Solvent-free selective aerobic oxidation of toluene by ultra fine nano-palladium catalyst

Article abstract of DOI:10.1016/j.apcata.2011.12.008

High activity ultrafine Pd catalyst was synthesized by both functional polymer encapsulated and impregnation methods. Catalysts were characterized and used to catalyze solvent-free aerobic toluene oxidation. Reaction temperature, time, catalyst mass, air pressure and catalyst reusability were investigated. Catalyst synthesized by encapsulating and immobilizing Pd inside titanium oxide is more active and has a better reusability.

Full text of DOI:10.1016/j.apcata.2011.12.008

Applied Catalysis A: General 415–416 (2012) 47–52
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Solvent-free selective aerobic oxidation of toluene by ultra fine nano-palladium
catalyst
Baosong Fu, Xiaowen Zhu, Guomin Xiao∗
School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
High activity ultrafine Pd catalyst was synthesized by both functional polymer encapsulated and impreg-
nation methods. Catalysts were characterized and used to catalyze solvent-free aerobic toluene oxidation.
Reaction temperature, time, catalyst mass, air pressure and catalyst reusability were investigated. Cat-
alyst synthesized by encapsulating and immobilizing Pd inside titanium oxide is more active and has a
better reusability.
Received 25 September 2011
Received in revised form
30 November 2011
Accepted 2 December 2011
Available online 11 December 2011
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Nano-palladium catalyst
Solvent-free
Toluene aerobic oxidation
Heterogeneous catalysis
1. Background
[4]. Reports show that for aerobic toluene oxidation, many hetero-
geneous catalysts have been studied, including copper [5], silver
Selective oxidation of toluene to produce its derivatives (such as
benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate)
has been of great importance for the past decades. There has been
a great increase in attraction towards how to convert this less valu-
able raw material, which is usually considered as volatile organic
compounds (VOCs) liberated from industrial processes as higher-
value chemical products instead of being fully combusted. Benzyl
alcohol, benzaldehyde, benzoic acid and benzyl benzoate are com-
mercially significant versatile intermediates in the manufacture of
pharmaceuticals, dyes, solvents, perfumes, plasticizers and preser-
vatives.
Pollutions and less efficient operation process usually come
along with homogeneous catalysis reactions. Today, liquid phase
toluene oxidation catalyzed by homogeneous metal salt catalyst
using halogens or acidic acid as solvent to produce benzaldehyde,
benzoic acid industrially is still the mainstream, employing oxygen
or peroxide as the oxidant [1–3]. The use of solvent and homo-
geneous catalyst causes difficulties in catalyst–product separation
and equipments. The process does not support green chemistry.
Developing solvent-free toluene oxidation catalyzed by active het-
erogeneous catalyst to make production processes pollution free
and easier has attracted special attention, and oxidation of organic
compounds catalyzed by metal has already been widely applied
[6], manganese [7,8], cobalt [9], chromium [10], iron [11], gold
[12], palladium [13], platinum [14] and some bimetallic composi-
tion [15–18]. For the metal supported catalysts mentioned above,
some of them are focused on the catalytic process of deep oxida-
tion or combustion at relative high temperatures which causes a
great loss of valuable carbon in aromatic compounds. While others
tested for toluene selective oxidation at mild conditions, Shen et al.
employed V–Ag–O/20% TiO2 to convert toluene to benzaldehyde
at 613 K with 7.3% of toluene conversion and 95% selectivity [6].
Suib et al. obtained the mixture of benzyl alcohol, benzaldehyde
and benzoic acid at 110 ◦C by gamma-MnO2 with 17.6% of toluene
conversion [7]. Guo et al. used air to oxidize toluene catalyzed by
cobalt in flow mode, recorded 8.9% of toluene conversion and 60%
selectivity of both benzyl alcohol and benzaldehyde [9]. However,
toluene catalyzed by the transition metal salts is usually accompa-
nied by low selectivity or consumes large amounts of solvents or
bromides [19,20]. Sometimes conversion needs to be sacrificed to
prevent overoxidation [8].
In most of the studies, Pd catalyst has been used for toluene
combustion [21–23] with only a few reports on its application for
toluene selective oxidation. For instance, 50% conversion of toluene
and 95% selectivity of benzyl benzoate were achieved by Hutch-
ings group using synthesized Au/Pd alloy nanoparticles [15]. Others
have also used Pd based nanoparticles as catalyst to oxidize toluene
to benzyl acetate [24,25]. The solvent free toluene oxidation sys-
tem catalyzed by single nano-size Pd catalyst was studied in this
research. We investigated the efficiency of ultra fine supported Pd
∗
Corresponding author. Tel.: +86 25 52090612; fax: +86 25 52090612.
E-mail address: xiaogm@seu.edu.cn (G. Xiao).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.12.008

48
B. Fu et al. / Applied Catalysis A: General 415–416 (2012) 47–52
nanoparticles synthesized by two different methods on catalysis
performance of the solvent free selective aerobic toluene oxidation
reactions as well as the effect of the reaction temperature, time, air
pressure, catalyst mass and reusability.
dispersion by first pre-treating the sample in a flow of pure O2 at
200 ◦C for 1 h and pure H2 for 0.5 h, followed by purging with He
for 0.5 h at the same temperature to remove O2. H2 pulses (100%)
were then passed in a stream of N2 over the samples in a U-tube
reactor at 80 ◦C to remove traces of O2. The results were recorded
by an on-line gas chromatography.
2. Experimental
2.3. Solvent free toluene aerobic selective oxidation
2.1. Catalyst preparation
Selective oxidation of toluene was carried out in an autoclave
(100 mL, Parr reactor) with stirring. The vessel was charged with
desired amount of toluene and Pd catalyst. After purging the reactor
for 5 times with air, it was then filled with air at a certain pres-
sure. Reaction time was measured when the expected temperature
reached. Both gas and liquid phases were analyzed by GC at the end
of each reaction and the results were compared with known com-
mercially pure standard samples. Gas sample was collected in an
airbag and transferred with an airtight syringe into gas chromatog-
raphy to identify any combustion reaction that may have occurred.
In order to determine the liquid phase generating products, com-
position quantitative and the external calibration methods were
employed. Conversions and products selectivity were calculated
based on the carbon balance.
Pd-PMHS/TiO2 was prepared according to the procedure pre-
viously reported for the production ultra fine and size tunable
Pd nanoparticles [26]. Palladium acetate (98%, Aldrich, China)
was added to a standardized solution of polymethylhydrosilane
(Aladdin Reagent Co. Ltd., China) which contained known con-
centrations of both cyanopropyl and silanol substituents. The Pd
acetate was reduced to Pd nanoparticles by the residual silane.
Tetrabutyl titanate (Aladdin Regent Co. Ltd., China) was then added
and reacted with the silanol groups to form a gel, which was dried
in air by heating to 60 ◦C for 2 h. The resulting catalyst contained
1.3 wt.% Pd on TiO2 with a Pd particle size of 1.3 0.41 nm (by
STEM).
Pd/ZSM-5 (1.45 wt.% Pd with a particle size of 3.8 0.39 nm) was
also prepared by ion-exchanging of 2.0 g Na-ZSM-5 in 40 mL 0.1 M
aqueous solution of PdCl2 for 24 h with mild stirring at ambient
temperature [27]. The solid obtained was washed, centrifuged 3
times and dried at 80 ◦C overnight. It was then heated at 200 ◦C in
an O2/Ar (10%) flow for 1 h to remove water, calcined at 500 ◦C for
6 h with a programmed rate of 1.5 ◦C/min, followed by its reduction
at 400 ◦C in flowing H2 for 1 h.
3. Result and discussion
3.1. Catalyst characterization
3.1.1. TEM
Fig. 1 shows the scanning transmission electron microscopy
(STEM) images of catalysts. A is a low magnification of Pd/ZSM-
5 catalyst with white cubes of nano ZSM-5. As can be seen in B,
Pd nanoparticle with the size of 3.8 0.39 nm is clearly displayed
on the substrate of ZSM-5 in higher resolution mode. Images C
and D are Pd-PMHS/TiO2 catalysts with the Pd particle size of
1.3 0.41 nm. Tunable Pd sample synthesized by functional poly-
mer encapsulated method has smaller particle size than that of
impregnation method.
2.2. Catalyst characterization
The Pd loadings were determined by inductively coupled
plasma-atomic emission spectroscopy (ICP-AES). An HF/HNO3
solution was used to dissolve the catalyst samples. Samples for
scanning transmission electron microscopy (STEM, FEI Tecnai G2
T20) were prepared by supersonically dispersing them in ethanol
and deposition onto a holy carbon support film. Diffuse reflectance
IR (Nicolet 5700) measurement of CO adsorption was conducted
by placing about 30 mg of sample in a diffuse reflectance cell. After
purging with He, CO (99.999%) was passed over the catalyst for
15 min, followed by purging with He for 15 min. H2 chemisorp-
tion measurements was also conducted to determine the metal
3.1.2. CO adsorption
CO chemisorptions on both Pd samples were investigated by
diffuse reflectance FTIR, which can confirm the accessibility of
Pd in prepared catalyst in small molecules. As demonstrated in
Fig. 1. STEM images and the particle size distributions of (A) Pd/ZSM-5 and (B) Pd-PMHS/TiO2.

B. Fu et al. / Applied Catalysis A: General 415–416 (2012) 47–52
49
0.10
0.08
0.06
0.04
0.02
0.00
actively than Pd/ZSM-5. However, for both catalysts, as the reaction
temperature increases, the selectivity of both benzyl alcohol and
benzaldehyde decreases. For the given reaction time with higher
temperature, more benzaldehyde turns into benzoic acid, which
further reacts to generate benzyl alcohol. When toluene experi-
ments catalyzed by Pd are carried out at 200 ◦C, besides the regular
liquid products, COx is also detected in gas phase at the end of each
run. For the control experiments conducted at 200 ◦C, data indicates
that even without catalyst, air can oxidize toluene to its derivatives
at higher temperature and longer reaction time. This phenomenon
can be explained by the theory which states that molecular O2 is a
di-radical and can initiate homogeneous oxidation process at ele-
vated temperature and pressure even without a catalyst [13]. In
order to remove the background reaction, the temperature limit of
160 ◦C is set.
Pd-PMHS/TiO2
Pd/ZSM-5
2100
2000
1900
1800
1700
Wavenumber (cm-1)
3.2.2. Reaction time effect on toluene air oxidation
Fig. 3 shows toluene conversion and products selectivity in the
oxidation process over Pd-PMHS/TiO2 as a function of reaction
time. Under this condition, toluene is seen slowly oxidized at the
beginning in the first 10 h before rapidly increased in the next
30 h. Toluene conversion attains its equilibrium as reaction time
elapsed. The products composition is mainly benzaldehyde and
benzyl alcohol at the beginning of the reaction which decreases
with the reaction time. Meanwhile, the selectivity of benzyl acid
first increases and then decreases, mainly because more benzalde-
hyde was oxidized to benzyl acid at the beginning of the reaction. As
time elapses, product benzyl acid further reacts with benzyl alco-
hol to form benzyl benzoate. This observation is consistent with the
trend of benzyl benzoate selectivity.
Fig. 2. Diffused reflectance infrared spectrum of CO adsorption on Pd catalyst sam-
ple: (A) Pd-PMHS/TiO2 and (B) Pd/ZSM-5.
Fig. 2, linearly adsorbed CO on Pd atoms at 2055 cm−1 and
2080 cm−1 as well as ␮2 bridge-bonded CO and ␮3 CO on 3-fold
hollow sites (1950–1850 cm−1) were observed on both samples.
CO adsorption peak at 2055 cm−1 on Pd-PMHS/TiO2 sample was
assigned to linear CO on (1 1 1/(1 1 1)) and (1 1 1/(1 0 0)) edge sites,
while sample Pd/ZSM-5 peak at 2079 cm−1 was assigned to CO on
Pd atoms at corners [28]. The relative intensities of the linear to
bridging CO were higher for sample Pd-PMHS/TiO2 than Pd/ZSM-5
when compared at the same pretreatment temperature. This was
consistent with smaller Pd particle size observed by STEM in Fig. 1.
3.2.3. Effect of catalyst mass on toluene air oxidation
3.1.3. Pd metal dispersion determined by H2 chemisorption
The effect of amount of Pd-PMHS/TiO2 catalysts on the reac-
tion is carried out by varying the catalyst mass between 50 mg
and 1000 mg, while other reaction condition parameters are kept
constant. Results shown in Fig. 4 show that toluene conversion
increases almost linearly with the catalyst mass addition before
600 mg. However, this conversion does not continue too much even
with further addition of 400 mg more catalyst. This phenomenon
can be explained by two possibilities: one is the oxygen solubil-
ity limitation in toluene, which makes the oxygen concentration
constant in the liquid phase. The second possibility may be the
observation provided by Sheldon [4], which states that sometimes,
metal complexes of transition metals, especially in media of low
polarity such as neat hydrocarbons, often acts as catalyst at low
loadings but inhibitors at high loadings.
H2 chemisorption was conducted to confirm Pd nanoparticle
dispersion. Before measurements were taken, all the samples were
pretreated at 200 ◦C O2 for 1 h, then H2 for 1 h followed by N2
degassing for 1 h and then cooled down to 80 ◦C. Certain amount
of H2 was pulsed at 80 ◦C to prevent the formation of bulk palla-
dium hydride and calculated assuming an H/Pd stoichiometry of
unity [29,30]. Uptake of H2 by the sample was determined from
the intensities of the TCD response to the pulses. Metal dispersion
is shown in Table 1. Sample with higher dispersion has smaller
metal size, which is also consistent with the result in Fig. 1.
3.2. Toluene catalytic oxidation
In general, Pd-PMHS/TiO2 is more active in the reaction, as lower
toluene conversion is observed on Pd/ZSM-5. However, all product
selectivities do not change much compared with the result cat-
alyzed by Pd-PMHS/TiO2 (see detailed in Tables S1–S3). Therein,
Pd-PMHS/TiO2 catalyst performance is mainly focused on catalyz-
ing toluene oxidation reaction influenced by varied parameters.
3.2.4. Effect of air pressure on toluene air oxidation
The effects of the air pressure on the toluene conversion and
products selectivity over Pd-PMHS/TiO2 catalyst are shown in Fig. 5.
Toluene conversion increases with the partial pressure of oxygen
due to the higher air pressure which favors higher oxygen solubility
in liquid phase. Also, confined in a limited space with certain pres-
sure, the amount of oxygen is proportional to gas pressure. The top
X axis is the amount of oxygen calculated by Clausius–Clapeyron
equation based on the associated air pressure (considered as the
ideal gas). Generally, at given conditions, pressure does not affect
toluene conversion too much; the increased in conversion is due to
high O2 partial pressure which enhances higher concentration of
dissolved oxygen in liquid phase. While selectivity of both ben-
zaldehyde and benzyl benzoate slightly increases, that of both
benzyl alcohol and benzyl acid decreases.
3.2.1. Reaction temperature influence on selective toluene
oxidation
Table 2 shows toluene conversion and selectivity to benzyl
alcohol, benzaldehyde, benzoic acid and benzyl benzoate as a
function of temperature. Reaction seldom occurs when tempera-
ture is at 140 ◦C or lower. Pd-PMHS/TiO2 catalyst performs more
Table 1
Pd dispersion determined by H2 chemisorption at 80 ◦C.
Sample
Dispersion (%)
Observed Pd particle size from STEM (nm)
Comparison experiment conducted on the reaction of toluene
oxidation with pure oxygen and air. It is evident in Table 3 that
with the given condition, toluene conversion increases with the
Pd-PMHS/TiO2
Pd/ZSM-5
84.8
40.7
1.3 0.41
3.8 0.39

50
B. Fu et al. / Applied Catalysis A: General 415–416 (2012) 47–52
Table 2
Liquid phase oxidation of toluene with molecular air catalyzed by Pd supported catalyst.
Catalyst
Temperature (◦C)
Conversion (%)
Selectivity (%)
Benzyl alcohol
Benzaldehyde
Benzoic acid
Benzyl benzoate
Impurity
TON
–
130
554
848
Pd-PMHS/TiO2
140
160
180
200
–
Trace
10.6
8.4
Trace
56.1
33.1
20.4
–
–
–
–
–
2.4
1.6
6.8
10.4
6.4
21.1
9.7
26.1
37.4
52.8
4.7
Pd/ZSM-5
140
160
180
200
–
–
–
–
–
–
–
–
1.7
–
80
373
629
1.1
5.1
8.6
14.5
9.6
7.3
55.1
36.1
30.1
10.5
20.7
10.8
19.9
33.6
50.1
Blank
Blanka
Blankb
160
200
200
<0.1
3.6
9.3
17.7
13.5
9.6
80.6
42.3
27.6
1.7
23.3
48.3
–
21.9
14.5
–
–
–
Reaction conditions: t = 8 h, catalyst amount 100 mg, stirring rate = 1000 rpm, toluene = 100 mmol (10.5 mL), Pair = 290 psi.
Turnover number (TON): (mole of products/mole of Pd metal). TON is calculated based on the total Pd loading metals.
Control experiments were carried out in the absence of catalyst, with other reaction parameters: toluene = 10 mmol (10.5 mL), Pair = 290 psi, stirring rate = 1000 rpm, reaction
time for blanka and blankb was 10 h and 20 h, respectively.
80
Toluene Conversion
70
60
50
40
30
20
10
0
Benzyl Alcohol Selectivety
Benzaldehyde Selectivety
Benzoic Acid Selectivity
Benzyl Benzoate Selectivity
0
10 20 30 40 50 60 70 80 90
Time (h)
Fig. 3. Toluene conversion and selectivity to benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate as a function of reaction time over catalyst Pd-PMHS/TiO2:
reaction temperature 160 ◦C, Pair = 290 psi, 100 mmol (10.5 mL) toluene, 200 mg of catalyst, stirring rate 1000 rpm.
100
90
80
70
60
50
40
30
20
10
0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Toluene Conversion
Benzyl Alcohol Selectivety
Benzaldehyde Selectivety
Benzoic Acid Selectivity
Benzyl Benzoate Selectivity
0
200 400 600 800 1000
Catalyst Mass (mg)
0
100 200 300 400 500 600 700 800 900 1000
Catalyst mass (mg)
Fig. 4. Toluene conversion and selectivity to benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate as a function of catalyst mass over catalyst Pd-PMHS/TiO2:
reaction temperature 160 ◦C, toluene 100 mmol (10.5 mL), Pair = 290 psi, 50–1000 mg of catalyst, toluene/Pd mole ratio = 16,300–810, reaction time 6 h, stirring rate = 1000 rpm.
The inserted legend was the amplified toluene conversion trend.
Table 3
Comparison experiment of toluene oxidation with pure oxygen and air.
Catalyst
O2 concentration (%)
Conversion (%)
Selectivity
Benzyl alcohol
Benzaldehyde
Benzoic acid
Benzyl benzoate
Pd-PMHS/TiO2
20
100
1.1
2.6
23.6
16.9
45.1
50.2
17.4
15.5
13.9
17.4
Toluene conversion and selectivity to benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate as a function of O2 concentration over catalyst Pd-PMHS/TiO2: reaction
temperature 160 ◦C, total gas pressure is 145 psi, and O2 was balanced with N2, reaction time 8 h, toluene 100 mmol (10.5 mL), 200 mg of catalyst, stirring rate 1000 rpm.

B. Fu et al. / Applied Catalysis A: General 415–416 (2012) 47–52
51
O2 mass (mmol)
4
6
8
10
12
14
16
18
2.5
2.0
1.5
1.0
0.5
0.0
60
55
50
45
40
35
30
25
20
15
10
5
Toluene conversion
Benzyl Alcohol Selectivity
Benzaldehyde Selectivity
Benzyl Acid Selectivity
Benzyl Benzoate Selectivity
50
100
150
200
250
300
Pressure (psi)
Fig. 5. Toluene conversion and selectivity to benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate as a function of air pressure over catalyst Pd-PMHS/TiO2:
reaction temperature 160 ◦C, reaction time 10 h, toluene 100 mmol (10.5 mL), 200 mg of catalyst, stirring rate 1000 rpm.
Table 4
Catalytic activity comparison of toluene oxidation over recycled Pd catalyst.
Catalyst
Recycle time
Conversion (%)
Products selectivity
Benzyl alcohol
Benzaldehyde
Benzoic acid
Benzyl benzoate
Pd-PMHS/TiO2
0
1
2
3
4
2.3
2.3
2.2
2.2
2.1
9.6
9.3
9.2
9.1
9.2
55.1
56.4
55.5
54.7
55.1
11.4
10.8
11.1
10.7
10.3
23.9
23.5
24.2
25.5
25.4
Pd/ZSM-5
0
1
2
3
4
1.7
1.1
0.8
0.7
0.5
13.5
24.1
28.7
30.3
29.8
54.1
56.9
58.7
60.4
63.1
8.5
8.3
5.7
4.6
3.6
21.9
10.7
7.9
4.7
3.5
Reaction temperature 160 ◦C, Pair = 290 psi, reaction time 8 h, toluene 100 mmol (10.5 mL), 200 mg of catalyst, stirring rate 1000 rpm.
oxygen partial pressure without significant change in the products
composition.
encapsulated methods in a size controlled way. Smaller Pd size and
metal immobilization enhances higher atom efficiency utility and
makes catalyst Pd-PMHS/TiO2 more active than Pd/ZSM-5 during
the reaction. Around 1 nm and 4 nm Pd samples observed by TEM
are obtained. Both catalysts active site are accessible and confirmed
by CO adsorption on diffuse reflectance FTIR.
Solvent-free selective aerobic toluene oxidation catalyzed by
heterogeneous Pd-PMHS/TiO2 catalyst has been investigated with
varied parameters. With limited amount of oxygen confined in
autoclave, the optimum temperature is 160 ◦C and 40 h reaction can
give about 10% toluene conversion. Higher oxygen partial pressure
favors higher toluene conversion. Pd-PMHS/TiO2 catalyst encapsu-
lated in titanium oxide has a better reusability.
3.2.5. Catalyst reusability
A set of experiments is conducted to confirm the stability of Pd
catalysts catalytic activity and its reusability. The comparison data
both Pd-PMHS/TiO2 and Pd/ZSM-5 tested are shown in Table 4. In
each experiment, reaction stops after 8 h and Pd catalyst is then
recycled by centrifuging. With very careful washing and drying,
the recycled catalyst is then used for the next run. The results in
Table 4 show that identical toluene conversion is obtained after
reusing Pd-PMHS/TiO2 catalyst thrice with almost similar prod-
ucts selectivity. For Pd/ZSM-5 catalyst, toluene conversion drops
with increased in recycle time, while the selectivity of both benzyl
alcohol and benzaldehyde increases.
Acknowledgements
The decrease in the toluene conversion can be explained by the
catalyst active site Pd leaching into liquid phase due to how the
catalyst was synthesized. Pd/ZSM-5 is prepared by impregnation
method and most of the Pd nanoparticles are on the outer surface of
the support. Meanwhile, for the Pd-PMHS/TiO2 catalyst, when Pd is
reduced, stabilized and well dispersed in the solution, TiO2 gelatin
is formed around Pd nanopaticles, and Pd is confined and immobi-
lized inside the TiO2 network. For Pd/ZSM-5 catalyst, the selectivity
of both benzyl alcohol and benzaldehyde slightly increases mainly
because with increased in recycles, the less active catalyst converts
less alcohol and benzaldehyde to benzoic acid and benzyl benzoate.
The authors appreciate the National Nature Scientific Foun-
dation of China (Grant No. 21076044) and Scientific Major Basic
Research Program of Southeast University (Grant No. 21076044)
for the financial support.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.apcata.2011.12.008.
References
4. Conclusion
[1] S. Sakaguchi, T. Iwahama, Y. Ishii, Adv. Synth. Catal. 343 (2001) 393–427.
[2] T.G. Carrell, S. Cohen, G.C. Dismukes, J. Mol. Catal. A: Chem. 187 (2002) 3–15.
[3] K. Nomiya, K. Hashino, Y. Nemoto, M. Watanabe, J. Mol. Catal. A: Chem. 176
(2001) 79–86.
High activity ultra fine Pd catalysts have been prepared by
two different methods, impregnation and functional polymer

52
B. Fu et al. / Applied Catalysis A: General 415–416 (2012) 47–52
[4] R.A. Sheldon, Metal-Catalyzed Oxidation of Organic Compounds, Academic
Press, New York, 1981.
[17] P. Li, C. He, J. Cheng, C.Y. Ma, B.J. Dou, Z.P. Hao, Appl. Catal., B 101 (2011)
570–579.
[5] A.P. Antunes, J.M. Silva, F.R. Ribeiro, M.F. Ribeiro, P. Magnoux, M. Guisnet, Appl.
Catal., B 33 (2001) 149–164.
[18] X. Li, J. Xu, L. Zhou, F. Wang, J. Gao, C. Chen, J.B. Ning, H. Ma, Catal. Lett. 110
(2006) 149–154.
[6] M.W. Xue, J.N. Yu, H. Chen, J.Y. Shen, Catal. Lett. 128 (2009) 373–378.
[7] L. Jin, C.H. Chen, V.M.B. Crisostomo, L.P. Xu, Y.C. Son, S.L. Suib, Appl. Catal., A
355 (2009) 169–175.
[8] F. Konietzni, U. Kolb, U. Dingerdissen, W.F. Maier, J. Catal. 176 (1998) 527–535.
[9] G. Huang, F. Xiang, T.M. Li, Y.X. Jiang, Y.A. Guo, Catal. Commun. 12 (2011)
886–889.
[10] M. Popova, Á. Szegedi, Z. Cherkezova-Zheleva, A. Dimitrova, I. Mitov, Appl.
Catal., A 381 (2010) 26–35.
[11] R. Bonelli, S. Albonetti, V. Morandi, L. Ortolani, P.M. Riccobene, S. Scirè, S. Zac-
chini, Appl. Catal., A 395 (2011) 10–18.
[12] M. Ousmane, L.F. Liotta, G. Di Carlo, G. Pantaleo, A.M. Venezia, G. Deganello, L.
Retailleau, A. Boreave, A. Giroir-Fendler, Appl. Catal., B 101 (2011) 629–637.
[13] J. Bedia, J.M. Rosas, J. Rodriguez-Mirasol, T. Cordero, Appl. Catal., B 94 (2010)
8–18.
[14] S.M. Saqer, D.I. Kondarides, X.E. Verykios, Top. Catal. 52 (2009) 517–527.
[15] L. Kesavan, R. Tiruvalam, M.H. Ab Rahim, M.I. bin Saiman, D.I. Enache, R.L. Jenk-
ins, N. Dimitratos, J.A. Lopez-Sanchez, S.H. Taylor, D.W. Knight, C.J. Kiely, G.J.
Hutchings, Science 331 (2011) 195–199.
[19] M.L. Kantam, P. Sreekanth, K.K. Rao, T.P. Kumar, B.P.C. Rao, B.M. Choudary, Catal.
Lett. 81 (2002) 223–232.
[20] A. Martin, U. Bentrup, A. Brückner, B. Lücke, Catal. Lett. 59 (1999) 61–65.
[21] S.C. Kim, W.G. Shim, Appl. Catal., B 92 (2009) 429–436.
[22] S. Morales-Torres, A.F. Perez-Cadenas, F. Kapteijn, F. Carrasco-Marin, F.J.
Maldonado-Hodar, J.A. Moulijn, Appl. Catal., B 89 (2009) 411–419.
[23] W.G. Shim, J.W. Lee, S.C. Kim, Appl. Catal., B 84 (2008) 133–141.
[24] S. Gatla, N. Madaan, J. Radnik, V.N. Kalevaru, M.M. Pohl, B. Lucke, A. Martin,
A. Bruckner, Appl. Catal., A 398 (2011) 104–112.
[25] V.N. Kalevaru, A. Benhmid, J. Radnik, M.M. Pohl, B. Lucke, A. Martin, Catal. Today
141 (2009) 317–324.
[26] B. Fu, M.N. Missaghi, C.M. Downing, M.C. Kung, H.H. Kung, G. Xiao, Chem. Mater.
22 (2010) 2181–2183.
[27] X.F. Lin, K.R. Poeppelmeier, E. Weitz, Appl. Catal., A 381 (2010) 114–120.
[28] T. Lear, R. Marshall, J.A. Lopez-Sanchez, S.D. Jackson, T.M. Klapotke, M.
Baumer, G. Rupprechter, H.J. Freund, D. Lennon, J. Chem. Phys. 123 (2005)
174701–174713.
[29] M. Boudart, H.S. Hwang, J. Catal. 39 (1975) 44–52.
[30] A. Szu˝ cs, F. Berger, I. Dékány, Colloids Surf., A 174 (2000) 387–402.
[16] T. Förster, S.A. Schunk, A. Jentys, J.A. Lercher, Chem. Commun. (Cambridge U.
K.) 47 (2011) 3254–3256.