Structural investigation of solid-acid-promoted Pd/SDB catalysts for ethyl acetate production from ethanol

Article abstract of DOI:10.1021/jp0032457

Catalyzed by styrene-divinylbenzene copolymer (SDB)-supported Pd (Pd/SDB) catalysts, ethyl acetate can be formed from water-containing ethanol via concomitant partial oxidation and esterification reaction. The partial oxidation reaction is carried out ove

Full text of DOI:10.1021/jp0032457

3400
J. Phys. Chem. B 2001, 105, 3400-3404
Structural Investigation of Solid-Acid-Promoted Pd/SDB Catalysts for Ethyl Acetate
Production from Ethanol
J.-F. Lee,† F.-S. Zheng,‡ and J.-R. Chang*,‡
Department of Chemical Engineering, National, Chung Cheng UniVersity, Chia-Yi, Taiwan, R. O. C., and
Synchrotron Radiation Research Center, Hsinchu, Taiwan, R. O. C.
ReceiVed: September 13, 2000; In Final Form: January 9, 2001
Catalyzed by styrene-divinylbenzene copolymer (SDB)-supported Pd (Pd/SDB) catalysts, ethyl acetate can
be formed from water-containing ethanol via concomitant partial oxidation and esterification reaction. The
partial oxidation reaction is carried out over palladium clusters on the catalysts. The esterification reaction is
catalyzed by protons formed from the spontaneous dissociation of acetic acid and can be enhanced by addition
of solid acid catalysts. To investigate the nature of solid acid in promoting the catalytic properties of Pd/SDB
catalysts, extended X-ray absorption fine structure (EXAFS) and inductively coupled plasma optical emission
(ICP) spectroscopy were used to characterize the reaction-induced morphology change of Pd clusters and
metal loss. After the reaction, there is no evidence of palladium oxide formation, suggesting that the oxidation
reaction takes place via the adsorbed oxygen. In addition, concomitantly with Pd leaching, increase of average
Pd cluster size was observed. Pd-Pd coordination number increases from 3.0 to 7.9 and the Pd content
decreases from 1.0 to 0.55 wt %. Addition of acid catalysts reduces leaching and growth of Pd clusters. This
effect increases with an increase in acid-to-Pd catalyst ratio of the mixed catalysts. As the acid-to-Pd catalyst
ratio increases from 1.0 to 4.0, Pd-Pd coordination number decreases from 7.2 to 6.5 and the Pd content
increases from 0.63 to 0.71 wt %.
Introduction
Acetic acid is formed from the oxidation of ethanol catalyzed
by Pd clusters. It can be further catalytically esterified to ethyl
acetate by the dissociated protons. However, acetic acid dis-
sociation is limited by a thermodynamic equilibrium and is not
enough for efficient catalytic esterification. To increase the
acidity of the catalyst system so as to decrease acetic acid
formation, resin-type solid acid catalysts were added to the Pd/
SDB catalysts. The change of yield pattern caused by the
addition of the acid catalysts might affect Pd-adsorbate
interactions, leading to a change in morphology of Pd clusters
and the consequent catalytic properties of Pd/SDB. Extended
X-ray absorption fine structure (EXAFS) technique has been
shown to be useful for quantitative characterization of the
structure of supported metal catalysts.7-11 It will also allow us
to investigate the nature of active sites for ethanol partial
oxidation. Moreover, the correlation of catalyst structure with
catalytic performance test results will help us to investigate the
role of acid catalysts in enhancing the catalytic properties of
the Pd catalysts. The results would point to a way for further
improving the catalyst performance.
In conversion of water-containing ethanol to ethyl acetate
catalyzed by conventional hydrophilic catalysts such as Pd/γ-
Al2O3, the water film formed in capillary condensation could
cover the palladium clusters. The water film not only impedes
the forward chemical reaction but also retards the diffusion of
reactants to actives sites.1 Because of the strong mass-transfer
limitation; hydrophilic Pd catalysts present a relatively lower
reaction rate than that catalyzed by hydrophobic styrene-
divinylbenzene copolymer (SDB)-supported Pd catalysts. How-
ever, the hydrophobic catalysts deactivates rather fast because
of the loss of Pd metal and the decrease of Pd dispersion during
the reaction.1,2
The metal loss results from leaching of palladium(II) acetate
via the reaction between palladium clusters and acetic acid.1
Since smaller clusters are leached preferentially in the process,
the dispersion of the Pd catalysts would thus be decreased.
However, the decrease of dispersion may also be caused by Pd
agglomeration. The works of Zhang et al., Anderson et al., and
Chang et al., indicate that the interactions between adsorbates
and metal clusters may weaken the metal-support interactions,
resulting in a migration and agglomeration of metal clusters.3-5
Although oxylchlorination is normally used for reactivation
of a supported metal catalyst by the redispersion of aggregated
metal clusters, it has not been applied in industry for SDB-
supported Pd catalysts.6 Besides, the activity loss caused by
metal leaching is not recoverable. Because of these two
shortcomings, the industrial application of Pd/SDB catalysts in
ethyl acetate production is difficult.
Experimental Section
Material and Catalyst Preparation. The SDB support with
a BET surface area of 465 m2/g was prepared by polymerizing
divinylbenzene in ethylvinylbenzene with 2,2-azobis(2-meth-
ylpropionitrile) as initiator. The Pd/SDB catalysts were prepared
by impregnating the SDB with an ethanol solution containing
a given amount of Pd(NH3)4Cl2·H2O. The amounts were chosen
so that adsorption of all the Pd precursors would yield a solid
containing 1.0 wt % Pd. The details of the preparation method
have been reported in a paper by Yaparpalvi and Chung.12
The resin-type solid acid catalysts used in this study are
sulfonic acid ion-exchange resins, Amberlyst 35 (Rohm Haas).
* Corresponding author. Tel: 886-5-2720411, ext 6239. E-mail: chmjrc@
ccunix.ccu.edu.tw.
† Synchrotron Radiation Research Center.
‡ Chung Cheng University.
10.1021/jp0032457 CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/06/2001

Investigation of Solid-Acid-Promoted Pd/SDB Catalysts
J. Phys. Chem. B, Vol. 105, No. 17, 2001 3401
TABLE 1: Summary of Catalytic Properties and Metal Loss
for Pd/SDB and Solid Acid Promoted Pd/SDB Catalystsa
Catalytic Performance. The catalytic performance tests were
carried out in a continuous downflow fixed-bed reactor with
an inside diameter of 2.1 cm and volume of 94.0 mL. The
reactor was heated with a water-bath circulator, and the reaction
temperature was monitored with a sensor in the center of the
catalyst bed. Two grams of Pd/SDB catalysts was mixed with
a certain amount of resin-type catalysts to give an acid-to-Pd
catalyst ratio of 1.0 and 4.0 by weight, respectively. The mixed
catalysts were diluted with 1.6 mm glass balls to a total catalyst
bed of about 50 mL. A gradient packing method was used to
minimize bypassing effects. Before the test the catalyst was
reduced in H2 at 150 °C for 8 h. The reaction then was carried
out with a weight hourly space velocity (WHSV) of 2.4 h-1 (g
of feed/h‚g of catalyst), at 95 °C, 35.4 atm, and a air/ethanol
molar ratio ) 2.37. The reaction products were trapped by a
condenser at -5 °C and analyzed using a gas chromatograph
(Shimadzu gas chromatograph model GC-14B; TCD and FID
detector, equipped with a DB-WAX capillary column, 30 m
long; and a SP4270 data processor). The metal leached was
analyzed using inductively coupled plasma optical emission
spectroscopy with a Jarnell-Ash 1100 instrument.
2 g
2 g Pd/SDB +
2 g Pd/SDB +
Pd/SDB 2 g Amberlyst 35 8 g Amberlyst 35
ethanol conversion, mol %
selectivity to ethyl acetate, % 54.6
selectivity to acetic acid, %
selectivity to acetaldehyde, %
selectivity to fuel gas, %
Pd loss during reaction, %
44.3
51.4
70.2
23.2
1.8
4.8
37.0
55.5
77.0
18.0
2.0
3.0
29.0
38.0
1.5
5.9
45.2
a Catalysts were lined out in the reaction system for 70 h.
the smaller clusters were selectively leached, the Pd leaching
rate decreased and became rather slow after 70 h on stream.
The leached species has been identified as palladium(II) acetate,
which was formed from reaction of Pd clusters with the reaction
intermediate, acetic acid. The decrease in metal loss with
increasing acid catalysts suggests that the addition of acid
catalyst promotes the esterification reaction, resulting in a
decrease of acetic acid concentration and succeeding palladium-
(II) acetate formation, thereby reducing Pd leaching.
Role of the Acid Catalyst in Product Selectivity. Addition
of acid catalysts enhanced the conversion of acetic acid to ethyl
acetate. As the acid catalyst was added to form a mixed catalyst
with a acid-to-Pd catalyst ratio of 4, the selectivity for ethyl
acetate increased from 55 to 77%, while the selectivity for acetic
acid decreased from 38 to 18% (Table 1). In this study, the
selectivity to ethyl acetate [(ethyl acetate yield/ethanol conver-
sion) 100%] has a relative standard deviation (RSD) of about
2%, caused by the deviation of gas chromatography measure-
ment.
X-ray Absorption Spectroscopy. The X-ray absorption
measurements were performed on X-ray beamline X-11 of the
National Synchrotron Light Source (NSLS) at Brookhaven
National Laboratory with a storage ring energy of 2.5 GeV and
a beam current between 150 and 250 mA. A Si(111) double-
crystal monochromator was used for energy selection, and it
was detuned 20% at E0 + 50 eV to suppress higher harmonic
radiation; resolution, ∆E/E, was estimated to be 2.0 × 10-4
.
The monochromator was scanned in the energy range from 200
eV below to 1200 eV above the palladium K absorption edge
(24 350 eV) edge. The catalyst samples were pressed into a self-
supporting wafer with the wafer thickness chosen to give an
absorbance of 2.5 and reduced at the same operation conditions
as those for the catalytic performance tests. The EXAFS
measurements were performed in the transmission mode at
liquid nitrogen temperature. The transmission measurement
geometry was arranged using gas-filled ionization chambers to
monitor the intensities of the incident and transmitted X-rays.
To gain the proper absorption ratio for the incoming X-rays,
the gas compositions in the ionization chamber were selected
at an argon to nitrogen mole ratio of 1/1 for the first chamber
and pure argon for the second chamber, respectively. X-ray
absorption data from three scans of each sample were averaged,
and then the preedge and background were subtracted. Each
resulting spectrum was divided by the edge height to obtain
EXAFS functions.13
Fuel gas, shown in Table 1, includes methane, ethylene, CO2,
and a trace of ethylene. CO2 is formed from the total oxidation
reaction and the cracking of oxygen-containing compounds,
methane from the cracking reaction, and ethylene from the
dehydration reaction. Fuel gas formation decreased with increas-
ing acid-to-Pd catalyst ratio, which might be a consequence of
increasing coke formation catalyzed by acid catalyst. Coke
deposited on the Pd sites might retard total oxidation and metal
cracking and thus reduced fuel gas formation. Coke deposition
might also reduce the adsorption of oxygen on Pd clusters,
leading to a slight increase of acetaldehyde formation.
Morphology of Pd Clusters on the Fresh and the Used
Pd/SDB Catalysts. The EXAFS data were analyzed using
experimentally determined reference files obtained from standard
materials of known structure. The Pd-Pd and Pd-O contribu-
tions were analyzed with phase shifts and backscattering
amplitudes extracted from EXAFS data for palladium foil and
palladium oxide, respectively, and the Ru-C contribution from
EXAFS data for Ru3(CO)12. The appropriateness of using the
Ru-C to represent Pd-C is justified by the theoretical
calculation of Teo and Lee.14 Their results show that the
amplitude and phase function of the nearest and next-nearest
neighbors in the periodic table are hardly different.
The comparisons of EXAFS spectra for the four samples are
shown in Figure 1. The raw EXAFS data for the samples have
a signal-to-noise ratio >40 (The noise amplitude was determined
at k ) 14 Å-1, and signal amplitude was determined at k ) 4
Å-1).
The Fourier transforms provide the qualitative information
about the morphology of the Pd clusters on the SDB support.
k3-weighted Pd-Pd phase- and amplitude-corrected Fourier
transforms were performed for the EXAFS functions (4.5 < k
< 14.0 Å) to investigate the morphology difference of Pd
clusters among the fresh catalysts and the used catalysts of
different acid-to-Pd-catalysts ratio.
Results and Discussion
Role of the Acid Catalyst in Ethanol Conversion and
Metal Loss. Similar to the reaction catalyzed by Pd/SDB
catalysts, the conversion of ethanol catalyzed by the mixed
catalysts increased with reaction time to about 25 h on stream
and then declined. At about 70 h on stream, the change of
catalytic properties as well as the leaching of Pd became
insignificant.1 The catalytic performance of the Pd/SDB catalysts
and the mixed catalysts was then examined by comparing
ethanol conversion, product selectivity, and Pd loss. The results
are summarized in Table 1. As expected, ethanol conversion
increased with acid-to-Pd catalyst ratio, while metal loss
decreased because of the increase of esterification reaction.
In a previous paper, we reported that Pd is leached out in the
reaction system as measured by ICP optical emission spectros-
copy. The Pd leaching rate decreased with time on stream.1 As

3402 J. Phys. Chem. B, Vol. 105, No. 17, 2001
Lee et al.
TABLE 2: EXAFS Resultsa,b
EXAFS
ref
shell
N
R, Å
a. Fresh Pd/SDB Catalyst
∆σ2
∆E0, eV
Pd-Csupport
Pd-Pd
2.2 ( 0.2
3.0 ( 0.2
2.01 ( 0.01
2.741 ( 0.003
0.002 ( 0.001
-0.0003 ( 0.0004
6 ( 2
-2.5 ( 0.4
Ru-C
Pd-Pd
b. Used Pd/SDB Catalyst
Pd-Osupport
Pd-Pd
0.25 ( 0.05
7.9 ( 0.1
2.16 ( 0.02
2.755 ( 0.001
-0.009 ( 0.002
-0.0016 ( 0.0001
13 ( 4
1.3 ( 0.1
Pd-O
Pd-Pd
c. Used Pd/SDB Catalyst Promoted by Acid Catalysts with Acid-to-Pd Ratio of 1.0
Pd-Osupport
Pd-Pd
0.23 ( 0.03
7.2 ( 0.1
2.16 ( 0.01
2.760 ( 0.001
-0.010 ( 0.001
-0.0020 ( 0.0001
6 ( 3
1.1 ( 0.1
Pd-O
Pd-Pd
d. Used Pd/SDB Catalyst Promoted by Acid Catalysts with Acid-to-Pd Ratio of 4.0
Pd-Osupport
Pd-Pd
0.19 ( 0.05
6.6 ( 0.1
2.13 ( 0.02
2.745 ( 0.001
-0.010 ( 0.002
-0.0029 ( 0.0001
12 ( 5
0.8 ( 0.1
Pd-O
Pd-Pd
a Z is the atomic number; N the coordination number for the absorber-backscatterer pair; R the average absorber-backscatterer distance; ∆σ2 the
Debye-Waller factor, and ∆E0 the inner potential correction. b The number of parameters used to fit the data in this first shell is 8; the statistically
justified number is estimated from the Nyquist theorem, n ) (2∆k∆r/π) + 1, where ∆k and ∆r, respectively, are the k and r ranges used in the
forward and inverse Fourier transform.
metal shell (at about 2.7 Å) and higher shells (about 3.8, 4.8,
and 5.6 Å) are at the same positions and consistent with the
nearest four neighbors in bulk fcc (face centered cubic) Pd, while
the intensities of the Fourier-transformed EXAFS functions for
the three used catalysts are much higher than those of the fresh
catalysts and decreased with increasing acid-to-Pd catalyst ratio.
Since the intensity is proportional to coordination number of
Pd-Pd,7 the decrease of the intensity with increasing acid-to-
Pd catalyst ratio (Figure 2) indicates that the reaction-induced
Pd agglomeration was impeded by the addition of acid catalysts.
Selective oxidation can be catalyzed by bulk metal oxide, a
core of metal covered by a shell of metal oxide, or oxygen-
activated metal.16,17 The possibility of bulk metal oxide being
active sites for the oxidation was rule out on the basis of the
EXAFS spectra characterizing the used catalysts; bulk fcc Pd
clusters were characterized, indicating that no significant
contribution from bulk metal oxide was apparent and it
consequently could not be the active site.
Figure 1. Raw EXAFS data for the fresh Pd/SDB catalyst (solid line),
the used Pd/SDB catalyst (dashed-dotted line), the used Pd/SDB
catalyst promoted by solid acid catalysts with acid-to-Pd catalyst ratio
of 1.0 (dashed line), and the used Pd/SDB catalyst promoted by solid
acid catalysts with an acid-to-Pd catalyst ratio of 4.0 (dotted line).
Since the residual spectrum obtained from the subtraction of
Pd-Pd contributions from raw EXAFS data represented the
metal-support interactions, metal-adsorbate interactions, or the
metal oxide shell, further discrimination of the characteristics
of active sites could be obtained from the residual spectrum.
Detailed EXAFS Analysis and Metal-Adsorbate Interac-
tions. A k2-weighted Fourier transformation without correction
was performed on the EXAFS function over the range 4.09 <
k < 14.88 Å-1 for the fresh catalyst sample and 3.34 < k <
15.31 Å-1 for the used one. The major contributions were
isolated by inverse Fourier transformation of the data in the
range 1.11 < r < 3.14 Å for the fresh catalyst sample and 1.35
< r < 3.17 Å for the used catalyst samples. The Fourier-filtered
EXAFS data were analyzed by a difference files techniques with
a nonlinear least-squares multiple-shell fitting routine.15 The
resulting coordination parameters and the corresponding standard
deviations are summarized in Table 2. The number of parameters
used to fit the data in this main-shell analysis is 8; the
statistically justified number, calculated from the Nyquist
theorem, is 14.9
Figure 2. Magnitude of Fourier transform (k3-weighted, ∆k ) 4.5-
14.0 Å-1, Pd-Pd phase and amplitude corrected) of the raw EXAFS
data for the fresh Pd/SDB catalyst (solid line), the used Pd/SDB catalyst
(dashed-dotted line), the used Pd/SDB catalyst promoted by solid acid
catalysts with acid-to-Pd catalyst ratio of 1.0 (dashed line), and the
used Pd/SDB catalyst promoted by solid acid catalysts with acid-to-
Pd catalyst ratio of 4.0 (dotted line).
For an X-Y absorber-backscattering pair, peaks that have
a positive imaginary part of the phase-corrected EXAFS function
are due to neighbors of atom type Y.18 For the fresh catalyst,
the Ru-C phase-corrected Fourier transformation of the residual
spectrum of raw EXAFS data minus Pd-Pd contributions shows
a positive peak at 2.0 Å (Figure 3), suggesting interactions
between palladium clusters and SDB supports; carbon in SDB
is the backscattering atom.
As shown in Figure 2, the Pd-Pd phase- and amplitude-
corrected Fourier-transformed EXAFS functions of all the
samples show that the peaks corresponding to the first metal-

Investigation of Solid-Acid-Promoted Pd/SDB Catalysts
J. Phys. Chem. B, Vol. 105, No. 17, 2001 3403
and aggregating of Pd during the reaction. As expected, the
reaction intermediate, acetic acid, was decreased by the catalytic
esterification reaction and the selective oxidation reaction was
increased by the abatement of metal loss and metal agglomera-
tion (Table 1). However, because the esterification reaction is
limited by a thermodynamic equilibrium, the presence of acetic
acid in a significant amount is inevitable. The presence of a
high level of acetic acid leads to corrosion of the equipment
and damage to the catalyst. To overcome this problem, several
azeotropic distillation columns with recycle as well as catalytic
distillation should be used, leading to a complicated and
expensive operation. A relatively cheap and simple method to
overcome the thermodynamic limitation in the esterification
reaction is to develop a catalyst with a different affinity for each
reaction species. On the basis of the experimental results in this
study, dual function catalysts with poor affinity for ethyl acetate
relative to other polar species, mainly water, ethanol, and acetic
acid, were developed.20 By use of the catalyst, esterification is
catalyzed by the acidic component of the catalyst and takes place
mainly on the catalyst surface. Thus, a thermodynamic equi-
librium among the reaction mixture can be reached on the
catalyst surface. Since ethyl acetate desorbed faster than other
species, it was selectively and continuously removed from the
reacting surface to overcome the thermodynamic equilibrium
limitation. The reduction in acetic acid concentration in the
system also minimized the leaching and aggregating of Pd metal.
Figure 3. Fourier transform (k1-weighted, Ru-C phase corrected for
the fresh catalyst and Pd-O phase corrected for used catalysts, ∆k )
4.5-10.0 Å-1) for original filtered EXAFS data minus the calculated
Pd-Pd EXAFS: the fresh Pd/SDB catalyst (solid line), the used Pd/
SDB catalyst (dashed-dotted line), the used Pd/SDB catalyst promoted
by solid acid catalysts with acid-to-Pd catalyst ratio of 1.0 (dashed
line), and the used Pd/SDB catalyst promoted by solid acid catalysts
with acid-to-Pd catalyst ratio of 4.0 (dotted line).
For the used Pd/SDB samples, the magnitude of Pd-O phase-
corrected Fourier transformation of the residual spectra extend
down to about 1.8 Å. The positive peak of the imaginary part
in the envelope appeared at about 2.2 Å (Figure 3) and was
assigned to contribution from the interactions between palladium
clusters and oxygen. Another peak appeared at about 1.85 Å,
which might be contributed from metal-support interactions,
Pd-C. However, since the Pd-C and Pd-O spectra in Figure
3 practically overlap and the peak of Pt-C decreases with
reaction-induced Pd agglomeration, only the main contribution,
Pd-O, of the spectra was analyzed.
The Pd-O contribution is about 0.15 Å longer than the bond
distance of palladium oxide. The possibility of a core of metal
covered by a shell of metal oxide might thus be ruled out. Hence,
we suggested that chemisorbed oxygen-containing Pd clusters
provide the active sites for the oxidation reaction. The reaction
mechanism is consistent with selective ethylene oxidation on
supported silver catalysts.16,19
The Pd-O contribution might also be assigned as the
contribution from the interactions between Pd clusters and the
carboxyl group of acetic acid. The assignment was consistent
with the leaching of Pd clusters via the formation of palladium-
(II) acetate and the agglomeration of Pd clusters. At the initial
stage of palladium(II) acetate formation, the interactions between
Pd clusters and acetic acid may weaken metal-support interac-
tions, leading to a mobile Pd cluster. The mobile Pd cluster
may either form palladium(II) acetate and be extracted from
the support or migrate to strongly bound Pd clusters on the
support and attach to them. Since smaller clusters are leached
easily, this process concomitantly leaches out small Pd cluster
from catalysts and transfers to bigger one.
Since the affinity of Pd for the organic species in the reaction
system might be greater than that for SDB support, those organic
species might bond to Pd clusters more strongly and loosen the
interaction between Pd clusters with support. After the formation
of organo-Pd complex, the complex might be leached and then
reacted with acetic acid to form palladium(II) acetate. In
addition, it might migrate on the SDB surface and then coalesced
to form a bigger cluster.
Conclusions
On the basis of EXAFS spectroscopy characterizing the fresh
and used Pd/SDB catalyst, we suggested that chemisorbed
oxygen on Pd metal is the active species in selective oxidation
of ethanol to acetic acid. Part of the acetic acid was further
catalytically converted to ethyl acetate by the proton dissociated
from acetic acid. However, because of the deterioration of the
catalysts caused by leaching and the aggregation of Pd clusters
during reaction, it is difficult to develop an industrial process
for ethyl acetate production using Pd/SDB catalysts. The
drawbacks of the catalysts were alleviated by mixing resin-type
solid acid catalyst with Pd/SDB to enhance the acidity of the
catalyst system. ICP and EXAFS spectroscopy characterizing
the used catalysts indicated that the leaching and aggregation
of Pd clusters were decreased with increasing acid-to-Pd catalyst
ratio. Performance tests suggest that the improvement in catalytic
properties was mainly due to the reduction of acetic acid
resulting from esterification catalyzed by the acid catalysts. The
alleviation of the interaction between acetic acid and metal
clusters reduces palladium(II) acetate formation, thereby de-
creasing the transportation of relatively mobile small clusters
to form big clusters. As a result, both ethanol conversion and
selectivity to ethyl acetate were increased.
Acknowledgment. The EXAFS data were analyzed using
the XDAP Data Analysis Program, developed by M. Vaarkamp,
J. C. Linders, and D. C. Koningsberger, and the reference files
were provided by Dr. B. C. Gates. This research was supported
by the National Science Council of the Republic of China
(Contract No. NSC 88-2214-E-194-004). We are grateful to the
staff of beam line X-11A at the National Synchrotron Light
Source for their assistance.
References and Notes
(1) Lin, T.-B.; Chung, D.-L.; Chang, J.-R. Ind. Eng. Chem. Res. 1999,
38, 1275.
(2) Lin, T.-B.; Chuang, K. T.; Tsai, K.-Y.; Chang, J.-R. Process for
Ethyl Acetate Production, U.S. Patent 5,770,761, 1998.
We have attempted to add acid catalyst to Pd catalysts to
minimize formation of acetic acid, thereby relieving the leaching

3404 J. Phys. Chem. B, Vol. 105, No. 17, 2001
Lee et al.
(3) Zhang, Z.; Chen, H.; Sheu, L.-L.; Sachtler, W. M. H. J. Catal.
1991, 127, 213.
(11) Thomas, J. M.; Thomas, W. J. Heterogeneous Catalysis VCH
Publishers Inc., New York, 1997.
(4) Anderson, S. L.; Mizushima, T.; Udagawa, Y. J. Phys. Chem. 1991,
95, 6603.
(5) Chang, J.-R.; Koningsberger, D. C.; Gates, B. C. J. Am. Chem.
Soc. 1992, 97, 4196.
(6) Fung, S. C. CHEMTECH 1994, Jan, 40.
(7) Kampers, F. W. H. EXAFS in Catalysis: Instrumentation and
Application; Ph.D. Dissertation, Eindhoven University of Technology, The
Netherlands, 1988.
(8) Vaarkamp, M. The Structure and catalytic Poperties of Supported
Platinum Catalysts; Ph.D. Dissertation, Utrecht University, The Netherlands,
1993.
(12) Yaparpalvi, R.; Chuang, K. T. Ind. Eng. Chem. Res. 1991, 30, 2219.
(13) van Zon J. B. A. D. Extended X-ray Absorption Fine Structure
Spectroscopy Design of a Spectrometer and Application to Rhodium
Supported on Alumina Catalysts. Ph.D. Dissertation, Eindhoven University
of Technology, The Netherlands, 1988.
(14) Teo, B.-K.; Lee, P. A. J. Am. Chem. Soc. 1979, 101, 11, 2819.
(15) Varrkamp, M. XDAP User’s Guide. XAFS Services International,
1996.
(16) Marcinkowsky, A. E.; Berty, J. M. J. Catal. 1973, 29, 494.
(17) Oyama, S. T.; Hightower, J. W. Catalytic SelectiVe Oxidation
American Chemical Society, Washington, DC, 1993.
(18) Lee, P. A.; Beni, G. Phys. ReV. 1977, B15, 2862.
(19) Kenson, R. E. J. Phys. Chem. 1970, 74, 1493.
(9) Koningsberger, D. C.; Prins, R. X-ray Absorption; Principles,
Applications, Techniques of EXAFS, SEXAFS, and XANES. John Wiley &
Sons: New York, 1988.
(10) Gates, B. C. Catalytic Chemistry John Wiley & Sons: New York,
1992.
(20) Yan, T.-Y.; Chang, J.-R. Process for Production of Aliphatic Ester,
U.S. patent in application, serial number 09/559339, 2000.