The catalytic use of supported gold nanoparticles for styrene synthesis via oxidative dehydrogenation of ethylbenzene

Article abstract of DOI:10.1007/s10562-010-0470-5

A series of supported gold catalysts have been prepared and tested as a new type of catalyst for the oxidative dehydrogenation of ethylbenzene to styrene. The effects of the supports (α-Mn₂O₃, Fe ₂O₃, TiO_2<

Full text of DOI:10.1007/s10562-010-0470-5

Catal Lett (2011) 141:198–206
DOI 10.1007/s10562-010-0470-5
The Catalytic Use of Supported Gold Nanoparticles for Styrene
Synthesis Via Oxidative Dehydrogenation of Ethylbenzene
•
Jie Xu Jun Huang Yong-Mei Liu
•
•
•
Yong Cao Yong-Xin Li Kang-Nian Fan
•
Received: 16 August 2010 / Accepted: 8 October 2010 / Published online: 26 October 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A series of supported gold catalysts have been
prepared and tested as a new type of catalyst for the oxi-
dative dehydrogenation of ethylbenzene to styrene. The
effects of the supports (a-Mn2O3, Fe2O3, TiO2, Al2O3, and
CeO2), preparation methods, gold loadings, and reaction
conditions have been investigated. Among the catalysts
tested, the Au/CeO2 sample containing a 6.0 wt% gold
content prepared via a routine deposition–precipitation
method exhibited the highest ethylbenzene conversion
(66.9%) and remarkable styrene selectivity (91.0%). The
superior catalytic performance of the Au/CeO2 catalysts
can be attributed to a dramatic increase in the oxygen
mobility and storage capacity of the parent CeO2 material
in association with the closely contacted Au nanoparticles,
which is confirmed by the TPR, total OSC, and XPS
measurements.
1 Introduction
In the past decade, catalysis by gold has emerged as one of
the most intensively studied topics in chemistry. Au was
historically considered to be chemically inert and hence a
poor catalyst [1, 2]. However, when finely divided as small
particles (B5 nm) and suitably deposited onto an oxide
support [3, 4], Au could become a highly active and
selective catalyst in many reactions including oxidation
[5–7], hydrogenation [8], selective isomerization [9] and
one-pot multistep reactions [10–12]. The outstanding cat-
alytic ability of Au is related to the size and shape of the
nanoparticles (NPs), the degree of coordinative unsatura-
tion of the Au atoms, and the interactions between Au and
the oxide support [2–4]. Of particular interest to the current
chemical community is the Au-catalyzed selective oxida-
tion, which is believed to be essential for the development
of new alternative and greener routes toward sustainability
[7, 13]. One recent focus in this area is to expand the scope
of the selective aerobic oxidations [5–7] that can be effi-
ciently catalyzed by supported Au NPs. In this context,
several liquid phase aerobic oxidations, including the
selective oxidation of alcohols [13–16], aldehydes [17],
amines [12, 18, 19], oximes [20] and olefinic hydrocarbons
[7, 13] have been developed. Despite significant research
effort, there have been few studies on the selective oxi-
dation of less reactive hydrocarbons in the gas phase over
the supported Au NPs [21, 22], probably due to the fact that
both the reactants and products are prone to undesired
combustion in the presence of molecular oxygen at high
temperatures [23–25].
Keywords Gold Á Ceria Á Oxidative dehydrogenation
(ODH) Á Ethylbenzene
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-010-0470-5) contains supplementary
material, which is available to authorized users.
J. Xu Á Y.-X. Li (&)
College of Chemistry and Chemical Engineering, Changzhou
University, Gehu Road 1, Changzhou, Jiangsu 213164,
People’s Republic of China
e-mail: liyx@em.jpu.edu.cn
Styrene (ST) is one of the most important monomers
extensively used in the chemical industry for the manu-
facture of polymers, copolymers and reinforced plastics
[26]. In 2009, the worldwide production of ST was more
J. Huang Á Y.-M. Liu Á Y. Cao Á K.-N. Fan
Shanghai Key Laboratory of Molecular Catalysis and Innovative
Materials, Department of Chemistry, Fudan University,
Shanghai 200433, People’s Republic of China
123

Catalytic Use of Supported Gold Nanoparticles
199
than 23 megatons (http://www.sriconsulting.com/WP/Pub
lic/Reports/styrene/). Most of the ST monomer is com-
mercially produced by means of the direct catalytic dehy-
drogenation (DH) of ethylbenzene (EB) at high reaction
temperatures (600–650 °C), with multi-promoted potas-
sium-iron oxide as a catalyst [27, 28]. Due to its highly
endothermic nature, this traditional route suffers from
several pronounced disadvantages such as intensive energy
consumption and rapid coking. In the last few years, con-
siderable research efforts have been directed toward the
development of less energy-intensive processes for the
production of ST [26]. The catalytic oxidative dehydro-
genation (ODH) of EB in the presence of air or molecular
oxygen (O2) is an attractive alternative to the traditional
DH process [29–31], which is thermodynamically favored
at much lower temperatures and usually does not lead to
the formation of coke. However, this selective oxidation is
particularly challenging, given the high reactivity of ST
toward further oxidation.
DP-derived materials at 450 °C for 4 h in 5 vol%H2/Ar
gas. The final catalyst is denoted as nAu/CeO2-DP here-
inafter where DP denotes the routine NaOH-mediated DP
method, n represents the nominal Au loading.
To investigate the effect of preparation method on Au
ODH activity, two additional 4 wt% Au/CeO2 samples
were prepared by urea-mediated deposition–precipitation
(UDP) and conventional wet impregnation (IMP) methods.
In addition, a Au/a-Mn2O3 catalyst was prepared, as
Au/a-Mn2O3 catalysts had been reported to show good low
temperature CO activity [37]. Au was deposited to the
a-Mn2O3 support by the UDP method. A further series of
gold catalysts including Au/TiO2 (Type A, Lot no.
Au/TiO2 #02-1), and Au/Fe2O3 (Type C, Lot no. Au/Fe2O3
#02-5) were supplied by the World Gold Council,
Au/Al2O3 (catalogue no. 79-0160) was provided by Mintek.
2.2 Characterization of Catalysts
To date, the most promising catalysts suggested for this
process have been confined to several carbon nanostruc-
tures including onion like carbon (OLC) [30, 32] or carbon
nanofibers (CNF) [33, 34]. Nevertheless, the fine powdered
nature, and intrinsically low resistance to combustion of the
carbon-based nanomaterials have greatly hindered their
practical applications [35]. Very recently, we have reported
that high surface area (180 m2 g-1) mesostructured ceria
material featuring superior low temperature redox proper-
ties can catalyze the ODH of EB at temperatures around
450 °C [36]. In the present work, we report the develop-
ment of new efficient ceria supported gold catalyst system
exhibiting significantly enhanced activity and stability for
the ODH of EB. Our results have shown that the intro-
duction of gold nanoparticles can lead to a dramatic
increase in the oxygen mobility and oxygen storage
capacity of the parent CeO2 material, which makes the
catalysts highly active and stable for the reaction.
Structural analysis of the various Au/CeO2 catalysts was
carried out on a Bruker D8 Advance X-ray diffractometer
equipped with a graphite monochromator, operating at
40 kV and 40 mA and employing nickel-filtered Cu-Ka
˚
radiation (k = 1.5406 A). The morphologies of all
Au/CeO2 catalysts were studied by JEOL 2010 electron
microscope. The bulk loading amount of Au in all
Au/CeO2 catalysts were measured by inductively coupled
plasma atomic emission spectroscopy (ICP-AES). Tem-
perature programmed reduction (TPR) profiles were
obtained on a homemade apparatus. The samples were
pretreated in a mixed gas (O2/N2 = 1/8) at 450 °C for
30 min and cooled to room temperature. Subsequently, the
samples were reduced with 5 vol% H2/Ar at 40 mL min-1
with a ramping rate of 5 °C min-1 to ca. 900 °C. The H2
consumption was monitored by an on-line thermal con-
ductivity detector (TCD). X-ray photoelectron spectra
(XPS) analysis was performed on a Perkin Elmer PHI
5000C spectrometer using Mg Ka radiation (1253.6 eV,
pass energy of 20.0 eV). The carbonaceous C 1s line
(284.6 eV) was used as the reference to calibrate the
binding energies (BE).
2 Experimental
2.1 Catalyst Preparation
2.3 Catalytic Activity Measurements
A series of Au/CeO2 catalysts were prepared via a routine
deposition–precipitation (DP) method with NaOH as the
precipitation agent [1]. Briefly, 1 g CeO2 (Evonic, Adnano
90, surface area: 90 m2 g-1) was added to an aqueous
solution with desired amount of HAuCl4 and NaOH
(NaOH/Au = 100, molar ratio). The suspension was then
heated to 80 °C and stirred for 4 h, followed by filtering
and washing for several times with distilled water. The
resulting solid product was dried overnight and finally a
purple colored catalyst was obtained by reduction of the
The activity of the catalysts for ODH of EB was measured
in the temperature range of 350–500 °C at atmospheric
pressure using a fix-bed, down-flow, tubular quartz reactor
(i.d. 4 mm, length 400 mm). Each run used approximately
50 mg of catalyst in the form of 60–80-mesh particles,
mixed with 300 mg of silicon carbide grains of similar size
for best temperature control. EB was evaporated at 35 °C
in flowing N2 and subsequently mixed with O2. Unless
otherwise stated, the corresponding flow rate of EB, O2,
123

200
J. Xu et al.
and N2 is fixed at 0.5, 0.25 and 20 mL min-1
(GHSV = 19,972 h-1), respectively. Prior to testing, the
catalysts were pretreated in a mixed gas (O2/N2 = 1/8) at
450 °C for 30 min. The products were analyzed by an on-
line gas chromatograph (Agilent GC 6820). Permanent
gases (O2, CO, CO2) were separated using a TDX-01
column connected to a TCD detector and other reaction
products were analyzed employing a FFAP column con-
nected to a FID detector. The catalytic data were acquired
after 1 h on stream of the reaction. The carbon balance
closed to 100 5% and was additionally monitored by the
COx content after catalytic combustion of organic species
in a final total oxidation reactor.
2.0Au/CeO2-DP (Table 1, entry 5) prepared by the routine
DP method showed the highest activity in terms of the
selective formation of ST. The steady-state ST selectivity
obtained was as high as 90.0% which indicated the success
in depressing secondary oxidation, in sharp contrast to what
was observed for most of the other supported Au catalysts
(Table 1, entries 1–4). A clear advantage of the Au/CeO2-
DP catalyst over other noble metals was also noticed when
the reaction was performed using Pt/CeO2 or Ru/CeO2
under otherwise identical conditions (Table 1, entries 6, 7).
It is important to remark that in the presence of small
amount of O2 (nO2/nEB = 0.5), the performances of
Au/CeO2 were comparable to or even higher than those of
the typical iron catalysts (Supporting Information, Table
S1), noting that we did not introduce any steam in the ODH
tests. However, for the commercial DH process, steam (with
high steam/oil ratio (S/O)) as an inert diluent is always
required to provide heat, to regenerate the iron-based active
sites from coking and to shift the equilibrium conversion of
EB, which results in large energy consumption.
2.4 Total OSC Measurement
The total oxygen storage capacity (OSC) measurement was
tested at 450 °C. 25 mg ceria-supported Au catalyst diluted
with 300 mg silicon carbide grains of similar size was
placed in a quartz U-shape reactor. The concentration of
the three components (H2, H2O, and He) in the outlet gas
was monitored by an on-line mass spectrometer (Balzers
OmniStar, QMS 200). A sample was exposed to alternating
H2 (40 mL min-1 for 10 s) and He (40 mL min-1 for 80 s)
pulses, and the alternating pulsation lasted until the signal
intensity of H2 reached a balance (100 5%). Total OSC
was calculated by integrating the consumption of H2 [lmol
[O] g-1].
Further detailed studies were carried out using the
2.0Au/CeO2-DP catalyst to gain insights into the catalytic
requirements for the ODH of EB. First, the effect of the
reaction temperature was investigated and is illustrated in
Fig. 1. The EB conversion increased rapidly as the reaction
temperature was raised from 350 to 450 °C but leveled off
at 500 °C, with the selectivity of ST decreases gradually
from ca. 97% to 85%. In all cases, ST was obtained as the
major product, accompanied by appreciable amounts of
COx and very small amount of other byproducts such as
benzaldehyde or methyl benzyl alcohol. Presumably,
higher temperature should give rise to better catalytic
activity for the ODH reaction. However, as is well known
in the literature [2], higher reaction temperature (well
above the Tammann temperature of bulk gold, see below)
may also lead to the sintering or growth of Au NPs, which
can greatly compromised the performance of 2.0Au/CeO2-
DP under these conditions. Moreover, studies on the effect
of the oxygen concentration revealed that the stoichiome-
tric O2/EB ratio (nO2/nEB = 0.5) was the ratio of choice
3 Results and Discussion
3.1 Catalytic Tests
Initially, a range of Au catalysts supported on various
inorganic supports were applied to the ODH of EB under a
previously established reaction condition at 450 °C [36]. As
can be seen from Table 1, the chemical nature of the sup-
port has a strong influence on the catalytic performance of
the Au NPs. Of the various Au-based catalysts tested,
Table 1 Catalytic performance
of various catalysts for ODH of
EB
Entry
Catalysts
Au loading
(wt%)
Conv.
(%)
Selec.
(%)
Yield
(%)
1
2
3
4
5
6
7
Au/a-Mn2O3
Au/Fe2O3
Au/TiO2
2.0
4.5
1.5
1.5
2.0
2.0
2.0
7.9
10.1
15.2
12.1
32.7
8.4
12.6
40.8
59.1
44.3
90.0
17.5
24.2
1.0
4.1
9.0
Au/Al2O3
2.0Au/CeO2-DP
Pt/CeOa2
5.4
a
29.4
1.5
Pt/CeO2, Ru/CeO2 prepared
by wet impregnation (IMP), see
supporting information for the
detailed preparation methods
Ru/CeOa2
9.5
2.3
123

Catalytic Use of Supported Gold Nanoparticles
201
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
To gain further insights into the function of Au, we have
investigated the effect of Au loading on the catalytic per-
formance. As shown in Table 2, EB could only be poorly
converted over the parent ceria support [36], whereas the
introduction of Au remarkably enhanced EB conversion
and selectivity for the partial oxidation products. High
selectivity to ST was obtained over the Au/CeO2 catalysts
with higher Au content (Table 2, entries 2–4) and the ST
formation increased with the gold loading up to 6.0 wt%
Au. However, an even higher Au loading amount with
8.0 wt% would compromise the catalytic activity. As will
be discussed later, the undesired formation of larger Au
particles ([5 nm) may account for such activity deterio-
ration. The best performance was observed for the catalyst
containing 6.0 wt% Au (Table 2, entry 4), which was
characterized by high selectivity comparable to the best yet
reported for EB ODH [29, 34, 38]. Moreover, in a com-
parison of three different preparation methods (Table 2,
entries 3, 6, 7), it is observed that the Au/CeO2 catalyst
prepared by DP method is more effective. The evolution of
the catalytic performance at 450 °C as a function of reac-
tion time for the Au/CeO2-DP catalysts is shown in Fig. 3.
Remarkably, the 6.0 wt% Au/CeO2 was found to be stable
during the reaction, and the ST yield did not undergo
appreciable changes with the time on stream.
350
400
450
500
Temperature (°C)
Fig. 1 Catalytic behavior of the 2.0Au/CeO2 at different reaction
temperatures
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
con.
sel.
3.2 Catalyst Characterization
The ICP-AES analysis (Table 2) shows that the real
amount of gold deposited on CeO2 is ca. 10–25% lower
than the nominal Au loading, consistent with the known
fact that only limited amount of gold contained in the
solution can be deposited onto an oxide support via the
routine DP method [3]. The specific surface areas for
the various Au/CeO2-DP catalysts were similar to those for
the parent support (Table 2). The XRD pattern of the
parent ceria (Fig. 4) show well-defined diffraction feature
characteristics of the cubic fluorite structure of CeO2
(JCPDS card no. 34-0394). After the deposition of Au NPs
onto the ceria support, an almost identical XRD pattern
0.25
0.5
1.0
2.0
O2:EB
Fig. 2 Effect of molar ratio of O2 to EB on the catalytic ODH
performance of the 2.0 Au/CeO2-DP catalyst
(Fig. 2). It was clarified that both lower and higher O2/EB
ratios would lead to a great reduction in the reaction rate
for the selective formation of ST.
Table 2 Catalytic performance
of the Au/CeO2 catalysts for
ODH of EB
Entry
Catalysts
Actual Au
loading
(wt%)
Surface
area
(m2 g)
Conv.
(%)
Selec. (%)
Yield
(%)
ST
COx
Othersa
1
2
3
4
5
6
7
CeO2
–
88
78
75
70
68
65
70
19.5
32.7
50.6
66.9
65.4
40.2
47.0
80.2
90.0
92.4
91.0
88.1
57.2
57.4
17.2
6.6
2.6
3.4
15.6
29.4
46.8
60.9
57.6
23.0
26.9
2.0Au/CeO2-DP
4.0Au/CeO2-DP
6.0Au/CeO2-DP
8.0Au/CeO2-DP
4.0Au/CeO2-IMP
4.0Au/CeO2-UDP
1.5
2.8
4.0
6.2
3.8
3.2
3.7
3.9
0.3
8.7
3.4
8.5
a
Benzene, benzaldehyde, and
methylbenzyl alcohol based on
GC analysis
10.4
8.5
32.4
34.1
123

202
J. Xu et al.
100
90
80
70
60
50
40
30
20
10
0
100
80
60
40
20
0
TEM was used as a complementary technique to
examine the structures of gold particles. Representative
TEM images for the various catalysts are shown in Fig. 5.
In the case of the Au/CeO2-DP samples, the Au NPs were
small and evenly dispersed over the 2.0Au/CeO2-DP with
an average particle size of ca. 3.6 nm. With increasing gold
loading, a progressive increase in the Au particle size can
be observed. A considerable fraction of Au particles with
particle size larger than 5.0 nm was detected over the
catalyst containing 8.0 wt% Au. The TEM analysis of the
4.0Au/CeO2-IMP as well as 4.0Au/CeO2-UDP also showed
the presence of appreciable fraction of Au particles larger
than 5 nm over the support, in good agreement with the
XRD data as described above. All these results strongly
suggest that the NaOH DP method is more suitable to
achieve a high dispersion of Au NPs with small Au particle
size (\5 nm) over the ceria support. Additionally, it is
interesting to point out that after 5 h on stream of the
reaction at 450 °C, the size of Au NPs has not undergone
noticeable changes, which could partly explain the stability
of the catalyst. We note that this lack of agglomeration
indicates that, when properly prepared and in association
with a suitable support, supported gold NPs can serve as a
stable catalyst for high temperature applications, although
it is known that gold has a relatively low Tammann tem-
perature (395 °C) [39]. Presumably, the presence of a
strong metal-support interaction (SMSI) between the gold
particles and the underlying CeO2 support may play a key
role in stabilizing the Au particles [40, 41].
Conversion
Selectivity
0
30
60
90 120 150 180 210 240 270 300
Time on stream (min)
Fig. 3 Time on stream of EB ODH on 6.0Au/CeO2-DP
4.0Au/CeO2-UDP
4.0Au/CeO2-IMP
8.0%Au/CeO2-DP
6.0Au/CeO2-DP
4.0Au/CeO2-DP
2.0Au/CeO2-DP
CeO2
TPR experiments were carried out to gain an insight into
the redox properties of the various catalysts. As shown in
Fig. 6, two main peaks at low (peak a) and high temper-
ature (peak b) are observed for all samples, assignable to
the reduction of surface- capping oxygen and bulk oxygen
species, respectively. While the blank ceria showed a broad
low temperature reduction profile in the range 250–500 °C,
the introduction of Au species drastically decreases the
temperature of the peak a. The lowest temperature (ca.
77 °C) was observed over 6.0Au/CeO2-DP, a feature sig-
nifying superior low temperature reducibility. In addition,
OSC measurements at 450 °C revealed a limited OSC of
ca. 140 lmol [O] g-1 over the parent ceria material
(Fig. 7). This value is consistent with the broad literature
[42–44] showing that the reduction of ceria surface layers
is limited to 5.0%. When Au NPs were deposited onto the
ceria, the XP spectrum of the Au 4f7/2 core level shows a
predominant contribution from metallic Au0 at a binding
energy of 84.0 eV [45] (Fig. 8). Notably, it was found that
the loading of Au caused a significant modification in the
oxygen storage behavior of the ceria materials. These
results can be rationalized by assuming that the presence of
small Au NPs can result in the favorable enhanced oxygen
mobility in the surface layers of ceria, mostly due to the
20
30
40
50
60
70
80
90
2θ (°
Fig. 4 XRD patterns of Au/CeO2-DP, 4.0Au/CeO2-IMP and 4.0Au/
CeO2-UDP samples
was obtained for Au/CeO2-DP comparing with CeO2,
indicating that the crystalline structure and the average size
of the crystalline domain of the CeO2 support are well
maintained in the gold samples. Moreover, no peaks due to
gold species were detected, except in the case of the 8.0Au/
CeO2-DP sample, where a distinct metallic Au reflection
line at 2h = 38.2° appears. Figure 4 also compared the
effect of the preparation methods on the size of the Au
NPs. It is revealed that the UDP- and IMP-derived 4.0Au/
CeO2 catalysts already show distinct metallic Au diffrac-
tion lines, in sharp contrast to the absence of any Au fea-
tures as observed for the 4.0Au/CeO2-DP sample with a
similar gold content. The average gold crystalline size,
calculated by Scherrer equation, was 5.3, 6.2 and 10.3 nm
for the 8.0Au/CeO2-DP, 4.0 Au/CeO2-UDP and 4.0Au/
CeO2-IMP samples, respectively.
123

Catalytic Use of Supported Gold Nanoparticles
203
(a)
(b)
(c)
45
40
35
30
25
20
15
10
5
(A)
0
2
3
4
5
6
7
8
Mean size (nm)
45
40
35
30
25
20
15
10
5
(B)
0
2
3
4
5
6
7
8
Mean size (nm)
40
35
30
25
20
15
10
5
(C)
0
2
3
4
5
6
7
8
Mean size (nm)
Fig. 5 TEM images of 2.0Au/CeO2-DP (a), 4.0Au/CeO2-DP (b), 6.0Au/CeO2-DP (c), 8.0Au/CeO2-DP (d), 4.0Au/CeO2-IMP (e), 4.0Au/CeO2-
UDP (f), and the spent 6.0Au/CeO2-DP (g) samples
creation of a high abundance of oxygen vacancies in ceria
lattice, which are responsible for the considerably
enhanced reduction degrees as observed for the Au/CeO2
catalysts.
Bearing in the mind that the catalytic behaviors of ceria-
based materials is highly sensitive to the mobility or
amount of the lattice oxygen, to gain further insight into the
nature of the DP derived Au/CeO2 catalysts in relation to
123

204
J. Xu et al.
(d)
(e)
(g)
40
30
20
10
0
(D)
2
3
4
5
6
7
8
Mean size (nm)
(F)
40
30
20
10
0
(G)
2
3
4
5
6
7
8
Mean size (nm)
Fig. 5 continued
their ODH activity, the total OSC of the various catalysts
are plotted against with the corresponding reaction rate. As
shown in Fig. 7, the amount of available lattice oxygen
species in the Au/CeO2 material directly correlates the
catalytic activity of CeO2 in the ODH of EB reaction,
permitting a rational explanation for the positive effect of
Au loading on the performance of the catalyst. We there-
fore infer that the present ODH of EB over the Au/CeO2-
based catalysts may proceed via a simple redox mechanism
involving the Ce4?/Ce3? couple, in which the catalyst
123

Catalytic Use of Supported Gold Nanoparticles
205
undergoes reduction (by EB) and reoxidation (by O2)
cycles. In this sense, the overall reaction pathway can be
envisaged to involve a delicate redox interplay between Au
clusters and the CeO2 matrix during the EB ODH process,
i.e., the reaction proceeds via a facile Au-mediated oxygen-
transfer mechanism in which the consumption and
replenishment of the ceria lattice surface oxygen species
vicinal to Au NPs play a key role in the reaction process.
To testify this hypothesis, XPS studies on Au/CeO2 sub-
jected to sequential EB/O2 exposures were carried out. The
results show that the consumption and replenishment of the
lattice oxygen, as reflected by the distinct atmospheric-
dependent variation of the ratio of Ce4?/Ce3? (Fig. S1) is
essential for this reaction.
77
6.0Au/CeO2-DP
4.0Au/CeO2-DP
85
88
2.0Au/CeO2-DP
CeO2
351
100
200
300
400
500
600
700
800
900
Temperature ( °C)
Fig. 6 TPR profiles of the Au/CeO2-DP and CeO2 samples
4 Conclusions
20
In summary, a novel Au-decorated ceria catalyst, featured
with superior low temperature catalytic performance, has
been developed for the oxidative dehydrogenation of eth-
ylbenzene to styrene. Compare to other noble metal-oxide
support combinations, the Au/CeO2-DP catalysts prepared
via a routine deposition–precipitation method exhibited a
high activity and selectivity toward the reaction. In the
presence of small amount of O2 (nO2/nEB = 0.5), a stable
styrene yield over 60% can be obtained over the 6.0Au/
CeO2-DP catalyst at temperatures around 450 °C. Based on
the TPR profiles and total OSC results, it was clarified that
the introduction of Au nanoparticles (B5 nm) has drasti-
cally enhanced the oxygen mobility and storage capacity of
the ceria, thus leading to the significant improvement of its
catalytic activity. Furthermore, the XPS results implied that
the ODH of ethylbenzene over the Au/CeO2 catalyst may
proceed via a simple surface redox mechanism involving
the Ce4?/Ce3? couple.
Reaction rate
Total OSC
0.6
0.5
0.4
0.3
0.2
0.1
15
10
5
0
0
2.0
4.0
6.0
8.0
Au-loading amount (%)
Fig. 7 Correlation between the reaction rates of the Au/CeO2
catalysts with their corresponding total OSC at 450 °C
3+
Acknowledgments This work was financially supported by the
National Natural Science Foundation of China (20633030, 20721063,
20803012, and 20873026), the National High Technology Research and
Development Program of China (2006AA03Z336), and the National
Basic Research Program of China (2009CB623506), Science & Tech-
nology Commission of Shanghai Municipality (08DZ2270500).
Au0 4 5/2
f
Au
4
f
Au0 4 7/2
f
7/2
87.7 eV 85.9 eV 84.0 eV
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