Gold supported on mesostructured ceria as an efficient catalyst for the chemoselective hydrogenation of carbonyl compounds in neat water

Article abstract of DOI:10.1039/c0gc00937g

Rapid and efficient selective hydrogenation of a range of α,β-unsaturated carbonyl compounds to their corresponding allylic alcohols was achieved in neat water using gold supported on a mesostructured CeO₂ matrix. Both the activity and chemoselectivity for the reduction of carbonyl compounds improved significantly on going from organic solvents to water for the reaction media. Results in the intermolecular competitive hydrogenation showed that the intrinsic higher rate for the Au-catalyzed aldehyde reduction in water was responsible for the high activity and chemoselectivity observed. The Royal Society of Chemistry.

Full text of DOI:10.1039/c0gc00937g

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Cao et al.
Gold supported on mesostructured ceria as an efficient catalyst for
chemoselective hydrogenation of carbonyl compounds in water.

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PAPER
Gold supported on mesostructured ceria as an efficient catalyst for the
chemoselective hydrogenation of carbonyl compounds in neat water
Miao-Miao Wang, Lin He, Yong-Mei Liu, Yong Cao,* He-Yong He and Kang-Nian Fan
Received 21st December 2010, Accepted 17th January 2011
DOI: 10.1039/c0gc00937g
Rapid and efficient selective hydrogenation of a range of a,b-unsaturated carbonyl compounds to
their corresponding allylic alcohols was achieved in neat water using gold supported on a
mesostructured CeO2 matrix. Both the activity and chemoselectivity for the reduction of carbonyl
compounds improved significantly on going from organic solvents to water for the reaction media.
Results in the intermolecular competitive hydrogenation showed that the intrinsic higher rate for
the Au-catalyzed aldehyde reduction in water was responsible for the high activity and
chemoselectivity observed.
gold deposited on other supports, including iron oxides,7a TiO2,7b
Introduction
CeO2 and Mg2AlO7d have revealed that supported gold cata-
7c
Chemoselective hydrogenation of a,b-unsaturated carbonyl
compounds (unsaturated aldehydes or ketones, UALs or UKEs)
lysts are also highly effective for the hydrogenation of UALs to
produce the desired allylic alcohols in the liquid phase. Despite
to the corresponding allylic alcohols is an important step in
their high chemoselectivity, one critical limitation associated
the industrial synthesis of fine chemicals, particular of phar-
with the current Au-catalyzed carbonyl compounds reductions is
maceuticals, perfumes and cosmetics.1 Although extensively
the limited hydrogen-delivery rate compared to the conventional
studied, selective allylic alcohol synthesis facilitated by catalytic
hydrogenation metals.5a,5c Moreover, these Au-based hydrogena-
hydrogenation rather than traditional stoichiometric reduction
tion processes suffer from some general drawbacks,5c,7 including
remains a challenging issue. Conventional hydrogenation cat-
the need of relatively high temperature/pressure and the use of
alysts based on supported Pt,2a Pd,2b Ru,2c and Rh2d produce
hazardous organic solvents as the reaction media.
mainly saturated aldehydes. Therefore, great efforts have been
During the last decade, the increasing awareness of envi-
made to overcome this problem over the past decades, either by
ronmental concerns has stimulated the development of metal-
the use of special additives or promoters (Lewis acids or bases),2b
catalyzed reactions in aqueous media,8 since water represents
modifying the active metal with a second metal component,3
the most benign, abundant and inexpensive solvent known.9 In
or a fine tuning the particle sizes of the catalysts.4 Although
addition, the use of water as the reaction medium has reportedly
these modified systems are effective, catalyst preparation often
led to unique reactivity and selectivity that can not be obtained
remains tedious and elusive, and the amount of the modifying
in conventional organic solvents.10 In this sense, chemoselective
agent must be precisely controlled.3 Alternative simple and effi-
reduction of UALs and UKEs with hydrogen in water would
cient catalyst that would enable the preferential hydrogenation
lead to a particularly green process. However, as far as we know,
of the C O group versus C C is highly desirable.
In recent years, catalysts based on supported gold nanopar-
few publications are available that address the use of supported
metal NPs for producing allylic alcohols from hydrogenation of
ticles (NPs) have attracted considerable attention as new
carbonyl compound in an aqueous environment.11
promising carbonyl hydrogenation materials owing to their high
In the continued search for greener methods for chemos-
intrinsic selectivity toward the formation of the desired allylic
elective C O reduction, there is a definite need for new
alcohols.5 This was prompted by Hutchings and coworkers’s
environmentally benign and clean protocols that enable facile
discovery of exceptionally high selectivity of ZnO and ZrO2
carbonyl reduction in aqueous media. Very recently, we have
supported gold NPs for the gas phase hydrogenation of the
described an efficient and selective reduction method of UALs
conjugated C O bond.1c,6 Subsequent studies by evaluating
using supported gold catalysts in the presence of CO/H2O.12 The
improved performance of Au catalysts for aqueous CO/H2O-
mediated reduction has prompted us to investigate the possibil-
ities offered by Au for environmentally clean selective reduction
of UALs and UKEs with H2 under aqueous conditions. Herein,
we demonstrate for the first time that gold supported on
Shanghai Key Laboratory of Molecular Catalysis and Innovative
Materials, Department of Chemistry, Fudan University, Shanghai,
200433, P. R. China. E-mail: yongcao@fudan.edu.cn; Fax: (+86-21)
65643774; Tel: (+86-21) 55665287
602 | Green Chem., 2011, 13, 602–607
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©

mesostructured ceria can catalyze the reduction of UALs and
UKEs to the corresponding allylic alcohols in high yields in
aqueous media. Our results have shown that the replacement
of organic solvents with neat water can result in a significant
improvement in both the activity and selectivity of gold-
catalyzed conjugated C O hydrogenation.
Results and discussion
Catalyst characterization
Mesostructured ceria was synthesized through a surfactant-
assisted precipitation method, with the use of cetyltrimethyl
ammonium bromide (CTAB) as templating agent.8b,13 Fig. 1
shows the nitrogen adsorption-desorption isotherm and the
pore-size distribution of the resultant material. According to
the IUPAC classification, the isotherm can be classified as
a type IV one, typical of mesostructured materials and the
hysteresis loop is type H1 indicating a complex mesoporous
structure. The Brunauer-Emmett-Teller (BET) surface area of
the CeO2 was 150 m2 g-1 and the mean pore diameter was
3.8 nm with a narrow distribution. The X-ray diffraction (XRD)
pattern for the support was shown in Fig. 2a. The diffraction
pattern of the mesostructured CeO2 sample was found to be
very broad, showing a semicrystalline nature of this material.
The peak intensities and their 2q angles have been identified as
characteristic of the cubic fluorite structure of CeO2 (JCPDS
no. 34-0394). The average crystallite size of CeO2 sample was
4.5 nm.
Fig. 2 XRD diffractograms: (a) meso-CeO2 and (b) Au/meso-CeO2.
Fig. 3 TEM images of Au/meso-CeO2: (a) before reaction; (b) after
four runs.
metal oxide nanoparticles,13 which is further supported by the
N2 adsorption-desorption isotherm data as illustrated in Fig. 1.
The size of the nanoparticles is around 5 nm, consistent with the
crystallite size obtained by XRD. However, the identification of
the small Au particles was unsuccessful, possibly due to the poor
contrast between Au and ceria support.14
Catalytic hydrogenation
The catalytic properties of the Au/meso-CeO2 catalyst in various
solvents were investigated using chemoselective hydrogenation
of crotonaldehyde (CAL) as a model reaction. The hydrogena-
tion reactions were carried out in a 50 mL Parr stainless-steel
reactor.
Fig.
1
N2 adsorption-desorption isotherms of meso-CeO2 and
Table 1 presents the initial activities and selectivities to crotyl
alcohol (CROL) at 50% conversion for CAL hydrogenation at
100 ◦C and 1.0 MPa H2 over Au/meso-CeO2 in water and a
range of organic solvents. When employing the most commonly
used isopropanol as the solvent, Au/meso-CeO2 catalyzed CAL
Au/meso-CeO2. The inset shows BJH pore size distribution.
When gold NPs were deposited onto the as-synthesized sup-
port (denoted as Au/meso-CeO2; see details in the Experimental
section), the surface area decreased slightly to 138 m2 g-1 while
the mean pore size increased to 4.6 nm. An almost identical
XRD pattern was obtained for Au/meso-CeO2 comparing with
meso-CeO2 (Fig. 2b), indicating the crystalline structure and
the average size of the crystalline domain of the support were
well maintained in the gold samples. No peaks due to metallic
Au were detected, owing to the fact that the gold particle sizes
were very small (<5 nm). Transmission electron microscopy
(TEM) experiments have been carried out to observe a possible
structure of the metallic Au particles (Fig. 3a). The image does
not clearly show the presence of ordered mesopores, but reveal
a rather foam-like structure resulting from closely aggregated
-1
to CROL with an initial activity of 78.4 mmol gAu s-1 and 38%
selectivity. Note that this result is fully comparable with the
work of Campo et al.,7b who found that ceria-supported gold
NPs gave similar activity and selectivity for CAL hydrogenation
in isopropanol solution. The use of other organic solvents
was much less effective with lower than 30% selectivity being
achieved for the chemoselective hydrogenation of CAL under
identical reaction conditions. Surprisingly, when neat water
was applied as the solvent, the specific rate of the initial
activity is dramatically boosted to an unprecedented value
of 226.4 mmol gAu s-1, which is almost 3 times that of the
-1
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Table 1 Catalytic performance of various catalysts for the reduction of
crotonaldehyde by H2 in various solventsa
Initial activityb/ CROL select-
-1
Entry Catalyst
Solvent
mmol gAu s-1
ivity (%)c
1
Au/meso-CeO2 water
Au/meso-CeO2 water
Au/meso-CeO2 isopropanol 78.4
Au/meso-CeO2 ethanol
Au/meso-CeO2 dioxane
Au/meso-CeO2 cyclohexane 22.0
226.4
202.8
90
88
38
29
25
25
81
24
33
21
—
2d
3
4
5
6
7
52.5
43.8
Au/CeO2
Au/TiO2
Au/Fe2O3
Au/Al2O3
meso-CeO2
water
water
water
water
water
146.2
68.4
31.0
24.8
—
8e
9e
10e
11
Fig. 4 Composition of products and selectivity for crotonyl alcohol for
the hydrogenation of crotonaldehyde over Au/meso-CeO2 as a function
of crotonaldehyde conversion. (ꢀ) CROL; (᭢) BAL; (᭡) BOL; (ꢁ)
CROL selectivity. Reaction conditions: 1 mmol CAL, Au/meso-CeO2
(Au: 1.0 mol%), 15 mL H2O, 100 ◦C, 1.0 MPa H2. CROL: crotyl alcohol,
BAL: butanal, BOL: butanol.
a Reaction conditions: 1 mmol CAL, 1.0 mol% Au, 15 mL solvent,
100 ◦C, 1.0 MPa H2. b Measurement at 10 min of reaction. c Selectivities
were compared at 50% of conversion. d Results for the fourth run.
e Au/TiO2 and Au/Fe2O3 provided by the World Gold Council,
Au/Al2O3 provided by Mintek. CAL: crotonaldehyde, CROL: crotyl
alcohol.
isopropanol system and nearly one order of magnitude higher
than that for cyclohexane, with an excellent selectivity up to
ca. 90% can be achieved for CROL production. No conversion
was found in the absence of catalysts or in the presence of Au-
free meso-CeO2 under identical conditions (Table 1, entry 11),
illustrating that the presence of gold was indispensable for high
catalytic activity.
The remarkable activity of the Au/meso-CeO2 catalyst for the
chemoselective hydrogenation of CAL in aqueous media can be
further seen from the product evolution profiles as a function
of CAL conversion as shown in Fig. 4. The high selectivity
for CROL (up to 85%) is maintained even at 100% CAL
conversion. The by-products, mainly butanal (BAL, product of
to CROL (ca. 21–33%). Note that Au/CeO2 gave a much
-1
higher activity (148.1 mmol gAu s-1), with 81% selectivity
to CROL. Comparing the results of Au/CeO2 with those
corresponding to Au/meso-CeO2 indicated that an increased
surface area of ceria support (meso-CeO2, 150 m2 g-1) is favorable
for obtaining a gold catalyst with enhanced catalytic activity
and selectivity. A similar phenomenon has also been found
by Campo and co-workers in their work on the liquid phase
hydrogenation of CAL over Au/CeO2 catalysts with isopropanol
as the solvent.7b
Furthermore, Au/meso-CeO2 was easily separated by sim-
ple filtration after CAL hydrogenation, and could be reused
four times without appreciable loss of its catalytic activity and
selectivity (Table 1, entry 2). This was consistent with the
characterization results for this catalyst. XPS results (Fig. 5)
showed essentially no changes in the dispersion of the Au NPs
and in the metallic state of Au, respectively, after the four
successive runs. No gold particles were detected on the same
sample after four repeated hydrogenation by TEM (Fig. 3b).
To examine the scope of the present aqueous hydrogenation
system with Au/meso-CeO2, we extended our studies to a
range of UALs. Results in Table 3 showed that aliphatic,
aromatic aldehydes were smoothly hydrogenated to give the
corresponding unsaturated alcohols in high yields, and the
Au/meso-CeO2 was also effective for a heterocyclic aldehyde.
CAL displayed a significantly higher activity than 2-methyl-2-
pentene aldehyde (entries 1, 2), revealing that the activity is
largely influenced by the presence of a b-bulky group due to steric
C
C hydrogenation) and butanol (BOL, reduction of C O
and C C bonds), did not exceed 15% with no detectable
amount of other side products. To the best of our knowledge,
this is the highest CROL yield (ca. 85%) reported to date in the
literature for liquid phase CAL hydrogenation over Au-based
catalysts (Table 2). Of particular note is that this value compares
favorably with 82% reported recently on the CO/H2O–Au/CeO2
system.12
We also compared the activity and selectivity of Au/meso-
CeO2 with those of gold deposited on commercial CeO2 (Evonic,
Adnano 90, surface area: 90 m2 g-1), TiO2, Fe2O3 and Al2O3
in aqueous medium. Results from Table 1 indicated that gold
deposited on meso-CeO2 was the most active and selective
catalyst. The Au/TiO2, Au/Fe2O3 and Au/Al2O3 lead to low
-1
activity (ca. 25–70 mmol gAu s-1) and very poor selectivity
Table 2 Catalytic results reported recently for crotonaldehyde hydrogenation over Au catalysts
Catalyst
Solvent
Reaction conditions
CAL conv. (%)a
CROL sel. (%)a
Reference
Au/a-Fe2O3
Isopropanol
Isopropanol
Ethanol
Hexane
Water
100 ◦C, 1.0 MPa
80 ◦C, 1.0 MPa
120 ◦C, 0.9 MPa
120 ◦C, 2.0 MPa
100 ◦C, 1.0 MPa
62
31
52
76
88
31
29
62
75
87
Lenz et al., 20097a
Volpe et al., 20097b
Chen et al., 20107c
Yang et al., 20097d
This work
Au/CeO2
Au/Mg2AlO
Au–In/APTMS-SBA-15
Au/meso-CeO2
a Conversion and selectivity measured at 3 h of reaction. CAL: crotonaldehyde, CROL: crotyl alcohol.
604 | Green Chem., 2011, 13, 602–607
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Table 3 Hydrogenation of a,b-unsaturated carbonyl compounds in
4-chlorocinnamaldehyde, which was manifested in the required
reaction time and a shift in selectivity from unsaturated alcohol
to saturated alcohol (entries 3–5). Notably, the chemoselective
hydrogenation of furan-2-acrolein also gave the corresponding
aldehyde isolated yield of 62% (entry 6). To the best of our
knowledge, this study presents the first chemoselective hydro-
genation of furan-2-acrolein in the presence of heterogeneous
catalysts.
watera
Conv. Sel.
Entry Substrate
1
Product
Time/h (%)
(%)
0.5
3.5
45
90
>99 86(84)
2
0.5
6.0
28
90
84
81(68)
Moreover, it is noteworthy that citral, which is considered one
of the most difficult UALs to hydrogenate to the allylic alcohol
3b
0.5
3.0
48
96
97
due to including three unsaturated bonds15 (conjugated C
O
and C C bonds as well as an isolated C C bond), was also
smoothly converted to give highly valuable geraniol/nerol in
excellent yield (Table 3, entry 7). It is remarkable that a high
degree of chemoselectivity (ca. 92%) in terms of geraniol/nerol
production can be achieved for close to 100% conversion of
citral. Such reaction efficiency, notably the absence of citronellal
owing to C C hydrogenation, is unique when compared with
the conventional catalytic systems.2c,2d
4b
5b
0.5
2.0
50
94
95
92(85)
0.5
4.0
32
97
90
87(82)
a,b-Unsaturated ketones were more challenging as substrates
because of the steric hindrance in the carbonyl-component.16
The chemoselective hydrogenation of UKEs in aqueous media
with Au/meso-CeO2 was also studied by hydrogenation of
benzalacetone and 4-methyl-3-penten-2-one. In the case of
benzalacetone (Table 3, entry 9), Au/meso-CeO2 gave 97%
conversion with 66% selectivity to 4-phenyl-3-buten-2-ol at
higher pressure (2.0 MPa). It is of note that the initial activity
6b
7
0.5
3.5
39
96
72
66(62)
0.5
2.5
48
95
>99 92(90)
8
0.5
4.5
29
94
64
59(52)
of 152.3 mmol gAu s-1 in this process was more than 50 times
-1
higher than that of the alcohol system catalysed by Au/Fe2O3
9c
0.5
4
34
97
67
66(63)
-1
(2.8 mmol gAu s-1) with 61% selectivity to the unsaturated
alcohol17b indicating the high efficiency of the aqueous media
with Au/meso-CeO2. Similar results were also obtained in
chemoselective hydrogenation of 4-methyl-3-penten-2-one to the
corresponding allylic alcohol (Table 3, entry 8). All these results
clearly showed the efficiency of the Au/meso-CeO2 system in the
chemoselective hydrogenation of both UALs andUKEs in water.
To rationalize the beneficial effect achieved by using H2O
as a solvent, an intermolecular competitive hydrogenation of
benzaldehyde and styrene using the Au/meso-CeO2 catalyst
in different media under similar reaction conditions has been
investigated (Fig. 6). It is revealed that the preferential reduction
a Reaction conditions:
1 mmol substrate, Au/meso-CeO2 (Au:
1.0 mol%), 15 mL H2O, 100 ◦C, 1.0 MPa H2. b 1 mmol substrate,
Au/meso-CeO2 (Au: 1.0 mol%), 12 mL H2O, 3 mL EtOH, 100 ◦C,
1.0 MPa H2. c 1 mmol substrate, Au/meso-CeO2 (Au: 1.0 mol%), 12 mL
H2O, 3 mL EtOH, 100 ◦C, 2.0 MPa H2. Numbers in parenthesis refer to
isolated yield of products.
Fig. 5 XP spectra of the Au (4f) signal for Au/meso-CeO2: (a) before
reaction; (b) after four runs.
Fig. 6 Competitive reductive hydrogenation of benzaldehyde and
styrene over Au/meso-CeO2 in various solvents. Reaction conditions:
1 mmol benzaldehyde, 1 mmol styrene, Au/meso-CeO2 (Au: 1.0 mol%),
15 mL H2O, 100 ◦C, 1.0 MPa H2, 1 h.
hindrance. In the case of aromatic UALs, owing to its substantial
electro-donating effect, 4-methylcinnamaldehyde was relatively
difficult to hydrogenate as compared with cinnamaldehyde and
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Table 4 H2 solubility of various solvents17
water) was added to a stirred solution of Ce(NO3)3·6H2O (4.34
g) and CTAB (2.19 g) in 200 mL distilled water at room
temperature. The mixture was then maintained in a sealed glass
Solvent
H2 solubilitya/mmol cm-3
◦
vessel under stirring for 24 h. After thermal aging at 90 C for
Water
Isopropanol
Ethanol
Dioxane
Cyclohexane
0.80
3.90
3.59
1.95
3.72
3 h, the pale yellow precipitate was filtered and washed with
◦
hot water (80 C) to remove the residual CTAB. The resultant
powder was dried at 100 ◦C for 6 h and then calcined at 450 ◦C
for 4 h. The Brunauer-Emmett-Teller (BET) surface area of the
as-synthesized meso-CeO2 was 150 m2 g-1.
a The H2 solubility (cL) is related to the Bunsen coefficient (a) by cL
=
a/v0, where v0 is the molar volume of the gas in cm3 mol-1 at 0 ◦C, a is
calculated at 293.15 K and 101.325 kPa (1 atm) partial pressure of the
gas.
Preparation of Au/CeO2 catalysts
Au/CeO2 catalysts were prepared by a routine deposition-
precipitation (DP) method. An appropriate amount of aqueous
solutions of chloroauric acid (HAuCl4) was heated to 70 ◦C
under vigorous stirring. The pH was adjusted to 9 by dropwise
addition of NaOH (0.2 M), and then 1.0 g of CeO2 powders
(Evonic, Adnano 90, specific surface area: 90 m2 g-1) or meso-
CeO2 was dispersed in the solution. The mixture was aged for 1 h,
followed by filtering and washing several times with deionized
water to remove Cl-. The resulting solid product was dried
overnight before reduction at 300 ◦C for 2 h in 5% H2/Ar. The
two catalysts were designated Au/CeO2 and Au/meso-CeO2,
respectively. The gold loading of the as-prepared catalysts was
1.9 wt% Au/CeO2 and 2.1 wt% Au/meso-CeO2 as determined
by ICP-AES.
of benzaldehyde proceeds much more rapidly in water, in sharp
contrast to that occurred in organic solvents. Therefore, the
intrinsic higher rate for the Au-catalyzed aldehyde reduction
in water is responsible for the high chemoselectivity observed.
Previous investigations concerning the use of gold-based
catalysts for selective UALs and UKEs reduction have shown
that a number of factors such as the reaction conditions and
operation mode (e.g. gas or liquid phase system),5b,18 metal
and support nature19 as well as the use of solvents20 have
to be considered in order to account for the phenomena
involved in the chemoselective reduction of UALs and UKEs.
Presumably, the superior performance of the present aqueous
Au-hydrogenation system can be attributed to a beneficial water-
assisted orientation of the hydrophilic C O moiety2d,21 on the
specific surface active sites of Au/meso-CeO2 which favored
chemoselective hydrogenation. It should be mentioned here that
the differences cannot be attributed to hydrogen availability since
the solubility of H2 in water is significantly lower than that in
organic solvents (Table 4).17a,22
Catalyst characterization
Elemental analysis. The Au loading of the catalysts was
measured by inductively coupled plasma atomic emission spec-
troscopy (ICP-AES) using a Thermo Electron IRIS Intrepid II
XSP spectrometer (Hitachi 4010).
X-Ray photoelectron spectroscopy (XPS). XPS analysis was
performed using a Perkin Elmer PHI 5000 C system equipped
with a hemispherical electron energy analyzer. The Mg Ka (hn =
1253.6 eV) was operated at 15 kV and 20 mA. The energy scale
was internally calibrated by setting the C1s peak at 284.6 eV.
Conclusion
In summary, we have described a green and efficient gold-
catalyzed reaction system for the chemoselective reduction
of a,b-unsaturated carbonyl compounds via hydrogenation in
aqueous medium. This new catalytic system has been demon-
strated to be suitable for the environmentally clean reduction of a
range of unsaturated aldehydes or ketones. The unprecedented
high efficiency achieved for the clean synthesis of allyl alco-
hols via aqueous Au-catalyzed hydrogenation is preliminarily
attributed to a significant beneficial effect of water as a solvent
in facilitating the preferential hydrogenation of the hydrophilic
Nitrogen adsorption-desorption measurements. Nitrogen
sorption at -196 ◦C was measured using a Micromeritics TriStar
3000 after the samples were degassed (1.33 ¥ 10-2 Pa) at 300 ◦C
overnight. The specific surface area was calculated using the
BET method, and pore size distribution was determined by the
BJH method.
C
O group vs. C C.
X-Ray diffraction (XRD) measurements. The X-ray powder
diffraction (XRD) of the catalysts was carried out on a German
Bruker D8 Avance spectrometer using nickel filtered Cu-Ka
(l = 0.15418 nm), operated at 40 kV and 20 mA. CeO2 particle
size was determined from the half-height width of the (111)
fluorite phase diffraction peak (2q = 28.5◦) by using the Scherrer
equation.
Experimental
Catalytic preparation
1.5 wt% Au/TiO2 (type A, lot no. Au/TiO2 no. 02-1) and 4.5
wt% Au/Fe2O3 (type C, lot no. Au/Fe2O3 no. 02-5) were supplied
by the World Gold Council (WGC). 1.0 wt% Au/Al2O3 (Strem
catalogue number: 79-0160) was supplied by Mintek.
Transmission electron microscopy (TEM) analysis. TEM
images for supported gold catalysts were taken with a JEOL
2011 electron microscope operating at 200 kV. Before being
transferred into the TEM chamber, the samples dispersed with
ethanol were deposited onto a carbon-coated copper grid and
then quickly moved into the vacuum evaporator.
Preparation of mesostructured ceria materials
Meso-CeO2 was prepared by a template-assisted precipitation
method.7b Typically, a NaOH solution (2 g in 300 mL of distilled
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Catalytic activity measurements
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General procedure for the reduction of UALs and UKEs.
Supported gold catalyst (1.97 mg Au, 0.01 mmol) was placed
in a 50 mL Parr reactor (Model Number. 4792), followed by the
addition of solvent (15 mL) and UALs or UKEs (1 mmol), and
then the reaction mixture was vigorously stirred (800 rpm with
a magnetic stir bar) at 100 ◦C under 1.0 MPa of H2 atmosphere.
No variation in reduction rate was observed over a rage of stirrer
speeds (400–1000 rpm) indicating the lack of external diffusion
limitations. After the reaction, the reaction mixture was filtered
and the catalyst was washed thoroughly with ethanol. The
products were thoroughly extracted with EtOAc (3 ¥ 20 mL)
when water was applied as the solvent. In this case, the organic
washings were combined, dried over MgSO4, and then the
final product was subjected to GC analysis for identification
and quantification of the allylic alcohols. The conversion and
product selectivity were periodically determined by GC analysis
(Agilent 6820 equipped with a HP-WAX capillary column
(0.25 mm, 30 m, 0.32 mm) and a flame ionization detector
(FID)) using n-decane as an internal standard. For isolation,
the combined organic layer was concentrated under reduced
pressure by using a rotator evaporator. The crude product
was purified by column chromatography on silica gel (EtOAc–
hexane as eluant) to afford the product. All the products
were characterized by GC-MS and further confirmed by the
comparison of their GC retention time, mass with those of
authentic samples.
Recovery and reuse of Au/meso-CeO2. The catalyst was
collected after filtration washed with acetone for three times
and then with distilled water for several times. The catalyst was
then dried at 100 ◦C for 12 h before used for next reaction.
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Competitive reaction of benzaldehyde and styrene. Au/meso-
CeO2 (1.97 mg Au, 0.01 mmol) was placed in a 50 mL Parr
reactor (Model Number. 4792), followed by the addition of
solvent (15 mL), benzaldehyde (1 mmol) and styrene (1 mmol),
and then the reaction mixture was vigorously stirred (800 rpm
with a magnetic stir bar) at 100 ◦C under 1.0 MPa of H2
atmosphere.
Acknowledgements
17 C. L. Young, Hydrogen and Deuterium, Pergamon, Solubility data
This work was supported by the National Natural Science Foun-
dation of China (20873026, 21073042), New Century Excellent
Talents in the University of China (NCET-09-0305), the State
Key Basic Research Program of PRC (2009CB623506), and
Science & Technology Commission of Shanghai Municipality
(08DZ2270500).
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