In-situ ATR-IR investigation of methylcinnamic acid adsorption and hydrogenation on Pd/Al2O3

Article abstract of DOI:10.1016/j.catcom.2011.09.040

The adsorption and hydrogenation of C = C in α-methylcinnamic acid in dichloromethane over the concentration range 2-16 mM have been studied on Al₂O₃ and Pd/Al₂O₃ using in-situ attenuated total reflection infrar

Full text of DOI:10.1016/j.catcom.2011.09.040

Catalysis Communications 17 (2012) 13–17
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
In-situ ATR-IR investigation of methylcinnamic acid adsorption and hydrogenation
on Pd/Al O3
2
Xiaojing Sun, Christopher T. Williams ⁎
Department of Chemical Engineering and NanoCenter, Swearingen Engineering Center, University of South Carolina, Columbia, SC 29208, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 July 2011
Received in revised form 27 September 2011
Accepted 30 September 2011
Available online 7 October 2011
The adsorption and hydrogenation of C=C in α-methylcinnamic acid in dichloromethane over the concen-
tration range 2–16 mM have been studied on Al
2
O
3
and Pd/Al
, the spectra reveal that the acid adsorbs both molecularly and
only the latter is observed. In the case of molecular adsorption,
2 3
O using in-situ attenuated total reflection
infrared (ATR-IR) spectroscopy. For Al
dissociatively, while for 1 wt.% Pd/Al
2
O
3
2
O
3
−
1
−1
C=O stretching vibrations arising from adsorbed monomer (1710 cm ) and dimer (1684 cm ) species
−
1
were observed. In the case of dissociatively adsorbed carboxylate, the typical asymmetric (1522 cm ) and
Keywords:
Enantioselective hydrogenation
α-methylcinnamic acid
symmetric (1378 cm− ) vibrations are observed. No changes in adsorbed species were observed in the
1
2 2 3
presence of solution-phase H over alumina, whereas significant changes occurred for Pd/Al O . While
2
Pd/γ-Al O
3
bands associated with monomer/dimer and carboxylate species still persist on the surface in the presence
ATR-IR
Heterogeneous catalyst
of H , new vibrational features associated with adsorbed product (i.e., α-methylhydrocinnamic acid) are
detected. The results demonstrate that the product is strongly adsorbed under hydrogenation conditions,
2
which likely influences the catalytic performance of this system.
©
2011 Elsevier B.V. All rights reserved.
1
. Introduction
the hydrogenation of prochiral C_O bonds. In contrast, chiral C_C
bond hydrogenation with these catalysts has been less successful. The
first study was apparently published in 1985, and involved prochiral
cinnamic acid hydrogenation over Pd/C catalysts [3]. Largely over
the past decade, there have been a number of studies [4–28] that
have followed up on this initial work. The groups of Nitta [4–14], Bartok
[15–18], and Baiker [19–28] have been the most active with the
majority having explored hydrogenation of α, β- unsaturated C_C
bonds adjacent to carboxylic acid groups with cinchonidine as modifier.
The importance of synthesis of chemicals containing one or more
chiral centers has been appreciated and addressed in the manufacture
of pharmaceuticals, agrochemicals, and fragrances for decades. For
example, the three top-selling drugs for 2008 – Lipitor (atorvastatin
calcium), Plavix (clopidogrel bisulfate) and Nexium (esomeprazole
magnesium), with total sales of $30 billion – were all single-enantiomer
drugs [1]. The move toward enantiopure chemicals has been driven
both by performance requirements and government regulations, as
well as environmental concerns. While homogeneous catalytic asym-
metric catalysis continues to progress rapidly, intrinsic drawbacks
exist such as difficult (and expensive) catalyst separation and catalyst
instability. Such issues may help to explain the relatively wide gap
between R&D output from academics and industry versus commer-
cial application [2]. In this respect, the eventual use of heterogeneous
catalysts can offer several major advantages, including ease of catalyst
separation, reduction of solvent usage, simplification of the synthetic
route, and increased selectivity towards desired products. If optimized,
these properties could result in significant economic and environmental
benefits.
It is suggested that cinchonidine (CD) and acids form a CD(acid)
2
complex during the enantioselective hydrogenation [26]. In addi-
tion, aromatic acids are more easily hydrogenated in polar solvents,
as opposed to aliphatic acids that prefer non-polar environments.
These (and other) studies of the cinchonidine-modified metal cata-
lytic system have largely involved kinetics studies, as opposed to
probing the surface molecular environment. In addition, the in-situ
vibrational spectroscopic studies available have focused almost entirely
on the cinchona alkaloid modifier interaction with the catalyst surface
under different conditions [15,29,30].
The present communication reports an in-situ attenuated total reflec-
tion infrared spectroscopic study of the interaction of α-methylcinnamic
Cinchonidine-modified supported Pt-group metals are well-known
and effective heterogeneous enantioselective catalysts, especially for
2 3
acid with a Pd/Al O catalyst. This molecule consists of a prochiral C_C
bond located between COOH and phenyl groups (Fig. 1), and is a good
model compound for the study of C=C hydrogenation in aryl substituted
substrates. Overall, the conversion and enantioselectivity of this molecule
is reported to be very low over cinchonidine-modified catalysts [15,16].
It was the aim of this work to begin to elucidate the surface molecular
properties that may influence this behavior.
⁎
Corresponding author at: Department of Chemical Engineering, University of South
Carolina, Columbia, SC 29208, United States. Tel.: +1 803 777 0143; fax: +1 803 777
8
1
265.
E-mail address: willia84@cec.sc.edu (C.T. Williams).
566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.09.040

14
X. Sun, C.T. Williams / Catalysis Communications 17 (2012) 13–17
Fig. 1. Hydrogenation of α-methylcinnamic acid.
2
. Experimental section
with a final solvent flush. For hydrogenation, after spectra were acquired
in H -saturated pure solvent for 2 h, the flow was switched to H -satu-
rated 0.016 M acid solution for 2 h. Finally the solution was purged
with H -saturated solvent for 2 h. The adsorption and hydrogenation
of α-methylhydrocinnamic acid (which is the product of the hydro-
genation reaction) on 1 wt% Pd/Al was studied with ATR-IR to help
2
2
2
.1. Materials
2
Dichloromethane (CHROMASOLV®), α-methylcinnamic acid (MCA,
9%) and α-methylhydrocinnamic acid (MHA, 98%) were obtained
9
2 3
O
from Aldrich and used without further purification. The gas used for
the experiments was ultrahigh purity hydrogen from National Welders
Supply. PdCl (Premion®, 99.999% (metals basis), Pd 59.5% min) and
2
gamma aluminum oxide powder (99.5%, metal basis) were obtained
from Alfa Aesar.
interpret the hydrogenation spectra. In these experiments, a back-
ground was taken after bubbling hydrogen in solvent for 1 h, after
which spectra in pure solvent were collected for 1 h. This was followed
by 0.016 M product acid for 1 h, and finally pure solvent.
Vibrational assignments were assisted using spectral curve fitting
to deconvolute overlapping peaks. Specific band assignments were
aided by density functional theory (DFT) calculations on a single mol-
ecule in the gas phase using Gaussian 03 W, Revision B.02 [33] with
the Becke three-parameter-Lee-Yang-Parr (B3LYP) method and the
6–31 G(d) basis set. The results were corrected by scaling factor 0.97.
2
.2. Catalyst preparation
1
2 3
wt.% Pd/γ- Al O catalyst was synthesized via wet- impregnation.
Palladium chloride was used as the precursor and the support γ- Al
2 3
O
2
powder had a mean particle size of 37 nm and a surface area of 45 m /g.
The catalyst prepared had around 50% dispersion based on H chemi-
2
3. Results and discussion
sorption, with a mean palladium particle size of 2.6 nm, confirmed by
high-resolution transmission electron microscopy.
3.1. Reactant acid adsorption
2
.3. ATR-IR Spectroscopy
The first step to study the hydrogenation of α-methylcinnamic acid
is to understand the adsorption behavior of this reactant on the γ-Al
2 3
O
An FTIR spectrometer (Nicolet 670) equipped with an ATR-IR
support and Pd/Al catalyst. Prior to this, the ATR-IR spectra of the
2 3
O
accessory (SpectraTech) was used for these studies, as reported previ-
ously [31,32]. In the accessory there are two mirrors that allow the
horizontal infrared light to be reflected vertically into the ATR-IR
cell. Two holes in the bottom of the cell are designed to let the infrared
light enter the ZnSe element sealed within the cell. A 60° zinc selenide
acid solution in contact with the bare ZnSe element were examined.
The first plot in Fig. 2 shows typical spectra taken from acid solution
in contact with the bare element as a function of the concentration pro-
file described before. The seven spectra shown from the bottom to the
top were the spectra taken at the end of each indicated experimental
−
1
−1
(
ZnSe) crystal (Spectra Tech) was selected for use as the ATR element
step. Two clear peaks are observed at 1715 cm
From the literature [19], the 1715 cm peak is associated with C=O
stretching from acid monomers, while the 1685 cm peak is associated
and 1685 cm
.
−
1
upon which the catalyst film is deposited. The film was coated onto
the ATR element using a suspension of 25 mg catalyst in 20 ml DI
water. This mixture had been first placed in an ultrasonic bath overnight
in order to obtain a uniform suspension. A thin layer of this suspension
was spread into the ATR element and dried under a lamp. This proce-
dure was repeated four times, giving an average film thickness of
−
1
−
1
with acid dimer species. The small peak at 1492 cm is assigned to the
−
1
−1
ring vibration, while peaks at 1448 cm and 1407 cm correspond to
methyl group vibrations. Usually, the monomer acid is favored in very
dilute solution in non-polar solvents, or in the vapor phase. Indeed,
the relative sizes of the peaks change with concentration, showing
that the dimer species is favored at higher concentrations. However,
most importantly, these liquid phase peaks disappear completely
upon switching to pure solvent; this confirms that there is no strong
adsorption on the ZnSe surface.
1
0± 2 μm, as found using optical microscopy (Olympus BX50 micro-
scope and Simple PCI image analysis software by Compix).
The liquid solutions are kept in glass flasks (i.e., reservoirs) with
magnetic stirring. Two separate reservoirs were used during the
experiment without mixing between acid solutions and pure solvent
(
CH
2
Cl
2
). Gas can be bubbled into the solution for hydrogenation
line attached to porous glass frit capped
Fig. 3 shows ATR-IR spectra obtained in the same fashion, but for
an Al O film. As can be seen, the peak intensities are increased and
2 3
experiments using an H
2
tube submerged in the reservoir. Pumps recycle the solution from the
reservoirs, through the flow cell and back during the experiment. The
flow path was altered by three-way valves that were automated and
controlled using Labview (National Instruments). All experiments
were carried out at room temperature and atmospheric pressure.
For acid adsorption experiments, pure solvent was flowed through
the flow cell overnight prior to taking the background. At time zero, a
spectral background was acquired and utilized for all the spectra taken
during the experiment. Spectra were acquired continuously every ca
there are peaks remaining after removal of liquid-phase acid, suggesting
that acid is adsorbed on the alumina. The peak associated with monomer
C=O decreased, while the dimer-related peak increased, relative to the
−
1
liquid phase. In addition, there is prominent peak at around 1640 cm
,
to
−
1
which is assigned to C=C stretching [19]. Peaks around 1350 cm
−
1
1500 cm
methyl group, while the features from 1500 to 1600 cm
were mainly associated with C–H bending vibrations in the
−
1
arise from
ring stretching vibrations. All of these assignments are shown in
Table 1, and were made based on comparisons with characteristic fre-
quency tables and the DFT calculation results. Fig. 4 shows that similar
spectra were observed for the same experiment performed on the
2
min during the experiment with 128 scans per spectrum using a reso-
−
1
lution of 4 cm . Pure solvent was continued for 1 hour, followed by
mM MCA in CH Cl for 1 hour. Then the cycle is repeated, with solvent
followed by acid solution, but for 16 mM acid and 8 mM acid, ending
2
2
2
1 wt.% Pd/Al
2 3
O sample, although some peak intensities are a little
−
1
higher. Indeed, the peaks from 1500 to 1600 cm are clearly increased

X. Sun, C.T. Williams / Catalysis Communications 17 (2012) 13–17
15
g
0.001
0.001
f
e
h
d
c
b
a
k
1800
1700
1600
1500
1400
1300
1800
1700
1600
1500
1400
1300
-1
wavenumber (cm-1)
wavenumber (cm )
Fig. 2. ATR-IR spectra for α-methylcinnamic acid (MCA) in contact with a bare ZnSe element. The spectra were acquired in order after exposure to a) pure solvent, b) 2 mM MCA,
c) pure solvent, d) 16 mM MCA, e) pure solvent, f) 8 mM MCA and g) pure solvent. The plots on the right (h) are curve fitting for d). See text for details.
compared to Al
2
O
3
alone, while the ratio of peaks found between 1600–
lineshapes, while the peaks from adsorbed species were modeled by a
hybrid Lorentzian/Gaussian function. Several constraints were placed
on the liquid peak parameters during the fitting routine within a
given data set. The ratios, positions, and full widths at half maximum
(FWHM) of the liquid peaks were kept constant, with only the inten-
sity of the peaks allowed to vary. The same constraints were placed
on the peak parameters for adsorbed acid on alumina when fitting
−
1
−1
1700 cm and 1350–1500 cm
changed.
The spectra during adsorption experiments are complex and con-
tain many overlapping peaks from a variety of sources, especially at
the highest acid concentration of 0.016 M. To distinguish more clearly
the peaks arising from bulk liquid and adsorbed species, the spectra
were deconvoluted using least squared regression analysis. Before fitting
could proceed, the peaks used to model liquid phase were deter-
mined. This was accomplished by fitting the IR spectra obtained
from the bare element in 0.016 M acid, as shown in Fig. 3. The
peaks at 1450, 1407, 1492, 1680, and 1715 cm
assigned to liquid-phase acid. The resulting parameters for these liquid
peaks were then used when fitting the IR spectra obtained in the pres-
ence of a film (i.e. Al O or Pd/Al O ). Initial inputs for surface adsorbed
2 3 2 3
2 3
the 1 wt.% Pd/Al O spectrum. Finally, the intensities of any adsorbed
acid peaks on Pd were allowed to vary while keeping other parameters
constant. All the fitted spectra shown in the right plots in Figs. 2–4
were those taken for the highest concentration acid (0.0016 M)
flowing through the cell. In these spectra, the red peaks are those
arising peaks from liquid-phase acid, blue are those coming from
adsorbed acid on alumina, and green are those observed on the Pd
metal.
−
1
can be readily
acid-related peaks were chosen based on the shape of the overall spec-
tra and examination of residuals after subtraction of such liquid signals.
The peaks from liquid-phase acid were modeled by pure Gaussian
Based on this curve fitting, and vibrational frequencies calculated
by DFT, peak assignments have been made and are summarized. Of
0.001
0.001
g
h
f
e
i
d
c
h+i
k
b
a
1800
1700
1600
1500
1400
1300
1800
1700
1600
1500
1400
1300
-1
wavenumber (cm-1)
wavenumber (cm )
Fig. 3. ATR-IR spectra for α-methylcinnamic acid (MCA) adsorption on Al
2 3
O . The spectra were acquired in order after exposure to a) pure solvent, b) 2 mM MCA, c) pure solvent,
d) 16 mM MCA, e) pure solvent, f) 8 mM MCA and g) pure solvent. The plots on the right are curve fitting for d), with the curves indicated for spectral contributions from the
h) liquid and i) adsorption on alumina. See text for details.

16
X. Sun, C.T. Williams / Catalysis Communications 17 (2012) 13–17
Table 1
Vibrational peak assignments.
during the enantioselective hydrogenation. The present spectra
obtained during adsorption suggest that such complexes may indeed
be necessary to facilitate molecular adsorption on the surface.
Vibrational mode
Peak assignment
Experimental
Calculation
3.2. Hydrogenation
Bare ZnSe
element
Al
2
O
3
1 wt.% Pd/
Al
B3LYP/6-31 G(d)
2 3
O
2 3 2 3
After examining the adsorption of acid onto Al O and Pd/Al O
C=O str. (monomer)
C=O str. (dimer)
C=C str.
Ring str.
Asymmetric COO vib
Ring symmetric vib.
Methyl group asymmetric
C–H vib
Methyl group symmetric
C–H vib
1716
1684
1710
1738
catalyst, preliminary studies of α-methylcinnamic acid hydrogenation
were performed. Based on the literature, this hydrogenation can be
carried out effectively at room temperature and atmospheric hydrogen
pressure, albeit with low activity. Fig. 5A and B show typical spectra for
1672
1637
1554
1529
1491
1450
1632
1547
1522
1491
1447
1621
1566
-
1492
1448
1483
1457
hydrogenation of 0.016 M acid on alumina and 1 wt.% Pd/Al
2 3
O , respec-
tively. The relevant spectra for reactant adsorption in the absence of H
2
at the same concentration are taken from Fig. 3. Finally, a spectrum is in-
cluded for the adsorption of the product α-methylhydrocinnamic acid
in dichloromethane directly after exposure of the catalyst to a
1407
1386
1423
1384
1403
1392
1359
-
Symmetric COO vib
C–H vibration(H–C=C)
1378
1346
0
2 3
.016 M concentration step for 1 h. It was expected that the Al O
would not show any surface reactivity towards hydrogenation. Indeed,
Fig. 5A supports this supposition, since the spectrum taken in the
particular interest are the peaks ~1529 cm− and ~1384 cm−1
1
,
presence of H
in H -free solution.
In contrast, Fig. 5B shows that in the case of catalyst, a very signif-
2
-saturated acid is essentially identical to that obtained
which are confidently assigned as asymmetric and symmetric COO-
vibrations base on the available literature [34,35]. The presence of
these peaks shows that the reactant acid is dissociatively adsorbed
on both the alumina and Pd surfaces. It is well known that different
binding structures of carboxylates can be assigned based on the dif-
2
−
1
icant shoulder appears above 1700 cm
2
in the presence of H . Based
on comparison with the spectrum obtained during product adsorp-
tion, this new peak can readily be assigned to the C=O stretch of
dimerized adsorbed product acid. Both the monomer and dimer
C=O stretching frequencies for the product are blue shifted by
-
ference between asymmetric and symmetric COO vibration peaks.
−
1
−1
For example, a difference between 350 cm
to 500 cm
indicates a bridging bidentate
indicates a chelating bidentate. Thus, the
indicates
−
1
−1
a unidentate mode, 150–180 cm
about 50 cm , due to the absence of an adjacent C_C bond. In addi-
−
1
−1
mode, and 60–100 cm
tion, there is a broad feature around 1600 cm , which can be
bidentate bridging configuration, with the two oxygen atoms of the
carboxylate bridging between two sites on the surface, is apparently
favored under the conditions examined here.
assigned to ring stretching combined with the higher frequency
C=C stretching peak from the reactant, which is still also adsorbed
on both Pd and Al
2 3 2
O . When the H -saturated acid was replaced by
Overall, considering the C=O stretching bands in these curve
fitted plots, both monomer and dimer acid species exist in the bulk
liquid phase. In contrast, only dimer is present on the alumina sur-
face, and no significant dimer or monomer peaks are observed Pd.
Thus, these spectra reveal that the acid adsorbs both molecularly
and dissociatively on alumina but only dissociatively on Pd, at these
conditions. It has been suggested previously [26] that on the cincho-
H -saturated pure solvent, the peak intensity decreased only slightly.
2
Thus, once the product acid is formed on the surface, it apparently
adsorbs strongly on the metal and/or support surface. Other than
the C_C bond, the benzene ring is another possible unsaturated
bond that can be hydrogenated. However, preliminary batch kinetic
studies (not shown) of the same catalyst for this hydrogenation system
at the same temperature and pressure indicate that only the C_C bond
is hydrogenated under these conditions.
nidine (CD)-modified Pd surface, a CD(acid)
2
complex is present
0
.001
0.001
h
g
f
i
j
e
d
c
h+i+j
k
b
a
1
800
1700
1600
1500
1400
1300
1800
1700
1600
1500
1400
1300
-1
wavenumber (cm-1)
wavenumber (cm )
Fig. 4. ATR-IR spectra for α-methylcinnamic acid (MCA) adsorption on 1 wt.% Pd/Al
2 3
O . The spectra were acquired in order after exposure to a) pure solvent, b) 2 mM MCA,
c) pure solvent, d) 16 mM MCA, e) pure solvent, f) 8 mM MCA and g) pure solvent. The plots on the right are curve fitting for spectrum d), with the curves indicated for spectral
contributions from h) liquid, i) adsorption on alumina, and j) adsorption on Pd. See text for details.

X. Sun, C.T. Williams / Catalysis Communications 17 (2012) 13–17
17
2 3
Fig. 5. ATR-IR spectra obtained during hydrogenation of MCA on alumina and 1 wt.% Pd/Al O . MCA and product (MHA) adsorption spectra acquired in separate adsorption experiments in
the absence of H are shown for comparison.
2
[
8] Y. Nitta, T. Kubota, Y. Okamoto, Bulletin of the Chemical Society of Japan 74
2001) 2161–2165.
9] Y. Nitta, Bulletin of the Chemical Society of Japan 74 (2001) 1971–1972.
4
. Conclusions
(
[
The adsorption of α-methylcinnamic acid in dichloromethane at
room temperature on Al and 1 wt.% Pd/Al powder thin films
was characterized by ATR-IR. While both monomer and dimer acid
species are present in the liquid phase, the only molecular adsorp-
[10] Y. Nitta, Topics in Catalysis 13 (2000) 179–185.
[
11] Y. Nitta, T. Kubota, Y. Okamoto, Bulletin of the Chemical Society of Japan 73
2000) 2635–2641.
12] Y. Nitta, Chemistry Letters 28 (1999) 635–636.
2
O
3
2 3
O
(
[
[13] Y. Nitta, Y. Okamoto, Chemistry Letters 27 (1998) 1115–1116.
[14] Y. Nitta, A. Shibita, Chemistry Letters 27 (1998) 161–162.
2 3
tion on Al O was in dimer form. In contrast, there was essentially
[
[
[
[
[
[
15] G. Szollosi, T. Hanaoka, S. Niwa, F. Mizukami, M. Bartok, Journal of Catalysis 231
no observed molecular adsorption on the Pd surface. The presence
(2005) 480–483.
-
of asymmetric and symmetric COO vibration peaks and their band
16] G. Szollosi, S. Niwa, T. Hanaoka, F. Mizukami, Journal of Molecular Catalysis A:
Chemical 230 (2005) 91–95.
17] K. Szori, G. Szollosi, K. Felfoldi, M. Bartok, Reaction Kinetics and Catalysis Letters
separation indicated adsorbed bidentate bridging carboxylate species
on both Al
larly and dissociatively on Al
tion of solution phase hydrogen had no effect on the surface speciation
on Al alone. In contrast, strongly adsorbed product was formed in
the presence of Pd/Al , where it may reside on the metal and/or
O
2 3
and Pd. Thus, this substituted acid adsorbs both molecu-
84 (2005) 151–156.
2 3
O , but only dissociatively on Pd. Introduc-
18] I. Kun, B. Torok, K. Felfoldi, M. Bartok, Applied Catalysis A: General 203 (2000)
71–79.
19] D. Ferri, T. Burgi, A. Baiker, Journal of the Chemical Society, Perkin Transactions 2
2 3
O
(2002) 437–441.
2 3
O
20] K. Borszeky, T. Burgi, Z. Zhaohui, T. Mallat, A. Baiker, Journal of Catalysis 187
(1999) 160–166.
the support. Present studies are focused on elucidating the interac-
tion of adsorbed acid with cinchonidine modifier in the presence
and absence of solution-phase hydrogen, and correlating these mea-
surements with observed reaction kinetics studies conducted under
the same conditions.
[21] K. Borszeky, T. Mallat, A. Baiker, Catalysis Letters 59 (1999) 95–97.
[22] K. Borszeky, T. Mallat, A. Baiker, Tetrahedron-Asymmetry 8 (1997) 3745–3753.
[23] M. Maris, T. Burgi, T. Mallat, A. Baiker, Journal of Catalysis 226 (2004) 393–400.
[24] M. Maris, W.-R. Huck, T. Mallat, A. Baiker, Journal of Catalysis 219 (2003) 52–58.
[25] W.-R. Huck, T. Burgi, T. Mallat, A. Baiker, Journal of Catalysis 205 (2002) 213–216.
[26] W.-R. Huck, T. Burgi, T. Mallat, A. Baiker, Journal of Catalysis 200 (2001) 171–180.
[27] W.-R. Huck, T. Mallat, A. Baiker, Journal of Catalysis 193 (2000) 1–4.
Acknowledgment
[28] W.-R. Huck, T. Mallat, A. Baiker, Catalysis Letters 69 (2000) 129–136.
[29] T. Mallat, E. Orglmeister, A. Baiker, Chemical Reviews 107 (2007) 4863–4890.
[30] W.-R. Huck, T. Mallat, A. Baiker, Catalysis Letters 87 (2003) 241–247.
[31] I. Ortiz-Hernandez, C.T. Williams, Langmuir 19 (2003) 2956–2962.
This work was funded by a National Science Foundation (CBET-
0
731074). The authors also would like to thank Dr. Douglas Blom from
[32] I. Ortiz-Hernandez, C.T. Williams, Langmuir 23 (2007) 3172–3178.
[
33] Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman,
J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.;
Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega,
N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.;
Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo,
J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli,
C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg,
J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.;
Wong, M. W.; Gonzalez, C.; and Pople, J. A.; Gaussian, Inc., Wallingford CT, 2004.
EM center in USC for the help of HR-TEM characterization for the catalyst.
References
[
1] IMS Health, Top 15 global products 2008, 2008 Global Prescription Sales Information,
Top-line Industry Data, Press Room, 22.04.2009, 2009.
2] A.M. Rouhi, Chiral chemistry, Chemical and Engineering News 82 (2004) 47–62.
3] J.R.G. Perez, J. Malthete, J.C.R. Jacques, Academy of Sciences of the Paris Serie II
[
[
3
00 (1985) 169–172.
4] T. Sugimura, J. Watanabe, T. Uchida, Y. Nitta, T. Okuyama, Catalysis Letters 112
2006) 27–30.
5] Y. Nitta, J. Watanabe, T. Okuyama, T. Sugimura, Journal of Catalysis 236 (2005)
64–167.
6] T. Sugimura, J. Watanabe, T. Okuyama, Y. Nitta, Tetrahedron-Asymmetry 16
2005) 1573–1575.
7] Y. Nitta, T. Kubota, Y. Okamoto, Journal of Molecular Catalysis A: Chemical 212
2004) 155–159.
[
[
[
[
(
1
[34] K. Dobson, A. McQuillan, Spectrochimica Acta Part A 56 (2000) 557–565.
[35] J. van den Brand, O. Blajiev, P.C.J. Beentjes, H. Terryn, J.H.W. de Wit, Langmuir 20
(2004) 6308–6317.
(
(