Nano Research
Nano Res
DOI
10.1007/s12274-014-0614-9
Globin-like mesoporous CeO2: A CO assisted approach
based on carbonate hydroxide precursors and their
applications in low temperature CO 0xidation
Yeheng He, Xin Liang (), Biaohua Chen
Nano Res., Just Accepted Manuscript • DOI 10.1007/s12274-014-0614-9
http://www.thenanoresearch.com on October 22, 2014
© Tsinghua University Press 2014
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TABLE OF CONTENTS (TOC)
Globin-like
Mesoporous
CeO2:
A
CO
Assisted
Approach Based on Hydroxide Carbonate Precursors
and their applications in Low Temperature CO
Oxidation
Yeheng He, Runduo Zhang, Biaohua Chen, Xin Liang*
Chemical Engineering College, Beijing University of
Chemical Technology,Beijing, 100029, China
A CO-assisted hydrothermal approach has been developed to prepare
globin-like mesoporous CeO2 and a possible formation mechanism is
proposed.
Provide the authors’ webside if possible.
Author 1, webside 1
Author 2, webside 2
Nano Research
DOI (automatically inserted by the publisher)
Research Article
Globin-like Mesoporous CeO2: A CO Assisted
Approach Based on Carbonate Hydroxide Precursors
and their applications in Low Temperature CO
Oxidation
Yeheng He, Xin Liang (), Biaohua Chen
Received:
ABSTRACT
Revised:
Globin-like mesoporous CeO2 has been constructed by using a CO-assisted
synthetic approach based on hydroxide carbonate precursors, in which CO
plays a key role in the formation of the globin-like mesoporous precursors as
the carbon source because of its preferential adsorption on Ce3+ in the
hydrothermal conditions. The formation mechanism and the thermal
transformation process from globin-like mesoporous CeCO3OH to CeO2 have
been investigated by X-ray diffracton, scanning electron microscopy,
transmission electron microscopy, BET surface area measurement, thermal
analysis, fourier transform infrared spectroscopy, ultraviolet-visible
spectroscopy and X-ray photoelectron spectroscopy. Rod-like building blocks
interconnected by nanoparticles circle around to form each globin-like CeO2
sphere, leading to the formation of mesoporous structure simultaneously. The
globin-like mesoporous CeO2 shows much better performance in CO catalytic
oxidation than the ordinary CeO2 nanoparticles obtained by directly calcining
ceria nitrate. Moreover, the globin-like mesoporous CeO2 can act as an ideal
matrix for supported catalysts. The metallic Au particles can be well dispersed
in the globin-like CeO2 matrix to form Au/CeO2 supported catalysts, which
exhibit excellent activity for CO oxidation at room temperature.
Accepted:
© Tsinghua University Press
and Springer-Verlag Berlin
Heidelberg 2014
KEYWORDS
Ceria,
synthesis,
structure,
oxidation
CO-assisted
mesoporous
CO catalytic
Introduction
Ceria has received considerable interests as an
important component in three-way catalysts and CO
removal for its strong oxygen storage and release
ability arising from the facile conversion between
Ce3+ and Ce4+.[1-4] Well-defined mesoporous ceria
materials display extended surface area and unique
pore pathway, could sever as excellent supporting
materials, which are highly desirable in the field of
catalysis.[5-7] For example, Yadong Li’s group
synthesized mesoporous ceria spheres to construct
Ag/CeO2 catalysts, which show excellent catalytic
performance in the CO removal and formaldehyde
oxidation.[3] Au/CeO2 catalysts have been proved to
be efficient for the carbon monoxide oxidation.[8-11]
The mesoporous structures of the ceria support play
important influence on their catalytic performance by
tuning the characteristics of the support surface, as
well as the gold-support interactions.[12, 13] Thus,
rational synthesis of ceria mesoporous structures
have attracted a lot of research interests.
Address correspondence to First A. Firstauthor, email1; Third C. Thirdauthor, email2
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Nano Res.
Recently, cerium carbonate hydroxide (CeCO3OH)
becomes an ideal precursor to prepare ceria (CeO2)
without changing its original morphology.[14-17]
Different kinds of 3D structures of CeO2, such as
flowerlike
micro/nano-structure,[13]
3-fold
[15]
[18]
dendrites,
and apple-like structure,
have been
synthesized by using CeCO3OH as precursors.
Rational synthesis of CeCO3OH materials becomes
an effective way to construct ceria materials with
unique morphology and structure. Tranditionally,
the carbaon sources for the formation of CeCO3OH
precursors ranges from the inorganic carbonates,[16]
inorganic-organic hydrid complex to organic
ligands.[15, 17] For example, sodium tartrate was used
to synthsize CeCO3OH 3-fold dendrites.[15] Urea was
used as carbon source to synthesize CeCO3OH
microstructures.[14] However, most of the carbon
sources, such as ingoranic carbonate salt, and
complex organic ligands not merely introduce
heterogeneous impurities,[19] but also are hard to
remove in the post-treatment. A facile and clean
method for building well-ordered 3D structures of
CeCO3OH would be disirable.
Recent studies have shown that small molecules in
the hydrothermal system could effectively induce the
conversion of crystal morphology and futher guide
the crystal growth.[20, 21] Our earlier work reveals that
there are the strong interactions between Ce ions and
CO molecules, which could guide the growth of ceria
nanocrystals by introducing CO molecules into the
synthetic system.[22] In this study, we proposed a
CO-assisted hydrothermal approach with only
ethylene glycol (EG), water and cerium nitrate in the
aqueous
phase
to
synthesized
globin-like
mesoporous (GLM) CeCO3OH/CeO2 by using CO
molecules as the carbon source. Rod-like building
blocks interconnected by nanoparticles circle around
to form each sphere of 3D curved structure. The
unique curved and mesoporous structure can
effectively prevent further aggregation and maintain
high catalytic activity of these GLM CeO2 structures
which could serve as excellent catalyst supports. The
Au/GLM CeO2 catalysts achieve almost 100%
conversion for CO oxidation at room temperature.
1.
Experimental
1.1 Chemicals
All reagents were of analytical grade and used as
received without further purification. Deionized
water was used throughout. Ethylene glycol and
cerium nitrate were supplied by TianJin GuangFu
Fine Chemical Research Institute. Pure helium and
carbon monoxide (equilibrium gas is helium, the
percentage of carbon monoxide is 4.98%) were of
chemical grade and purchased from Beijing Haipu
Gas Company. LTD.
1.2 Synthesis of globin-like mesoporous CeO2
In a typical synthesis,[23] 1 mL 0.5 M Ce(NO3)3
solution and 4 mL H2O was added in 30 mL glycol
under magnetic stirring. After about 10 min of
stirring, the obtained solution was transferred into a
50 mL stainless autoclave. The vessel was purged
with carbon monoxide ten times to exhaust air, and
then pressurized up to 0.6 MPa and heated at 180 °C
for 16 h. Then the reactor was allowed to cool to
room temperature. The products were centrifuged,
washed several times with ethanol, dried at 60 °C for
10 h, and then calcined at 400 °C for 4 h.
1.3 Synthesis of Au/globin-like mesoporous CeO2
Au was deposited on the calcined GLM CeO2 by the
method of deposition-precipitation (DP) with
NaOH.[24] An aqueous solution of 100 mL HAuCl4
(2.4*10-3 M) was adjusted to pH 8 by the additional of
0.2 M NaOH, and then 1.896 g of calcined GLM CeO2
was dispersed in the solution, and the pH of the
slurry was readjusted to 8 with NaOH. The gold
concentration in the solution corresponds to a
theoretical Au loading of 1 wt% in the case of a
complete deposition-precipitation. The suspension
was stirred at room temperature for 1 h,
gold-deposited
samples
were
isolated
by
centrifugation and was washed several times with
dilute ammonia solution (4 M) to eliminate residual
chloride ions. Finally, the samples were dried at
100 °C for 5 h and calcined at 400 °C for 4 h in the air.
1.4 Materials characterization
The X-ray diffraction (XRD) patterns were obtained
on a Bruker D8-advance X-ray diffractometer with
Cu Kα radiation (λ = 1.54056 Å ). The sizes and
morphologies of the samples were examined by a
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JEOL JEM-2010 transmission electron microscope
(TEM) at 120 kV, and a high-resolution transmission
electron microscope (HRTEM) at 200 kV. Scanning
electron microscopy (SEM) was carried out on an
SUPRA 55/55VP scanning electron microscope. The
nitrogen sorption isotherms was measured on a
Sorptomatic 1990 instrument (Thermo Electron) at
liquid N2 temperature (-196 °C), using the
Brunauer-Emmett-Teller (BET) method, with outgas
pretreatment at 350 °C under vacuum. Thermo
gravimetric (TG) analysis and differential thermal
analysis (DTA) were performed using a HCT-1
Microcomputer of differential thermal balance at a
heating rate of 10 °C·min-1 in static air. The FT-IR
spectra for the samples were obtained on a Bruker
Tensor27 infrared spectrometer at room temperature.
The XPS spectra for the samples were detected on a
Thermo-Fisher ESCALAB 250 X-ray photoelectron
spectrometer, taking the C 1s peak at 285 eV of the
surface adventitious carbon as reference. The Uv-vis
spectra were obtained on a Shimadzu UV-3600
UV-vis spectrophotometer.
Figure 1 XRD patterns of (a) GLM CeCO3OH (before
calcination) and (b) GLM CeO2 (after calcination)
1.5 CO oxidation
The catalytic activities for CO oxidation were
evaluated in a fixed-bed quartz tubular reactor. The
100 mg catalyst samples after annealed at 400 °C for
4h were placed in the reactor. The reactant gases
(2.0% CO, 18% O2, balanced with nitrogen) went
through the reactor at a rate of 30 mL/min. The
composition of the gas exiting the reactor was
monitored by gas chromatography (Varian CP3800).
2. Results and discussion
2.1 Morphological and structural studies
The crystal structure of the precursors synthesized by
the CO-assisted hydrothermal approach was
characterized by X-ray diffraction. The XRD pattern
(Fig. 1a) was assigned to the hexagonal phase of
CeCO3OH (a = 7.238 Å , c = 9.960 Å , JCPDS Card No.
32-0189). Then the precursor CeCO3OH was calcined
at 400 °C for 4 h, and the diffraction peaks (Fig. 1b) of
the calcined sample could be indexed as the cubic
phase of ceria (Fm3m, a = 5.41134 Å , JCPDS Card No.
34-0394),
indicating
the
crystal
structure
Figure 2 (a-b) TEM and (c-d) SEM images of GLM CeCO3OH;
(e) HRTEM and (f) SEM image of GLM CeO2
transformation from pure hexagonal CeCO3OH to
cubic ceria of the samples during the calcinations
process.
Fig. 2(a-b) and Fig. 2(c) show the transmission
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electron microscope (TEM) image and lowmagnification scanning electron microscopy (SEM)
image of CeCO3OH, respectively. It is clearly
observed that the samples are mainly globin-like
spheres with diameters about 2-3 μm. The
high-magnification SEM image (Fig. 2(d)) shows that
each sphere is organized by nano-sized building
blocks curving around it; the building blocks are
interconnected by nanoparticles. As the Fig. 2(f)
shown, the morphology can be maintained after
thermal conversion of CeCO3OH to CeO2. Some
stacking mesoporous can be observed in the
high-magnification SEM image (Fig. 2(d) and (f)). A
representative high resolution TEM image taken
from the GLM CeO2 is shown in Fig. 2(e). The clear
lattice fringes with interplanar spacing of 0.191nm is
corresponding to the spacing of CeO2 (220) planes.[25]
Figure 3 Nitrogen sorption isotherms of the GLM CeO2; insets
are BET specific surface area and pore volume
2.2 BET analysis
Nitrogen adsorption/desorption isotherm (Fig. 3) of
the GLM CeO2 exhibits the type IV isotherm with an
apparent H4-type hysteresis loop in the P/P0 range of
0.5-1, indicating the CeO2 spheres are mainly
mesoporous. The hysteresis loop of H4 type is owing
to the formation of slit-like pores via the stacking of
those rod-like building blocks.[26] The BET specific
surface area and pore volume of the GLM CeO2 are
57.13 m2/g and 0.086 cm3/g, respectively. Accordingly,
the pore size distribution curve was determined from
the adsorption isotherm using BJH model. As shown
in Fig. 4, the curve of GLM CeO2 exhibits a
mesoporous distribution and gives a maximum pore
radius at 13 nm, which is consistent with the stacking
mesopores observed by SEM images.
Figure 4 Pore size distribution curve of the GLM CeO2 by an
analysis of the adsorption isotherm using BJH model
2.3 Thermal and FTIR analysis
The thermal decomposition process from GLM
CeCO3OH to GLM CeO2 was investigated by
TG/DTA analysis and FT-IR spectra. The TG curve
(Fig. 5a) shows a slight weight loss at temperatures
between 20 and 200 °C, relating to the loss of H2O
and trapped solvent. No obvious weight loss could
be observed above 400 °C. A dramatic weight loss
happens in the temperature range from 200 to 400 °C,
which is due to the removal of organic residues and
Figure 5 TG/DTA curves of thermal decomposition of the
as-prepared GLM CeCO3OH at a heating rate of 10oC min-1 in
static air
the thermal conversion of CeCO3OH as the following
reaction shown:[17, 27]
4CeCO3OH+O2→4CeO2+2H2O+4CO2
The DTA curve (Fig. 5b) shows two endothermic
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Nano Res.
peaks around 220 °C and 275 °C, corresponding to
the combustion of organic residues and endothermic
behavior during the decomposition of CeCO3OH to
CeO2, respectively.
Figure 6 FT-IR spectra of the GLM spheres (a) CeCO3OH
(before calcination) and (b) CeO2 (after calcination)
As FTIR spectrum of GLM CeCO3OH shown in Fig.
6a, the bands in the range of 3300-3700 cm-1
correspond to O-H stretching of surface adsorbed
water and hydroxyl groups of the EG molecules.
There are two peaks at 2845 and 2923 cm-1, which are
assigned to –CH2 asymmetric stretchs in the EG
molecules.[13] Both above results indicate that EG
molecules absorbed on the crystal surfaces and acted
as capping agent during the crystallization. The
peaks at 1078, 840 and 720 cm-1 can be ascribed to
νC-O, δCO32-, and νasCO2, respectively.[16, 28] The peaks
at 1400-1500 cm-1 are also ascribed to carbonate
species. As compared in Fig. 6b, these bands
corresponding to the carbonate species are almost
eliminated after heat treatment due to the thermal
decomposition from GLM CeCO3OH to GLM CeO2.
2.4 Formation mechanism for GLM CeO2
Based on the above results, the formation mechanism
of the GLM CeCO3OH is proposed. The schematic
illustration for the formation mechanism of GLM
CeO2 is shown in Fig 7.
The initial reaction solution is consist of EG, H2O,
Ce(NO3)3 and CO. Under the conditions,
Ce(NO3)3·6H2O firstly dissolved in the solution to
release corresponding ions. Previous experimental
and theoretical studies have proven the strong
interaction between CO and Ce3+, and CO molecules
are easily adsorbed on Ce3+ sites.[22, 29] With the system
temperature arising, the adsorbed CO would be
oxidized by NO3- to form CO32-. The EG molecules
would not reduce NO3- to form CO32- in that the
products obtained in the absence of CO were ceria
(Fig. S3) rather than CeCO3OH. Then each carbonate
ion binds to two mental centers to form carbonate
ligands through chelation or bridging function.[30]
The interaction can be well affirmed by FTIR analysis
in that the stretching of CO32- and O-Ce-O (587 cm-1)
are obvious in the spectrum of GLM CeCO3OH (Fig.
6a).[26] Then the newly formed carbonate-ligands
react with OH- to produce CeCO3OH anisotropic
building blocks through a homogeneous nucleation
and growth process. As the building blocks formed
in the solution, ethylene glycol, which possesses
abundant hydroxyl groups, then selectively adsorb
onto the crystal surfaces by hydrogen-bond
interaction or other possible chemical forces.[31] The
EG effectively neutralize the surface charges,
therefore, the self-assembly takes place. The formed
nanoparticles capped by organic agent further
aggregate to form rod-like building blocks. They
likely tend to rotate to lower the interface strain
energy and finally assemble into unique curved
structure. In the formation of GLM CeCO3OH, CO
plays an important role, which serves as a chelating
ligand to form stable complex with Ce3+ and further
kinetically control the reaction rate. Carbon
monoxide, the carbon source from gas phase, is
important in the forming process. We replaced the
CO gas by other carbonate source (Na2CO3) and
failed to yield assembled curved structure in the
absence of CO.
The GLM CeCO3OH could easily convert to GLM
CeO2 without changing its original morphology.
The GLM CeO2 is an ideal supporting material to
construct supported catalysts due to their
mesoporous curved structure. The active components,
such as Au nanoparticles and other noble metal
nanoparticles can be easily dispersed in the GLM
CeO2 matrix in directing high performance catalysts.
2.5 XPS and UV-vis analysis
The UV-vis analysis was carried out to characterize
the absorption property of GLM CeCO3OH and CeO2.
As shown in Fig. 8, both spectra of the samples
exhibit strong absorption band in the UV region. The
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Figure 7 Schematic illustration for the formation of GLM CeCO3OH/CeO2 via the CO-assisted synthesis; the red, grey and yellow
atoms are refer to oxygen, carbon and cerium, respectively; inset (left bottom) shows the model of the Au/GLM CeO2 and the orange
dots are refer to Au nanopartices
absorption band is below 500 nm in the spectrum of
GLM CeO2, while it shifts to below 400 nm and is less
stronger in that of GLM CeCO3OH. This difference
stems from the lower charge transfer energy of Ce 4+
than that of Ce3+.
X-ray Photoelectron Spectroscopy (XPS) has been
used as a powerful technique to investigate the
surface composition of the synthetic compounds. Fig.
9 shows the Ce 3d XPS spectra of GLM CeCO3OH
and CeO2. The peaks labeled v (v0, v, v1, v2, v3) and u
(u0, u, u1, u2) are corresponding to the Ce 3d5/2 and Ce
Figure 8 The UV-vis absorption spectra of (a) GLM CeCO3OH
and (b) GLM CeO2
3d3/2 levels. The peaks denoted v, v2, v3 are assigned
to the states of Ce4+, and v0, v1 have been assigned to
the states of Ce3+. The assignment of u labels is
similar to the v labels.[32] As shown in the spectra of
CeCO3OH (Fig. 9a), only v0, v1, u0 and u1 can be
observed, indicating that the oxidation state of ceria
was Ce3+. The spectrum of the CeO2 illustrates that
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Figure 9 XPS Ce 3d spectra for (a) GLM CeCO3OH and (b)
GLM CeO2
both Ce4+ and Ce3+ exist in the calcined sample. These
spectra are in agreement with the results reported
previously.[13]
According to the C 1s spectra (Fig. 10), three types of
carbon species can be identiﬁed. The CI type peak
was set to correct sample charging. The CII type peak
is assigned to the carbon-oxygen bonds (C-OH,
C-O-C). Obviously, the CII type peak in the spectrum
of GLM CeCO3OH is much stronger than that of
CeO2, which is due to the abundant EG molecules
existing in the former sample. The CIII
Figure 11 XPS O 1s spectra for (a) GLM CeCO3OH and (b)
GLM CeO2
type peak can be partly ascribed to the carbon
contamination on the surface of the samples. In
addition, the carbon-oxygen bonds (O-C-O, C=O)
could contribute to the CIII type peak.[33] Because of
the more O-C-O and C=O bonds from the CO32- in the
precursor, the area of CIII type peak in the spectrum
of CeCO3OH is much larger than that of CeO2.
O 1s XPS spectra are shown in Fig. 11. The low
binding energy peaks (OI: 529.7–530.5 eV) are
assigned to lattice oxygen in the samples. The
binding energy of lattice oxygen is shifted towards
lower binding energy from CeCO3OH to CeO2, which
may attribute to the change of charge state from Ce3+
to Ce4+. The high binding energy peak (OII: 531.9 eV)
can be ascribed to oxygen vacancies and surface
adsorbed oxygen (O2− or O−),[34] which has an
important influence on the catalytic activity.
2.6 CO catalytic oxidation
Figure 10 XPS C 1s spectra for (a) GLM CeCO3OH and (b)
GLM CeO2
CO oxidation is a simple but widely studied reaction
in heterogeneous catalytic reactions. Ceria materials
have been extensively applied as active components
or supports due to its strong ability to store and
release oxygen.[4]
In this study, the CO oxidation activity over GLM
CeO2 is evaluated. For comparison, we also prepared
ceria (named as CeO2-DC) by directly calcining ceria
nitrate at 400 °C for 4h and the CO oxidation over
CeO2-DC was taken. The results are shown in Fig. 12.
Table 1 summarized the results of CO catalytic
activity tests. Under the same experimental
conditions (GHSV=18000 h-1), the value of T50 in GLM
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CeO2 is 162 °C, while it in CeO2-DC shows a increase
of 110 °C. At 210 °C, the CO conversion is 96% over
GLM CeO2 and 4% over CeO2-DC; the corresponding
rates of CO conversion are 0.21 and 0.01 mmol/(g·s),
respectively. Therefore, the rate of conversion over
GLM CeO2 is 21 times higher than that over CeO2-DC
at 210 °C. Arrhenius plots of CO oxidation over the
two catalysts are shown in Fig. 13,[35] indicating that
the activation energy for GLM CeO2 is lower than
that for CeO2-DC. All of these results show that the
GLM CeO2 synthesized in the presence of CO are
more active than the ceria obtained by direct thermal
decomposition.
Moreover, Au/GLM CeO2 catalysts were synthesized
by a DP method. The HRTEM image (Fig. S1)
confirmed that the metallic Au particles (2-3nm) were
highly dispersed on the GLM CeO2 surface. In
comparison with the GLM CeO2, the Au/ GLM CeO2
shows a decrease in pore size (Fig. S2), further
confirming the Au particles were well dispersed in
the mesoporous GLM CeO2 structure. Fig. 12(c)
shows that the CO conversion over (1%) Au/ GLM
CeO2 reached almost 100% when the reaction was
performed at 22 °C.
Table 1 Comparison of CO catalytic activities over GLM CeO2
and CeO2-DC
sample
T50 ( oC )a
rate ( mmol/g·s )b
Ea ( kJ/mol )
GLM CeO2
162
0.21(210 oC)
71.05
272
0.01(210 oC)
110.86
CeO2-DC
a
Temperatures corresponding to 50% conversion of CO
b The corresponding rate of CO conversion at 210 oC
Figure 13 The Arrhenius plots of CO oxidation over (a) GLM
CeO2 and (b) CeO2-DC (conversions<20%)
3. Conclusions
In summary, we proposed a CO-assisted synthetic
method to prepare globin-like mesoporous CeO2. It
provides a novel way to synthesis 3D self-assembly
structures. Furthermore, the product is a good
catalyst support due to the high surface area and
unique mesoporous via the stacking of building
blocks. Globin-like mesoporous CeO2–supported
gold catalyst show good performance in CO catalytic
oxidation at low temperature.
Acknowledgements
This work was financially supported by National
Natural Science Foundation of China (NSFC) (grant
number 21476012 and 21121064), Beijing Higher
Education Young Elite Teacher Project (grant 386
number YETP0484) and the State Key Project of
Fundamental Research for Nanoscience and
Nanotechnology (grant number 2011CB932402).
Electronic Supplementary Material: The HRTEM (Fig.
S1) and BET (Fig. S2) analysis of the Au/GLM CeO2.
The XRD patterns of products obtained with and
without CO in the synthetic system.
Figure 12 Percentage conversion versus temperature plots for the
oxidation of CO over (a) GLM CeO2, (b) CeO2-DC, and (c) Au/
GLM CeO2
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Nano Res.
Electronic Supplementary Material
Globin-like Mesoporous CeO2: A CO Assisted
Approach Based on Carbonate Hydroxide Precursors
and their applications in Low Temperature CO
Oxidation
Yeheng He, Xin Liang (), Biaohua Chen
Supporting information to DOI 10.1007/s12274-****-****-* (automatically inserted by the publisher)
The HRTEM analysis
Fig. S1 HRTEM image of Au/GLM CeO2 and the insets show magnified views of the specific highlighted areas
A representative high resolution TEM image taken from the Au/GLM CeO2 is shown in Fig. S1. The insets
exhibit clear lattice fringes with interplanar spacing of 0.236nm, which is corresponding to the spacing of
Au(111) planes.
The BET analysis
Address correspondence to First A. Firstauthor, email1; Third C. Thirdauthor, email2
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Nano Res.
Fig. S2 (a) Nitrogen sorption isotherms of the Au/GLM CeO2 (insets are BET specific surface area and pore volume) and (b) Pore size
distribution curve of the Au/GLM CeO2 by an analysis of the adsorption isotherm using BJH model
In comparision with the GLM CeO2, the Au/ GLM CeO2 shows a decrease in pore size (Fig. S2(b)), pore
volume and BET surface area (Fig. S2(a)), further confirming the Au particles were well dispersed in the
mesoporous GLM CeO2 structure.
The XRD patterns
Fig. S3 The XRD patterns of products obtained (a) with and (b) without CO in the synthetic system.
The XRD patterns of products obtained with and without CO in the synthetic system were shown in Fig.
S3. The pattern of product (Fig. S3(a)) obtained in the absence of CO could be indexed as the cubic phase of
ceria (Fm3m, a=5.41134Å , JCPDS Card No. 34-0394). When the autoclave was equipped with high pressure
carbon monoxide (0.6MPa), the precipitate was collected as ceria precursor, the XRD pattern (Fig. S3(b)) of
which was assigned to the hexagonal phase of CeCO3OH(a=7.238Å , c=9.960Å , JCPDS Card No. 32-0189).
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