MnO:X-CeO2@TiO2 core-shell composites for low temperature SCR of NOx

Article abstract of DOI:10.1039/c9nj03461g

In this study, a MnO_x-CeO₂@TiO₂ catalyst for NH₃-SCR of NO_x at low temperature was successfully prepared. TiO₂ was distributed on the MnO_x-CeO₂ nanorod surface to form the core-shell structure. MnO_x-CeO₂@TiO₂ had excellent catalytic performance and SO₂ resistance. Characterization results indicated that the excellent catalytic performance of MnO_x-CeO₂@TiO₂ could be mainly attributed to the large specific surface area, the presence of oxygen vacancies, the strong redox ability and the abundant acidic sites. Moreover, the catalytic active sites of MnO_x-CeO₂@TiO₂ could be protected from SO₂ poisoning due to the existence of the TiO₂ shell. MnO_x-CeO₂@TiO₂ was proven to be an excellent low temperature SCR catalyst.

Full text of DOI:10.1039/c9nj03461g

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Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
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MnOx-CeO2 @ TiO2 core-shell composites for low
temperature SCR of NOx
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Dingren Ma,ab Liu Yang,a Bingjie Huang,a Liting Wang,a Xiao Wang,a Zhongyi
Sheng*ac and Fan Dongbd
In this study, MnOx-CeO2 @ TiO2 catalyst for NH3-SCR of NOx at low
temperature was successfully prepared. TiO2 was distributed on MnOx-CeO2 nanorod
surface to form the core-shell structure. MnOx-CeO2 @ TiO2 had excellent catalytic
performance and SO2 resistance. Characterization results indicated that excellent
catalytic performance of MnOx-CeO2 @ TiO2 could be mainly attributed to the large
specific surface area, the presence of oxygen vacancies, the strong redox ability and
the abundant acidic sites. Moreover, the catalytic active sites of MnOx-CeO2 @ TiO2
could be protected from SO2 poisoning due to the existence of the TiO2 shell.
MnOx-CeO2 @ TiO2 was proved to be an excellent low temperature SCR catalyst.
a School of Environment, Nanjing Normal University, Nanjing 210023, Jiangsu, China
b Chongqing Key Laboratory of Catalysis and New Environmental Materials, College of
Environment and Resources, Chongqing Technology and Business University, Chongqing 400067,
China
c Suzhou Industrial Technology Research Institute of Zhejiang University, Suzhou 215163,
Jiangsu, China
d Research Center for Environmental Science & Technology, Institute of Fundamental and Frontier
Sciences, University of Electronic Science and Technology of China, Chengdu 611731, China

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1. Introduction
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A large number of nitrogen oxides (NOx) from coal-fired power plants have
caused great harm to the environment and human beings.1-3 Selective catalytic
reduction (SCR) by urea or ammonia is one of the most effective technologies for the
abatement of NOx.4-6 However, there are many defects in commercial SCR catalysts,
such as narrow and high working temperature.7-9 Therefore, the development of low
temperature SCR catalysts is of great significance. MnOx has excellent catalytic
activity to remove NOx at low temperature.5 And CeO2 has strong redox ability,
oxygen storage capacity and acid-base property, which make it become a good
catalyst.10-17 The combination of MnOx and CeO2 exhibits superior catalytic
performance. Therefore, MnOx-CeO2 catalysts are considered to be promising low
temperature SCR catalysts. But the poor sulfur resistance of MnOx-CeO2 catalysts at
low temperature still disturbs researchers.10
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In order to improve the SO2 tolerance of MnOx-CeO2 catalysts, researchers have
used a variety of methods. Gao et al. found that MnOx-CeO2 modified by NiO and
CoO3 had larger surface area and more active sites, which improved catalytic activity
and SO2 resistance.18 Chang et al. reported that Sn4+ doped MnOx-CeO2 also had
excellent SO2 resistance.19, 20 Leng et al. investigated the Mn-Ce composite oxide
catalyst supported on TiO2 had excellent catalytic activity and sulfur resistance at low
temperature.21 Furthermore, core-shell nanostructures have been widely studied for
special properties which can protect active components from migrating and
sintering.22 MnOx @ TiO2 core-shell catalyst not only showed excellent catalytic
activity at low temperature, but also had good SO2 resistance.23 Chen et al. found that

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hierarchical Fe-ZSM-5 @ CeO2 catalyst constructed a fast-SCR environment and
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exhibited favorable water resistance.24 Moreover, mesoporous TiO2 @ Fe2O3
core-shell composites were prepared to improve the low temperature SO2-tolerant.25
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Herein, in order to take advantages of core-shell structure, MnOx-CeO2 nanorods
were first prepared by a template method. Then the surface of MnOx-CeO2 nanorods
was covered by TiO2 particles and core-shell structure catalyst marked as MnOx-CeO2
@ TiO2 was successfully prepared. The effects of MnOx-CeO2 @ TiO2 with unique
core-shell structure on catalytic activity and SO2 resistance at low temperature were
investigated. The MnOx-CeO2 @ TiO2 catalyst may act as a potential candidate for the
NH3-SCR reaction at low temperature due to its excellent performance.
2. Experimental
2.1. Catalyst preparation
2.1.1. MnOx-CeO2 @ TiO2
MnOx-CeO2 @ TiO2 was prepared by a three-step method. Ce(OH)CO3
templates were first prepared and then MnOx-CeO2 nanorods were prepared by an
oxidation-reduction process. Finally, MnOx-CeO2 @ TiO2 was prepared by a versatile
kinetics-controlled coating method.26
o
In an oil bath at 80 C, 0.02 mol Ce(NO3)3·6H2O and 0.12 mol urea were
sequentially added to 400 mL deionized water and stirred for 24 h. The solution was
centrifuged to obtain white precipitate, and the precipitate was washed with distilled
water to remove excess impurities until the pH of supernatant was about 7.

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Ce(OH)CO3 was obtained after drying at 60 oC for 6 hours in an oven.
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20 mL Mn(NO3)2 (0.025M) was first prepared and 1.25g Ce(OH)CO3 was added
to the solution under magnetic stirring. The mixture was further stirred ceaselessly for
30 min and then kept still for 6 days. The sediment was sequentially washed with 1M
HNO3 and deionized water. Finally, MnOx-CeO2 composite was acquired by drying at
80 oC for 12 hours.
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0.26 g MnOx-CeO2 was distributed uniformly in 100 mL ethanol. 0.3 mL
ammonia was added to the above solution under ultrasonic processing for 30 minutes.
Then 0.75 mL tetrabutyl titanate was added to the mixture under magnetic stirring for
24 hours at 45 oC. The precipitate was rinsed three times with deionized water. At last,
o
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the resulting powder was dried at 80 C for 12 hours and calcined in air at 500 C for
2 hours. The sample was denoted as MnOx-CeO2 @ TiO2.
2.1.2. MnOx-CeO2 / TiO2
The corresponding MnOx-CeO2 / TiO2 sample was prepared by a one-step
hydrothermal method. 0.03 mol Ce(NO3)3·6H2O was dissolved in 100 mL Mn(NO3)2
(0.025M) solution at room temperature. Then 7.5 mL ammonia and 19 mL tetrabutyl
titanate were added to the above solution. The mixture was further stirred ceaselessly
o
for 30 minutes and then sealed in a Teflon-lined stainless steel autoclave at 130 C for
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12 hours. The sediment was washed with deionized water and dried at 80 C for 12
o
hours. Finally, the powder was calcined in air at 500 C for 2 hours, which was
defined as MnOx-CeO2 / TiO2.

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2.2. Catalysts characterization
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X-ray diffraction (XRD) with Cu-Kα radiation was used for testing the
crystalline structures of samples. The morphology and structure of samples were
analyzed by transmission electron microscopy (TEM). The pore distribution and
surface area were calculated by Brunauer-Emmett-Teller (BET) equation using
Micromeritics ASSP 2020 equipment at 77K by N2 physisorption. The Raman spectra
of samples were collected by Raman spectrometer (Renishaw RM 2000) with a laser
at 514 nm. X-ray photoelectron spectroscopy (XPS) was used for analyzing the
surface atomic states of samples. NH3 temperature-programmed desorption
(NH3-TPD) was performed on the TP 5080 automatic multi-purpose adsorption
instrument (Xianquan, China). The samples (150 mg) were pretreated at 300 ℃ in a
flow of N2 (30 mL·min-1) for 0.5 h and cooled to 100 ℃ under N2 flow. Then the
samples were saturated with NH3 at 100 ℃ for 1 h, followed by N2 purging for 0.5 h
until there was no NH3 signal detected. Finally, the temperature was raised to 800 ℃
in N2 at a ramping rate of 10 ℃·min-1. And the results of H2 temperature-programmed
reduction (H2-TPR) were recorded on the same instrument.
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2.3 Activity measurements
NH3-SCR activity measurements were performed in a temperature controlled
fixed-bed. In the experiment, air flow rate was 1600 mL·min-1 and airspeed was
24000 h-1. The concentration of reaction gases were as follows: 500 ppm NO, 500
ppm NH3 and 5% O2, (200 ppm SO2) and N2 as the balance gas. The inlet and outlet

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concentrations of SO2, O2, NO2 and NO were measured by a flue gas analyzer (MRU
Vario Plus, Germany). And the outlet concentration of N2O was monitored by another
gas analyzer (G200). NOx conversion and N2 selectivity of samples were calculated as
follows respectively:
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in
o t
in
on r ion
o t
ti it
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in
in
o t
o t
where NOx = NO + NO2 + 2N2O.
3. Results and discussion
3.1 XRD patterns
The phase compositions of MnOx-CeO2 / TiO2 and MnOx-CeO2 @ TiO2 were
determined by XRD. Fig. 1 shows the XRD patterns of MnOx-CeO2 / TiO2 and
MnOx-CeO2 @ TiO2. Characteristic peaks of CeO2 (JCPDS card No. 81-0792) and
TiO2 (JCPDS card No. 89-4921) can be found in both samples. There are no obvious
peaks of MnOx, indicating that MnOx are highly dispersed on the samples. And highly
dispersed active components would contribute to increase the catalytic activity of
catalysts.27 Compared with MnOx-CeO2 / TiO2, the characteristic peaks of CeO2 in
MnOx-CeO2 @ TiO2 are significantly reduced. The reasons for this are that CeO2 and
MnOx are well integrated and MnOx-CeO2 is wrapped by TiO2, resulting in a decrease

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of the strength of the CeO2 diffraction peak.28
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 CeO
. TiO
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MnO -CeO / TiO
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
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2
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MnO -CeO @ TiO
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TiO
JCPDS No.89-4921
JCPDS No.81-0792
2
CeO
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2 ()
Fig. 1 XRD patterns of MnOx-CeO2 / TiO2 and MnOx-CeO2 @ TiO2
3.2 TEM images
The morphologies and structures of the samples were observed by TEM. As
shown in Fig. 2a, the nanoparticles have a large spacing from each other, indicating
that MnOx-CeO2 / TiO2 has no special core-shell structure. In Fig. 2b, Mn-Ce
nanorods are wrapped by TiO2 nanoparticles to form the core-shell structure. The
formation of the core-shell structure is consistent with the conclusions obtained in
XRD. Fig. 2c shows a HRTEM image of MnOx-CeO2 @ TiO2. It can be seen that the
nanorod structure is very clear and some nanoparticles are attached to the nanorod.
The distinct lattice fringes are measured to be about 0.306 nm and 0.292 nm, which
matche well with the (311) crystal plane of CeO2 and the (105) crystal plane of TiO2,
respectively. Moreover, Fig. 2d shows that MnOx-CeO2 @ TiO2 is polycrystalline.29

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Fig. 2 TEM images of MnOx-CeO2 / TiO2 (a) and MnOx-CeO2 @ TiO2 (b), HRTEM image and
SAED pattern of MnOx-CeO2 @ TiO2 (c, d).
3.3 Raman Patterns
Raman spectroscopy was performed to further analyze the crystal structures of
samples. As shown in Fig. 3, MnOx-CeO2 / TiO2 presents bands located at 142, 460
and 577 cm−1. Band at 142 cm-1 coincides with anatase TiO2,30, 31 characteristic band
at 460 cm-1 belongs to pure CeO2 32and band at 577 cm-1 can be assigned to
α-MnO2.33 b io , th α-MnO2 characteristic band of MnOx-CeO2 @ TiO2 shifts
to higher wavenumber compared with MnOx-CeO2 / TiO2, which is the result of the
action of oxygen vacancies.34 The presence of oxygen vacancies facilitates the
destruction of N-O bonds and thus increases catalytic activity.32 The CeO2 band of

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MnOx-CeO2 @ TiO2 exhibits a red shift compared with MnOx-CeO2 / TiO2, DwOhI:i1c0h.10i3s9/C9NJ03461G
related to the formation of Mn-Ce nanorods. Due to the interaction of TiO2 and
Mn-Ce nanorods, the band of TiO2 shifts to lower wavenumber.34
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TiO
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CeO
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MnO -CeO @ TiO
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MnO -CeO / TiO
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Raman shift (cm-1)
Fig. 3 Raman spectra of MnOx-CeO2 / TiO2 and MnOx-CeO2 @ TiO2
3.4 BET analysis
The pore size distributions and BET surface areas of the different samples are
shown in Table 1. And the N2 adsorption-desorption isotherms are displayed in Fig. 4.
Both curves in Fig. 4 have significant hysteresis loops in the P/P0 range of 0.6 to 1
and are assigned to the type IV according to IUPAC classification, indicating that the
samples have large amounts of mesoporous.35 Rich mesoporous structure would
provide channels for the reaction gases to enter into the inner surface of catalyst to
improve the catalytic performance.36 As shown in Table 1, the specific surface area of
MnOx-CeO2 @ TiO2 is larger than MnOx-CeO2 / TiO2, which is conducive to the
improvement of catalytic performance. The large specific surface area of MnOx-CeO2
@ TiO2 may be due to the formation of hollow nanorods.37

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Table 1 BET surface areas and pore parameters of catalysts
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S
BET（m2/g） Pore volume（10-2 cm3/g） Average pore diameter（nm）
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MnOx-CeO2@TiO2
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MnO -CeO @ TiO
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Relative pressure (P/P )
0
Fig. 4 N2 adsorption-desorption isotherms of MnOx-CeO2 / TiO2 and MnOx-CeO2 @ TiO2
3.5 XPS
The XPS spectra of Mn, Ce, Ti and O are shown in Fig. 5 and relative atomic
concentrations are listed in Table 2. In Fig. 5a, Mn 2p3/2 spectra can be divided into
two characteristic peaks which correspond to Mn3+ at 640.90eV and Mn4+ at
642.80eV respectively.38 Mn 2p1/2 peak appear at 652.80 eV, which is related to
Mn4+.39 As shown in Table 2, the content of Mn is higher on the surface of
MnOx-CeO2 / TiO2 than that of MnOx-CeO2 @ TiO2, which is due to the formation of
nanorod and core-shell structure. Moreover, the NO conversions decreased in the
order of MnO2 > Mn5O8 > Mn2O3 > Mn3O4 in low-temperature SCR reaction.10 The

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proportion of Mn4+ in MnOx-CeO2 @ TiO2 is higher than MnOx-CeO2 / TiO2,
DOI: 10.1039/C9NJ03461G
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indicating that MnOx-CeO2 @ TiO2 has excellent catalytic activity.
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The XPS results of Ce 3d spectra are shown in Fig. 5b. It can be seen that Ce 3d
spectra can be divided into eight different peaks. These eight peaks can be divided
into two kinds, one is the 3d3/2 corresponding peaks labeled as u and the other is the
3d5/2 corresponding peaks labeled as v. The peaks denoted as u, u", u'" and v, v", v'"
are assigned to Ce4+ while u' and v' are assigned to Ce3+.40 As shown in Table 2, Ce
mainly exists in the form of Ce4+ in samples. Interestingly, the production of Ce3+ is
related to the formation of oxygen vacancies.32 According to the Raman results, the
oxygen vacancies in MnOx-CeO2 @ TiO2 favor the formation of Ce3+, which is
consistent with the higher Ce3+ content of MnOx-CeO2 @ TiO2.
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Fig. 5c shows the XPS results of Ti 2p. Th p ak at aro nd 459.5ꢀ V orr pond
to TiO2.41 Ti exists in the form of Ti4+ on the surface of MnOx-CeO2 / TiO2 and
MnOx-CeO2 @ TiO2. The content of Ti in MnOx-CeO2 @ TiO2 is higher than
MnOx-CeO2 / TiO2. This result indicates that MnOx-CeO2 is wrapped by TiO2, which
consistent with the results of TEM.
In Fig. 5d, two distinct peaks appear. One is chemisorbed oxygen (Oα) located at
530.9eV and the other is lattice oxygen (Oβ) located at 528.8 eV.1 The higher the
content of Oα, the more conducive to the SCR catalytic reaction.6 Table 2 shows that
the ratio of Oα in MnOx-CeO2 @ TiO2 is higher than MnOx-CeO2 / TiO2, which can
promote the oxidation of NO to NO2, thereby increasing the catalytic activity.42

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u'''
(b)
(a)
u
v'''
Ce 3d
v
u'
u''
v'
v''
Mn 2p
7
Mn 2p
Mn 2p
1/2
3/2
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A
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B
B
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Binding energy (eV)
Binding energy (eV)
O
(d)
Ti 2p
(c)
O 1s
O
Ti 2p
Ti 2p
1/2
3/2
A
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536
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530
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526
Binding energy (eV)
Binding energy (eV)
Fig. 5 XPS spectra of catalyst surface elements Mn 2p (a), Ce 3d (b), Ti 2p (c) and O 1s (d)
（A: MnOx-CeO2 / TiO2; B: MnOx-CeO2 @ TiO2）
Table 2 Atomic surface composition of the catalysts as determined by XPS
Atomic composition (%)
Relative atomic ratio (%)
O Ce
Samples
Mn
Mn
Ti
14
O
Ce
Mn4+ Mn3+
Oα
Oβ
Ce4+
Ce3+
4.16
53.75 7.53
48.9
51.1 12.26 87.74 86.22 13.78
MnOx-CeO2/TiO2
MnOx-CeO2@TiO2
3.6 NH3-TPD
4.01 15.84 56.6
5.32 67.42 32.58 23.42 76.58 85.61 14.39

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Obviously, the surface acidity of samples play an important role in the NH3-SCR
reaction.4 In order to explore the surface acidity of samples, NH3-TPD results are
shown in Fig. 6. There is a broad peak at 200°C for the samples, which is formed by
the desorption of adsorbed NH3 on medium acid and weak acid sites.34 The peak
located in the temperature range from 200 to 500 °C is attributed to the Brønsted acid
sites.43 It can be seen that the peak area of MnOx-CeO2 @ TiO2 is larger than
MnOx-CeO2 / TiO2, especially in the Brønsted acid position, indicating that
MnOx-CeO2 @ TiO2 has more acidic sites.44 Obviously, MnOx-CeO2 @ TiO2
possesses excellent NH3 adsorption capacity, which is conducive to the NH3-SCR
reaction.
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MnO -CeO / TiO
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400
500
Temperature (C)
Fig. 6 NH3-TPD pattern of MnOx-CeO2 / TiO2 and MnOx-CeO2 @ TiO2
3.7 H2-TPR
In order to examine the reducibility of the samples, H2-TPR measurements were
performed. As shown in Fig. 7, MnOx-CeO2 @ TiO2 has two peaks located at 241°C
and 345°C respectively. The peak at 241°C is due to the reduction of MnO2 to Mn3O4.

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And the peak at 345°C corresponds to the reduction of Mn3O4 to MnO when the
surface capping oxygen of CeO2 is reduced.45 Furthermore, MnOx-CeO2 / TiO2 has
two peaks similar to MnOx-CeO2 @ TiO2. But the two peaks shift to higher
temperature, indicating the oxidation performance of MnOx-CeO2 / TiO2 is weaker
than MnOx-CeO2 @ TiO2.46
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345
MnO -CeO @ TiO
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x
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292
378
MnO -CeO / TiO
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x
2
100 150 200 250 300 350 400 450 500 550
Temperature (C)
Fig. 7 H2-TPR patterns of MnOx-CeO2 / TiO2 and MnOx-CeO2 @ TiO2
3.8 Catalytic Performance
The catalytic performance of prepared samples towards NO removal was
evaluated. As shown in Fig. 8a, MnOx-CeO2 / TiO2 and MnOx-CeO2 @ TiO2 exhibit
high catalytic activity at low temperature. The NOx conversion of MnOx-CeO2 @
TiO2 reaches around 100% at 140 oC. And the catalytic activity of MnOx-CeO2 / TiO2
is lower than MnOx-CeO2 @ TiO2, which is consistent with the conclusions obtained
before. N2 selectivity is a crucial role in evaluating the catalytic activity of SCR
catalyst. In Fig. 8b, the N2 selectivity of MnOx-CeO2 / TiO2 gradually decreases with
the increase of temperature. These results can be attributed to the formation of N2O

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under high load and partial oxidation of NH3 at elevated temperatures. And
Mn-based catalysts, due to their oxidative power, promote the formation of undesired
products (N2O and NO2).48 In addition, the N2 selectivity of MnOx-CeO2 @ TiO2
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remains above 95% from 40 to 200 C. As shown in the Raman spectra, a synergistic
interface effect exists between MnOx-CeO2 (core) and TiO2 (shell), which facilitates
NH3-SCR activities of MnOx-CeO2 @ TiO2 catalysts and N2 selectivity.49 The
o
stability of MnOx-CeO2 @ TiO2 at 160 C is shown in Fig. 8c. And the NOx
conversion of MnOx-CeO2 @ TiO2 remains unchanged in the whole test, which is due
to the formation of the core-shell structure.50 Core-shell nanostructures protect active
components from migrating and reuniting. It can be concluded that MnOx-CeO2 @
TiO2 has high N2 selectivity, good stability and high SCR activity, which is closely
related to its special core-shell structure.
100
(a)
80
60
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x
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20
0
MnO -CeO @ TiO
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x
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80 100 120 140 160 180 200 220
Temperature (oC)

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(b)
(c)
100
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0
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MnO - CeO @ TiO
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x
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MnO -CeO / TiO
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x
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MnO -CeO @ TiO
2
2
2
40
60
80
100 120 140 160 180 200
0
100 200 300 400 500 600 700 800 900
Reaction time (min)
Temperature(C)
Fig. 8 Catalytic activity (a) and N2 selectivity (b) for different samples and stability of
MnOx-CeO2 @ TiO2 catalyst at 160 °C (c)
3.9 Influence of SO2
High SO2 durability is usually required for the potential low-temperature
NH3-SCR catalysts. 200ppm SO2 was added into the system on the basis of the
catalytic activity test. The catalytic activity of MnOx-CeO2 / TiO2 and MnOx-CeO2 @
TiO2 are shown in Fig. 9.
After 200ppm SO2 was introduced into flue gas system for 3.5 hours, catalytic
activity of MnOx-CeO2 / TiO2 and MnOx-CeO2 @ TiO2 decreased from 100% to 47%
and 70% respectively, verifying that SO2 had a poisoning effect on SCR activity at
low temperature. Catalytic activity of MnOx-CeO2 / TiO2 could not recover after the
removal of SO2, indicating that SO2 caused irreparable damage to MnOx-CeO2 / TiO2.
Compared with MnOx-CeO2 / TiO2, the activity of MnOx-CeO2 @ TiO2 restored to
around 85% after turning off the SO2.

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200ppm SO on
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MnO -CeO @ TiO
2
x
2
MnO -CeO / TiO
x
2
2
0
100
200
300
400
Reaction time (min)
Fig. 9 SO2 tolerance of MnOx-CeO2 / TiO2 and MnOx-CeO2 @ TiO2 at 180 oC
According to literatures, the formation and deposition of ammonium sulfates
which clog the pore channels and the competitive adsorption between NO and SO2
partially contribute to the deactivation of catalyst. And the main cause of catalyst
deactivation is the sulfation of the active center atoms.51 Gao et al. reported that
MnOx-based catalysts have poor resistance to SO2.52 MnOx-based catalysts can easily
react with SO2 to generate a large amount of sulfate, resulting in a decrease of the
amount of the active component of Mn4+. When SO2 was added into system,
MnOx-CeO2 @ TiO2 had higher catalytic activity than MnOx-CeO2 / TiO2. As shown
in Fig.2a, the active components of MnOx-CeO2 / TiO2 were completely exposed. The
surface of MnOx-CeO2 / TiO2 was covered with ammonium sulfate to prevent the
adsorption of the reaction gas. Moreover, the active components of MnOx-CeO2 /
TiO2 reacted with SO2 to generate a large amount of sulfate that did not contribute to
NO degradation, which was the reason why the catalytic activity of MnOx-CeO2 /
TiO2 could not recover after the removal of SO2. Compared with MnOx-CeO2 / TiO2,

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the special core-shell structure in MnOx-CeO2 @ TiO2 caused ammonium sulfate to
deposit on the outer shell, which reduced the blockage of the catalyst channel by
ammonium sulfate. Interestingly, the active center is not easily exposed to SO2 due to
the presence of the TiO2 outer shell.32 MnOx-CeO2 @ TiO2 still had a large number of
active centers after SO2 was added into the system for several hours. So MnOx-CeO2
@ TiO2 had higher catalytic activity than MnOx-CeO2 / TiO2. And the decomposition
of ammonium sulfate and the disappearance of competitive adsorption of SO2 were
probably responsible for the recovery of MnOx-CeO2 @ TiO2 activity after the
removal of SO2.
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Fig. 10 The SO2 deactivation mechanism over different catalysts. (a) MnOx-CeO2 / TiO2; (b)
MnOx-CeO2 @ TiO2.
4. Conclusion
In summary, core-shell structure MnOx-CeO2 @ TiO2 was successfully
fabricated as high-performance de-NOx catalyst. Compared with MnOx-CeO2 / TiO2,
MnOx-CeO2 @ TiO2 has larger specific surface area and pore volume, which make

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the catalyst have more active sites and channels for the reaction gas to fully contact
the active sites. Moreover, more oxygen vacancies and acidic sites in MnOx-CeO2 @
TiO2 make NO more susceptible to oxidation. Obviously, The TiO2 shell not only
does not inhibit the catalytic activity of MnOx-CeO2 @ TiO2, but improves the
physicochemical properties of the catalysts. The superior SO2 tolerance could be
attributed to the unique core-shell structure lowers the possibility of surface active
sites poisoned by SO2 and meanwhile prevents the formation of ammonium sulfate
species from covering the active sites. The MnOx-CeO2 @ TiO2 catalyst could serve
as a promising candidate for the NH3-SCR catalyst at low temperature.
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Conflicts of interest
There are no conflicts to declare.
Acknowledgments
This work was funded by the National Natural Science Foundation of China (no.
41877469 and 51508281).
Notes and references
1.
2.
3.
J. Yu, Z. C. Si, X. K. Li, L. Chen, X. D. Wu and D. Weng, Catal. Today, 2016,
267, 47-55.
A. Beretta, A. Lanza, L. Lietti, S. A. Clave, J. Collier and M. Nash, Chem. Eng.
J., 2019, 359, 88-98.
H. Hu, S. X. Cai, H. R. Li, L. Huang, L. Y. Shi and D. S. Zhang, Acs Catal.,
2015, 5, 6069-6077.
4.
5.
X. L. Li and Y. H. Li, J. Mol. Catal. a-Chem., 2014, 386, 69-77.
Y. R. Yang, M. H. Wang, Z. L. Tao, Q. Liu, Z. Y. Fei, X. Chen, Z. X. Zhang, J.

New Journal of Chemistry
Page 20 of 23
1
2
3
4
5
View Article Online
DOI: 10.1039/C9NJ03461G
H. Tang, M. F. Cui and X. Qiao, Catal. Sci. & Technol., 2018, 8, 6396-6406.
6.
Z. M. Liu, Y. Li, T. L. Zhu, H. Su and J. Z. Zhu, Ind. & Eng. Chem. Res., 2014,
6
7
8
9
53, 12964-12970.
7.
W. Y. Yao, X. Q. Wang, Y. Liu and Z. B. Wu, Appl. Surf. Sci., 2019, 467,
439-445.
C. Liu, F. Li, J. Wu, X. Hou, W. Huang, Y. Zhang and X. G. Yang, J. Hazard.
Mater., 2019, 363, 439-446.
8.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
9.
L. Cao, X. D. Wu, Y. F. Xu, Q. W. Lin, J. F. Hu, Y. Chen, R. Ran and D. Weng,
Catal. Commun., 2019, 120, 55-58.
Z. Y. Sheng, Y. F. Hu, J. M. Xue, X. M. Wang and W. P. Liao, J. Rare Earth.,
2012, 30, 676-682.
C. Niu, X. Y. Shi, K. Liu, Y. You, S. X. Wang and H. He, Catal. Commun.,
2016, 81, 20-23.
S. Han, J. Cheng, Q. Ye, S. Y. Cheng, T. F. Kang and H. X. Dai, Micropor.
Mesopor. Mat., 2019, 276, 133-146.
H. Liu, Z. X. Fan, C. Z. Sun, S. H. Yu, S. Feng, W. Chen, D. Z. Chen, C. J.
Tang, F. Gao and L. Dong, Appl. Catal. B-Environ., 2019, 244, 671-683.
L. Q. Chen, F. L. Yuan, Z. B. Li, X. Y. Niu and Y. J. Zhu, Chem. Eng. J., 2018,
354, 393-406.
T. R. Zhang, S. B. Ma, L. Q. Chen, R. Li, X. S. Leng, Y. S. Li, F. L. Yuan, X. Y.
Niu and Y. J. Zhu, Appl. Catal. a-Gen., 2019, 570, 251-261.
Z. Y. Fei, Y. R. Yang, M. H. Wang, Z. L. Tao, Q. Liu, X. Chen, M. F. Cui, Z. X.
Zhang, J. H. Tang and X. Qiao, Chem. Eng. J., 2018, 353, 930-939.
Y. Jiang, C. Z. Lai, S. J. Liu, G. T. Liang, C. Z. Bao, W. Y. Shi and S. Y. Ma,
Aerosol Air Qual. Res., 2019, 19, 422-430.
F. Y. Gao, X. L. Tang, H. H. Yi, J. Y. Li, S. Z. Zhao, J. G. Wang, C. Chu and C.
L. Li, Chem. Eng. J., 2017, 317, 20-31.
H. Z. Chang, J. H. Li, X. Y. Chen, L. Ma, S. J. Yang, J. W. Schwank and J. M.
Hao, Catal. Commun., 2012, 27, 54-57.
H. Z. Chang, X. Y. Chen, J. H. Li, L. Ma, C. Z. Wang, C. X. Liu, J. W.
Schwank and J. M. Hao, Environ. Sci. & Technol., 2013, 47, 5294-5301.
X. S. Leng, Z. P. Zhang, Y. S. Li, T. R. Zhang, S. B. Ma, F. L. Yuan, X. Y. Niu
and Y. J. Zhu, Fuel Process. Technol., 2018, 181, 33-43.
K. Yang, H. Yi, X. Tang, S. Z. Zhao, F. Y. Gao, Y. H. Huang, Z. Y. Yang, J. G.
Wang, Y. R. Shi and X. Z. Xie, Chem. Eng. J., 2019, 364, 420-427.
Z. Y. Sheng, D. R. Ma, D. Q. Yu, X. Xiao, B. J. Huang, L. Yang and S. Wang,
Chinese J. Catal., 2018, 39, 821-830.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
L. Chen, X. X. Wang, Q. L. Cong, H. Y. Ma, S. J. Li and W. Li, Chem. Eng. J.,
2019, 369, 957-967.
L. P. Han, M. Gao, J. Y. Hasegawa, S. X. Li, Y. J. Shen, H. R. Li, L. Y. Shi and
D. S. Zhang, Environ. Science & Technology, 2019, 53, 6462-6473.
W. Li, J. P. Yang, Z. X. Wu, J. X. Wang, B. Li, S. S. Feng, Y. H. Deng, F.
Zhang and D. Y. Zhao, J. Am. Chem. Soc., 2012, 134, 11864-11867.
Q. Li, X. Li, W. Li, L. Zhong, C. Zhang, Q. Y. Fang and G. Chen, Chem. Eng.

Page 21 of 23
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ03461G
J., 2019, 369, 26-34.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
C. Wang, F. Yu, M. Y. Zhu, C. J. Tang, K. Zhang, D. Zhao, L. Dong and B. Dai,
J. Environ. Sci., 2019, 75, 124-135.
Y. M. Abbas, A. B. Mansour, S. E. Ali and A. H. Ibrahim, J. Magn. and Magn.
Mater., 2019, 482, 66-74.
D. Salinas, P. Araya and S. Guerrero, Appl. Catal. B-Environ., 2012, 117,
260-267.
W. Zhao, S. P. Dou, K. Zhang, L. C. Wu, Q. Wang, D. H. Shang and Q. Zhong,
Chem. Eng. J., 2019, 364, 401-409.
X. J. Yao, L. Chen, J. Cao, Y. Chen, M. Tian, F. M. Yang, J. F. Sun, C. J. Tang
and L. Dong, Chem. Eng. J., 2019, 369, 46-56.
Y. J. Xie, Y. Y. Yu, X. Q. Gong, Y. Guo, Y. L. Guo, Y. Q. Wang and G. Z. Lu,
Crystengcomm, 2015, 17, 3005-3014.
S. B. Ma, X. Y. Zhao, Y. S. Li, T. R. Zhang, F. L. Yuan, X. Y. Niu and Y. J. Zhu,
Appl. Catal. B-Environ., 2019, 248, 226-238.
M. Kong, Q. C. Liu, L. J. Jiang, W. Tong, J. Yang, S. Ren, J. L. Li and Y. M.
Tian, Chem. Eng. J., 2019, 370, 518-526.
A. J. Xie, Y. R. Tang, X. Y. Huang, X. Jin, P. F. Gu, S. P. Luo, C. Yao and X. Z.
Li, Chem. Eng. J., 2019, 370, 897-905.
C. L. Li, X. L. Tang, H. H. Yi, L. F. Wang, X. X. Cui, C. Chu, J. Y. Li, R. C.
Zhang and Q. J. Yu, Appl. Surf. Sci., 2018, 428, 924-932.
F. X. Li, J. L. Xie, K. Qi, P. J. Gong and F. He, Catal. Lett., 2019, 149,
788-797.
A. Y. Zhou, D. Q. Yu, L. Yang and Z. Y. Sheng, Appl. Surf. Sci., 2016, 378,
167-173.
X. Y. Wang, K. Zhang, W. T. Zhao, Y. Y. Zhang, Z. X. Lang, T. H. Zhang, Y. H.
Xiao, Y. F. Zhang, H. Z. Chang and L. L. Jiang, Ind. & Eng. Chem. Res., 2017,
56, 14980-14994.
D. Dogu, K. E. Meyer, A. Fuller, S. Gunduz, D. J. Deka, N. Kramer, A. C. Co
and U. S. Ozkan, Appl. Catal. B-Environ., 2018, 227, 90-101.
Y. Geng, X. L. Chen, S. J. Yang, F. D. Liu and W. P. Shan, Acs Appl. Mater. &
Inter., 2017, 9, 16952-16959.
T. Lee and H. Bai, Ind. & Eng. Chem. Res., 2018, 57, 4848-4858.
Y. Wang, H. H. Li, S. K. Wang, X. Wang, Z. He and J. J. Hu, Fuel Process.
Technol., 2019, 188, 179-189.
L. Chen, X. J. Yao, J. Cao, F. M. Yang, C. J. Tang and L. Dong, Appl. Surf. Sci.,
2019, 476, 283-292.
A. J. Xie, Y. Y. Tao, X. Jin, P. F. Gu, X. Y. Huang, X. M. Zhou, S. P. Luo, C.
Yao and X. Z. Li, New J. Chem., 2019, 43, 2490-2500.
S. J. Yang, C. X. Liu, H. Z. Chang, L. Ma, Z. Qu, N. Q. Yan, C. Z. Wang and J.
H. Li, Ind. & Eng. Chem. Res., 2013, 52, 5601-5610.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
41.
42.
43.
44.
45.
46.
47.
48.
49.
B. H. Zhao, R. Ran, X. G. Guo, L. Cao, T. F. Xu, Z. Chen, X. D. Wu, Z. C. Si
and D. Weng, Appl. Catal. a-Gen., 2017, 545, 64-71.
J. X. Liu, J. Liu, Z. Zhao, J. B. Tan, Y. C. Wei and W. Y. Song, Aiche J., 2018,

New Journal of Chemistry
Page 22 of 23
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ03461G
64, 3967-3978.
50.
51.
52.
S. X. Cai, D. S. Zhang, L. Y. Shi, J. Xu, L. Zhang, L. Huang, H. R. Li and J. P.
Zhang, Nanoscale, 2014, 6, 7346-7353.
L. J. Jiang, Q. C. Liu, G. J. Ran, M. Kong, S. Ren, J. Yang and J. L. Li, Chem.
Eng. J., 2019, 370, 810-821.
L. Gao, C. T. Li, S. H. Li, W. Zhang, X. Y. Du, L. Huang, Y. C. Zhu, Y. B. Zhai
and G. M. Zeng, Chem. Eng. J., 2019, 371, 781-795.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
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New Journal of Chemistry
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View Article Online
DOI: 10.1039/C9NJ03461G
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MnOx-CeO2 @ TiO2 catalyst presents excellent NH3-SCR activity and TiO2 shell is
responsible for the good SO2 tolerance.