Ordered mesoporous carbons with Ia3d symmetry supported Pt catalyst for efficient asymmetric hydrogenation

Article abstract of DOI:10.1007/s10562-012-0843-z

Pt nanoparticles supported on CMK-8 ordered mesoporous carbons (OMCs) with Ia3d symmetry after chirally modified with cinchonidine (CD) proved to be highly efficient for asymmetric hydrogenation of α-ketoesters. Up to 34,819 h^-1 TOF with 75 % ee was furnished for the enantioselective hydrogenation of ethyl 2-oxo-4-phenylbutyrate with CD-modified Pt/CMK-8 catalyst. To the best of our knowledge, these results obtained with chirally modified Pt/CMK-8 catalyst are the best ones among those with Pt catalysts supported on carbon materials. It is suggested that both the physical structure features ofCMK-8 OMCs and the chemical nature of Pt catalyst are beneficial for the asymmetric hydrogenation.

Full text of DOI:10.1007/s10562-012-0843-z

Catal Lett (2012) 142:1033–1039
DOI 10.1007/s10562-012-0843-z
Ordered Mesoporous Carbons with Ia3d Symmetry Supported Pt
Catalyst for Efficient Asymmetric Hydrogenation
•
Bo Li Xiaohong Li Yue Ding Peng Wu
•
•
Received: 10 February 2012 / Accepted: 10 May 2012 / Published online: 30 May 2012
Ó Springer Science+Business Media, LLC 2012
Abstract Pt nanoparticles supported on CMK-8 ordered
mesoporous carbons (OMCs) with Ia3d symmetry after
chirally modified with cinchonidine (CD) proved to be
highly efficient for asymmetric hydrogenation of a-keto-
esters. Up to 34,819 h-1 TOF with 75 % ee was furnished
for the enantioselective hydrogenation of ethyl 2-oxo-4-
phenylbutyrate with CD-modified Pt/CMK-8 catalyst. To
the best of our knowledge, these results obtained with chi-
rally modified Pt/CMK-8 catalyst are the best ones among
those with Pt catalysts supported on carbon materials. It is
suggested that both the physical structure features of CMK-8
OMCs and the chemical nature of Pt catalyst are beneficial
for the asymmetric hydrogenation.
(CNTs) [6, 7], etc. have been used to support Pt nanopar-
ticles for this reaction. Nevertheless, most of supported Pt
catalysts showed inferior results to the commercial
Pt/Al2O3 catalysts [1]. A few exceptions arose recently. The
Pt nanoparticles confined in the mesoporous alumina
composites Al2O3@SBA-15 and the Pt nanocatalyst
encapsulated within CNTs showed superior performance in
the enantioselective hydrogenation of a-ketoesters than the
well-known Pt/Al2O3 under the same reaction conditions
[5, 7].
Ordered mesoporous carbons (OMCs) have attracted
much attention since their discovery due to periodic mes-
opores, uniform pore size, high surface areas, adequate
pore volume and high thermal, chemical and mechanical
stabilities [8, 9]. Among the OMCs families, CMK-3
OMCs with P6mm symmetry are widely known and used
[10]. CMK-8 OMCs with Ia3d symmetry are another kind
of OMCs synthesized using KIT-6 silica matrix with Ia3d
symmetry as hard templates, sucrose as carbon source and
sulfuric acid as carbonization catalyst using a nano-casting
route [11, 12]. Since the synthesis of CMK-8 OMCs, they
have been used as hard templates to synthesize nano-
structured materials, such as SiCN, SiN3, ordered meso-
porous alumina and ordered mesoporous magnesium oxide,
etc. [13–15]. Due to the structural features including three-
dimensional cubic structure, large pore volume and wall
thickness of the framework, CMK-8 OMCs have better
adsorption characteristics compared with the CMK-3 ana-
logues [16]. Hence, the mass transportation is anticipated
easier if a reaction occurs with a CMK-8 OMCs-based
catalyst.
Keywords Asymmetric hydrogenation Á Supported Pt
catalyst Á Ordered mesoporous carbons Á Ethyl pyruvate Á
Ethyl 2-oxo-4-phenylbutyrate
1 Introduction
Enantioselective hydrogenation of a-functionalized ketones
has received great attention in the past decades. Important
information has been collected since the first report by Orito
and co-workers [1–3] about the enantioselective hydroge-
nation of pyruvate esters on supported Pt catalysts after
chirally modified with cinchona alkaloids. With the devel-
opment of porous materials, FDU-14 mesopolymers [4],
mesoporous alumina composites [5] and carbon nanotubes
B. Li Á X. Li (&) Á Y. Ding Á P. Wu
Encouraged by our previous achievements in CMK-3
OMCs entrapped Pt nanoparticles, which showed remark-
able performance in the enantioselective hydrogenation of
ethyl pyruvate [17], we are motivated to investigate the
Shanghai Key Laboratory of Green Chemistry and Chemical
Processes, Department of Chemistry, East China Normal
University, 3663 North Zhongshan Rd, Shanghai 200062, China
e-mail: xhli@chem.ecnu.edu.cn
123

1034
B. Li et al.
H
different Pt loadings were prepared mainly according to Ref.
[4]: CMK-8 was impregnated with a solution containing
H2PtCl6 and stirred for 4–6 h. Then the mixture was evap-
orated to remove excess solvent, followed by a drying at
353 K overnight. Subsequently, the catalyst precursor
was reduced in an aqueous solution of sodium for-
mate. According to diffusion medium of Pt precursor, the
Pt/CMK-8 catalysts were denoted as Pt/CMK-8-W/E, where
W represents water and E represents ethanol, respectively.
The X-ray diffraction (XRD) patterns of samples were
collected on a Bruker D8 ADVANCE instrument using Cu-
Ka radiation. The nitrogen sorption isotherms were mea-
sured at 77 K on a Quantachrome Autosorb-3B system
after the samples were evacuated at 373 K for 10 h. The
BET specific surface area was calculated 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-8 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 electromicroscopy with an
acceleration voltage of 200 kV.
O
O
H
N
Pt/CMK-8
Cinchonidine, H2
O
O
H
C
N
OH
O
OH
(R)-(+)-ethyl lactate
ethyl pyruvate
Cinchonidine
O
O
O
Pt/CMK-8
O
Cinchonidine, H2
OH
O
(R)-(+)-ethyl 2-hydroxy-4-
phenylbutyrate
ethyl 2-oxo-4-phenylbutyrate
(EOPB)
((R)-(+)-EHPB)
Scheme 1 Enantioselective hydrogenation of a-ketoesters on
CD-modified Pt/CMK-8 catalysts
asymmetric hydrogenation of a-ketoesters with Pt/CMK-8
catalyst (Scheme 1). We expected Pt/CMK-8 catalyst after
chirally modified with cinchonidine (CD) would show
superior performance especially towards the asymmetric
hydrogenation of ethyl 2-oxo-4-phenylbutyrate (EOPB)
that bears a benzene ring with relatively large molecular
size. To our delight, the CD-modified Pt/CMK-8 catalyst
furnished a TOF over 34,000 h-1 with 75 % ee for the
enantioselective hydrogenation of EOPB. To the best of
our knowledge, these results are the best ones about the
asymmetric hydrogenation of EOPB among those with the
Pt catalysts supported on carbon materials until now.
CO chemisorption of samples was measured at 308 K
on a Quantachrome 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 dis-
persion 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 9 10-20 m2
and a stoichiometric factor of one, using nominal platinum
concentrations. The Pt content of catalysts or the leached
amount of Pt atoms into solution was measured or detected
with a Thermo Elemental IRIS Intrepid II XSP inductively
coupled plasma-atomic emission spectroscopy (ICP-AES).
The surface electronic state of Pt was examined using
X-ray photoelectron spectroscopy (XPS) measurements
with a Thermo Fisher Scientific ESCALAB 250 spec-
trometer with Al-Ka radiation (1486.6 eV) as incident
beam with a monochromator
2 Experimental
2.1 Catalyst Preparation and Characterization
The procedures for preparing Pt/CMK-8 catalyst are
graphically illustrated in Fig. 1. The CMK-8 OMCs were
synthesized using KIT-6 silica matrix with Ia3d symmetry
as hard templates, sucrose as carbon source and sulfuric acid
as carbonization catalyst using a nano-casting route
according to Refs. [11, 12]. The Pt/CMK-8 catalysts with
Fig. 1 Schematic illustration
for preparation of Pt/CMK-8
catalyst
123

Chiral Hydrogenation on Ordered Mesoporous Carbons Supported Pt Catalysts
1035
Fig. 2 Low-angle XRD
patterns of Pt/CMK-8 catalysts
and Raman spectrum of CMK-8
recorded with a 632.8 nm laser
(inset)
a KIT-6
D band
1332
(211)
G band
1594
b CMK-8
c Pt/CMK-8-W
d Pt/CMK-8-E
2650 2914
(220)
500
1000
1500
2000
2500
3000
3500
Raman shift (cm-1)
(420)
b
c
d
a
1
2
3
4
5
2 Theta (degree)
2.2 Catalytic Tests
Similar to that of CMK-3 OMCs [17], the Raman spectrum
of CMK-8 OMCs was also dominated by the G and D
bands at 1,594 and 1,332 cm-1 respectively, together with
two broad and weak bands centered at 2,650 and
2,914 cm-1 (inset of Fig. 2). This indicates that the CMK-8
OMCs are also composed of disordered graphene and small
amount of amorphous carbon.
For a standard reaction, 0.1 g 5 wt% Pt/CMK-8 catalyst was
pretreated in a hydrogen flow at 673 K for 2 h before use.
The catalyst was then mixed with a certain amount of CD,
21.07 mmol ethyl pyruvate or 26.45 mmol EOPB, 20 ml
acetic acid and transferred to a 100 ml autoclave with stir-
ring. The hydrogenation reaction began at room temperature
after hydrogen was introduced into the autoclave. The
reaction was stopped after a period and then the products
were analyzed by GC-FID (GC 2014, Shimadzu) equipped
with a capillary chiral column (HP19091G-B213, Agilent).
The optical yield was expressed as ee value: ee (%) =
([R] - [S])/([R] ? [S]) 9 100.
The Pt particle size was firstly characterized using the
wide-angle XRD (Fig. 4). All the samples did not show
distinct diffraction peaks assignable to Pt crystalline
planes, demonstrating that the Pt nanoparticles were uni-
formly dispersed and did not aggregate to form large par-
ticles. The TEM images in Fig. 5 also confirmed that the Pt
particles were uniformly dispersed. The Pt particle size and
dispersion were also calculated according to the CO
chemisorption. Consistent with the wide-angle XRD and
TEM characterizations, the mean Pt particle size for the Pt/
CMK-8-W and Pt/CMK-8-E catalysts was 2.3 and 4.2 nm,
respectively.
3 Results and Discussion
3.1 Catalyst Preparation and Characterization
The procedures for preparing CMK-8 supported Pt cata-
lysts are graphically illustrated in Fig. 1. The well ordered
mesoporous structure with Ia3d symmetry of CMK-8
OMCs was still maintained even after loaded with Pt
nanoparticles, which was confirmed by the low-angle XRD
patterns and nitrogen adsorption–desorption isotherms of
Pt/CMK-8 catalysts (Figs. 2, 3). As listed in Table 1, the
specific surface areas for Pt/CMK-8 catalysts ranged from
1,233 to 1,318 m2 g-1. To obtain further information on
the CMK-8 structure, Raman spectroscopy was carried out.
3.2 Enantioselective Hydrogenation of a-Ketoesters
Based on the findings in the enantioselective hydrogenation
of a-ketoesters with Pt/CMK-3 catalysts [17], we firstly
carried out the asymmetric hydrogenation of ethyl pyruvate
with CD modified 5 wt% Pt/CMK-8 catalysts. As also
listed in Table 1, 97.8 % conversion with 74.7 % ee of
(R)-(?)-ethyl lactate was afforded with CD-modified
5 wt% Pt/CMK-8-W catalyst (Table 1, entry 2). With
regard to the same reaction with 5 wt% Pt/CMK-8-E
123

1036
B. Li et al.
Fig. 3 N2 sorption isotherms
and pore size distribution
of Pt/CMK-8 catalysts
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
1000
900
800
700
600
500
400
300
200
100
0
2
8
10
Pore4diame6ter (nm)
KIT-6
CMK-8
Pt/CMK-8-W
Pt/CMK-8-E
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (P/P0)
Table 1 Relevant parameters of Pt/CMK-8 catalysts and the related samples and the results obtained on chirally modified Pt catalysts for the
enantioselective hydrogenation of ethyl pyruvate
Entry
Catalyst
Pt content
(wt%)
SBET
(m2/g)
Pore size
(nm)
Pore volume
(cm3/g)
Pt diameter
(nm)
Pt dispersion
(%)
Conv.
(%)
ee (%)
1
2
3
4
5
CMK-8
–
1364
1318
1233
892
3.5
3.7
1.50
1.43
1.40
1.07
0.9
–
–
0
0
5 wt% Pt/CMK-8-W
5 wt% Pt/CMK-8-E
5 wt% Pt/Ca
3.7
nmc
4.0
3.7
2.3
4.2
10.3
3.5
48.8
27.5
11
97.8
67.5
16.8b
98.6b
74.7
53
3.5
3.8
56.3
92.6
5 wt% Pt/Al2Oa3
147
18.4
32.8
Reaction conditions: Pt catalyst (0.026 mmol Pt), CD (0.034 mmol), ethyl pyruvate (21.07 mmol), acetic acid (20 ml), H2 (4 MPa), 1,000 rpm,
RT, 5 min and the main configuration of product is R
a
Purchased from Alfa Aesar and pretreated in a hydrogen flow at 673 K for 2 h before use
b
The results are quoted from Ref. [17]
c
Not measured
catalyst, 67.5 % conversion with 53 % ee was achieved
under the same conditions (Table 1, entry 3).
5 wt% Pt/C catalyst, which afforded only 16.8 % conver-
sion and 56.3 % ee (Table 1, entry 4). Hence, it is sug-
gested that the large pore volume of CMK-8 OMCs is
beneficial for the mass transfer.
The activity of 5 wt% Pt/CMK-8-W catalyst for the
enantioselective hydrogenation of ethyl pyruvate was
higher than that of 5 wt% Pt/CMK-3-W catalyst, which
had the similar Pt particle size and gave 81 % conversion
with 82.2 % ee under the same conditions [17]. We also
compared the performance of 5 wt% Pt/CMK-8 catalysts
with that of the commercial 5 wt% Pt/Al2O3 and 5 wt%
Pt/C catalysts in the asymmetric hydrogenation of ethyl
pyruvate. Although the ee value obtained with 5 wt%
Pt/CMK-8-W catalyst was slightly lower than that with
5 wt% Pt/Al2O3 catalyst, the conversions were comparable
under the same conditions (Table 1, entry 5). Additionally,
the 5 wt% Pt/CMK-8 catalysts were much more active than
In order to broaden the substrate scope, EOPB bearing a
benzene ring with relatively large molecular size was taken
as the other substrate. As listed in Table 2, the 5 wt%
Pt/CMK-8-W catalyst furnished 93.4 % conversion and
75 % ee of (R)-(?)-EHPB under our conditions (Table 2,
entry 1). The 5 wt% Pt/CMK-8-E catalyst gave 54.2 %
conversion with 46.5 % ee (Table 2, entry 2). The com-
mercial 5 wt% Pt/Al2O3 catalyst furnished 83.2 % con-
version with 83.5 % ee (Table 2, entry 3). In terms of
EOPB conversion under the same conditions, the 5 wt% Pt/
CMK-8-W catalyst is even superior to the 5 wt% Pt/Al2O3
123

Chiral Hydrogenation on Ordered Mesoporous Carbons Supported Pt Catalysts
1037
Table 2 Reaction results obtained on chirally modified Pt/CMK-8
catalysts and related Pt catalysts for the chiral hydrogenation of
EOPB
Entry
Catalyst
Pt particle
size (nm)
Conv.
(%)
ee (%)
Pt/CMK-8-E
Pt/CMK-8-W
1
2
3
4
5 wt% Pt/CMK-8-W
5 wt% Pt/CMK-8-E
5 wt% Pt/Al2Oa3
5 wt% Pt/Ca
2.3
4.2
93.4
54.2
83.2
19.7
75
46.5
83.5
73.4
3.5
10.3
Reaction conditions: Pt catalyst (0.026 mmol Pt); CD (0.034 mmol);
EOPB (26.45 mmol); acetic acid (20 ml); H2 (4 MPa); 1,000 rpm;
RT; 5 min and the main configuration of product is R
CMK-8
a
Purchased from Alfa Aesar and pretreated in a hydrogen flow at
673 K for 2 h before use
30
40
50
60
70
80
2 theta (degree)
Fig. 4 Wide-angle XRD patterns of Pt/CMK-8 catalysts
Table 3 Optimization of reaction parameters for the chiral hydro-
genation of EOPB with chirally modified Pt/CMK-8-W catalysts
Entry
Pt loading
(wt%)
CD amount
(mmol)
Time
(min)
Conv.
(%)
ee (%)
1
2
3
4
5
6
5
5
0
5
5
5
2
5
5
3.8
92.2
75.6
41.2
39.6
94.0
0
0.017
0.051
0.034
0.034
0.034
74.5
75.4
75.5
70.0
75.5
5
5
3
10
Reaction conditions: Pt catalyst (0.026 mmol Pt); EOPB
(26.45 mmol); acetic acid (20 ml); H2 (4 MPa); 1,000 rpm; RT and
the main configuration of product is R
seires of experiments were carried out. The effect of Pt
loading, reaction time and CD amount on the catalytic
performance was investigated in detail. The 3 and 10 wt%
Pt/CMK-8-W catalysts were prepared and investigated in
the chiral hydrogenation of EOPB. The 3 wt% Pt/CMK-8-
W catalyst gave 39.6 % EOPB conversion with 70 % ee
value (Table 3, entry 5), while the 10 wt% Pt catalyst
furnished 94 % conversion with 75.5 % ee value (Table 3,
entry 6). The conversion and ee value were greatly
increased when the Pt loading reached 5 wt% compared
with those obtained with 3 wt% Pt/CMK-8-W catalyst.
However, there was no obvious increase in both activity
and enantioselectivity if the Pt loading was further
increased from 5 to 10 wt%. The chiral hydrogenation of
EOPB with 5 wt% Pt/CMK-8-W catalyst was also per-
formed within 2 min. A 41.2 % conversion of EOPB with
75.5 % ee value was obtained (Table 3, entry 4). Addi-
tionally, the CD amount was also varied and as a result,
10 mg CD was the optimal dosage.
Fig. 5 TEM images of a Pt/CMK-8-W catalyst and b Pt/CMK-8-E
catalyst
catalyst although the enantioselectivity is slightly lower. As
for the commercial 5 wt% Pt/C catalyst, the lowest activity
of 19.7 % conversion was obtained with 73.4 % ee
(Table 2, entry 4).
To optimize the reaction parameters for the chiral
hydrogenation of EOPB with Pt/CMK-8-W catalyst, a
Among these catalysts, the 5 wt% Pt/CMK-8-W catalyst
afforded the highest activity, resulting in a TOF of
123

1038
B. Li et al.
34,819 h-1 based on the EOPB conversion within 2 min
and the exact Pt content of 3.7 wt%. Of particular note is
that the 5 wt% Pt/CMK-8-W catalyst is even more active
than the Pt nanocatalyst confined within CNTs, which
afforded higher than 20,000 h-1 TOF for the same reaction
under the similar conditions [7]. The high activity of
Pt/CMK-8-W catalyst might be mainly attributed to that
the three-dimensional mesostructure with adequate pore
volume is helpful for the asymmetric hydrogenation.
Although the ee value achieved with the 5 wt% Pt/CMK-
8-W catalyst for the chiral hydrogenation of ethyl pyruavate
and EOPB was a little lower, the catalytic activity of 5 wt%
Pt/CMK-8-W catalyst was comparable with or even higher
than the commercial 5 wt% Pt/Al2O3 catalyst. In order to
identify how the Pt catalyst surface property affects the cat-
alytic performance, the 5 wt% Pt/CMK-8-W catalyst was
further characterized by XPS (Fig. 6). There are two
Pt species for the 5 wt% Pt/CMK-8-W catalyst deduced from
the deconvoluted Pt4f peaks (Fig. 6a). The one is Pt2? spe-
cies (the peaks of 4f7/2 = 73.4 eV, 4f5/2 = 76.8 eV), which
is originated from re-oxidation of Pt when exposed to air. For
the other Pt species, the Pt 4f7/2 and 4f5/2 peaks are observed
at 72 and 75.3 eV and these values are shifted to higher
binding energy compared with Pt0 species (the peaks of 4f7/2
= 71.2 eV, 4f5/2 = 74.5 eV) [18]. This result indicates that
electrons are donated from Pt to CMK-8 OMCs support and
Pt exists as Ptd?. Compared with the commercial Pt/alumina
catalyst, which has Ptd? and Pt0 species deduced from the
diffuse reflectance infrared fourier transform spectroscopic
studies using CO as a probe molecule, the dominant Ptd?
species for the home-made Pt/CMK-8-W are beneficial for
the activation of carbonyl groups, so that higher activity was
achieved with Pt/CMK-8 catalyst [17, 19].
a
Pt4f
72.0
75.3
200
73.4
76.8
84
81
78
75
72
69
66
Binding Energy (eV)
b
C1s
284.7
285.0
10000
286.1
288.8
291.1
291
297
294
288
285
282
Binding Energy (eV)
Fig. 6 XPS spectra for a Pt4f and b C1s regions of 5 wt% Pt/CMK-8-W
catalyst
The XPS analysis of C1s region indicated that the
CMK-8 OMCs are mainly composed of disordered graph-
ene. For the sp2-C, the C1s peak is observed at 284.7 eV.
Besides the sp2-C, there still exist sp3-C (285 eV), oxygen
containing C groups (286.1 and 288.8 eV). The results
match well with the Raman characterization. This deduced
that the high electron density of Pt/CMK-8 catalyst surface
probably inhibits the adsorption of CD by quinoline moiety
via the p interaction. As a result, slightly lower ee values
were induced by CD-modified Pt/CMK-8 catalyst.
with the fresh catalyst, whereas 82.8 % conversion of ethyl
pyruvate was achieved in the fourth run (Fig. 7a). The
enantioselectivity was maintained during the reuse since
the fresh CD was added to each run.
By comparison, the reusability of Pt/CMK-8-W catalyst
towards the enantioselective hydrogenation of EOPB is a
little poor although the enantioselectivity was maintained
(Fig. 7b). The fresh catalyst gave 93.4 % conversion of
EOPB, while the second run afforded 79 % conversion.
The third and the fourth runs only gave 58.7 and 48 %
conversion, respectively.
3.3 The Reusability of Pt/CMK-8 Catalyst
In order to make clear why EOPB conversion decreased
dramatically during the reuse processes, the ICP-AES was
carried out to detect the leached Pt atoms in the filtrate. As
a result, about 7.8 % of Pt atoms were leached into the
solution during the first run of EOPB hydrogenation, which
is nearly eight times higher than that in the enantioselective
hydrogenation of ethyl pyruvate with the same catalyst. We
deduce that the d–p conjugation interaction between Pt
The reusability of Pt/CMK-8 catalyst is also an important
matter to consider, so we also investigated the reusabil-
ity of CD-modified Pt/CMK-8-W catalyst in detail. The
Pt/CMK-8-W catalyst can be reused for almost 4 times for
the enantioselective hydrogenation of ethyl pyruvate,
although the conversion was gradually decreased with
reaction runs. As a result, 97.8 % conversion was obtained
123

Chiral Hydrogenation on Ordered Mesoporous Carbons Supported Pt Catalysts
1039
ethyl pyruvate and EOPB under the mild conditions. The
Pt/CMK-8 catalyst can also be reused for several times
without significant loss of activity and enantioselectivity
under the optimal conditions. Furthermore, the Pt/CMK-8
catalyst is much more active than the commercial Pt/C
catalyst and even shows higher activity than the commer-
cial Pt/Al2O3 catalyst in the chiral hydrogenation of EOPB.
Of particular note is that the TOF higher than 34,000 h-1
and 75 % ee were achieved in the enantioselective hydro-
genation of EOPB. To the best of our knowledge, these
results with Pt/CMK-8 catalyst are the best ones among
those obtained with Pt catalysts supported on carbon
materials, including activated carbon, CNTs and OMCs.
conversion
ee
a 100
80
60
40
20
0
1
2
3
4
Number of run
Acknowledgments This work was supported by the National Nat-
ural Science Foundation of China (20703018) and Shanghai Leading
Academic Discipline Project (B409).
100
b
conversion
ee
80
60
40
20
0
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atoms and benzene ring of EOPB makes Pt atoms easier to
dissolve in the solution. Since the leached Pt can not be
ignored in this case, the separation and recovery of leached
Pt should be paid much attention, particularly considering
that the enantioselective reactions are mainly employed in
Pharma industry. To the best of our knowledge, there are
two main solutions about the leached Pt. The leached Pt
can be recovered using an ion exchange resin scavenger
such as DOWEX M-43 [20]. Alternatively, the leached Pt
can be recovered as diammonium hexachloroplatinate by
precipitation using ammonium chloride [21].
19. Li X, You X, Ying P, Xiao J, Li C (2003) Top Catal 25:63
20. http://www.dowwaterandprocess.com/products/periodic_table/pt_
pt_pd.htm. Accessed Feb 1999
21. Barakat MA, Mahmoud MHH (2004) Hydrometallurgy 72:179
4 Conclusions
The CD-modified Pt/CMK-8 catalyst proved to be highly
active and enantioselective for the chiral hydrogenation of
123