Shape effect of MnOx-decorated CeO2 Catalyst in the Diesel Soot Oxidation

Article abstract of DOI:10.1246/bcsj.20170022

A series of MnO_x-decorated CeO₂ (MnCeO) catalysts with various morphologies was prepared via shape-controlled synthesis of single-crystalline CeO₂, e.g., nanorod, nanoparticle, and nanocube, by a hydrothermal method followed by the deposition of MnO_x phase by a simple impregnation method. The MnO_x/CeO₂ nanorod (MnCeO-NR) showed remarkable carbon soot combustion activity at lower temperature under tight contact mode with a T₅₀ temperature of 317°C, which is attributed to larger surface area and higher oxygen release rate, as compared with particle and cubic catalysts. Also, MnCeO-NR exhibited the higher catalytic activity (a shift of T₅₀ by 127°C) in the NO-assisted soot combustion under a loose contact mode. Not only the higher surface area but also the superior NO conversion ability at low temperature, as well as larger NO absorption property contributes to the improved catalytic activities. The MnCeO-NR further demonstrated high stability and satisfied recyclability without significant catalytic activity loss. The use of cheaper combinations without noble metals makes the MnO_x/CeO₂ catalyst a promising candidate to satisfy future requirements in industry.

Full text of DOI:10.1246/bcsj.20170022

Advance Publication Cover Page
Shape Effect of MnOx-Decorated CeO2 Catalyst in the Diesel Soot Oxidation
Kohsuke Mori,* Yusuke Miyauchi, Yasutaka Kuwahara, and Hiromi Yamashita*
Advance Publication on the web February 7, 2017
doi:10.1246/bcsj.20170022
© 2017 The Chemical Society of Japan

Shape effect of MnOx-decorated CeO2 Catalyst in the Diesel Soot Oxidation
Kohsuke Mori,1,2,3* Yusuke Miyauchi,1 Yasutaka Kuwahara,1,2 and Hiromi Yamashita1,2*
1Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871
2Elements Strategy Initiative for Catalysts Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-8520
3JST, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012
E-mail: mori@mat.eng.osaka-u.ac.jp, yamashita@mat.eng.osaka-u.ac.jp >
Kohsuke Mori
Kohsuke Mori received his PhD degree from the Graduate School of Engineering Science at Osaka University under the
supervision of Prof. K. Kaneda in 2003. In 2004, he joined University of California, Berkeley as a postdoctoral fellow.
He moved to current faculty in 2005 and then became an Associate Professor in 2009. His current research interests
focus on hybrid photocatalysts based on visible-light responsible metal complexes, metal and alloy nanoparticle catalysts
to establish clean and environmentally-friendly chemical processes, and diesel automobile catalysts.
Hiromi Yamashita
Hiromi Yamashita has been a professor of Osaka University since 2004. He received PhD degree from Kyoto University
in 1987. He was an assistant professor of Tohoku University, an associate professor of Osaka Prefecture University, and
an invited professor of University Pierre and Marie Curie (UPMC). He was also visiting research fellows of the
Pennsylvania State University, the University of Texas at Austin, California Institute of Technology. His research interests
include the design of single-site photocatalysts and nanostructured catalysts.
Abstract
A series of MnOx-decorated CeO2 (MnCeO) catalysts
crystallographic planes play an important role in determining
the catalytic activity and selectivity, which also influence on
the nature of combined metal nanoparticles and/or metal oxides
on their surfaces.
with different morphologies have been prepared by the
shape-controlled synthesis of single-crystalline CeO2, such as
nanorod, nanoparticle, and nanocube, by a hydrothermal
method followed by the deposition of MnOx phase by a simple
impregnation method. Their shape-dependent physicochemical
properties were investigated by means of XRD, BET, UV-vis,
HRTEM, XPS, TPR and oxygen storage/release properties
measurements. The MnOx/CeO2 nanorod (MnCeO-NR) showed
prominent carbon soot combustion activity at lower
temperature under tight contact mode with a T50 temperature of
317 °C, which is attributed to larger surface area and higher
oxygen release rate, as compared with particle and cubic
catalysts. MnCeO-NR also exhibited the higher catalytic
activity (a shift of T50 by 127°C) in the NO-assisted soot
combustion under a loose contact mode. Not only the higher
surface area but also the superior NO conversion ability at low
temperature as well as larger NO absorption property
contributes to the improved catalytic activities. The
MnCeO-NR further displayed high stability and satisfied
recyclability without significant loss of catalytic activity. The
use of cheaper combinations without noble metals makes the
MnOx/CeO2 catalyst a promising candidate to satisfy future
requirements in industry.
Cerium oxide (CeO2) and related ceria-containing materials
are key active components or support materials for catalytic
applications in the environment and energy fields, such as soot
oxidation,16 CO oxidation,17 water-gas shift reactions,18, 19 and
methane reforming etc.20 In general, such catalytic reactions
take advantage of the outstanding redox property and excellent
oxygen storage capacity (OSC) of the ceria-based catalysts,
which are originated from the rapid and reversible switching
between Ce3+ and Ce4+ oxidation states.21, 22 Since such unique
characteristics are strongly associated with the nature of the
different exposed crystallographic planes, considerable efforts
have also been devoted to the development of ceria-based
nanomaterials with controlled morphologies.23, 24 For example,
CeO2 nanorods (NRs) have a tendency to preferentially expose
four (110) and two (100) planes, whereas the CeO2 nanocubes
(NCs) expose six (100) planes.25 The shape of conventional
polycrystalline CeO2 is mainly dominated by (111)-enclosed
octahedral.26 With decreasing the size of particles, the edge
truncated nanoparticles (NPs) are formed, which expose (110),
(110), and (111) planes, respectively.27 It has been reported that
the CeO2 NRs exposing (110) and (100) planes on the surface
are more active than conventional polycrystalline CeO2 with
preferred exposure of (111) planes for the CO oxidation
reactions.28 This structure-dependent activity is explained based
on the DFT calculations; the chemical activity of the different
CeO2 planes is surface sensitive and follows in the order (110)
< (100) < (111), indicating that the energy for the formation of
reactive oxygen vacancy on the (100) surface is much lower
than on the (111) surface.29
1. Introduction
In recent years, nanostructured catalyst materials with
controlled composition, size, and morphologies have attracted
great attention because of their interesting physicochemical
properties.1-3 Understanding the correlation between the
precisely controlled single-crystalline natures of the
nanomaterials and their catalytic performances is a crucial task
for developing novel catalysts with exceptional activity.4-7 It is
well accepted that the properties of nanomaterials are
significantly affected by not only their crystal sizes but also
their morphologies, such as rods, cubes, and polycrystalline.8-15
These findings clearly suggest that the preferentially exposed
Diesel engines have been commonly used in a variety of
vehicles owing to their economical fuel efficiency and
favorable high export power compared with gasoline engines.30
Unfortunately, their exhausts contain particulate matters (PM),
whose main components are aggregated carbonaceous soot, and
NOx gas. In order to control their emissions, a promising

strategy that can completely eliminate soot and NOx emissions
is desired.31-34 The most reasonable technique is a diesel
particulate filter (DPF), where trapped carbon soot on the filters
are periodically renewed by catalytic combustion at high
temperature.35, 36 Therefore, the design and synthesis of high
performance catalysts enabling direct oxidation of soot at lower
combustion temperature is of great importance. Among
investigated, CeO2 has been recognized as an ideal catalyst for
diesel soot combustion,37, 38 and therefore the characteristics of
Pt/CeO2 and Ag/CeO2 have been intensively examined.39, 40 The
catalytic carbon soot oxidation occurs at the three-phase
boundary among a solid catalyst, a solid soot, and a gaseous
reactant (O2),40, 41 and the catalytic performances would be
significantly correlated with OSC of CeO2, the diffusion of O2,
and the physical mixture condition between catalysts and
soot.42 Therefore, it can be anticipated that CeO2 morphologies
have a great impact on the intrinsic physicochemical properties
as well as contact conditions with soot. Recently, Trovarelli et.
al reported that soot combustion activity is dependent on not
only the surface areas, but also the shape of CeO2 with different
exposed planes.43 Unfortunately, pure CeO2 alone cannot be
employed at high temperature because of its relatively low
activity and decreased OSC at high temperature. In this context,
the investigation of the shape-dependent activity of the more
active CeO2 heterostrucures modified with metal oxides (MOx)
is vital from the viewpoints of design of practical catalysts.44-47
Mn was deposited by a conventional impregnation method.
CeO2-NR (0.5 g) was added into 75 mL of aqueous solution of
Mn(NO3)2·6H2O (0.36 g, 30 mol%) and mixed at 60 °C for 1 h.
Subsequently, the water phase was evaporated under vacuum to
impregnate the Mn and the obtained powder was dried, and
finally calcined in air at 400 °C for 4 h, resulting in
MnOx/CeO2 (MnCeO-NR) as a pale brown powder. In this way,
MnCeO-NP and MnCeO-NC were also synthesized using
CeO2-NP and CeO2-NC, respectively. MnCeO-NR with
different Mn contents (5, 10, 30, and 50 mol%) were also
prepared according to this procedure.
As a reference sample, MnO2 was prepared by participation
method. NH3 solution was drop wisely added into an aqueous
solution of Mn(NO3)2·6H2O (100 ml, 0.4 M) and pH was
adjusted to 10. After impregnation, the sample was dried and
further calcined at 80 °C for 4 h.
Characterization: X-ray diffraction (XRD) patterns for the
catalysts were recorded using
a
Rigaku Ultima IV
diffractometer with Cu Kα (λ = 1.5406 Å) radiation source.
Brunauer–Emmett–Teller (BET) surface area measurements
were performed at -196 °C using a BEL-SORP Max (Bel Japan,
Inc.). Each sample was degassed under vacuum at 70 °C for 24
h prior to analysis. UV-vis diffuse reflectance spectra were
collected using a Shimadzu UV-2450 spectrophotometer.
BaSO4 was used as a reference and the absorption spectra were
obtained using the Kubelka-Munk function. Transmission
Electron Microscopy (TEM) micrographs were measured using
a Hitachi H-800 electron microscope equipped with an
energy-dispersive X-ray (EDX) detector, operated at 200 kV.
HR-TEM images were obtained using FEI TITAN80-300.
X-ray photoelectron spectroscopy (XPS) data were recorded
using a Shimadzu ESCA 3400 HSE and the quantitative
analyses were calculated by the integrated intensities of the
spectra. Temperature programed reduction with H2 (H2-TPR)
was performed using BEL-CAT by heating 0.05 g sample at
10 °C/min form 100 °C to 800 °C under a 5%H2/Ar flow. For
NO-TPD, 0.05 g sample was loaded in was heated to 400 °C
and maintained for 1.5 h under an Ar flow. Then the sample
was cooled down to 80 °C and saturated with NO (2000 ppm in
He and Ar) for 1 h. After the removing the physically adsorbed
NO by flushing Ar for 1 h, the sample was heated to 660 °C at
10 °C/min. Temperature programed oxidation with NO/O2
(TPO-NO/O2) were performed at 5 °C/min form 50 °C to
760 °C under a gas flow of 1000 ppm NO and 13% O2 in He.
In this study, we have synthesized
a
series of
shape-controlled MnOx/CeO2 catalysts with rod, nanoparticle,
and cubic morphologies. The aim is to compare their potential
effects of the MnOx/CeO2 nanocrystal shape on their
physicochemical properties as well as catalytic activity in the
soot oxidation for the first time. It has been reported that the
addition of MnOx to CeO2 improved catalytic activity because
of the synergic effect between MnOx and CeO2 at their
heterostructure interface as well as the presence of multiple
valence of Mn (2+, 3+, and 4+). Additionally, Mn is
considerably inexpensive than noble metals such as Pt, Rh, and
Pd, which minimize the consumption of precious metals from
the viewpoint of atomic economy. This study allows the
understanding of shape-dependent characteristics of
MnOx/CeO2 heteronanostructures and gives the insight into the
design strategy of the efficient catalysts in terms of potential
practical application for soot oxidation.
2. Experimental
Materials: Mn(NO3)2·6H2O was purchased from Wako Pure
Chemical Ind. Ce(NO3)2·6H2O was obtained from Nacalai
Tesque. CeO2 nanopowder obtained from Aldrich was used as a
model of nanoparticle sample. A commercial carbon black,
Printex V (Degussa) supplied from the Catalysis Society of
Japan was employed as a model of diesel soot.
Catalytic study: The catalytic soot combustion activity was
estimated using a thermogravimetry (TG) technique (Rigaku,
Thermo Plus EVO). For the preparation of samples, two type of
contact modes (tight and loose) were employed. For tight
contact mode, the solid mixture grinded together in an agate
mortar for 10 min to ensure a close contact between catalyst
and soot. In order to prepare a various mixture of catalysts and
soot with different bulk densities, the mixing time with a
mortar was further continuously varied (10s, 30s, and 2 min)
for the tight contact mode. For loose contact mode, the solids
were mixed by a spatula prior to the experiment. The
catalyst/soot mixture in a 10/1 weight ratio (10 mg) was
preheated from room temperature to 120 °C under an air
atmosphere (30 ml/min) to remove the adsorbed water. After 60
min, the sample chamber was heated at 5 °C/min from 120 °C
to 800 °Cunder an air atmosphere (30 ml/min). NO-assisted
soot combustion was performed under a flowing NO and O2
mixture (1000ppm NO, 13% O2 in He). Reproducibility of the
results was verified by running similar experiments, and the
results in terms of T50 (the temperature at which 50 % of carbon
Catalyst synthesis: CeO2 nanostructures with different
morphologies were synthesized by a hydrothermal reaction
23
under different conditions.
Ceria nanorod (CeO2-NR) was
prepared by adding dropwise a NaOH solution (175 mL, 11.4
M) into an aqueous solution of Ce(NO3)2·6H2O (25 ml, 0.4 M).
After sttring for 30 min, the mixture was transfer to the
teflon-lined cylinder and sealed in a stainless steel autoclave,
and heated at 90 °C for 24 h, followed by cooling, separatation,
washing with etanol and water, and drying at 60 °C, giving a
pale yellow powder. Ceria nanocube (CeO2-NC) was prepared
by a similar manner by changing the NaOH concentration (6.85
M) and heating temperature (180°C) in the hydrothermal
treatment. Ceria nanoparticle (CeO2-NP) were obtained from
Aldrich.

in
which
MnCeO-NR
Table 1. Textural properties and catalytic performance of the CeO2 and MnCeO.
possesses higher number of
Ce3+ ions than MnCeO-NP
and MnCeO-NC.
SBET
sample
Mn /mol%
a0 / Å
T10 / ⁰C
T50 / ⁰C
T90 / ⁰C
/ m2·g‒1
76.5
Pure soot
CeO2-NR
-
-
-
495
202
173
199
231
252
237
236
318
298
571
345
333
326
317
345
351
337
369
373
609
373
350
339
341
371
376
356
396
391
XRD pattern of the pure
CeO2 and MnCeO samples
are shown in Figure 1. All
MnCeO samples exhibited
distinct peaks associated with
fluorite-like structure of
CeO2. The broadening of the
reflections for the CeO2-NR
and MnCeO-NR is ascribed
to
nature, while the sharper
reflections for the
nanoparticles and nanocubes
indicated their larger sizes as
86.0
77.1
77.2
68.8
60.9
57.4
40.3
15.1
17.1
5.410
5.398
5.395
5.391
5.376
5.417
5.413
5.415
5.413
MnCeO-NR
MnCeO-NR
MnCeO-NR
MnCeO-NR
CeO2-NP
5
10
30
50
-
MnCeO-NP
CeO2-NC
30
-
their
nanocrystalline
MnCeO-NC
30
soot is converted) were within ±5°C.
compared with the nanorod samples. No peaks due to Mn oxide
phases could be confirmed. In the case of the MnCeO-NR, the
diffraction peaks became gradually wider with increasing the
Mn content, and were shifted to higher Bragg angles compared
to pure CeO2-NR. The lattice constant (a0) calculated through
the most prominent (111) crystallographic plane are
summarized in Table 1. The calculated lattice constants of all
MnCeO samples were smaller than those of original CeO2,
suggesting that the Mnx+ ions are incorporated into the CeO2
lattice to form the MnxCe1-xO2-δ solid solutions due to the
smaller ionic radius of Mnx+ (Mn4+; 0.083 nm, Mn3+; 0.065 nm,
Mn2+; 0.053 nm) than those of Cex+ (Ce4+; 0.097 nm, Ce3+;
0.114 nm).52 It has been reported that the solubility of Mn
cations in the CeO2 lattice is limited to 5-10 mol%.53 Since the
nominal Mn content (30 mol%) is above this limit, two kinds of
Mn species are existed in the samples, namely the doped Mn
cations within the CeO2 lattice and the highly dispersed MnOx
phase. It should be noted that more significant alternation in the
lattice constant can be observed for MnCeO-NR, indicating that
the replacement of Cex+ with Mnx+ is most favorable in the
MnCeO-NR, presumably because of the presence of more
defective CeO2 lattice as well as high surface area. On the
contrary, change in the lattice constant for the MnCeO-NC is
quite small. This result indicates that most of the Mn species
exist as MnOx phase, which probably suppress the decrease in
surface area even after the deposition of Mn.
Measurement of oxygen storage/release property: Oxygen
storage capacity (OSC) of the samples was evaluated based on
the weight change during TG analysis.48 Prior to the
experiments, the catalyst (10 mg) was pretreated at 10 °C/min
from room temperature to 400 °C under an O2(21%)/N2
atmosphere. Next, a H2(19%)/N2 mixture was introduced after
purging with N2 while keeping temperature at 400°C for 10
min. The observed weight loss is originated from oxygen
removal by H2 to form H2O, and it can be associated with OSC
at this temperature. Oxygen release rate (ORR) was determined
by the slope of the weight loss step in the OSC measurement.
Measurement of activation-energy in the soot combustion
reaction: The apparent activation energy (Ea; kJ/mol) under
tight contact mode was determined based on the Ozawa method
according to the following equation.49, 50
E 1
a
ln B  0.4567
 C
R T
a
where B denotes the heating rate (2, 5, and 10 °C/min), Ta is the
temperature at a % of soot conversion, and C is a constant. In
the TG analysis, a mixture of catalyst/soot with a weight ratio
of 10/1 (10 mg) were examined under different heating rates
from 30 to 700 °C in air.
3. Results and Discussion
Structural and Morphological Characterization
The
BET
surface
areas
measured
by
N2
adsorption/desorption are listed in Table 1. It should be noted
that the larger surface area was obtained in the order of
MnCeO-NR (68.8 m2/g)
> >
MnCeO-NP (40.3 m2/g)
MnCeO-NC (17.1 m2/g) for 30 mol% Mn loading. In the case
of the MnCeO-NR, surface areas gradually decreased with
increasing the amount of Mn loading. The N2
adsorption/desorption isotherms showed a gradual increase in
the amount of N2 without a significant hysteresis loop (Figure
S1), which can be classified as a type III isotherm reflecting the
absence of micropores. The observed straight line through the
origin in the t-plot method also confirm the non-porosity of the
samples. In the UV-vis diffuse reflectance spectra, all samples
display a strong characteristic absorption peak due to cubic
fluorite CeO2 at around 350 nm (Figure S2). It was found the
red shift of the absorption band, which is due to the presence of
surface defect sites such as oxygen vacancies, can be observed
in the order of MnCeO-NR > MnCeO-NP > MnCeO-NC.51
This result is well consistent with the XPS results (see below),
Figure 1. XRD pattern of (A) CeO2 and MnCeO (Mn:
30 mol%) samples with different shapes and (B)
CeO2-NR and MnCeO2-NR with different Mn loadings.

The morphology and surface microstructures were
investigated by TEM and HR-TEM images. Figure 2a shows
the TEM image of the original CeO2-NR, with an almost
uniform diameter in ca. 10 nm and a less-uniform length of
50-250 nm. In the HR-TEM image, three kinds of lattice fringe
directions due to (111), (002), and (220) can be observed
(Figure 2b and c). The nanorod show a 1D growth structure
enclosed by (220) and (200) planes with a favored growth
direction along [110].54 Partially, surface irregularities, such as
defect and surface roughness, was observed, which is well
reflected by UV-vis spectra. From the TEM image of
MnCeO-NR, it can be concluded that the deposition of Mn and
subsequent calcination does not result in any significant change
in morphology (Figure 2d). Figure 3a shows the TEM image
of CeO2-NP. It has been reported that the conventional CeO2
nanoparticles have a octahedral structure dominated by (111)
facet and a truncated octahedral shape enclosed by the (111),
(110), and (100) facet.26, 27 In the case of MnCeO-NP, truncated
particles with a mean diameter of ca. 15 nm was mainly
observed, because the thermal treatment causes the structural
transformation, resulting in the exposure of more reactive (100)
and (110), accompanied with the gradual decrease of (111)
exposure (Figure 3b). TEM image of CeO2-NC displayed
homogeneous cubic structure with different sizes, in which the
edges of the cubes range from 20-100 nm (Figure 4a). The
(002) and (020) crystallographic plane of CeO2 can be
distinguished in the HR-TEM images of those nanocubes
oriented along the [100] direction (Figure 4b and c), implying
that the CeO2-NC are only enclosed by the (100) facet.43 Even
after the deposition of Mn followed by the calcination step,
MnCeO-NC keeps its cubic morphology and sizes (Figure 4c).
In the XPS spectra, the Mn 2p3/2 spectra of the MnCeO
samples can be deconvoluted by three components attributed to
Mn2+, Mn3+, and Mn4+ ions (Figure S3).55 The co-existence of
the various Mn ions with different oxidation state contribute to
the electron transfer process.56 Especially, it has been reported
that surface reactive species like Mn4+ ions are strongly
responsible for the enhancement in the soot oxidation activity,
Figure 2. (a) TEM image, (b) HR-TEM images, and (c)
SEAD of CeO2-NR. (d) TEM image of MnCeO-NR
(Mn: 30 mol%) .
Figure 3. TEM images of (a) CeO2-NP and (b)
MnCeO-NP (Mn: 30 mol%).
because they often associate with active oxygen species with
45
high mobility.44,
The ratio of Mn species with various
oxidation state are summarized in Table 2. MnCeO-NR
exhibited the larger ratio of high valence Mn ions compared
with MnCeO-NP and MnCeO-NC. The O 1s spectra can be
fitted into three peaks assigned to lattice oxygen species (O2-)
at lower binding energy and chemisorbed oxygen species (O-
-
and O2 ) at higher binding energy, respectively (Figure S4).57
The peak intensity of the chemisorbed oxygen species, which
would give rise to unusual catalytic properties for the soot
oxidation, in the MnCeO-NR become stronger than those of
MnCeO-NP and MnCeO-NC (Table 2). Ce 3d XPS spectra
clearly indicated the coexistence of both Ce3+ and Ce4+ for all
samples (Figure S5).58 It is well known that the presence of the
Figure 4. (a) TEM image, (b) HR-TEM images, and (c)
SEAD of CeO2-NC. (d) TEM image of MnCeO-NC
(Mn: 30 mol%).
To gain insight in the reducibility of Mn species deposited
on different CeO2 supports, H2-temperature programed
reduction (TPR) experiments were performed, since such
reducibility of the active species is crucial for the high catalytic
activity in the soot combustion. In a preliminary experiment,
the peak intensities
Ce3+ ions could lead to
a charge imbalance, whose
concentration is directly related to the amount of oxygen
vacancies as well as redox property.59 It is clear that the
MnCeO-NR possesses higher number of Ce3+ ions than
MnCeO-NP and MnCeO-NC (Table 2).
Table 2. Surface compositions and oxidation state of Mn, O, and Ce species of MnCeO calculated
from XPS results.
of the H2-TPR
peaks for Mn-free
CeO2 samples were
negligible (Figure
S6). The peaks
Mn 2p / %
Mn3+
27.6
O 1s / %
O–
Ce 3d / %
sample
Mn2+
39.5
49.0
70.3
Mn4+
32.9
32.9
21.4
O2–
34.1
48.6
45.9
O2
Ce3+
Ce4+
81.4
83.6
85.6
–
MnCeO-NR
MnCeO-NP
MnCeO-NC
27.9
18.4
18.1
38.0
33.0
36.0
18.6
16.4
14.4
with
a
bimodal
was
18.1
8.3
shape
observed between

250 °C and 450 °C for all MnCeO samples (Figure 5), which
are attributed to the stepwise reduction of Mn species, i.e.
MnO2 → Mn2O3 and Mn2O3 → MnO.60 It is well accepted that
the reduction of MnO into Mn0 generally does not occur even
up to a reduction temperature of 800 °C because of its large
negative reduction potential.61 The reduction peak of all
MnCeO samples shifted towards much lower temperature
compared to the bulk MnO2 and Mn2O3, which can be ascribed
to strong interaction between the cerium and manganese
cations in the lattice originated from the formation of
MnxCe1-xO2-δ solid solutions. Interestingly, more significant
shift toward lower temperature can be observed in the case of
MnCeO-NR. The former reduction peak is maximized at
296 °C, which is lower than those compared to MnCeO-NP
(312 °C) and MnCeO-NC (317 °C). Such good redox property
of the MnCeO-NR at low temperature is related to its higher
surface area as well as favorable formation of MnxCe1-xO2-δ
solid solutions, as also confirmed by UV-vis, XRD, and XPS
measurements, and further expecting the increasing mobility of
lattice oxygen species.
method is well collaborated with the above results (Figure S7).
The measured Ea values of 73–87 kJmol−1 with the MnCeO-NR
were lower than 77–85 kJmol−1, 90–101 kJmol−1, and 150–160
kJmol−1 obtained with MnCeO-NP, MnCeO-NC, and without
catalyst, respectively.
Figure 6. T50 values in the carbon soot combustion
under tight contact mode using CeO2 and MnCeO with
different morphologies and Mn loadings.
Particularly, the T50 attained by the MnCeO-NR is lower than
those previously reported other ceria-based catalysts, such as
CuO/CeO2 (413 °C),62 CuOx/CeO2 nanocube (373 °C),46
MnOx-CeO2/SBA-15 (382 °C),45 CuOx/CeO2 nanocube
(383 °C),44 Ce0.8Mn0.2
O
(489 °C),63 Au@CeO2-δ/ZrO2
(364 °C),64 Pt@CeO2-δ (330 °C),40 and CoOx/nmCeO2
(368 °C).38 Such efficient combustion performance as well as
the use of less expensive manganese as a catalyst metal fulfil
the forthcoming diesel emission criteria. Moreover, the
potential catalytic durability of the MnCeO-NR was explored,
as depicted in Figure S8. The recovered catalyst can be
repeatedly used without a significant decrease in the essential
activity; the increased T50 values can be suppress within 15 °C
and complete combustion of carbon soot can be attained at least
fifth times. This characteristic renders the MnCeO-NR a vital
contribution to the design of a practical catalyst.
In the direct soot oxidation route under tight contact mode,
soot is principally oxidized at the boundary between solid
catalyst and solid soot by the potentially active oxygen, in
which the Mn4+/Mn3+/Mn2+ redox pair has an important role in
the present catalytic system using MnCeO samples. The
released active oxygen species from MnOx or MnxCe1-xO2-δ
solid solutions are supplemented continuously by atmospheric
O2 through the oxygen vacancies in the adjacent CeO2. The
involvement of the O22− species generated on the CeO2 phase in
the direct combustion of soot cannot be excluded, since the
original CeO2 without MnOx phase also perform as an active
catalyst.
Figure 5. H2-TPR spectra of MnCeO (Mn: 30 mol%)
samples and reference Mn oxides.
Carbon soot combustion under tight contact mode
The effect of various catalysts on the soot combustion
under an air atmosphere are shown in Figure 6. The direct
oxidation of carbon soot without a catalyst start at 480 °C, and
T50 was 571 °C. The T50 using bare CeO2 without Mn
deposition were 355, 361, and 373 °C for CeO2-NR, CeO2-NP,
and CeO2-NC, respectively. A reference MnO2, which was
prepared by a precipitation method, showed a relatively high
T50 temperature of 389 °C. Especially, the deposition of Mn
noticeably increased the catalytic activity of CeO2-NR: the soot
combustion of MnCeO-NR (Mn: 30 mol%) began at ca. 200 °C,
with a T50 of 317 °C. MnCeO-NP also showed a significant
improvement in comparison with the original one, whereas no
enhancement in catalytic activity was observed in the case of
the MnCeO-NC. The amount of Mn content also plays a crucial
role in the improvement of the catalytic activity, in which
maximum activity was obtained at 30 mol% Mn loading. Such
volcano-type activity order based on the Mn contents clearly
suggests the importance of the formation of MnxCe1-xO2-δ solid
solutions as well as high surface area. The apparent activation
energy (Ea) in the soot oxidation determined using the Ozawa
Table 3. Oxygen storage and release properties of
MnCeO samples at 400 °C.
OSC
/mmol·g–1
OSC/SBET
/ mmol·m–2
ORR
/mmol·min–1
sample
MnCeO-NR
MnCeO-NP
MnCeO-NC
0.45
0.38
0.34
0.66 × 10–2
0.87 × 10–2
2.0 × 10–2
0.17
0.08
0.10
Therefore, the storage/release properties of the lattice oxygen
species may be one important characteristic for attaining

efficient soot combustion under tight contact mode.65 The
oxygen storage capacity (OSC) and oxygen release rate (ORR)
determined by weight change under a cycled feed-stream
conditions (21%O2/N2 or 19%H2/N2, 10 min intervals) at
400 °C are summarized in Table 3 and Figure S9. MnCeO-NR
showed relatively higher OSC property compared to the
MnCeO-NP and MnCeO-NC, but the former has large surface
area than those of later. In an effort to examine the effect of
crystal morphology on the OSC behavior, the obtained OSC
values were divided by each BET surface areas, which are also
listed in Table 3. It was found that the OSC/SBET follows the
order of MnCeO-NC > MnCeO-NP > MnCeO-NR. On the
contrary, MnCeO-NR exhibited higher ORR, determined by the
slope in the weight change. The original CeO2 also displayed
the weight change, but the small oscillation amplitude under a
cycled feed-stream conditions indicates redox cycle essentially
occurs only near the solid surface. Such observations strongly
suggest that the deposition of MnOx phase on the CeO2 phase
creates synergetic effects and that partially formed
MnxCe1-xO2-δ solid solution function as oxygen storage sites
owing to its flexible redox property.66 It can also be suspected
that the large OSC is not essential factor for attaining the high
catalytic activity; the ORR rather than quantity of oxygen
species would be a significant factor to accomplish low
temperature soot combustion.
The effect of contact mode of catalyst-soot mixture on the
catalytic activity was first investigated using the MnCeO-NR.
For the loose contact, the catalyst was mixed with soot by a
spatula for several times. For the tight contact, the mixing time
with a mortar was continuously varied (10s, 30s, 2 min, and 10
min), affording a various mixture of catalysts and soot with
different bulk densities (449, 462, 481, and 541 g·L–1), as
depicted in Figure 7A. Without the flowing NO (only 13% O2
in N2), the loose contact sample showed a relatively low
catalytic activity, whose T50 temperature was 556 °C (Figure
7B). The T50 temperature sharply decreased with increasing the
bulk density of the mixture, and the lowest T50 was attained
with 10 min tight contact. The NO-assisted carbon soot
combustion under a flowing NO and O2 mixture (1000ppm NO,
13% O2 in N2) significantly lowered the combustion
temperature at low bulk density region. In the case of the loose
contact mode, T50 temperature decreased 127 °C, as compared
without NO flowing. The degree of the lowing temperature
gradually decreased with increasing the bulk density of the
mixture, and the difference in T50 temperatures was
insignificant at higher bulk density region. Interestingly, these
results clearly suggest that the NO-assisted carbon soot
combustion can only be attained under loose contact mode,
while the effect of NO assistance is negligible under tight
contact mode. The NO concentration also played an important
role for the lowering the combustion temperature, and the T50
temperature gradually decreased with increasing the NO
concentration (Figure S10). Such NO-assist effect was also
dependent on the morphologies of the MnCeO samples. All
MnCeO samples displayed almost similar T50 temperatures at
around 550 °C in the absence of NO, while the degree of the
lowering combustion temperatures in the presence of NO
followed in the order of MnCeO-NR (127 °C) > MnCeO-NP
(106 °C) > MnCeO-NC (87 °C) (Figure 8). It is well known
that the catalysts containing low-melting-point potassium
compounds, such as KOH and KNO3, show superior activity
toward soot combustion, even under loose contact conditions,
since the contact points between the catalysts and soot can be
improved by the in situ generated molten salts.70 However, the
addition of the low-melting-point components display the
significant disadvantage in the catalyst recycling. The free from
such additional components in the MnCeO-NR provides an
essential contribution to the purification of actual diesel
exhaust for practical application.
NO-assisted carbon soot combustion under loose contact
mode
The real diesel engine exhaust involves several
oxygen-containing gases, such as O2, NO, H2O and CO2, that
could potentially react with soot. The reactivity of NO, H2O
and CO2 is too low to directly react with soot, while the in situ
generated NO2 by the catalytic NO oxidation is more reactive
than NO and O2,67, 68 thus it is expected the lowing of the
combustion temperature. Ceria-based catalyst is able to
catalyze the oxidation of NO to NO2 when the reaction
temperature is above ca. 300 °C. Another important aspect to
be considered for the evaluation of soot combustion reaction is
the nature of contact between the soot and catalyst phase,
which significantly influence on the kinetics of catalytic
combustion experiments. Generally, the loose contact mixture
is more comparable to practical application, but shows a higher
combustion temperature.69 On the other hand, the samples
prepared with tight contact present a lower combustion
temperature, but affords more close-fitting than the real
conditions.
Figure 7. (A) Pictures of catalyst (MnCeO-NR, Mn: 30
mol%) and soot mixture with different bulk density
prepared by varying the mixing time with a mortar. (B)
Effect of bulk density of the catalyst and soot mixture on the
T50 values in the carbon soot combustion with and without
flowing NO gas.
Figure 8. Effect of MnCeO (Mn: 30 mol%)
morphologies on the T50 values in the carbon soot
combustion under loose contact mode with and without
flowing NO gas.

In order to investigate the
adsorption/desorption behavior of NO,
the
NO-temperature
programed
desorption (TPD) experiments were
performed. As shown in Figure 9A,
all MnCeO samples exhibited two
broad peaks, in which first peak
observed at lower temperature region
is ascribed to the desorption of weakly
adsorbed NO and the decomposition
−
of surface nitrites (NO3 ), while the
second one observed at higher region
is due to the strongly bound nitrites
−
−
(NO3 )
and/or
nitrate
(NO2 )
species.45
MnCeO-NR
and
MnCeO-NP showed relatively large
desorption peak at around 120 °C,
while the second peak in the
MnCeO-NR appeared at higher
temperature (388 °C) compared to the
MnCeO-NP (325 °C), indicating the
superior NO storage ability of the
Figure 10. Schematic illustrations of soot combustion mechanism under tight
and loose contact mode with MnCeO catalyst.
temperature and high storage capacity of NO make the MnCeO
MnCeO-NR. In spite of the small integral area of the NO-TPD
profile of the MnCeO-NC due to its small specific surface, both
desorption peaks shifted to higher temperatures. Since the
normal operation temperature in the diesel exhaust ranges at
around 200-400 °C, not only the surface area but also the high
NO adsorption and release capacities in this temperature range
is important for attaining efficient NO-assisted carbon soot
combustion. Moreover, the NO-temperature programed
oxidation (TPO) experiments were carried out to study the
catalytic performances in the NO-assisted carbon soot
combustion. All MnCeO catalysts displayed good NO
oxidation ability at low temperatures (Figure 9B). The
temperatures with maximal NO2 concentration of the
MnCeO-NR centered at 401°C, which was lower than those of
MnCeO-NP (434 °C) and MnCeO-NC (432°C). This tendency
is found to be correlated with the catalytic performance in the
NO-assisted carbon soot combustion under loose contact mode,
revealing the predominance of MnCeO-NR catalyst.
catalysts suitable for the NO-assisted carbon soot combustion.
Especially, the MnCeO-NR showed the significant lowering
effect in the presence of the NO.
Upon consideration of these fact, schematic illustration for
soot combustion over MnCeO catalysts are shown in Figure 10.
In the case of the tight contact mode, the direct combustion by
the active oxygen formed in the lattice of MnOx/CeO2 phase
predominantly occurs. The active oxygen liberated from MnOx
can be successively compensated by gaseous O2 through the
oxygen vacancies in the adjacent CeO2 phase. Thus the large
surface area and the superior oxygen release rate of the
MnCeO-NR are essential for attaining high activity. The
contribution of the active NO2 oxidant is negligible, as
demonstrated in Figure 7B, which also supports that the soot
combustion reaction occurs at the closely attached catalyst–soot
interface. Under the loose contact mode, NO-assisted pathway
occurs dominantly, while the direct oxidation by the potentially
active oxygen generated on the MnOx/CeO2 phase would be
minor pathway, which presumably because the such active
oxygen cannot not be released from the catalyst surface. The
significant lowering effect of the NO-assisted combustion
temperature in the presence of the MnCeO-NR are originated
from not only the large surface area to increase the contact
point between soot and catalyst, but also the good NO2
formation ability at low temperature, since the adsorption step
of NO molecules on the surface of catalyst also influence on
the reaction pathway. MnCeO-NC demonstrates relatively high
NOx storage capacity in the NO-TPD experiments, but small
surface area may seriously reduce its inherent catalytic
activities.
4. Conclusion
Figure 9. (A) NO-TPD profiles and (B) evolution of
NO2 during the NO-TPO experiments with MnCeO
(Mn: 30 mol%).
The shape-dependent physicochemical properties and the
catalytic activities of a series of MnOx-decorated CeO2, such as
nanorod, nanoparticle, and nanocube, in the diesel carbon soot
oxidation were investigated. The MnOx/CeO2 nanorod showed
effective carbon soot combustion activity at lower temperature
under tight contact mode, as compared with particle and cubic
catalysts. Its large surface area and the superior oxygen release
rate (ORR) of the MnCeO-NR are essential for attaining high
activity. MnOx/CeO2 nanorod also exhibited the significant
positive effect on the lowering temperature in the NO-assisted
soot combustion under a loose contact mode. Not only the
The combination of strong oxidative ability of MnOx
associated with the flexible oxygen storage capacity of CeO2
contributes to the efficient soot oxidation, in which synergic
redox cycle between manganese (Mn4+ ↔ Mn3+) and the
support (Ce4+ ↔ Ce3+) at the MnOx-CeO2 interface plays a
crucial role. Furthermore, NO oxidation activity at low

higher surface area but also the rapid oxygen release rate
originated from the synergic redox properties due to strong
MnOx-CeO2 nanorod interface interactions. The superior NO
conversion ability at low temperature as well as larger NO
absorption properties also play crucial role in improving
catalytic activities. Furthermore, the MnCeO NR system
displays high robustness and reusability while keeping its
performances. The use of such convenient Mn-based catalyst
rather than precious metals contributes to the possible
application as a cost-effective catalyst in the diesel market.
23 H.-X. Mai, L.-D. Sun, Y.-W. Zhang, R. Si, W. Feng, H.-P.
Zhang, H.-C. Liu, C.-H. Yan, J. Phys. Chem. B 2005, 109,
24380-24385.
24 Z.-A. Qiao, Z. Wu, S. Dai, ChemSusChem 2013, 6,
1821-1833.
25 Y. Chen, S. Lv, C. Chen, C. Qiu, X. Fan, Z. Wang, J. Phys.
Chem. C 2014, 118, 4437-4443.
26 Z. L. Wang, X. Feng, J. Phys. Chem. B 2003, 107,
13563-13566.
27 E. Aneggi, J. Llorca, M. Boaro, A. Trovarelli, J. Catal.
2005, 234, 88-95.
Supporting Information
28 C. Pan, D. Zhang, L. Shi, J. Fang, Eur. J. Inor. Chem. 2008,
2008, 2429-2436.
29 D. C. Sayle, S. A. Maicaneanu, G. W. Watson, J. Am.
Chem. Soc. 2002, 124, 11429-11439.
30 D. N. Belton, K. C. Taylor, Curr. Opinion Solid State
Mater. Sci. 1999, 4, 97-102.
N2-adsorption/desorption isotherm, UV-vis spectra, XPS
spectra, apparent activation energy, recycling experiment,
oxygen storage/release properties, and the effect of NO
concentration.
Acknowledgement
31 J. C. Summers, S. Van Houtte, D. Psaras, Appl. Catal., B
1996, 10, 139-156.
32 J. P. A. Neeft, M. Makkee, J. A. Moulijn, Fuel Proc. Tech.
1996, 47, 1-69.
This work was performed under a management of ‘Elements
Strategy Initiative for Catalysts & Batteries (ESICB)’ supported
by MEXT.
33 B. R. Stanmore, J. F. Brilhac, P. Gilot, Carbon 2001, 39,
2247-2268.
References
1
2
M. Niederberger, Acc. Chem. Res. 2007, 40, 793-800.
Y. Xia, Y. Xiong, B. Lim, S. E. Skrabalak, Angew. Chem.
Inter. Ed. 2009, 48, 60-103.
34 K. Mori, Y. Iwata, M. Yamamoto, N. Kimura, A. Miyauchi,
G. Okamoto, T. Toyoshima, H. Yamashita, J. Phys. Chem.
C 2014, 118, 9078-9085.
3
4
W. Huang, Acc. Chem. Res. 2016, 49, 520-527.
W.-I. Hsiao, Y.-S. Lin, Y.-C. Chen, C.-S. Lee, Chem. Phys.
Lett. 2007, 441, 294-299.
35 B. A. A. L. van Setten, M. Makkee, J. A. Moulijn, Catal.
Rev. 2001, 43, 489-564.
36 M. Jeguirim, V. Tschamber, J. F. Brilhac, J. Chem. Tech.
Biotech. 2009, 84, 770-776.
37 A. Setiabudi, J. Chen, G. Mul, M. Makkee, J. A. Moulijn,
Appl. Catal., B 2004, 51, 9-19.
38 J. Liu, Z. Zhao, J. Wang, C. Xu, A. Duan, G. Jiang, Q.
Yang, Appl. Catal., B 2008, 84, 185-195.
39 K. i. Shimizu, H. Kawachi, A. Satsuma, Appl. Catal., B
2010, 96, 169-175.
40 Y. Wei, Z. Zhao, J. Liu, C. Xu, G. Jiang, A. Duan, Small
2013, 9, 3957-3963.
41 K. Mori, K. Watanabe, T. Sato, H. Yamashita,
ChemPhysChem 2015, 16, 1347-1351.
42 E. Aneggi, V. Rico-Perez, C. de Leitenburg, S. Maschio, L.
Soler, J. Llorca, A. Trovarelli, Angew. Chem. Inter. Ed.
2015, 54, 14040-14043.
5 I. Lee, F. Delbecq, R. Morales, M. A. Albiter, F. Zaera, Nat.
Mater. 2009, 8, 132-138.
6
7
8
9
N. Tian, Z.-Y. Zhou, S.-G. Sun, Y. Ding, Z. L. Wang,
Science 2007, 316, 732-735.
X. Xie, Y. Li, Z.-Q. Liu, M. Haruta, W. Shen, Nature 2009,
458, 746-749.
K. Zhou, Y. Li, Angew. Chem. Inter. Ed. 2012, 51,
602-613.
N. Wang, W. Qian, W. Chu, F. Wei, Catal. Sci. Tech. 2016,
6, 3594-3605.
10 G. Navlani, iacute, M. a, K. Mori, M. Wen, Y. Kuwahara,
H. Yamashita, Bull. Chem. Soc. Jpn 2015, 88, 1500-1502.
11 K. Mori, A. Kumami, M. Tomonari, H. Yamashita, J. Phys.
Chem. C 2009, 113, 16850-16854.
12 K. Mori, T. Hara, T. Mizugaki, K. Ebitani, K. Kaneda, J.
Am. Chem. Soc. 2004, 126, 10657-10666.
13 K. Mori, A. Kumami, H. Yamashita, Phys. Chem. Chem.
Phys. 2011, 13, 15821-15824.
14 M. Navlani-García, K. Mori , A. Nozaki, Y. Kuwaharaꢀ, H.
YamashitaꢀChemistrySelect 2016, 1, 1879-1886.
15 F. Zaera, ChemSusChem 2013, 6, 1797-1820.
16 A. Bueno-López, Appl. Catal., B 2014, 146, 1-11.
17 H. Guo, Y. He, Y. Wang, L. Liu, X. Yang, S. Wang, Z.
Huang, Q. Wei, J. Mater. Chem. A 2013, 1, 7494-7499.
18 S. D. Senanayake, D. Stacchiola, J. Evans, M. Estrella, L.
Barrio, M. Pérez, J. Hrbek, J. A. Rodriguez, J. Catal. 2010,
271, 392-400.
43 E. Aneggi, D. Wiater, C. de Leitenburg, J. Llorca, A.
Trovarelli, ACS Catalysis 2014, 4, 172-181.
44 S. Putla, M. H. Amin, B. M. Reddy, A. Nafady, K. A. Al
Farhan, S. K. Bhargava, ACS Appl. Mater. Interfaces 2015,
7, 16525-16535.
45 H. Zhang, F. Gu, Q. Liu, J. Gao, L. Jia, T. Zhu, Y. Chen, Z.
Zhong, F. Su, RSC Adv. 2014, 4, 14879-14889.
46 P. Sudarsanam, B. Hillary, B. Mallesham, B. G. Rao, M. H.
Amin, A. Nafady, A. M. Alsalme, B. M. Reddy, S. K.
Bhargava, Langmuir 2016, 32, 2208-2215.
47 W.-T. Chen, K.-B. Chen, M.-F. Wang, S.-F. Weng, C.-S.
Lee, M. C. Lin, Chem. Commun. 2010, 46, 3286-3288.
48 A. Suda, K. Yamamura, H. Sobukawa, Y. Ukyo, T. Tanabe,
Y. Nagai, F. Dong, M. Sugiura, J. Ceram. Soc. Jpn. 2004,
112, 623-627.
19 N. Yi, R. Si, H. Saltsburg, M. Flytzani-Stephanopoulos,
Appl. Catal., B 2010, 95, 87-92.
20 Y. Zhu, S. Zhang, J.-j. Shan, L. Nguyen, S. Zhan, X. Gu, F.
Tao, ACS Catalysis 2013, 3, 2627-2639.
21 M. Machida, Y. Murata, K. Kishikawa, D. Zhang, K. Ikeue,
Chem. Mater. 2008, 20, 4489-4494.
49 T. Ozawa, J. Thermal Anal. 1970, 2, 301-324.
50 T. Ozawa, J. Thermal Anal. 1975, 7, 601-617.
51 X. Lu, D. Zheng, P. Zhang, C. Liang, P. Liu, Y. Tong,
Chem. Commun. 2010, 46, 7721-7723.
22 R. Si, Y.-W. Zhang, S.-J. Li, B.-X. Lin, C.-H. Yan, J. Phys.
Chem. B 2004, 108, 12481-12488.
52 B. Murugan, A. V. Ramaswamy, D. Srinivas, C. S.
Gopinath, V. Ramaswamy, Chem. Mater. 2005, 17,
3983-3993.

53 C. Y. Kang, H. Kusaba, H. Yahiro, K. Sasaki, Y. Teraoka,
Solid State Ionics 2006, 177, 1799-1802.
54 K. Zhou, X. Wang, X. Sun, Q. Peng, Y. Li, J. Catal. 2005,
229, 206-212.
55 E. López-Navarrete, A. Caballero, A. R. González-Elipe, M.
Ocaña, J. Eur. Ceramic Soc. 2004, 24, 3057-3062.
56 F. Arena, Catal. Sci. Tech. 2014, 4, 1890-1898.
57 Y. Wei, J. Liu, Z. Zhao, A. Duan, G. Jiang, J. Catal. 2012,
287, 13-29.
58 E. Bêche, P. Charvin, D. Perarnau, S. Abanades, G.
Flamant, Surf. Interface Anal. 2008, 40, 264-267.
59 C. He, B. Shen, J. Chen, J. Cai, Environ. Sci. Tech. 2014,
48, 7891-7898.
60 W. Xingyi, K. Qian, L. Dao, Appl. Catal., B 2009, 86,
166-175.
61 J. Carnö, M. Ferrandon, E. Björnbom, S. Järås, Appl. Catal.,
A 1997, 155, 265-281.
62 K. Nakagawa, T. Ohshima, Y. Tezuka, M. Katayama, M.
Katoh, S. Sugiyama, Catal. Today 2015, 246, 67-71.
63 Y. Sheng, Y. Zhou, H. Lu, Z. Zhang, Y. Chen, Chinese J.
Catal. 2013, 34, 567-577.
64 Y. Wei, Z. Zhao, X. Yu, B. Jin, J. Liu, C. Xu, A. Duan, G.
Jiang, S. Ma, Catal. Sci. Tech. 2013, 3, 2958-2970.
65 D. W. McKee, J. Catal. 1987, 108, 480-483.
66 R. Zhang, J. T. Miller, C. D. Baertsch, J. Catal. 2012, 294,
69-78.
67 H. Yamashita, A. Tomita, H. Yamada, T. Kyotani, L. R.
Radovic, Energy Fuels 1993, 7, 85-89.
68 H. Yamashita, H. Yamada, A. Tomita, Appl. Catal. 1991,
78, L1-L6.
69 N. Zouaoui, M. Issa, D. Kehrli, M. Jeguirim, Catal. Today
2012, 189, 65-69.
70 H. Shimokawa, Y. Kurihara, H. Kusaba, H. Einaga, Y.
Teraoka, Catal. Today 2012, 185, 99-103.

Graphical Abstract
<Title>
Shape effect of MnOx-decorated CeO2 Catalyst in the Diesel Soot Oxidation
<Authors>
Kohsuke Mori,* Yusuke Miyauchi, Yasutaka Kuwahara, and Hiromi Yamashita*
<Summary>
The MnOx/CeO2 nanorod (MnCeO-NR) exhibited the higher catalytic activity in the NO-assisted soot combustion under a loose
contact mode. Not only the higher surface area but also the superior NO conversion ability at low temperature as well as larger NO
absorption property contributes to the improved catalytic activities. The MnCeO-NR further displayed high durability and good
recyclability.