Nano Res

1

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

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:

Revised:

Accepted:

© Tsinghua University Press

and Springer-Verlag Berlin

Heidelberg 2014

KEYWORDS

Ceria, CO-assisted

synthesis, mesoporous

structure, CO catalytic

oxidation

ABSTRACT

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.

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.

Nano Research

DOI (automatically inserted by the publisher)

Address correspondence to First A. Firstauthor, email1; Third C. Thirdauthor, email2

Research Article

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2 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

dendrites,[15] and apple-like structure,[18] 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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3 Nano Res.

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.

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 1 XRD patterns of (a) GLM CeCO3OH (before

calcination) and (b) GLM CeO2 (after calcination)

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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4 Nano Res.

electron microscope (TEM) image and low-

magnification 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]

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.

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 3 Nitrogen sorption isotherms of the GLM CeO2; insets

are BET specific surface area and pore volume

Figure 4 Pore size distribution curve of the GLM CeO2 by an

analysis of the adsorption isotherm using BJH model

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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5 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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6 Nano Res.

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 Ce4+

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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7 Nano Res.

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 10 XPS C 1s spectra for (a) GLM CeCO3OH and (b)

GLM CeO2

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

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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8 Nano Res.

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

CeO2-DC

162

272

0.21(210 oC)

0.01(210 oC)

71.05

110.86

a Temperatures corresponding to 50% conversion of CO b The corresponding rate of CO conversion at 210 oC

Figure 12 Percentage conversion versus temperature plots for the

oxidation of CO over (a) GLM CeO2, (b) CeO2-DC, and (c) Au/

GLM CeO2

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.

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www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano Research

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).