Pt nanoparticles entrapped in ordered mesoporous carbon for enantioselective hydrogenation

Article abstract of DOI:10.1016/j.molcata.2011.05.023

Pt nanoparticles entrapped in CMK-3 ordered mesoporous carbon materials, prepared by a facile impregnation method, were found to be efficient for the enantioselective hydrogenation of α-ketoesters by modification with cinchona alkaloids. The initial activity of higher than 23,000 h^-1 TOF and 82% ee were obtained for the chiral hydrogenation of ethyl pyruvate with cinchonidine (CD)-modified Pt/CMK-3 catalyst. With regard to the chiral hydrogenation of ethyl 2-oxo-4-phenylbutyrate, the CD-modified Pt/CMK-3 catalyst afforded the highest TOF of 5615 h^-1 and 64% ee. For comparison, commercially available Pt/C and Pt/Al₂O₃ catalysts were investigated as well. The Pt/CMK-3 catalysts were more efficient than the commercial Pt/C catalyst. Of particular note is that the Pt/CMK-3 catalyst exhibited good stability; only below 0.005% Pt atoms were leached into solution after the chiral hydrogenation of ethyl pyruvate in acetic acid, while the Pt leaching amount for the commercial Pt/Al₂O₃ and Pt/C catalysts was 0.15% and 0.25%, respectively. In addition, the Pt/CMK-3 catalyst could also be reused for more than 5 times without distinct loss of activity and enantioselectivity, while the reusability for the commercial Pt/C and Pt/Al₂O₃ catalysts was poor. Based on IR and Raman spectroscopic characterization, it is suggested that both the physical structure features, including high specific surface area, adequate pore volume, ordered mesopores and small Pt particle size with high dispersion, and the chemical nature of catalyst surface with high electron density would improve the performance of Pt/CMK-3 catalysts.

Full text of DOI:10.1016/j.molcata.2011.05.023

Journal of Molecular Catalysis A: Chemical 345 (2011) 81–89
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Pt nanoparticles entrapped in ordered mesoporous carbon
for enantioselective hydrogenation
Bo Li, Xiaohong Li∗, Hongna Wang, Peng Wu
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Pt nanoparticles entrapped in CMK-3 ordered mesoporous carbon materials, prepared by a facile impreg-
nation method, were found to be efficient for the enantioselective hydrogenation of ␣-ketoesters by
modification with cinchona alkaloids. The initial activity of higher than 23,000 h−1 TOF and 82% ee were
obtained for the chiral hydrogenation of ethyl pyruvate with cinchonidine (CD)-modified Pt/CMK-3 cata-
lyst. With regard to the chiral hydrogenation of ethyl 2-oxo-4-phenylbutyrate, the CD-modified Pt/CMK-3
catalyst afforded the highest TOF of 5615 h−1 and 64% ee. For comparison, commercially available Pt/C
and Pt/Al2O3 catalysts were investigated as well. The Pt/CMK-3 catalysts were more efficient than the
commercial Pt/C catalyst. Of particular note is that the Pt/CMK-3 catalyst exhibited good stability; only
below 0.005% Pt atoms were leached into solution after the chiral hydrogenation of ethyl pyruvate in
acetic acid, while the Pt leaching amount for the commercial Pt/Al2O3 and Pt/C catalysts was 0.15% and
0.25%, respectively. In addition, the Pt/CMK-3 catalyst could also be reused for more than 5 times without
distinct loss of activity and enantioselectivity, while the reusability for the commercial Pt/C and Pt/Al2O3
catalysts was poor. Based on IR and Raman spectroscopic characterization, it is suggested that both the
physical structure features, including high specific surface area, adequate pore volume, ordered meso-
pores and small Pt particle size with high dispersion, and the chemical nature of catalyst surface with
high electron density would improve the performance of Pt/CMK-3 catalysts.
Received 27 January 2011
Received in revised form 19 April 2011
Accepted 26 May 2011
Available online 2 June 2011
Keywords:
Asymmetric hydrogenation
Pt nanoparticles
Ordered mesoporous carbon
Ethyl pyruvate
Ethyl 2-oxo-4-phenylbutyrate
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
mesopolymer [20] were adopted as supports for Pt nanoparticles
in the heterogeneous asymmetric catalysis, furnishing medium
Enantioselective hydrogenation of ␣-functionalized ketones to
alcohols is an important chemical process owing to great applica-
tion of chiral alcohols in synthesis of chiral drugs, pesticides, food
additives and perfumes, etc. [1–3]. The catalytic enantioselective
hydrogenation of ␣-ketoesters on the supported Pt catalysts after
chirally modified with cinchona alkaloids has been regarded as one
of the landmarks of heterogeneous asymmetric catalysis [4–8].
Since the heterogeneous enantioselective hydrogenation was
firstly reported by Orito and co-workers in 1978 [9–11], many
kinds of materials have been adopted to support Pt nanoparti-
cles. In the beginning, inorganic carriers like Al2O3, SiO2, TiO2,
etc. were considered to be suitable supports for Pt nanopar-
ticles, but these materials supported Pt catalysts showed only
mediocre performance in the asymmetric hydrogenation of pyru-
vate esters [12–17], except that CD-modified 5.0 wt.% Pt/Al2O3
catalysts induced good to excellent enantioselectivity [12,13].
With the rapid development of molecular sieves and periodic
mesoporous materials, MCM-41 [18], HNaY [19] and FDU-14
to good enantioselectivities in the chiral hydrogenation of ␣-
functionalized ketones.
Clearly, to the best of our knowledge, alumina supported Pt
catalyst seems to be one of the best catalyst for the asymmetric
hydrogenation of ␣-functionalized ketones until now. Neverthe-
less, the intrinsic drawback of Al2O3 with inferior stability in acetic
acid limits the reusability of Pt/Al2O3 catalysts due to peptization
of alumina under the acidic conditions [21]; whereas acetic acid
is one of the best solvents for the heterogeneous enantioselective
hydrogenation of ␣-functionalized ketones with cinchona alkaloids
modified Pt catalysts.
Carbon materials are one kind of the most rapidly developing
advanced materials due to potential applications in heterogeneous
catalysis and electrocatalysis. The relevant application of carbon
material as support for Pt nanoparticles to the heterogeneous enan-
tioselective catalysis can be traced back to the original work of
Ortio and co-workers about the asymmetric hydrogenation of ␣-
ketoesters [10,22], although the results did not arouse concern at
that time. More than 20 years later, Fraga et al. [23] investigated in
detail the surface chemistry of activated carbon on enantioselective
hydrogenation of methyl pyruvate over CD-modified Pt/C catalysts.
Under the optimal conditions, up to 35% ee value of (R)-(+)-methyl
∗
Corresponding author. Tel.: +86 21 6223 8590; fax: +86 21 6223 8590.
E-mail address: xhli@chem.ecnu.edu.cn (X. Li).
1381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.05.023

82
B. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 81–89
lactate was achieved. Meanwhile, Perosa et al. [24] studied the
enantioselective hydrogenation of acetophenone on commercially
available Pt/C catalysts after chirally modified with cinchona alka-
loids in a biphasic water–isooctane system. For comparison, the
chiral hydrogenation of ethyl pyruvate was also carried out under
the same conditions. As a result, up to 20% ee was obtained for
the chiral hydrogenation of acetophenone; while only 14% ee was
acquired for the asymmetric hydrogenation of ethyl pyruvate.
However, as well known, the ee value for the chiral hydrogena-
tion of ethyl pyruvate was much higher than that of acetophenone
with Pt/Al2O3 catalysts in a single phase system [25].
Herein we report the application of CMK-3 as a support to sta-
bilize Pt nanoparticles for the enantioselective hydrogenation of
␣-ketoesters after chirally modified with CD (Scheme 1). For com-
parison, the commercially available Pt/C and Pt/Al2O3 catalysts
were also applied. To the best of our knowledge, this is the first
report on the use of CMK-3 OMCs for the preparation of Pt catalysts
in the heterogeneous enantioselective catalysis.
2. Experimental
2.1. Materials
Recently, Xing et al. [26] adopted single-walled carbon nan-
otubes (SWNTs) to support Pt nanoparticles with different
loadings for the heterogeneous asymmetric hydrogenation of
ethyl pyruvate. After optimization of reaction parameters, 50%
ee of (R)-(+)-ethyl lactate was induced with CD-modified 20 wt.%
Pt/SWNTs catalyst. Very recently, TiO2 coated multi-walled carbon
nanotubes-supported Pd catalysts have been applied in the enan-
tioselective hydrogenation of a series of ␣-unsaturated carboxylic
acids using CD as chiral modifier, furnishing up to 52% ee for the
chiral hydrogenation of (E)-␣-phenylcinnaic acid [27]. In addition, a
highly mesoporous carbon xerogel has also been attempted to sup-
port Pd catalyst for enantioselective hydrogenation of isophorone
and of 2-benzylidene-1-benzosuberone [28,29]. Although inferior
ee values were induced for both substrates, the highly mesoporous
carbon xerogel supported Pd catalysts were a little more enantios-
elective than the more dispersed commercial Pd/C catalyst [30,31].
Ordered mesoporous carbons (OMCs) have attracted much more
attention since their discovery, due to periodic mesopores, uni-
form pore size, high surface areas, adequate pore volume and high
thermal, chemical and mechanical stabilities [32–34]. These fea-
tures make OMCs to be prospective candidates as adsorbents [35],
catalyst support and catalyst [36,37], electrode materials [38], and
templates for synthesis of nanostructured inorganic materials and
mesoporous polymer carbon composites [39,40]. CMK-3 carbons
are one kind of the widely studied OMCs, which can be synthesized
by a classic two-step nano-casting method, using mesoporous sil-
ica SBA-15 as template, sucrose as carbon source, sulphuric acid
as carbonization catalyst and carbonized at 1173 K [41]. They have
been proved stable even under acidic conditions and also exhibit
unique hydrophobic affinity towards organic reactants and sol-
vents [42].
Hydrogen
hexachloroplatinate
(IV)
hexahydrate
(H2PtCl6·6H2O), sodium formate and other chemicals were of
analytical grade. Pluronic 123 (EO20PO70EO20, MW = 5800) was
purchased from Sigma–Aldrich. Ethyl pyruvate (98%), ethyl 2-oxo-
4-phenylbutyrate (EOPB) (91%) and CD (99%) were purchased from
Alfa Aesar (A Johnson Matthey Company) and used as received. The
commercial Pt/C (5 wt.%) and Pt/alumina (5 wt.%) catalysts were
also purchased from Alfa Aesar. The other commercial Pt/C (5 wt.%)
catalyst was purchased from Sigma–Aldrich for comparison. For
convenience, the Pt/C catalysts purchased from Alfa Aesar and
from Sigma–Aldrich were designated hereinafter as Pt/C-AA and
Pt/C-SA, respectively.
2.2. Catalyst preparation
The CMK-3 OMCs were synthesized using mesoporous silica
SBA-15 as the hard template, sucrose as the carbon source and sul-
furic acid as the carbonization catalyst [41]. The 5.0 wt.% Pt/CMK-3
catalysts were prepared mainly according to Ref. [20]: CMK-3 was
impregnated with a solution containing H2PtCl6 and stirred for
4–6 h. Then the mixture was evaporated to remove the excess sol-
vent, followed by a drying at 353 K overnight. Subsequently, one
portion of catalyst precursor was directly reduced in an aqueous
solution of sodium formate, while the other portion was calcined
under vacuum at 423 K or at 523 K for 2 h before reduction using
the same method. Then the mixture was washed by plenty of water
to remove chlorine ions and dried at 353 K overnight. According to
the preparation procedures, the obtained Pt/CMK-3 catalysts are
denoted as Pt/CMK-3-W/E-T, where W/E represents different dif-
fusion medium of H2PtCl6, for example, W represents water and
Scheme 1. Enantioselective hydrogenation of ethyl pyruvate and EOPB on CD-modified Pt/CMK-3 catalysts.

B. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 81–89
83
E represents ethanol; T represents the calcination temperature in
Kelvin for the catalyst precursor before reduction. The description
without “T” stands for the Pt/CMK-3 catalysts without calcination
before reduction.
and then was purged with He for 30 min. When the sample was
cooled down to 308 K, CO was introduced into the IR cell until the
adsorption was saturated. Then the sample was flushed with a He
flow before the spectrum was recorded.
2.4. Catalytic tests
2.3. Characterization
For the enantioselective hydrogenation, unless otherwise men-
tioned, Pt/CMK-3, Pt/C or Pt/Al2O3 catalyst (0.026 mmol Pt) was
pretreated in a hydrogen flow (40 mL/min) at 673 K for 2 h
before use. The catalyst was then mixed with CD (0.034 mmol),
ethyl pyruvate (21.07 mmol) or EOPB (5.29 mmol), solvent (20 mL)
and transferred to a 100 mL autoclave with magnetic stirring
(1200 rpm). The hydrogenation reaction began at room tempera-
ture after hydrogen (4.0 MPa) was introduced into the autoclave.
The reaction was stopped after a proper time and the products were
analyzed by GC-FID (GC 2014, Shimadzu) equipped with a cap-
illary chiral column (HP19091G-B213, 30 m × 0.32 mm × 0.25 ␮m,
Agilent). The optical yield was expressed as ee value: ee
(%) = ([R] − [S])/([R] + [S]) × 100.
The X-ray diffraction (XRD) patterns of samples were collected
on a Bruker D8 Advance instrument using Cu-K␣ radiation. The
nitrogen adsorption–desorption isotherms were measured at 77 K
on a Quantachrome Autosorb-3B system, after the samples were
evacuated for 10 h at 373 K. The BET specific surface area was cal-
culated using adsorption data in the relative pressure range from
0.05 to 0.35. The pore size distribution curves were calculated from
the analysis of the adsorption branch of the isotherm using the
BJH algorithm. The Raman spectrum of CMK-3 carbon was taken
on a Renishaw inVia Raman Spectroscopy excited using a 632.8 nm
laser. The TEM images were taken on a Jeol JEM-2100 electromi-
croscopy with an acceleration voltage of 200 kV.
CO chemisorption of samples was measured at 308 K on a Quan-
tachrome CHEMBET-3000 pulse chemisorption analyzer after the
samples were pretreated in a 5 vol.% H2/95 vol.% Ar flow at 673 K
for 2 h. The degree of dispersion and the mean particle size (cubic
model) were estimated from the measured CO uptake, assuming a
cross-sectional area for a surface platinum atom of 8.0 × 10−20 m2
and a stoichiometric factor of one, using nominal platinum concen-
trations. The leached amount of Pt atoms into solution after reaction
was detected with a Thermo Elemental IRIS Intrepid II XSP induc-
tively coupled plasma-atomic emission spectroscopy (ICP-AES).
The surface electronic state of platinum particles was examined
by Diffuse Reflectance Infrared Fourier-Transform Spectroscopy
(DRIFTS) using CO as probe molecules. The analysis was carried
out with a Nicolet NEXUS 670 spectrometer. The catalyst sample
was pretreated in a 5 vol.% H2/95 vol.% Ar stream at 673 K for 2 h,
3. Results and discussion
3.1. Catalyst preparation and characterization
The procedures for preparing CMK-3 supported Pt catalysts are
graphically illustrated in Fig. 1, which consists of the preparation
of CMK-3 replica from SBA-15 and the impregnation of CMK-3
with H2PtCl6 dissolved in different media, followed by reduction
with sodium formate. Fig. 2 shows the low-angle X-ray diffrac-
tion (XRD) patterns of SBA-15 template, CMK-3 replica and the
resultant Pt/CMK-3 catalysts. Similar to SBA-15, CMK-3 exhib-
ited an intense diffraction peak together with two weak peaks
indexed as (1 0 0), (1 1 0) and (2 0 0) planes of hexagonal struc-
Fig. 1. Schematic illustration for preparation of Pt/CMK-3 catalysts.

84
B. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 81–89
0.06
800
0.05
0.04
G band
D band
0.03
700
0.02
0.01
0.00
0
2
4
6
8
10
600
500
400
300
200
Pore diameter (nm)
(100)
500 1000 1500 2000 2500 3000 3500
Raman shift (cm-1
)
(110)
CMK-3
(200)
f
Pt/CMK-3-W
Pt/CMK-3-E
Pt/CMK-3-W-423
Pt/CMK-3-W-523
e
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (P/P )
0
d
c
Fig. 3. N2 adsorption–desorption isotherms and pore size distribution (inset) of
CMK-3 and related catalysts.
was 1325 m2 g−1, while the specific surface area for Pt/CMK-3 cata-
lysts ranged from 1130 to 1290 m2 g−1. The Pt/CMK-3 catalysts also
had adequate pore volume higher than 1.0 cm3 g−1. These physical
features of Pt/CMK-3 catalysts would certainly be helpful to mass
transport.
To obtain further information on the CMK-3 structure, Raman
spectroscopy was carried out. The inset of Fig. 2 shows a repre-
sentative spectrum recorded at a laser excitation wavelength of
632.8 nm in the 500–3500 cm−1. As typically found for sp2 bonded
carbons, the spectrum was dominated by the G and D bands, located
in this case at 1594 and 1335 cm−1, respectively. The position of
the G band, together with the relatively strong intensity of the D
band, indicates that CMK-3 carbons mainly consist of disordered
graphene with a very small size. The broad and weak features
centered at 2627 and 2907 cm−1 also suggest existence of small
amount of amorphous carbon besides the disordered graphene
[43].
b
a
1
2
3
4
5
2 theta (degree)
Fig. 2. Low-angle XRD patterns of (a) SBA-15; (b) CMK-3; (c) Pt/CMK-3-W; (d)
Pt/CMK-3-E; (e) Pt/CMK-3-W-423; (f) Pt/CMK-3-W-523 and Raman spectrum
(inset) of CMK-3 recorded with a laser wavelength of 632.8 nm.
ture (p6mm). All the Pt/CMK-3 catalysts also displayed the distinct
(1 0 0) diffraction, similar to the support CMK-3. This demonstrates
that even if the CMK-3 support was impregnated with Pt precursor
solution for several hours and in some cases the catalyst precur-
sors were calcined at a high temperature, the meso-structure of
CMK-3 was still retained. As for the decreased intensity of (1 0 0)
diffraction peak after Pt nanoparticles loading, it can be explained
in terms of the reduced contrast between mesopores and pore
walls.
The well-ordered mesoporous structure of CMK-3 support could
be further confirmed by the N2 sorption isotherms of Pt/CMK-3
catalysts (Fig. 3). All the Pt/CMK-3 catalysts displayed the typ-
ical hysteresis loop in the relative pressure range from 0.45 to
0.8 and also showed narrow BJH pore size distribution centered
at 3.5 nm. As listed in Table 1, the specific surface area of CMK-3
The Pt particle size was firstly characterized using the wide-
angle XRD (Fig. 4). Except for Pt/CMK-3-W-523 catalyst, the
Pt/CMK-3 catalysts did not show the typical diffractions assigned to
Pt crystalline indexed as Pt(1 1 1), Pt(2 0 0) and Pt(2 2 0) planes, indi-
cating that the Pt particles were uniformly dispersed on the CMK-3
support and did not aggregate to form large crystalline for Pt/CMK-3
catalysts which were not calcined at above than 423 K. The cal-
cination at 523 K caused strong aggregation of Pt nanoparticles.
The morphology of some Pt/CMK-3 catalysts was also character-
ized using TEM. As can be revealed in the TEM images (Fig. 5), the
Pt/CMK-3-W and Pt/CMK-3-E catalysts retained the typical p6mm
meso-structure and the Pt nanoparticles were uniformly dispersed
inside the CMK-3 mesopores.
The Pt particle size and dispersion were also calculated accord-
ing to the measured CO chemisorption (also listed in Table 1). In
Table 1
Relevant parameters of CMK-3 and Pt/CMK-3, Pt/C-AA and Pt/Al2O3 catalysts.
Sample
SBET (m2 g−1
)
DPore (nm)
VPore (cm3 g−1
)
Pt sizea (nm)
Pt dispersiona (%)
CMK-3
1325
1290
1265
1230
1130
892
3.5
3.5
3.5
3.5
3.3
1.26
1.18
1.02
1.13
1.07
1.07
0.9
–
–
Pt/CMK-3-W
Pt/CMK-3-E
Pt/CMK-3-W-423
Pt/CMK-3-W-523
Pt/C-AA
2.6
2.2
2.8
10.7
10.3
3.5
43.7
52.5
41.2
10.6
11.0
32.8
3.8
18.4
Pt/Al2O3
147
a
Pt particle size and dispersion was determined by CO chemisorption.

B. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 81–89
85
Pt(111)
Pt(200)
Pt(220)
e
d
c
b
a
30
40
50
60
70
80
2 theta (degree)
Fig. 4. Wide-angle XRD patterns of (a) CMK-3; (b) Pt/CMK-3-W; (c) Pt/CMK-3-E;
(d) Pt/CMK-3-W-423; (e) Pt/CMK-3-W-523.
Fig. 5. TEM images of (a) Pt/CMK-3-W and (b) Pt/CMK-3-E. The inset bars in (a) and
(b) are 10 nm and 5 nm, respectively.
agreement with the results from the wide-angle XRD and TEM
analysis, the average Pt particle size for Pt/CMK-3-W catalyst was
around 2.6 nm with 43.7% dispersion, while the average Pt par-
ticle size for Pt/CMK-3-E catalyst was around 2.2 nm with 52.5%
dispersion. With calcination before reduction, the Pt particle size
was increased and as a result; the Pt particle size for Pt/CMK-
3-W-423 and Pt/CMK-3-W-523 catalysts were 2.8 and 10.7 nm,
respectively.
increased as well. When the CD amount was further increased
to 0.034 mmol, both the highest conversion of 81.0% and the
highest ee value of 82.2% were obtained. Too high CD concentra-
tion (0.051 mmol) caused the conversion and ee value decrease
strongly. Consequently, the CD amount of 0.034 mmol was added
in the following tests and thus the substrate to CD molar ratio was
about 620.
The relevant physico-chemical parameters for the commercial
Pt/C-AA and Pt/Al2O3 catalysts are also shown in Table 1. The
5 wt.% Pt/C-AA catalyst also had relatively large surface area and
pore volume, but the average Pt particle size was a little big-
ger (10.3 nm) with lower dispersion (11.0%). For the commercial
Pt/Al2O3 catalyst, the mean Pt particle size was comparable with
that of Pt/CMK-3 catalyst series, although the specific surface area
100
90
80
70
60
50
40
30
was only 147 m2 g−1
.
3.2. Effect of chiral modifier amount on Pt/CMK-3 catalyst
performance
To make sure optimum amount of chiral modifier, we firstly
investigated the influence of CD amount on the catalytic perfor-
mance in the asymmetric hydrogenation of ethyl pyruvate with
Pt/CMK-3-W catalyst. Fig. 6 shows the profiles of conversion and
ee value vs CD amount within 5 min. No addition of CD into
the reaction system, only 4.3% of ethyl pyruvate was converted
to ethyl lactate without enantioselectivity. When 0.0068 mmol
CD was added, 25.3% ethyl pyruvate conversion and 64.5% ee of
(R)-(+)-ethyl lactate were achieved, suggesting that the Pt/CMK-
3-catalyzed asymmetric hydrogenation of ethyl pyruvate was a
“ligand-accelerated” reaction.
20
Conversion
ee value
10
0
0.00
0.01
0.02
0.03
0.04
0.05
CD amount (mmol)
Fig. 6. Effect of CD amount on conversions and ee values in the chiral hydrogenation
of ethyl pyruvate with Pt/CMK-3-W catalyst. Reaction conditions: 5 wt.% Pt/CMK-
3-W catalyst (0.026 mmol Pt); ethyl pyruvate (21.07 mmol); acetic acid (20 mL); H2
(4.0 MPa); RT; 5 min; 1200 rpm.
With increase of CD amount to 0.017 mmol, the conversion of
ethyl pyruvate was further improved and the ee value was slightly

86
B. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 81–89
100
80
promoting the interaction of CD with substrate through hydrogen
bond [45,46]. Regarding the bad performance of the chiral hydro-
genation of ethyl pyruvate in water, it can be explained by that the
fine powders of quite hydrophobic CMK-3 materials are not soaked
well with water, in other words, the Pt/CMK-3 catalyst is either sus-
pended on the surface or adhered to the autoclave wall. As a result,
the catalyst could not get into water to contact and adsorb sub-
strates, hence the low activity was obtained. As for the solvent effect
of toluene, it could be partly owing to the polarity of toluene. The
Pt/CMK-3 catalyst could be dispersed uniformly in a single organic
phase where CD and substrate are dissolved when toluene is used
as solvent; therefore the substrate and chiral modifier can be easily
adsorbed and/or activated by Pt/CMK-3 catalyst, resulting in high
results [44]. With respect to the results obtained in ethanol, the
side reaction of ethanol with ethyl pyruvate might occur in ethanol,
affecting the chiral hydrogenation of ethyl pyruvate, so that the
performance in ethanol was mediocre [47].
60
40
acetic acid
toluene
ethanol
water
20
0
100
80
60
40
20
0
3.4. Enantioselective hydrogenation of ethyl pyruvate
Based on the findings in hand, we performed the chiral hydro-
genation of ethyl pyruvate on CD-modified different Pt/CMK-3
catalysts in acetic acid and stopped the reaction after 5 min. The
commercial Pt/C and Pt/Al2O3 catalysts were also applied for com-
parison.
acetic acid
toluene
ethanol
water
Table 2 lists the conversions of ethyl pyruvate and ee values of
(R)-(+)-ethyl lactate obtained on CD-modified Pt/CMK-3, Pt/C and
Pt/Al2O3 catalysts. As above mentioned, CD-modified Pt/CMK-3-
W catalyst gave 81.0% conversion together with 82.2% ee value of
(R)-(+)-ethyl lactate (Table 2, entry 2). To investigate the calcina-
tion influence for catalyst precursors on the catalytic performance
of Pt/CMK-3-W catalysts, some catalyst precursors were calcined
at 423 K or at 523 K for 2 h before reduced. Compared with those
obtained on Pt/CMK-3-W catalyst, the conversion of ethyl pyruvate
was greatly increased to 98.3% on CD-modified Pt/CMK-3-W-423
catalyst, affording an initial activity TOF (defined as the number
of moles of converted ethyl pyruvate per mole of Pt active sites
per hour) higher than 23,000 h−1, while the ee value was a little
declined (Table 2, entries 2 vs 4). However, if the calcination tem-
perature for the catalyst precursor was further elevated to 523 K,
the catalytic performance of Pt/CMK-3-W-523 catalyst was sharply
decreased and inferior results were afforded (Table 2, entries 2 vs 5).
The improvement caused by catalyst precursor calcination at
a relatively lower temperature in the catalytic activity may be
interpreted by that the decomposition of H2PtCl6 precursor and
suitable Pt particle size formed during the calcination will be ben-
eficial to the adsorption of substrate and chiral modifier; therefore,
higher conversion of ethyl pyruvate was acquired on Pt/CMK-3-
W-423 catalyst. As for that catalyst ever calcined at 523 K, the Pt
nanoparticles were aggregated to form large particles (10.7 nm),
correspondingly, lower results were obtained on Pt/CMK-3-W-523
catalyst [48].
Both the conversion (79.1%) and ee value (81.3%) obtained with
Pt/CMK-3-E catalyst were a little lower than those with Pt/CMK-3-
W catalyst (Table 2, entries 2 vs 6), although these two Pt/CMK-3
catalysts had comparable average Pt particle sizes. This probably
could be interpreted by the different exposed crystal faces of Pt
nanoparticles for the different Pt/CMK-3 catalysts, as both the rate
and the ee increased with increasing Pt(1 1 1)/Pt(1 0 0) ratio [49].
Considering good product solubility in water, we still wonder
how the Pt/CMK-3 catalyst behaves in a mixed solvent containing
water, although the reaction in neat water already proved slug-
gish. Accordingly, we carried out the chiral hydrogenation of ethyl
pyruvate with CD-modified Pt/CMK-3-W catalyst in mixed solvent
containing acetic acid and water with an equal volume. To our sur-
prise, 5 min was enough to completely convert ethyl pyruvate to the
0
5
10
15
20
25
Reaction time (min)
Fig. 7. Kinetic profiles of asymmetric hydrogenation of ethyl pyruvate in differ-
ent solvents. Reaction conditions: 5 wt.% Pt/CMK-3-W catalyst (0.026 mmol Pt);
CD (0.034 mmol); ethyl pyruvate (21.07 mmol); solvent (20 mL); H2 (4.0 MPa); RT;
1200 rpm.
3.3. Optimization of reaction conditions for enantioselective
hydrogenation of ethyl pyruvate
To optimize reaction conditions, including to screen solvent and
to determine reaction time, we compared the kinetic profiles of
enantioselective hydrogenation of ethyl pyruvate in acetic acid, in
toluene, in ethanol and in water, respectively, with CD-modified
Pt/CMK-3-W catalyst.
As shown in Fig. 7, the chiral hydrogenation of ethyl pyru-
vate in acetic acid ran faster than that performed in other three
solvents. In acetic acid, an 81% conversion of ethyl pyruvate was
obtained within 5 min and the total conversion was nearly com-
plete within 10 min. A slightly lower ethyl pyruvate conversion of
74.8% was afforded within 5 min in toluene, and the conversion
was finished within 10 min as well. Although the initial activity
obtained in ethanol was not too low, furnishing a 64.5% conversion
within 5 min, the reaction became sluggish and seemed stagnant
after 10 min. The reaction carried out in water was the slowest, as
only a 33.2% conversion was acquired within 5 min. The ee value
vs reaction time plots in four different solvents are also displayed
in Fig. 7. The enantioselectivities appeared independent on reac-
tion time under our conditions. An 82.2% ee value was furnished in
acetic acid, while 73.0%, 53.2% and 48.4% ee values were obtained in
toluene, in ethanol and in water, respectively. Thus the sequence
of activity and ee value obtained in different solvents was acetic
acid > toluene > ethanol > water.
Solvent plays an important role in determining the reaction
results for the enantioselective hydrogenation of ethyl pyruvate
in a complex way, which has been discussed elsewhere [44]. The
remarkable performance of chiral hydrogenation of ethyl pyruvate
in acetic acid can be mainly ascribed to the protonation of quinucli-
dine N atom of CD, which could improve the enantioselectivity by

B. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 81–89
87
Table 2
Reaction results obtained on chirally modified Pt/CMK-3 and related catalysts for the chiral hydrogenation of ethyl pyruvate.a
Entry
Catalyst
Pt size (nm)
Time (min)
Conv. (%)
ee (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
CMK-3
–
2.6
2.6
2.8
10.7
2.2
2.2
10.3
10.3
10.3
Not measured
3.5
10.3
2.6
3.5
5
5
5
5
5
5
5
5
5
5
5
5
2
2
2
0
0
Pt/CMK-3-W
Pt/CMK-3-W
Pt/CMK-3-W-423
Pt/CMK-3-W-523
Pt/CMK-3-E
Pt/CMK-3-E
Pt/C-AA
81.0
100b
98.3
23.2
79.1
85.2b
16.8
18.3
8.1
18.6
98.6
9.0
24.5
19.0
82.2
70.8
78.0
34.6
81.3
70.5
56.3
62.7
40.3
60.6
92.6
65.0
71.2
87.2
Pt/C-AAc
Pt/C-AAd
Pt/C-SAc
Pt/Al2O3
Pt/C-AAc
Pt/CMK-3-W
Pt/Al2O3
a
Reaction conditions: 5 wt.% Pt/CMK-3, Pt/C or Pt/Al2O3 catalyst (0.026 mmol Pt) pretreated at 673 K; CD (0.034 mmol); ethyl pyruvate (21.07 mmol); acetic acid (20 mL);
H2 (4.0 MPa); RT; 1200 rpm; and the configuration of product is R.
b
The mixed solvent of acetic acid and water with a volume ratio of 1 to 1 was used.
The catalyst was pretreated in a hydrogen flow at 573 K for 2 h.
The catalyst was used as received.
c
d
hydrogenation product. The conversion was increased by about 20%
compared with that in neat acetic acid, whereas the ee value was
decreased to 70.8% as a compromise (Table 2, entry 3). Similarly, the
conversion was increased from 79.1% to 85.2% while the ee value
was decreased from 81.3% to 70.5% when the chiral hydrogena-
tion of ethyl pyruvate was performed in the mixed solvent with
CD-modified Pt/CMK-3-E catalyst, compared with those obtained
in neat acetic acid (Table 2, entries 6 vs 7).
With regard to the common phenomena that the higher activ-
ity together with lower ee value on Pt/CMK-3-W and Pt/CMK-3-E
catalysts is obtained in the mixed solvent of acetic acid and water,
the tentative explanations may be the following two aspects. On
one hand, the co-solvent water molecules maybe interact with the
N atom of quinuclidine moiety in CD via hydrogen bond, so that the
possibility of interaction between CD with substrate on the cata-
lyst surface is reduced, resulting in lower ee value. On the other
hand, the interaction between water and CD also decreases the
competitive adsorption between CD and substrate; therefore, more
Pt active sites participate in hydrogenation of substrate rather than
in adsorption of CD, as a result, higher conversion of ethyl pyruvate
is furnished.
The commercial 5 wt.% Pt/Al2O3 and Pt/C-AA catalysts were also
applied to the chiral hydrogenation of ethyl pyruvate after chirally
modified with CD as reference catalysts. As can be anticipated, the
chirally modified Pt/Al2O3 catalyst showed excellent performance,
obtaining 98.6% conversion together with 92.6% ee under the same
conditions (Table 2, entry 12). The ee value obtained with CD-
modified Pt/Al2O3 catalyst is higher than our home-made Pt/CMK-3
catalysts, whereas the conversion afforded with Pt/Al2O3 catalyst
is comparable with that by Pt/CMK-3-W-423 catalyst under the
same conditions. However, for the commercial Pt/C-AA catalyst,
only 16.8% conversion and 56.3% ee value were afforded, much
lower than those obtained with Pt/CMK-3-W catalysts (Table 2,
entry 8).
In order to compete fairly between the commercial Pt/C and
our home-made Pt/CMK-3 catalysts, we also studied the effect
of pretreatment temperature for Pt/C-AA catalyst. As also listed
in Table 2, at lower pretreatment temperature such as 573 K in
a hydrogen flow looks like more reasonable for Pt/C-AA catalyst,
as slightly higher conversion (18.3%) and ee value (62.7%) were
achieved (entry 9); while the Pt/C-AA catalyst used as received
gave the lowest results (Table 2, entry 10). Although the optimiza-
tion of pretreatment method for Pt/C-AA catalyst could somewhat
improve the catalytic performance, the results were much lower
than those obtained with our home-made Pt/CMK-3-W catalyst.
Moreover, the other commercial 5 wt.% Pt/C-SA catalyst purchased
from Sigma–Aldrich was also applied as a reference. This commer-
cial Pt/C-SA catalyst furnished quite similar results to the other one
(Table 2, entry 11).
In addition, we also carried out the asymmetric hydrogenation
of ethyl pyruvate within 2 min in order to better evaluate and com-
pare the catalytic activity between different catalysts. As still listed
in Table 2 (entries 13–15), the initial activity with Pt/CMK-3-W cat-
alyst was the highest among the three Pt catalysts. It seemed that
there had an induction period for the Pt/CMK-3-W and the Pt/Al2O3
catalysts. We deduce that the good performance of Pt/CMK-3 cat-
alyst, compared with commercial Pt/C catalysts, can be partly
attributed to the periodic mesoporous structure features of CMK-3
OMCs that are advantageous to mass transport as the CMK-3 OMCs
indeed have the larger specific surface area and larger pore volume.
The smaller Pt particle size of Pt/CMK-3-W catalyst is beneficial to
higher conversion compared with Pt/C catalysts as well.
Besides the catalytic performance, the stability of Pt/CMK-3 cat-
alyst is also an important matter to consider. Hence we detected the
leached Pt atoms in the filtrate after the chiral hydrogenation in
acetic acid by the ICP-AES firstly. To our delight, only below 0.005%
Pt atoms were leached for the Pt/CMK-3-W catalyst under our con-
ditions, while for the commercial Pt/Al2O3 and Pt/C-AA catalyst, the
leached amount was up to 0.15% and 0.25%, respectively. Further-
more, the reusability of CD-chirally modified Pt/CMK-3-W, Pt/C-AA
and Pt/Al2O3 catalysts in the asymmetric hydrogenation of ethyl
pyruvate was also investigated and compared. Just as shown in
Fig. 8, the Pt/CMK-3-W catalyst can be reused for more than 5 times
without distinct loss of activity and enantioselectivity. However, for
the commercial Pt/C-AA and Pt/Al2O3 catalysts, the reusability was
poor, and the conversion was markedly decreased with reaction
runs. The mediocre reusability of Pt/Al2O3 catalyst could be mainly
owing to the Pt leaching and to the peptization of alumina support
in acidic medium. The good stability of Pt/CMK-3 catalyst might
be ascribed to that the Pt nanoparticles can be stabilized through
the ␲-donating interaction from the disordered graphene of CMK-3
OMCs [42].
3.5. Enantioselective hydrogenation of EOPB
In order to broaden the substrate scope, we also applied the
Pt/CMK-3 catalysts to the chiral hydrogenation of EOPB. It has
been discovered that (R)-(+)-ethyl-2-hydroxy-4-phenylbutyrate,

88
B. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 81–89
of higher than 5600 h−1 with 64.3% ee value was obtained on CD-
Pt/CMK-3-W
Pt/Al2O3
Pt/C-AA
(A)
100
90
80
70
60
50
40
30
20
10
0
modified Pt/CMK-3-W-423 catalyst (Table 3, entry 3). The ee values
obtained on Pt/CMK-3-W and Pt/CMK-3-W-423 catalyst were com-
parable under the same conditions, whereas a comparatively lower
ee value was achieved on Pt/CMK-3-E catalyst (Table 3, entry 2).
Of particular note is that the difference between the catalytic
activities obtained with different Pt/CMK-3 catalysts for the chi-
ral hydrogenation of EOPB can be negligible, while the difference
between the ee values achieved with Pt/CMK-3-W and Pt/CMK-3-
E catalysts was enlarged. The trend in the chiral hydrogenation of
EOPB is little different from that in the chiral hydrogenation of ethyl
pyruvate. This perhaps could be interpreted partly by the molec-
ular size of EOPB, which bears a benzene ring with comparatively
large size. The Pt/CMK-3-E catalyst has the smallest Pt particle size
of about 2.2 nm, which may be not beneficial to the co-adsorption
of CD and EOPB on its surface simultaneously, so that some EOPB
molecules were hydrogenated without participation of chiral mod-
ifier and accordingly, a little inferior ee value was afforded. In
addition, it is that the diffusion of reactants and products proba-
bly plays an important role in determining the catalytic activity in
the chiral hydrogenation of EOPB, therefore, the differences such
as metal–support interaction and catalyst surface affinity become
less important. This phenomenon is very similar to that previously
observed for Pt/Al2O3 catalyst in the same reaction [51].
1
2
3
4
5
6
Number of run
110
100
90
80
70
60
50
40
30
20
10
0
Pt/CMK-3-W
Pt/Al2O3
Pt/C-AA
(B)
The reference catalyst 5 wt.% Pt/Al2O3 also worked well in the
asymmetric hydrogenation of EOPB by modification with CD and
better results were obtained (Table 3, entry 6). The 5 wt.% Pt/C-AA
catalyst gave lower conversions of EOPB than the Pt/CMK-3 cat-
alyst did, but the ee values afforded with the two catalysts were
comparable (Table 3, entries 1 vs 4 and 5).
3.6. IR spectroscopic characterization of Pt/CMK-3 catalyst
1
2
3
4
5
6
The surface property of support material would inevitably affect
adsorption and dispersion of Pt nanoparticles on the support. As
already characterized by Raman spectroscopy, the CMK-3 carbons
mainly consist of the disordered graphene, which have plenty of ␲
electrons on the surface. Compared with CMK-3, the unsaturated
coordinated Al3+ species make the Al2O3 surface electron-deficient
[52]. In order to identify how the surface property of Pt catalyst
affect the catalytic performance, the Pt/CMK-3-W and Pt/Al2O3 cat-
alysts were further characterized by IR spectroscopy using CO as
probe molecules.
Fig. 9 shows the DRIFT spectra of CO adsorbed on Pt/CMK-3-
W and on Pt/Al2O3 catalysts at 308 K. For CO linearly adsorbed on
commercial Pt/Al2O3 catalysts, a band at 2083 cm−1 together with
a weak shoulder peak at 2050 cm−1 was observed (Fig. 9c). The IR
band at 2083 cm−1 can be attributed to CO linearly adsorbed on
Pt atoms with somewhat positive charge Pt␦+ sites derived from
the strong interaction of Pt with Al2O3, while the broad IR band
centered at 2050 cm−1 can be assigned to CO adsorbed on Pt0
atoms. Regarding CO adsorbed on Pt/CMK-3, the linearly adsorbed
CO almost disappeared after the sample was purged with helium
(Fig. 9d), although an extremely weak band at about 2060 cm−1
was observed when CO adsorption was saturated (Fig. 9b). It is sug-
gested that the adsorption of CO on the Pt/CMK-3 surface is very
weak, due to the electrostatic repulsion between CO molecules and
␲ electrons from the disordered graphene on the CMK-3 surface
with a high electron density.
Number of run
Fig. 8. Reusability of Pt/CMK-3-W, Pt/C-AA and Pt/Al2O3 catalysts in the asym-
metric hydrogenation of ethyl pyruvate in acetic acid. Reaction conditions: Pt
catalyst (0.026 mmol Pt); CD (0.034 mmol); ethyl pyruvate (21.07 mmol); acetic acid
(20 mL); H2 (4.0 MPa); RT; 5 min; 1200 rpm.
the hydrogenation product of asymmetric hydrogenation of EOPB,
can be widely used in the preparation of chiral medicine Enalapril,
which then can be used in therapy of many important symptoms
such as hypertension and myocardial infarction [50].
As acetic acid has been proved to be better solvent whereas
Pt/CMK-3-W-523 catalyst showed bad performance in the chiral
hydrogenation of ethyl pyruvate, we only applied Pt/CMK-3-W,
Pt/CMK-3-E and Pt/CMK-3-W-423 catalysts to the chiral hydro-
genation of EOPB in acetic acid. As listed in Table 3, higher than 93%
conversions were obtained within 5 min on CD-modified Pt/CMK-
3 catalysts in acetic acid (Table 3, entries 1–3). The highest TOF
Table 3
Reaction results obtained on chirally modified Pt/CMK-3 and related catalysts for
the chiral hydrogenation of EOPB.a
Entry
Catalyst
Pt size (nm)
Conv. (%)
ee (%)
1
2
3
4
5
6
Pt/CMK-3-W
Pt/CMK-3-E
Pt/CMK-3-W-423
Pt/C-AA
2.6
2.2
2.8
93.7
93.9
93.4
70.0
72.0
98.6
63.4
50.3
64.3
64.8
65.7
83.5
Compared with the commercial Pt/Al2O3 catalyst surface, the
Pt/CMK-3 catalyst surface with a high electron density would
increase feedback bonding from d orbital of Pt atoms to 2␲* orbital
of C O double bond in ethyl pyruvate, so that the C O bond energy
was decreased and accordingly the C O double band can be eas-
ily broken. As a result, the substrate can be easily activated by Pt0
atoms of Pt/CMK-3 catalyst, although the adsorption of reactant
10.3
10.3
3.5
Pt/C-AAb
Pt/Al2O3
a
Reaction conditions: 5 wt.% Pt/CMK-3, Pt/C or Pt/Al2O3 catalyst (0.026 mmol Pt)
pretreated at 673 K; CD (0.034 mmol); EOPB (5.29 mmol); acetic acid (20 mL); H2
(4.0 MPa); RT; 1200 rpm; 5 min, and the configuration of product is R.
b
The catalyst was pretreated in a hydrogen flow at 573 K for 2 h.

B. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 81–89
89
that the stability of Pt/CMK-3 catalyst was higher than the commer-
cial Pt/Al2O3 and Pt/C catalysts and Pt/CMK-3 catalyst also afforded
comparable ethyl pyruvate conversion with Pt/Al2O3 catalyst.
2083
Acknowledgements
2050
This work was supported by the NSFC (20703018) and Shanghai
Leading Academic Discipline Project (B409). The authors thank Mr.
Zhen Liu for his help in Raman spectrum measurements.
2060
a
References
[1] T. Burgi, A. Baiker, Acc. Chem. Res. 37 (2004) 909.
[2] M. Studer, H.U. Blaser, C. Exner, Adv. Synth. Catal. 345 (2003) 45.
[3] M. Bartok, Curr. Org. Chem. 10 (2006) 1533.
[4] M. Studer, S. Burkhardt, H.U. Blaser, Chem. Commun. (1999) 1727.
[5] A. Baiker, Catal. Today 100 (2005) 159.
b
[6] D.Y. Murzin, P. Maki-Arvela, E. Toukoniitty, T. Salmi, Catal. Rev.: Sci. Eng. 47
(2005) 175.
[7] G.J. Hutchings, Annu. Rev. Mater. Res. 35 (2005) 143.
[8] T. Mallat, E. Orglmeister, A. Baiker, Chem. Rev. 107 (2007) 4863.
[9] Y. Orito, S. Imai, S. Niwa, Preprints of the 43rd Catalysis Forum (Japan, 1978),
1978, p. 130.
[10] Y. Orito, S. Imai, S. Niwa, J. Chem. Soc. Jpn. 8 (1979) 1118.
[11] Y. Orito, S. Imai, S. Niwa, J. Chem. Soc. Jpn. 1 (1982) 137.
[12] B. Torok, K. Felfoldi, G. Szakonyi, K. Balazsik, M. Bartok, Catal. Lett. 52 (1998)
81.
c
d
[13] B. Torok, K. Balazsik, M. Torok, Gy. Szollosi, M. Bartok, Ultrason. Sonochem. 7
(2000) 151.
[14] M. Bartok, K. Balazsik, G. Szollosi, T. Bartok, J. Catal. 205 (2002) 168.
[15] S.P. Griffiths, P. Johnston, P.B. Wells, Appl. Catal. A: Gen. 191 (2000) 193.
[16] B. Torok, G. Szollosi, K. Balazsik, K. Felfoldi, I. Kun, M. Bartok, Ultrason.
Sonochem. 6 (1999) 97.
2080
2000
Wavenumber (cm-1)
[17] M.Y. Kim, S.B. Jung, M.G. Kim, Y.S. You, J.H. Park, C.H. Shin, G. Seo, Catal. Lett.
129 (2009) 194.
[18] S. Basu, M. Mapa, C.S. Gopinath, M. Doble, S. Bhaduri, G.K. Lahiri, J. Catal. 239
(2006) 154.
Fig. 9. DRIFT spectra of CO adsorbed on (a) Pt/Al2O3 catalyst, CO saturated; (b)
Pt/CMK-3-W catalyst, CO saturated; (c) Pt/Al2O3 catalyst, He purged; (d) Pt/CMK-3-
W catalyst, He purged.
[19] U. Bohmer, F. Franke, K. Morgenschweis, T. Beiber, W. Reschitilowski, Catal.
Today 60 (2000) 167.
[20] X. Li, Y. Shen, R. Xing, Y. Liu, H. Wu, M. He, P. Wu, Catal. Lett. 122 (2008) 325.
[21] X. Li, Ph.D Thesis, School of Graduate Students, Chinese Academy of Sciences,
(2004).
[22] Y. Orito, S. Imai, S. Niwa, G.H. Nguyen, J. Synth. Org. Chem. Jpn. 37 (1979) 173.
[23] M. Fraga, M. Mendes, E. Jordao, J. Mol. Catal. A: Chem. 179 (2002) 243.
[24] A. Perosa, P. Tundo, M. Selva, J. Mol. Catal. A: Chem. 180 (2002) 169.
[25] J.T. Wehrli, A. Baiker, D.M. Monti, H.U. Blaser, H.P. Jalett, J. Mol. Catal. 57 (1989)
245.
[26] L. Xing, F. Du, J. Liang, Y. Chen, Q. Zhou, J. Mol. Catal. A: Chem. 276 (2007) 191.
[27] G. Szollosi, Z. Nemeth, K. Hernadi, M. Bartok, Catal. Lett. 132 (2009) 370.
[28] G. Farkas, L. Hegedus, A. Tungler, T. Mathe, J. Figueiredo, M. Freitas, J. Mol. Catal.
A: Chem. 153 (2000) 215.
[29] E. Sipos, G. Fogassy, A. Tungler, P. Samant, J. Figueiredo, J. Mol. Catal. A: Chem.
212 (2004) 245.
[30] T. Tarnai, A. Tungler, T. Mathe, J. Petro, R.A. Sheldon, G. Toth, J. Mol. Catal. A:
Chem. 102 (1995) 41.
[31] E. Sipos, A. Tungler, I. Bitter, React. Kinet. Catal. Lett. 79 (2003) 101.
[32] R. Ryoo, S.H. Joo, M. Kruk, M. Jaroniec, Adv. Mater. 13 (2001) 677.
[33] R. Ryoo, S.H. Joo, Stud. Surf. Sci. Catal. 148 (2004) 241.
[34] J. Lee, S. Han, T. Hyeon, J. Mater. Chem. 14 (2004) 478.
[35] T. Ohkubo, J. Miyawaki, K. Kaneko, R. Ryoo, N.A. Seaton, J. Phys. Chem. B 106
(2002) 6523.
may be weakened due to the repulsive interaction of Pt/CMK-3
surface with a high electron density. Furthermore, Pt/CMK-3 cat-
alysts with ordered mesoporous structure also had high specific
surface area, adequate pore volume and small Pt particle size with
high dispersion, which enables easy mass transport, hence compa-
rable conversion in the chiral hydrogenation of ethyl pyruvate can
be achieved on CD-modified Pt/CMK-3 catalysts. Additionally, the
weak interaction of CO with Pt/CMK-3 catalyst can also deduce that
CD was also weakly adsorbed on the catalyst surface because the
high electron density from the disordered graphene of Pt/CMK-3
surface maybe hinders the adsorption of quinoline moiety of CD
through the ␲ interaction. Therefore, lower ee values were fur-
nished by CD-modified Pt/CMK-3 catalysts. Nevertheless, the high
electron density of CMK-3 support can also result in the strong ␲
donating interaction to stabilize the Pt nanoparticles, as a result,
only trace amount of Pt atoms were leached into the solution and
the Pt/CMK-3-W catalyst showed good reusability.
[36] L. Li, Z.H. Zhu, G.Q. Lu, Z.F. Yan, S.Z. Qiao, Carbon 45 (2007) 11.
[37] D. Su, J. Delgado, X. Liu, D. Wang, R. Schlogl, L. Wang, Z. Zhang, Z. Shan, F. Xiao,
Chem. Asian J. 4 (2009) 1108.
4. Conclusion
[38] J. Lee, S. Yoon, T. Hyeon, S.M. Oh, K.B. Kim, Chem. Commun. (1999) 2177.
[39] M. Kang, S.H. Yi, H.I. Lee, J.E. Yie, J.M. Kim, Chem. Commun. (2002) 1944.
[40] M. Choi, R. Ryoo, Nat. Mater. 2 (2003) 473.
[41] S. Jun, S. Joo, R. Ryoo, M. Kruk, J. Am. Chem. Soc. 122 (2000) 10712.
[42] R. Xing, Y. Liu, Y. Wang, L. Chen, H. Wu, Y. Jiang, M. He, P. Wu, Micropor. Mesopor.
Mater. 105 (2007) 41.
[43] M.S. Dresselhaus, A. Jorio, M. Hofmann, G. Dresselhaus, R. Saito, Nano Lett. 10
(2010) 751.
[44] Z. Ma, F. Zaera, J. Phys. Chem. B 109 (2005) 406.
[45] M. Arx, T. Burgi, T. Mallat, A. Baiker, Chem. Eur. J. 8 (2002) 1430.
[46] M. Minder, T. Mallat, P. Skrabal, A. Baiker, Catal. Lett. 29 (1994) 115.
[47] D. Ferri, T. Burgi, K. Borszeky, T. Mallat, J. Catal. 193 (2000) 139.
[48] D. Radivojevic, K. Seshan, L. Lefferts, Appl. Catal. A: Gen. 301 (2006) 51.
[49] E. Schmidt, A. Vargas, T. Mallat, A. Baiker, J. Am. Chem. Soc. 131 (2009) 12358.
[50] M.R. Attwood, C.H. Hassall, A. Krohn, G. Lawton, S. Redshaw, J. Chem. Soc. Perkin
Trans. I (1986) 1011.
5 wt.% Pt/CMK-3 catalysts were prepared via a facile impreg-
nation method using H2PtCl6 dissolved in different media as
Pt precursors. After chirally modified with cinchona alkaloids,
Pt/CMK-3 catalysts proved to be active and enantioselective for the
enantioselective hydrogenation of ␣-ketoesters under mild con-
ditions. The initial activity of higher than 23,000 h−1 TOF and up
to 82% ee were obtained with CD-modified Pt/CMK-3 catalysts for
the chiral hydrogenation of ethyl pyruvate. With regard to the
asymmetric hydrogenation of ethyl 2-oxo-4-phenylbutyrate, the
highest TOF of 5615 h−1and 64% ee were afforded. To the best of
our knowledge, the results achieved in this study with Pt/CMK-3
catalyst are the best ones among those obtained with Pt catalysts
supported on carbon materials, including activated carbon, carbon
nanotubes and ordered mesoporous carbons. Of particular note is
[51] X. Li, X. You, P. Ying, J. Xiao, C. Li, Top. Catal. 25 (2003) 63.
[52] V.M. Bermudez, J. Phys. Chem. C 113 (2009) 1917.