Highly Active and Stable Palladium Catalysts Supported on Surface-modified Ceria Nanowires for Lean Methane Combustion

Article abstract of DOI:10.1002/cctc.202001438

An efficient strategy was presented to synthesize highly active palladium catalyst supported on ceria nanowires modified by organosilanes (abbreviated as Pd/CeO₂NWs@SiO₂) for lean methane combustion. It is found that such a surface-modified strategy can significantly improve the dispersion of surface palladium species and strengthen the concentration of active surface-adsorbed oxygen species via reconstructing the surface microenvironment, invoking an efficient performance for methane oxidation. Under the space velocity of 60,000 mLg^?1h^?1, 0.5 wt% Pd/CeO₂NWs@SiO₂ displayed extraordinary catalytic activity with 90 % conversion rate at a temperature of around 327 °C, far lower than that of pristine Pd/CeO₂NWs (378 °C) under the same conditions. What's more, unexpected stability was observed under high temperature and the presence of water vapor conditions owing to the intense metal support interaction of Pd/CeO₂NWs@SiO₂ catalyst. The possible reaction mechanism of lean methane oxidation was probed by in situ DRIFT spectra. It is observed that the pivotal intermediate products (carbonate and carbon oxygenates) generated on Pd/CeO₂NWs@SiO₂ surface are more readily decomposed into CO₂. Importantly, the silicon hydroxyl groups (Si?OH) formed during the reaction can efficiently restrict the generation of the stable Pd(OH)_x phase and release more active sites to facilitate the catalytic performance. This study provides a convenient method to design the highly reactive and durable palladium-based catalyst for methane combustion.

Full text of DOI:10.1002/cctc.202001438

The European Society Journal for Catalysis
Supported by
Accepted Article
Title: Highly active and stable palladium catalysts supported on
surface-modified ceria nanowires for lean methane combustion
Authors: Mingwei Wu, Wenzhi Li, Ajibola T. Ogunbiyi, Ge Guo,
Fengyang Xue, Kun Chen, and Baikai Zhang
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.202001438
Link to VoR: https://doi.org/10.1002/cctc.202001438
0
1/2020

ChemCatChem
10.1002/cctc.202001438
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
Highly Active and Stable Palladium Catalysts Supported on Surface-modified
Ceria Nanowires for Lean Methane Combustion
a
a,b
a
a
a
Mingwei Wu , Wenzhi Li *, Ajibola T. Ogunbiyi , Ge Guo , Fengyang Xue , Kun
a
a
Chen , Baikai Zhang
a. Laboratory of Basic Research in Biomass Conversion and Utilization,
Department of Thermal Science and Energy Engineering, University of Science
and Technology of China, Hefei 230026, China
1
1
1
1
1
1
1
1
1
1
2
2
2
b. Institute of Energy, Hefei Comprehensive National Science Center, Hefei 230031,
China
ABSTRACT
An efficient strategy was presented to synthesize highly active palladium catalyst
supported on ceria nanowires modified by organosilanes (abbreviated as
Pd/CeO
2
NWs@SiO ) for lean methane combustion. It is found that such a surface-
2
modified strategy can significantly improve the dispersion of surface palladium species
and strengthen the concentration of active surface-adsorbed oxygen species via
reconstructing the surface microenvironment, invoking an efficient performance for
-1 -1
methane oxidation. Under the space velocity of 60,000 mLg h , 0.5 wt%
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
Pd/CeO
2
NWs@SiO
2
displayed extraordinary catalytic activity with 90% conversion
NWs
rate at a temperature of around 327℃, far lower than that of pristine Pd/CeO
2
(378℃) under the same conditions. What's more, unexpected stability was observed
under high temperature and the presence of water vapor conditions owing to the intense
metal support interaction of Pd/CeO
2
NWs@SiO catalyst. The possible reaction
2
mechanism of lean methane oxidation was probed by in situ DRIFT spectra. It is
observed that the pivotal intermediate products (carbonate and carbon oxygenates)
generated on Pd/CeO
Importantly, the silicon hydroxyl groups (Si–OH) formed during the reaction can
efficiently restrict the generation of the stable Pd(OH) phase and release more active
2
NWs@SiO
2
surface are more readily decomposed into CO .
2
x
sites to facilitate the catalytic performance. This study provides a convenient method to
design the highly reactive and durable palladium-based catalyst for methane
combustion.
Keywords ： palladium, ceria nanowires, surface-modified, reaction mechanism,
methane combustion
Introduction
Methane is one of the main volatile organic pollutants (VOCs), which is widely
generated from automobile exhaust and various industrial processes such as coal
[
1]
treatment, oil refining and natural gas treatment. With the increasing requirement of
environmental protection, the demand for efficient lean methane elimination
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
6
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
technology becomes more and more urgent. Methane (CH ) molecule contains four
4
equivalent C-H bonds and forms a highly symmetric tetrahedral configuration with sp3
orbital hybridization, thus the dissociation energy of first C-H bond is up to 435
[
2]
kJ/mol. Therefore, the catalytic combustion of methane is a significant method for
the effective treatment of lean methane to combat the serious environmental issue,
which possesses great application potential due to the advantages of low ignition
temperature, low energy consumption, good purification effect and no secondary
emissions of by-products.[3] It is widely recognized that the precious metal catalysts
such as palladium-based catalysts have excellent reactivity for lean methane
combustion（CCM）. However, improving the utilization rate and stability of precious
metals to boost their catalytic activity and commercial application has caused extensive
concern in the methane catalytic combustion.[2, 4] Besides, it is acknowledged that
cerium oxide is usually used as a robust support or active component for methane
oxidation which exhibits eminent oxygen storage capacity (OSC) as well as
4
+
3+
dynamically reversible redox properties because of the unique Ce /Ce redox pairs,
which can cause strong interactions with precious metal ions.[5] Herein, the Pd-CeO
catalytic system has been extensively studied for lean methane combustion（CCM）
over the past decades, which is attributed to the highly active ingredient (PdO ) and the
powerful Pd-CeO interaction. On the other hand, the formation of highly dispersed Pd-
Ce-O mixed oxides can result in more uncoordinated oxygen atoms and surface oxygen
2
x
2
4
+
2+
[6]
vacancies due to the similar radius of Ce (0.87 Å) ions and Pd (0.86 Å) ions.
Therefore, the thermal stability and catalytic activity of ceria-supported palladium
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
6
6
6
7
7
7
7
7
7
7
7
7
7
8
8
8
8
8
8
8
8
8
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
catalysts for CCM can be massively enhanced. Recent investigations manifest that the
catalytic activity and stability of Pd-based catalyst may be intensely related to the
intense metal–support interactions and the ambient environment of metal centers.[7]
Some researchers encapsulated the palladium nanoparticles into a nanoshell to
synthesize a core@shell structural catalyst which is a feasible strategy to inhibit metal
particle aggregation and protect active sites from toxic species.[8] For instance,
Cargnello et al. designed an ingenious catalyst with small cerium oxide NPs
encapsulated PdO NPs, which showed outstanding thermal stability for suppressing the
[
9]
aggregation of Pd NPs at high reaction temperature in CCM. Besides, the impact of
CeO support on catalytic performance is generally contributed to the interaction
between the CeO support and Pd or PdO species for the Pd-based catalysts. Colussi et
al. employed experiments and density functional theory (DFT) calculation to
2
2
demonstrate that the highly active Pd/CeO
2
catalyst possessed a reconstructed CeO
2
2
+
4+
surface due to the Pd ions substituted for Ce ions, therefore, this ordered Pd−O−Ce
fractions severed as high active sites for methane combustion.[10] Comparing with rod-
CeO
2
and cube-CeO
2
, octahedral-CeO showed higher activity for CCM, because of its
2
higher OSC, more oxygen vacancies and oxygen mobility.[3a] One-dimensional (1D)
nanowire materials have been regarded as excellent supports to anchor noble metal,
owning to high specific surface areas and abundant surface defects.[11] Besides,
previous reports demonstrated that the surface area, adsorption capacity and the
catalytic performance of Pd-based catalysts were strongly affected by the existence
pattern of Pd
x
O
y
clusters via altering metal-support interaction (MSI).[12] In general,
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
8
9
9
9
9
9
9
9
9
9
9
9
0
1
2
3
4
5
6
7
8
9
supported metal catalysts can expose more active sites via shrinking metal sizes, thus
significantly improving their catalytic efficiency. However, compared with the large
size metal particles, the small size metal species have higher surface free energy, which
tends to accumulate during the reaction process, leading to the decrease of catalytic
lifetime.[13] Thus, developing a convenient and effective strategy to improve the activity
and stability of precious metals for methane oxidation at high temperatures is a
significant and challenging task.
In this work, we devoted a strategy to design highly dispersed and thermal stable
palladium catalysts supported on surface-modified cerium dioxide nanowires and to
achieve extraordinary light-off activity for lean methane combustion. Briefly, CeO
2
nanowires were adopted as the support and modified by coating triethoxy(octyl)silane
(TEOOS) to produce amorphous organic silica sheath. After the deposition of
1
1
1
1
1
1
1
1
1
1
1
00
01
02
03
04
05
06
07
08
09
10
palladium, the obtained catalyst was denoted as Pd/CeO
CCM. Interestingly, the catalytic performance of relevant samples ranked as the
followed sequence: CeO NWs@SiO < CeO NWs < 0.5Pd/CeO NWs <
0.5Pd/CeO NWs@SiO . Subsequently, various characterization techniques were
2
NWs@SiO and tested for
2
2
2
2
2
2
2
carried out to evaluate the surface physicochemical properties of the as-synthesized
catalysts. More importantly, the reaction mechanism of methane combustion over the
palladium-containing catalysts was investigated through in situ DRIFTS
characterization.
Results and discussion
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Structures and Morphologies
The powder X-ray diffraction (Figure S1) patterns were chosen to identify the crystal
phase of as-prepared ceria supports and Pd/CeO catalysts. It is observed that all the
catalysts showed a typical face-centered cubic structure CeO crystal structure (JCPDS
2
2
No. 34-0394), indicating that the deposition of palladium species and the modification
of support did not change the surface crystal structure of the catalysts. Specifically, no
any new standard diffractions peak corresponding to metallic Pd (2θ = 40°, 46°) or PdO
phase (2θ = 33.9°, 42°) can be observed.[14] One conceivable reason is that the loaded
Pd species is well-dispersed on the outer surface. Meanwhile, although the existence of
Si species in CeO
2
NWs@SiO
2
and 0.5Pd/CeO
2
NWs@SiO samples was confirmed by
2
the Mapping and XPS spectra, no characteristic peak of Si species can be observed in
both samples, suggesting that the Si phase covering the surface of catalyst is almost
amorphous.
The TEM and HRTEM images were applied to investigate the morphology and size of
0.5Pd/CeO
as-synthesized 0.5Pd/CeO2NWs@SiO
a length of ~ 300 nm. The HRTEM images (Figure 1b) of 0.5Pd/CeO
2
NWs@SiO
2
and 0.5Pd/CeO
2
NWs samples. As depicted in Figure 1a, the
exhibited an average diameter of ~ 11 nm and
NWs@SiO
2
2
2
exposed an interplanar lattice spacing of 0.19 and 0.27 nm on the surface of ceria which
correspond to the (110) and (100) crystal planes, respectively.[15] It is noticeable that no
distinguishable palladium particles can be observed, but instead an amorphous phase
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
with uneven thickness was visible on the surface of 0.5Pd/CeO
2
NWs@SiO
2
, which was
amorphous silica attached on the surface. However, as depicted in Figure 1c, one can
find obvious palladium nanoparticles (size of 6-9 nm) attached on the surface of
0.5Pd/CeO NWs sample, and the palladium nanoparticle mainly exposed lattice
2
spacing of 0.23 nm and 0.30 nm assignable to the (111) and (100) crystal facets of
PdO.[16] EDX-mapping images (Figure 1d-g) were provided to inquiry the spatial
distribution of Pd and Si components in 0.5Pd/CeO
show that Pd and Si species were well dispersed on CeO
unambiguously indicated that the introduction of organosilane into the surface of
CeO NWs support could effectively improve the dispersion of Pd species and reduce
the size of Pd species, which insured sufficient exposure of the active Pd sites.
The N adsorption–desorption isotherm patterns of relevant catalysts were shown in
Figure S2, all samples displayed typical type-IV isotherms with H hysteresis loop at
P/P
= 0.8-1.0 corresponding to typical mesoporous materials.[17, 18] The BET surface
area and pore volume results were summarized in the Table 1. As can be seen, after
loading 0.5 wt% Pd, the BET specific surface areas of the 0.5Pd/CeO NWs@SiO
sample increased more significantly than that of 0.5Pd/CeO NWs samples. Compared
with CeO NW support, the pore volume of 0.5Pd/CeO NW obviously increased, while
that of 0.5Pd/CeO NWs@SiO slightly reduced compared with CeO NWs@SiO
2
NWs@SiO
2
catalyst, which clearly
2
NWs surface. These results
2
2
1
0
2
2
2
2
2
2
2
2
2
.
Formation mechanism
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
The whole synthetic strategy has been depicted in Scheme 1. The CeO nanowires were
2
synthesized by a hydrothermal method in term of previous report.[19] Lastly, the ceria
surface was modified by triethoxy-n-octysilane (TEOOS) to produce organic silicon
sheath around the nanowires in which the long-chain alkyl groups were retained under
reflux conditions. When ceria was modified by the TEOOS at 110℃, the alkoxy groups
tend to hydrolysis and then attach on the ceria surface to assemble Si–O–Ce bonds.
What’s more, the surface of CeO
to the reaction between the organosilane and support, after which the surface of
CeO NWs@SiO became hydrophobic and formed a space fence structure by the
hydrophobic alkyl-functionalized layer. Besides, it has been reported that Pd(OAc)
2
nanowires was covered by long alkyl chains thanks
2
2
2
exhibits a trimeric structure in toluene solvent, which is bridged by six acetate
ligands.[20] When the palladium acetate and modified support are simultaneously
impregnated in anhydrous toluene, the three-dimensional structure of the Pd(OAc)
the long alkyl chains of modified support surface are conducive to improve the
dispersion of palladium atoms. The TG-DTA analysis of modified CeO NWs@SiO
2
and
2
2
support was used to evaluate the evolution of organosilane on sample surface. As
depicted in Figure S3, the sample exhibited a significant weight loss at the region of
200-500°C, owing to the combustion of organic groups. Therefore, after calcination,
the alkyl chains readily turned into SiO films and the palladium atoms grafted onto the
2
surface of modified ceria in the form of small Pd cluster. The highly dispersed Pd sites
were conducive to boost the utilization rate of Pd species and enhance catalytic
performance towards methane oxidation compared with the large palladium
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
nanoparticles. Thus, this preparation method provides an effective strategy to shrink the
size of palladium nanoparticles by exploiting the spatial structures of the organosilane
and the palladium acetate in organic solvent.
Chemical and electronic states
XPS spectra were employed to probe the valence states and the chemical environment
of relevant surface composition for CeO
relevant results were summarized in Table 1. The Pd 3d XPS spectrum of
0.5Pd/CeO NWs and 0.5Pd/CeO NWs@SiO samples were depicted in Figure 2A. As
2
support and Pd-containing samples and the
2
2
2
can be seen, both samples display two similar Pd 3d5/2 peaks at 337 and 337.9 eV, which
can be attributed to two states of the surface Pd2+ species. As shown in previous
literature[6, 12], the binding energy (BE) value at 337 eV can be assigned to the Pd in
2+
crystalline PdO NPs located on CeO
to the Pd2+ in ceria matrix in the CeO
0.5Pd/CeO NWs, the characteristic peaks at 337 eV can be obviously observed and the
2
surface and the peak at 337.9 eV can be attributed
2
surface and subsurface. In the case of
2
2
+
Pd ratio in crystalline PdO NPs was 37.8% according to the fitting results, whereas
the proportion of Pd2+ in crystalline PdO NPs was only 12.5% in
0.5Pd/CeO
the ceria matrix as the solid-solution phase with the (-Pd -O -Ce -) linkages. The
aforementioned results indicate that the Pd species of 0.5Pd/CeO NWs@SiO has a
2
NWs@SiO
2
catalyst, indicating that the Pd species are mainly dispersed in
2
+
2-
4+
[21]
2
2
more homogeneous distribution as the sub-nanoparticle, which is in good agreement
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
99
00
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
with the TEM results.
The Si 2P XPS spectra (Figure 2B) of the samples containing silicon were carried out
to elucidate the effect of silicon species. As in previous reported studies, the binding
energies of Si 2P appeared at 98.8 - 99.7, 101.0 - 102.0 eV and 102.1 - 103.2 eV are
0
, respectively.[22] Therefore, the corresponding
NWs@SiO located at 101.7 eV and 102.1
and SiO , respectively. Such a phase
contributed to Si , SiO
x
(0<x<2) and SiO
and 0.5Pd/CeO
eV, which were caused by unsaturated SiO
transition is in line with the hypothesis about the thermal evolution of TEOOS
mentioned above. It is noteworthy that the peak of the calcined CeO NMs@SiO
appeared at 101.9 eV, shifting towards the lower BE direction. The presence of chemical
shift between the calcined CeO NWs@SiO and Pd/CeO NMs@SiO confirms that the
introduction of Si species can boost the metal-support interaction, thereby, enhances the
catalytic performance of 0.5Pd/CeO NWs@SiO . The evident coupling between Pd 3d
2
peaks of CeO
2
NWs@SiO
2
2
2
x
2
2
2
2
2
2
2
2
2
and Si 2P XPS results confirms that the silicon species should be a critical factor for
the reactivity of active Pd phase for CCM.
3
+
It is widely recognized that the Ce concentration can be used to reflect the amount of
oxygen vacancy on the ceria surface.[23] According to the previous literatures[3a, 24], the
XPS curves of the Ce 3d can be further decomposed into 10 groups. As shown in Figure
3
+
3A, the amount of surface Ce of relevant catalysts was calculated by the total peak
0
0
4+
area of S1 (v + v′+ u + u′) and the Ce concentration was calculated by S2 (v +
3
+
v″+ v‴ + u + u″+ u‴). Thus, the concentration of Ce can be decided by the relation
of S1/(S1 + S2) and the acquired results were listed in Table 1. Among these samples,
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
3
+
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
it can conclude that the Ce concentration on the surface raised significantly after
3
+
loading Pd and the 0.5Pd/CeO
2
NWs@SiO sample had the higher Ce value (27.4%)
2
than that of 0.5Pd/CeO NWs (20.4%), which indicated that the oxygen vacancies
2
exhibited lower formation energy on the modified ceria crystal facets. The
asymmetrical O 1s XPS spectra were shown in Figure 3B, in which three different
surface oxygen species were observed. According to previous reports[25], the binding
2
-
energy of 529.3 eV can be indexed to lattice oxygen species (O
α
, e.g, O ), the peak
, e.g, O 2
-, O -
or O ), and the
-
located at 531.1 eV can be caused by adsorbed oxygen (O
β
2
2
peak situated at 533-534 eV can be assigned to the weakly bound oxygen components
(O ). The O /O ratio is a measurement, as compiled in Table 1, to evaluate the
proportion of active oxygen vacancies.[26] The ratios of O
CeO NWs@SiO 0.5Pd/CeO NWs, 0.5Pd/CeO NWs@SiO
γ
β
α
/O
β α
for CeO
2
NWs,
2
2
,
2
2
2
samples were
approximately 24.3, 31.1, 25.6 and 36.6%, respectively. Consequently, the O 1s and Ce
3d XPS spectra results clearly reveal that the support decorated by silicon species can
release more active oxygen vacancies, which may partially clarify the unique activity
as a CCM catalyst.
Redox property and oxygen activity
In order to investigate the redox behavior and strong metal oxide interactions of
0.5Pd/CeO
2
NWs and 0.5Pd/CeO
2
NWs@SiO
2
, H -TPR experiment was performed and
2
the profiles were depicted in Figure 4A. As can be clearly seen, all curves exhibited two
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
H
2
consumption peaks in the low temperature zone of 60–120℃, in which the reduction
peak at around 88℃ belongs to the isolated PdO species and the peak at around 113℃
can be assigned to the reduction of the PdO nanoparticles interacting with CeO to
metallic Pd.[6, 27] The hydrogen consumption corresponding to individual PdO species
in 0.5Pd/CeO NWs@SiO catalyst was obviously less than that in 0.5Pd/CeO NWs
x
2
2
2
sample, which is associated with the intense metal support interaction (MSI) in
modified catalyst. Besides, it is worth noting that the broad reduction peak at 350-600℃
can be caused by the reduction of surface oxygen, in which the 0.5Pd/CeO
sample exhibited a significantly lower reduction temperature (420 ℃ ) than
0.5Pd/CeO NWs sample (552℃). This is convincing proof to reveal the powerful
synergetic effects between the deposited active components and CeO
indicating the outstanding oxygen delivery capacity in 0.5Pd/CeO NWs@SiO
2
NWs@SiO
2
2
2
support,
sample.
2
2
The peak at 700-900℃can be attributed to the reduction of lattice Ce species.[28] Overall,
these observations manifest that the presence of Si species on CeO crystals can
2
significantly facilitate the surface reducibility of the Pd-containing catalyst, resulting in
the enhanced catalytic activity for CCM.
The temperature-programmed desorption of O
were performed to further investigate the amount and mobility of surface oxygen
species of 0.5Pd/CeO NWs and 0.5Pd/CeO NWs@SiO catalysts. In order to compare
oxygen storage capacity of related samples at different temperatures, the samples were
pretreated by 4 vol% O /Ar for 30 min at 300°C and 400°C, respectively. There is a
2
(O
2
-TPD) experiments (Figure 4B)
2
2
2
2
broad overlapping desorption peak at 100-500°C for all catalysts, assigned to the
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
chemisorbed oxygen and lattice oxygen on the vacancies of CeO
2
. [6, 17] The amount of
adsorbed oxygen could be a reflection of the oxygen storage capacity of the catalyst.[ 29,
3
0]
Compared with the 0.5Pd/CeO
2
NWs catalyst, 0.5Pd/CeO
2
NWs@SiO exhibited a
2
larger peak area at the zone of 100-300°C, indicating that the modified catalyst can
store more reactive oxygen species, which was in agreement with the XPS results. In
brief, both H
2
-TPR and O
2
-TPD results indicated that the amount and activity of oxygen
NWs@SiO sample. Generally, these ingredients are
species was higher in 0.5Pd/CeO
2
2
beneficial to boost the catalytic oxidation activity for the combustion of lean methane.
Catalytic performance and stability
Figure
0.5Pd/CeO
under the space velocity of 60,000 mLg h . In contrast to the modified
CeO NWs@SiO support, pristine CeO NWs displayed relatively good catalytic
activity for CCM. Surprisingly, after loading the precious palladium, the
0.5Pd/CeO NWs@SiO catalyst showed superior catalytic activity with 90%
conversion at a low temperature of 327℃, much lower than that 378℃ of
0.5Pd/CeO NWs. Notable that the catalytic performance of these samples ranked as the
followed sequence: CeO NWs@SiO < CeO NWs < 0.5Pd/CeO NWs <
0.5Pd/CeO NWs@SiO , which was in good agreement with the order of the surface
oxygen mobility and reducibility attested by XPS and O -TPD experiment. In the
5A
exhibited the
light-off
performance
of
0.5Pd/CeO
2
NWs,
2
NWs@SiO
2
and corresponding support for the lean methane oxidation
-1 -1
2
2
2
2
2
2
2
2
2
2
2
2
2
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
2
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
87
88
89
90
91
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
Meanwhile, in order to disclose the utilization efficiency of Pd atoms, the
corresponding reaction rates and TOFs were also calculated at 275°C and the results
were listed in Table S1. The reaction rates of Pd/CeO samples at 275°C are ranked as
NWs (47.6 μmol g s ) < 0.5Pd/CeO NWs@SiO
(102 μmol g-1
catalyst for the methane
combustion at 275°C is 6.3 × 10 s , which is higher than that of 0.5Pd/CeO NWs
(2.9 × 10−2 s−1). Furthermore, CH
catalytic combustion activity over
2
-
1 −1
follows: 0.5Pd/CeO
2
2
2
−
1
-1
s ). The TOF (s ) value of 0.5Pd/CeO
2
NWs@SiO
2
−
2
−1
2
4
-1 -
0.5Pd/CeO
2
NWs@SiO
2
at a weight hourly space velocity (WHSV) of 30,000 mLg h
1
-1 -1
-1 -1
and 120,000 mLg h was tested, the CH conversion at 120,000 mLg h slightly
4
-1 -1
decreased compared with that at 60,000 mLg h . In addition, a battery of Pd loadings
(0.25, 0.5, 1.0 wt%) deposited on modified support has been probed to reveal the
optimum Pd content under the same condition and the results were summarized in
Figure S4. Notably, 0.5Pd/CeO
2
NWs@SiO
2
and 1.0Pd/CeO
2
NWs@SiO catalysts
2
showed superior 90% conversion at lower temperature. Thus, the sample with 0.5% Pd
loading content was selected to investigate the influence of this strategy on the CCM
performance. For comparison, a considerable number of recently reported Pd-based
catalysts developed for CH
performances were summarized in Table S2. As can be seen, 0.5Pd/CeO
catalyst displayed superior catalytic activity for CH combustion with a relatively
4
total combustion were collected and the catalytic
2
NWs@SiO
2
4
higher space velocity and lower content of palladium (0.5 wt %).
Besides low-temperature activity, high temperature stability and water tolerance are
also significant indexes for evaluating the practical application potential for a lean
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
methane combustion catalyst.[31] Therefore, the 0.5Pd/CeO
2
NWs@SiO
2
catalyst was
inspected under the conditions of high-temperature, water vapor for a while. As
depicted in Figure 6A, 0.5Pd/CeO NWs@SiO displayed outstanding on-stream
2
2
thermal reaction stability at 300 and 800℃, respectively. At these conditions, methane
conversion remained at a certain level over 120 h without obvious degradation,
indicating the catalyst’s brilliant thermal stability against deactivation. Interestingly,
one could also observe that the conversion of methane increased slightly at the initial
stage of reaction during the isothermal continuous experiment at 300℃, a result possibly
[9]
due to the restruction of active sites under the reaction condition. Even more exciting,
the TEM image (Figure S5) of the spent 0.5Pd/CeO NWs@SiO at 800℃ for 120 h
2
2
retained the intact structure, in which no distinct palladium nanoparticles can be
observed, demonstrating the modified support surface was conducive to anchor
palladium sub-nanoparticle and restrain them from sintering at high temperatures. The
hydrothermal stability of 0.5Pd/CeO
2
NWs@SiO was examined through 30 h on steam
2
methane combustion by injecting 5.0 vol% water within the time of 8-20 h, as shown
in Figure 6B. Notably, with the addition of 5 vol% water vapor in reactant feed, for
0.5Pd/CeO
92% at 500℃, while the conversion curve of 0.5Pd/CeO
dramatically from 100% to 53%. In addition, although the existent of water vapor had
a reversible negative effect on activity, the light-off behavior of 0.5Pd/CeO NWs@SiO
2
NWs@SiO
2
, the methane conversion decreased sluggishly from 100% to
2
NWs sample declined
2
2
could recover completely after removing the water vapor, further indicating its
exceptional structure stability under wet condition.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
In situ reaction mechanism
Temperature-dependent in situ DRIFT spectra analysis was carried out to explore the
role of introduced Si species and the possible mechanism about catalytic methane
combustion on the 0.5Pd/CeO
2
NWs and 0.5Pd/CeO
2
NWs@SiO
2
samples under the
same condition. As shown in Figure 7, the absorption bands at 3600-3800, 3014, 2357,
−
1
2308, 1550, 1480, 1034 cm could be obviously observed in both spectrum. The ones
−
1
appeared at 3014 and 1304 cm are caused by the C-H bond stretching of gaseous
−
1
[32]. The
methane and the bands at around 2357 and 2308 cm were assigned to CO
CH signals were gradually declining along with the rising temperature, while the CO
signals continuously increased. It can be found that the methane peaks in
0.5Pd/CeO NWs@SiO (Figure 7a) became hardly visible at 500℃, whereas identical
absorption peaks still remained visible at 500℃ over 0.5Pd/CeO NWs (Figure 7b),
2
4
2
2
2
2
which was in good agreement with the light-off curves results. The bands at around
1550 cm− and 1480 cm− could be assigned to CO 2
−
and –CO– (carbon oxygenates),
3
respectively, as the essential intermediate products.[33] Generally, the –CO– related
intermediates can be oxidized to CO 2−
(carbonate) by surface active oxygen, and then
decomposed into CO . Notably, the spectra of 0.5Pd/CeO NWs showed that the –CO–
intermediates gradually accumulated with the temperature increasing, while the signals
of CO kept unchanged up to 400℃. For 0.5Pd/CeO NWs@SiO , the intensity of the –
CO– peaks maintained barely visible while the signals of CO increased more rapidly,
3
2
2
2
2
2
2
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
indicating that the –CO– intermediates were not stable and effortless to be decomposed
into CO on the surface of 0.5Pd/CeO NWs@SiO . In addition, it is widely recognized
that the signals at 3600–3800 cm were caused by the stretching vibrations of hydroxyl
groups on catalyst surface[34]. For the 0.5Pd/CeO
NWs@SiO catalyst, the band at 3708
2
2
2
−
1
2
2
−
1
cm gradually became apparent with the temperature increasing, which could assign to
silicon hydroxyl (Si–OH) groups adsorbed on the surface.[35] It is reasonable to assume
that the generated silicon hydroxyl groups were initially produced on the active
palladium phase and then transferred to the silica phase on the surface of the support,
which could efficiently restrain the generation of inactive Pd(OH) species. In the
x
meanwhile, hydroxyl shifted to silica phase would improve metal utilization and release
more active sites during the CCM reaction. This explains why the
0.5Pd/CeO
2
NWs@SiO
2
catalyst possesses superior catalytic activity and water
tolerance during methane total combustion.
Based on the aforementioned results, the possible reaction models for methane
oxidation over Pd/CeO
2
NWs and Pd/CeO
2
NWs@SiO catalysts were proposed as
2
depicted in Scheme 2. It is recognized that the PdO species should act as the active sites,
and surface silicon species as a catalytic assistant. Meanwhile, the most possible CCM
reaction pathway should conform to the generally accepted Mars–van Krevelen (MvK)
redox mechanism.[36] In this pattern, CeO
support is closely involved in methane
2
oxidation reaction by storing abundant reactive oxygen species (O*) which can further
transfer to active PdO phase that adsorbs and dissociates methane molecules. It is
generally recognized that the highly dispersive Pd species and the continuously
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
supplied active O* by modified CeO support can greatly boost the activation of
2
methane molecule as well as the oxidation rate of pivotal intermediates (carbon
oxygenates), and therefore enhances the catalytic performance on methane combustion
of Pd/CeO
products generated on Pd/CeO
CO , in which silicon species play an essential role in fine-tuning of electronic structure
2
NWs@SiO
2
catalyst. In the meanwhile, the correlative intermediate
2
NWs@SiO surface is more readily decomposed into
2
2
and relevant chemical reactivity of the active Pd phase according forming silicon
hydroxyl groups (Si–OH) during the reaction.
Conclusions
In summary, Pd catalysts supported on surface-modified ceria nanowires were
successfully prepared via constructing space fence between the interface of support and
active species. It is significant that the introduced organosilicone could prominently
improve the dispersion of palladium species and strengthen the concentration of active
surface-adsorbed oxygen species on the catalyst surface. The resultant
0.5Pd/CeO
2
NWs@SiO catalyst exhibited extraordinary low temperature performance
2
-1
-1
with T90 at 327℃ (at WHSV of 60 000 ml g h ) for lean methane combustion. More
importantly, this catalyst possessed superior high temperature stability and water
tolerance during lean methane combustion because of the strong Pd-support interaction.
In situ DRIFTS results revealed that the indispensable intermediate products (carbon
oxygenates) generated on Pd/CeO
2
NWs@SiO surface were more readily decomposed
2
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
3
3
3
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
97
98
99
00
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
into CO
2
and the silicon hydroxyl groups (Si–OH) formed during the reaction can
species and release more active
efficiently restrict the generation of the stable Pd(OH)
x
sites to boost the catalytic performance. We believe that this work can provide a feasible
strategy to improve the utilization of palladium species in practical applications and
design efficient Pd-based catalysts for low temperature oxidation of methane.
Experimental Section
All the reagents were utilized without further purification.
Catalyst preparation
Synthesis of CeO
2
nanowires (NWs): The preparation of the CeO
2
nanowires was in a
typical method.[19] 60 mL CeCl
(2.5 mmol, Aladdin Industrial Corporation) aqueous
3
solution and sodium oleate (1.5 mmol, Aladdin Industrial Corporation) were added into
a 100 mL stainless-steel autoclave. After magnetically stirred for 0.5 h stirring at room
temperature, 5 mLn-butylamine was sequentially added into the above solution mixture
for another 0.5 h under stirring. Afterwards, the stainless-steel oven was heated at
170 °C for 12 h. The formed solid was collected by centrifugation and then washed
with distilled water and ethanol in turn, followed by drying at room temperature
overnight and calcining at 400℃for 4 h under ambient air.
Synthesis of modified CeO
2
NWs@SiO
2
: Briefly, 2.5 g of CeO nanowires support and
2
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
3 ml triethoxy(octyl)silane (TEOOS, 97%) were homogeneously dispersed into 80 ml
toluene solution and then ultrasound for 1 h. Subsequently, the mixed solution was
refluxed at 110℃for 3 hours under vigorous stirring. Afterwards, the solid product was
collected by centrifugation at 8000 rpm and washed by toluene several times. The
obtained sample was dried overnight in a vacuum oven at 110 C. The modified support
was labeled as CeO
Synthesis of 0.5% loading Pd/CeO
acetate and 1 g of hydrophobic CeO2 NWs@SiO
2
NWs@SiO
2
.
2
NWs@SiO
2
: A calculated amount of palladium
2
support were rapidly added into 5.0
mL toluene solution. Afterwards, the homogeneous solution was sonicated for 30
minutes and dried at 80 ℃ for 3 h and at 120 ℃ for 2 h. The obtained catalyst was
calcined at 500℃for 4 h in air. The final catalysts with a calculated Pd contents of 0.2,
0.5, and 1.0 wt% were donated as 0.2Pd/CeO
2
NWs@SiO
2
, 0.5Pd/CeO
2
NWs@SiO
2
and
1.0Pd/CeO NWs@SiO , respectively. For a comparison study, the pristine CeO
2
2
2
NWs
support was used as support by the same method and marked as Pd/CeO NWs.
2
Characterization
The X-ray diffraction (XRD) measurements were recorded on a Rigaku TTR-III
diffractor instrument operating, with Cu target Kα-ray irradiation (40 kV, 15 mA). The
diffraction scans were taken within a 2θ zone of 10 to 90° with a step of 0.02°. The BET
surface areas of relevant samples were obtained with nitrogen adsorption-desorption
method on Micromeritics Tristar III 3020 instrument at ~77 K. The inductively coupled
plasma atomic emission spectrometer (ICP-AES) was performed with an Optima 7300
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
DV to obtain the actual palladium content in Pd-based catalysts. The Field-emission
transmission electron microscope images of some relevant samples were carried out on
a 200 kV JEOL-JSM-2100F (Japan Electronics Co., Ltd.) instrument equipped with an
EDS detector. X-ray Photoelectron Spectroscopy (XPS) was performed in Thermo
ESCALAB 250 spectrometer system using an Al Kα x-ray (1486.6 eV) source. The
spectra were obtained with the XPSPEAK 4.1 software at ultrahigh vacuum and
calibrated using the C1s line (284.8 eV) as a reference. H
2
-Temperature-Programmed
reduction (H -TPR) measurement was determined by a Chemstar TPx chemisorption
2
apparatus equipped a TCD detector (Quantachrome, USA). Typically, sample (100 mg)
was placed in a U-type quartz tube. Prior to the reduction, the catalyst was pre-
processed in flowing 10% O
to a mixture of 10 vol% H /Ar stream (30 mL/min) and the temperature rise from 30℃
to 1000℃ with a ramp rate of 10℃/min. The signals caused by H consumption were
tested by a TCD detector. O -Temperature programmed desorption (O -TPD) was
conducted to study the oxygen properties of relevant samples. Briefly, 0.1g of sample
was first pretreated by 4 vol% O /Ar at 400 °C for 30 min and saturated with O at room
temperature. Afterwards, the sample was purged with ultra-high purity Ar flow for 60
minutes to stabilize the baseline and remove physically adsorbed O , after which the
2
/He at 300°C for 40 min. Afterwards, the gas was switched
2
2
2
2
2
2
2
sample was heated from 25℃ to 800℃ with a heating rate of 10℃/min. CO
chemisorption was conducted to measure the Pd dispersion of related catalysts at 25℃
(CO:Pd = 1:1) by Chemstar TPx chemisorption equipment. In situ DRIFTS experiments
were carried out using a Fourier transform infrared spectrometer (Nicolet iS 50)
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
-
1
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
equipped an elevated-pressure cell with a wavenumber resolution of 4 cm . Prior to the
measurement, the sample was first pretreated by 1 vol% methane (air as balance) at
500 ℃ for 1 hour with a flow rate of 10 sccm. The background was removed at room
temperature, and then the in situ DRIFTS were collected at the temperatures of 200,
250, 300, 350, 400, 450 and 500℃under the continuous reaction gas flow.
Catalytic activity measurements
Temperature-programmed lean methane oxidation experiments with 1.0 vol% methane
(balanced by air) as the reactant gas was evaluated using a fixed-bed quartz reactor.
Prior to the reaction, all catalysts were activated at 500℃ for 1 h under a continual
reaction gas to acquire a better initial activity. Typically, 20 mg of catalyst powder was
placed in a quartz tube (i.d. = 3 mm) while the steady flow rate of reactant gas (1 vol.%
CH , balanced with air) was maintained at 20 mL/min, corresponding to a gas hourly
4
space velocity (WHSV) of 60,000 mLh gcat-1. The outlet gas was detected by an on-
line gas chromatograph (GC 1690) equipped with a thermal conductive detector (TCD)
and a flame ionization detector (FID). Afterwards, the experimental results data were
collected between 200 and 600℃ at steady-state flow rates. Finally, the light-off
behaviors of the samples were tested according to the peak area of methane before and
after the reaction. For the water resistance tests of relevant samples, the uniform
reactant feed and about 5% water vapor (volume composition) were pumped into the
reactor through a water bubbler under the same condition.
-1
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
Acknowledgments
This work was supported by the Program of National Natural Science Foundation of
China (51976212), the Fundamental Research Funds for the Central Universities
(WK2090130026).
Notes
The authors declare no competing financial interest.
Reference
[1]
a) A. Eyssler, A. Winkler, P. Mandaliev, P. Hug, A. Weidenkaff, D. Ferri, Appl.
Catal. B-Environ 2011, 106, 494-502; b) J. H. Chen, H. Arandiyan, X. Gao, J.
H. Li, Catal. Surv. Asia 2015, 19, 140-171; c) N. Nunotam, N. Moriyama, K.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Matsuo, N. Imanaka, Acs. Appl. Mater. Inter. 2017, 9, 40344-40350.
[2]
[3]
Y. L. Dai, V. P. Kumar, C. J. Zhu, H. Y. Wang, K. J. Smith, M. O. Wolf, M. J.
MacLachlan, Adv. Funct. Mater. 2019, 29.
a) Y. Y. Lei, W. Z. Li, Q. C. Liu, Q. Z. Lin, X. S. Zheng, Q. F. Huan, S. N. Guan,
X. H. Wang, C. X. Wang, F. Y. Li, Fuel. 2018, 233, 10-20; b) D. Pi, W. Z. Li, Q.
Z. Lin, Q. F. Huang, H. Q. Hu, C. Y. Shao, Energy Technology. 2016, 4, 943-
949.
[4]
[5]
P. Gelin, M. Primet, Appl. Catal. B-Environ. 2002, 39, 1-37.
M. Cargnello, V. V. T. Doan-Nguyen, T. R. Gordon, R. E. Diaz, E. A. Stach, R.
J. Gorte, P. Fornasiero, C. B. Murray, Science. 2013, 341, 771-773.
Z. Hu, X. F. Liu, D. M. Meng, Y. Guo, Y. L. Guo, G. Z. Lu, Acs Catal. 2016, 6,
2265-2279.
[6]
[7]
[8]
P. Schwach, X. L. Pan, X. H. Bao, Chem. Rev. 2017, 117, 8497-8520.
a) M. Cargnello, N. L. Wieder, T. Montini, R. J. Gorte, P. Fornasiero, J. Am.
Chem. Soc. 2010, 132, 1402-1409; b) L. Adijanto, D. A. Bennett, C. Chen, A.
S. Yu, M. Cargnello, P. Fornasiero, R. J. Gorte, J. M. Vohs, Nano. Lett. 2013,
13, 2252-2257; c) K. Bakhmutsky, N. L. Wieder, M. Cargnello, B. Galloway, P.
Fornasiero, R. J. Gorte, Chemsuschem. 2012, 5, 140-148.
[9]
M. Cargnello, J. J. D. Jaen, J. C. H. Garrido, K. Bakhmutsky, T. Montini, J. J.
C. Gamez, R. J. Gorte, P. Fornasiero, Science. 2012, 337, 713-717.
[10] S. Colussi, A. Gayen, M. F. Camellone, M. Boaro, J. Llorca, S. Fabris, A.
Trovarelli, Angew. Chem. Int. Ed. 2009, 48, 8481-8484.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
[11] G. M. Zhou, L. Xu, G. W. Hu, L. Q. Mai, Y. Cui, Chem. Rev 2019, 119, 11042-
11109.
[12] K. Murata, Y. Mahara, J. Ohyama, Y. Yamamoto, S. Arai, A. Satsuma, Angew.
Chem. Int. Ed. 2017, 56, 15993-15997.
[13] a) A. Toso, S. Colussi, S. Padigapaty, C. de Leitenburg, A. Trovarelli, Appl.
Catal. B-Environ. 2018, 230, 237-245; b) L. De Rogatis, M. Cargnello, V.
Gombac, B. Lorenzut, T. Montini, P. Fornasiero, Chemsuschem. 2010, 3, 24-42.
[14] a) F. X. Yin, S. F. Ji, P. Y. Wu, F. Z. Zhao, C. Y. Li, J. Catal 2008, 257, 108-116;
b) J. J. Willis, A. Gallo, D. Sokaras, H. Aljama, S. H. Nowak, E. D. Goodman,
L. Wu, C. J. Tassone, T. F. Jaramillo, F. Abild-Pedersen, M. Cargnello, Acs
Catal. 2017, 7, 7810-7821.
[15] M. Danielis, S. Colussi, C. de Leitenburg, L. Soler, J. Llorca, A. Trovarelli,
Angew. Chem. Int. Ed. 2018, 57, 10212-10216.
[16] S. Zhang, C. R. Chang, Z. Q. Huang, J. Li, Z. Wu, Y. Ma, Z. Zhang, Y. Wang,
Y. Qu, J. Am. Chem. Soc. 2016, 138, 2629-2637.
[17] H. G. Peng, C. Rao, N. Zhang, X. Wang, W. M. Liu, W. T. Mao, L. Han, P. F.
Zhang, S. Dai, Angew. Chem. Int. Ed. 2018, 57, 8953-8957.
[18] A. Baylet, S. Royer, R. Marecot, J. M. Tatibouet, D. Duprez, Appl. Catal. B-
Environ. 2008, 77, 237-247.
[19] S. Bai, F. Liu, B. Huang, F. Li, H. Lin, T. Wu, M. Sun, J. Wu, Q. Shao, Y. Xu,
X. Huang, Nat. Commun. 2020, 11, 954.
[20] Q. Y. Duan, C. H. Zhang, S. Sun, Y. Pan, X. Zhou, Y. Liu, K. Chen, C. S. Li, X.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
Z. Wang, W. Z. Li, J. Mater. Chem. A. 2020, 8, 7395-7404.
[21] P. Pentyala, P. A. Deshpande, Ind Eng Chem. Res. 2019, 58, 7964-7972.
[22] a) T. L. Barr, Appl. Surf. Sci. 1983, 15, 1-35; b) S. P. Chenakin, G. Melaet, R.
Szukiewicz, N. Kruse, J. Catal. 2014, 312, 1-11.
[23] G. Spezzati, A. D. Benavidez, A. T. DeLaRiva, Y. Q. Su, J. P. Hofmann, S.
Asahina, E. J. Olivier, J. H. Neethling, J. T. Miller, A. K. Datye, E. J. M. Hensen,
Appl. Catal. B-Environ. 2019, 243, 36-46.
[24] Z. Wang, Z. P. Huang, J. T. Brosnahan, S. Zhang, Y. L. Guo, Y. Guo, L. Wang,
Y. S. Wang, W. C. Zhan, Environ. Sci. Technol. 2019, 53, 5349-5358.
[25] a) C. Wang, C. Wen, J. Lauterbach, E. Sasmaz, Appl. Catal. B-Environ. 2017,
206, 1-8; b) T. P. Senftle, A. C. T. van Duin, M. J. Janik, Acs Catal. 2017, 7,
327-332.
[26] X. Weng, H. Ren, M. Chen, H. Wan, Acs Catal. 2014, 4, 2598-2604.
[27] H. Y. Nie, J. Y. Howe, P. T. Lachkov, Y. H. C. Chin, Acs Catal. 2019, 9, 5445-
5461.
[28] Y. Q. Ding, Q. Q. Wu, B. Lin, Y. L. Guo, Y. Guo, Y. S. Wang, L. Wang, W. C.
Zhan, Appl. Catal. B-Environ. 2020, 266.
[29] a) C. Qian, W. Sun, D. L. H. Hung, C. Qiu, M. Makaremi, S. G. Hari Kumar, L.
Wan, M. Ghoussoub, T. E. Wood, M. Xia, A. A. Tountas, Y. F. Li, L. Wang, Y.
Dong, I. Gourevich, C. V. Singh, G. A. Ozin, Nat. Catal. 2018, 2, 46-54; b) Z.
Jin, L. Wang, E. Zuidema, K. Mondal, M. Zhang, J. Zhang, C. T. Wang, X. J.
Meng, H. Q. Yang, C. Mesters, F. S. Xiao, Science. 2020, 367, 193-+.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
[30] A. Toso, S. Colussi, J. Llorca, A. Trovarelli, Appl. Catal. A-Gen. 2019, 574, 79-
86.
[31] P. Losch, W. X. Huang, O. Vozniuk, E. D. Goodman, W. Schmidt, M. Cargnello,
Acs Catal. 2019, 9, 4742-4753.
[32] a) S. P. Mo, Q. Zhang, J. Q. Li, Y. H. Sun, Q. M. Ren, S. B. Zou, Q. Zhang, J.
H. Lu, M. L. Fu, D. Q. Mo, J. L. Wu, H. M. Huang, D. Q. Ye, Appl. Catal. B-
Environ. 2020, 264; b) M. Richard, D. Duprez, N. Bion, F. Can,
ChemSusChem.2017, 10, 210-219.
[33] a) W. Li, D. P. Liu, X. L. Feng, Z. Zhang, X. Jin, Y. Zhang, Adv. Energy. Mater.
2019, 9; b) W. R. Schwartz, L. D. Pfefferle, J. Phys. Chem. C. 2012, 116, 8571-
8578.
[34] O. Demoulin, M. Navez, P. Ruiz, Appl. Catal. A-Gen. 2005, 295, 59-70.
[35] a) S. Foraita, Y. Liu, G. L. Haller, E. Barath, C. Zhao, J. A. Lercher,
Chemcatchem. 2017, 9, 195-203; b) V. C. H. Kroll, H. M. Swaan, S. Lacombe,
C. Mirodatos, J. Catal. 1996, 164, 387-398.
[36] K. Fujimoto, F. H. Ribeiro, M. Avalos-Borja, E. Iglesia, J. Catal. 1998, 179,
431-442.
FIGURES
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
5
5
93
94
Figure 1．TEM and HRTEM images (a, b) 0.5Pd/CeO
2
NW@SiO
2
, (c) 0.5Pd/CeO NW,
2
5
5
5
95
96
97
(b)–(g) EDX mapping of 0.5Pd/CeO NW@SiO samples.
2
2
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202001438
5
5
98
99
Scheme 1. Schematic diagram of the synthesis of Pd/CeO
2
NWs@SiO catalyst.
2
6
6
6
6
6
6
6
6
6
6
00
01
02
03
04
05
06
07
08
09
This article is protected by copyright. All rights reserved.