyst showed
an intense desorption peak of CO2 in the temperature range
of 50–200°C centered at around 90°C. This was caused by
the decomposition of large amount of bicarbonates species
and thus indicates the presence of a large quantity of sur-
face hydroxyl groups on the Au/Al2O3 catalyst [23]. Usu-
ally γ-Al2O3 contains a large amount of Lewis acid sites
[24], and in this work Al2O3 with gamma phase was used
as the support. Thus, it might be deduced that the Au/Al2O3
catalyst processes both weak Bronsted acid sites (surface
hydroxyl groups) and strong Lewis acid sites.
weak Bronsted acid sites (surface hydroxyl groups) and
medium Lewis acid sites caused by In3+ cations [26].
Based on NH3-TPD and CO2-TPD measurements, it
becomes clear that the Au/MgO catalyst had only basic
sites with medium strength, while the Au/Al2O3 catalyst
possessed only acidic sites, including weak Bronsted acid
sites and strong Lewis acid sites. However, the Au/ZnO and
Au/In2O3 catalysts were characterized by both acidic and
basic sites. The Au/ZnO catalysts possessed strong Lewis
acid sites (Zn2+ cations) and strong basic sites (low coordi-
nation oxygen anions). The In2O3 catalysts had Lewis acid
sites with medium strength (In3+ cations) and the basic sites
with medium strength (oxygen in In3+ and O2− pairs), as
well as a small amount of weak Bronsted acid sites (surface
hydroxyl groups). Therefore, there may exist Lewis acid-
base (M+–O−) pairs on the Au/ZnO and Au/In2O3 catalysts.
Considering the fact that the Au/Al2O3 catalyst gave only
a very low selectivity of COL of 15%, much lower than that
of the Au/MgO catalyst (Table 2), it might be deduced that
the acidic sites on the Au catalysts could not guarantee the
achievement of high selectivity of COL. In addition, the
fact that the Au/MgO catalyst gave much lower selectiv-
ity of COL of 52% than that of the Au/ZnO and Au/In2O3
catalysts of above 80% might suggest that the basic sites on
the Au catalysts could not yet guarantee the achievement of
high selectivity of COL. Therefore, it seems that there is a
close relation between high selectivity of unsaturated alco-
hols (Table 2) and the acidity/basicity of the Au catalysts
(Fig. 4). As described above, two prerequisites should be
fulilled to achieve a higher selectivity towards COL: one
is preferential hydrogenation of C=O to C=C and the other
In Fig. 4a, the Au/ZnO catalyst gave a broad but rela-
tive weak desorption peak of NH3 in the temperature range
of 300–490°C, indicating the presence of small amount of
strong acidic sites, probably strong Lewis acid sites caused
by Zn2+ cations [25]. In Fig. 4b, the Au/ZnO catalyst dis-
played one very weak desorption peak of CO2 at around
90°C, meaning the presence of very small amount of sur-
face hydroxyl groups, and one desorption peak of CO2 in
the temperature range of 300–500°C, probably ascribed to
strong basic sites caused by low coordination oxygen ani-
ons [20, 21]. In Fig. 4b, the Au/In2O3 catalyst exhibited
one weak desorption of CO2 at around 90°C, caused by
surface hydroxyl groups, and one desorption of CO2 in the
temperature range of 120–220°C centered at 170°C, indi-
cating the presence of basic sites with medium strength,
probably oxygen in In3+ and O2− pairs [20, 21]. In Fig. 4a,
the Au/In2O3 catalyst displayed a broad desorption peak of
NH3 in the temperature range of 75–305°C, indicating the
presence of acidic sites with diferent strength, probably
1 3

Y. Zhang et al.
Priority Research Program” of the Chinese Academy of Sciences
(XDA09030103), and National Natural Science Foundation of China
(No. 21473186).
is the suppression of successive hydrogenation of COL
to HCOL. As shown in Fig. 2, CAL conversion monoto-
nously increased on the Au/ZnO and Au/In2O3 catalysts
with extending the reaction time, but the selectivity of COL
was kept also consistent of above 80%. This indicates that
the C=O group in CAL was preferentially adsorbed and
activated over the Au/ZnO and Au/In2O3 catalysts. Fur-
thermore, even after the formation of unsaturated alcohols
(COL), successive hydrogenation of remaining C=C group
in COL did not occur obviously.
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Gold particles with sizes of 2.5–3.2 nm were uniformly
dispersed on a series of oxides through a colloid-immobi-
lization strategy. The resulting Au catalysts were tested for
the hydrogenation of CAL, and it was found that the acidic-
basic properties of the oxide-support afected the selectivity
of COL signiicantly. The Au/ZnO and Au/In2O3 catalysts
provided the highest selectivity of COL of about 86%, pri-
marily because of the proper acidity and basicity. By virtue
of the synergistic cooperation between the acidic and basic
sites, the C=O group in CAL was preferentially activated
and hydrogenated, while the successive hydrogenation of
COL to HCOL was efectively suppressed.
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Acknowledgements This work was inancially supported by
the Young Thousand Talents Program of China, the “Strategic
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