The effect of different metal oxides on the catalytic activity of a Co3O4 catalyst for toluene combustion: Importance of the structure-property relationship and surface active species

Article abstract of DOI:10.1039/c9nj01783f

Herein, Co₃O₄ catalysts modified with different metals M (M = La, Mn, Zr and Ni) were used in the catalytic combustion of toluene to demonstrate the importance of the structure-property relationship and surface active species. The results revealed that the Co-La catalyst exhibited optimum catalytic performance and CO₂ selectivity, and 90% toluene conversion was obtained at 243 °C, which might be closely related to the formation of the LaCoO₃ perovskite. Furthermore, the specific surface area, pore volume and low-temperature reducibility over these samples decreased as follows: Co-La > Co-Mn > Co-Zr > Co-Ni; this was completely consistent with the catalytic activity results. In addition, the Co-La sample possesses the most Co³⁺ species and abundant adsorbed oxygen species; this indicates that this sample has excellent oxygen storage capacity. Note that Co-Ni possesses the highest O_ads/O_latt ratio but exhibits the lowest activity; this infers that the active species Co³⁺ and O_ads participate cooperatively in the redox reaction. In brief, its excellent catalytic activity can be significantly attributed to its high specific surface area, excellent low-temperature reducibility and more abundance of surface active species (Co³⁺ and O_ads).

Full text of DOI:10.1039/c9nj01783f

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Volume 40 Number
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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

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The effect of different metal oxides on catalytic activity of the Co O4
3
catalyst for toluene combustion: Importance of structure-property
and surface active species
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a
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b, *
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Xuejun Zhang , Min Zhao , Zhongxian Song , Heng Zhao , Wei Liu , Jinggang
a
a
a
Zhao , Zi’ang Ma , Yun Xing
a
College of Environmental and Safety Engineering, Shenyang University of
Chemical Technology, Shenyang 110142, People’s Republic of China
b
Faculty of Environmental and Municipal Engineering, Henan Key Laboratory of
Water Pollution Control and Rehabilitation Technology, Henan University of Urban
Construction, Pingdingshan, 467036, People’s Republic of China
Corresponding Authors:
*Z. X. Song: email, songzhongxian@126.com, Tel., (+86)-375-2089031

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DOI: 10.1039/C9NJ01783F
Abstract: The catalysts based on different metals M (M = La, Mn, Zr and Ni)
modified Co O catalysts were used in the catalytic combustion of toluene to
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importance of structure-property and surface active species. The results revealed that
Co-La catalyst exhibited the optimum catalytic performance and CO selectivity, and
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0% toluene conversion was obtained at 243 °C, which might be closely related to the
formation of LaCoO perovskite. Furthermore, the specific surface area, pore volume
3
and low-temperature reducibility over these samples decreased as follows: Co-La >
Co-Mn > Co-Zr > Co-Ni, which was completely consistent with the catalytic activity
results. Besides, Co-La sample possessed the most Co3+ species and abundant
adsorbed oxygen species, indicating that it owed excellent oxygen storage capacity.
Noticeably, Co-Ni possessed the highest O /O ratio, but exhibited the lowest
ads latt
3+
activity, inferring that the active species Co and O participated cooperativity in
ads
the redox rection. In brief, the excellent catalytic activity could be greatly attributed to
the highest specific surface area, excellent low-temperature reducibility and more
3
+
available surface active species (Co and O ).
ads
3
+
Keywords: Catalytic combustion of toluene; Co O ; Co species; Adsorbed oxygen
3
4

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1
. Introduction
Most of volatile organic compounds (VOCs) produced from industrial and
vehicles activities, the exhaust gas of factory and automobile offgas were mostly toxic
and harmful to the environment and life health [1-2]. Therefore, strict control for
emission value of VOCs concentration in the environment was significant [3]. There
were many technologies for control the emissions of VOCs, such as adsorption,
bio-degradation, thermal oxidation and catalytic combustion [4-5]. Among the various
approaches, catalytic combustion was an efficient and promising applied technology
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for the remove of VOCs [6-7]
.
Currently, the reported efficient catalysts for catalytic oxidation of VOCs were
supported noble metals (such as Pt, Pd, Ag and Au) [8-11] and non-noble metal oxides.
Noble metals catalysts could exhibit excellent catalytic performance at relatively low
temperature [12-14]. But their application was limited because of the high price, scarce
resources and low thermal stability [15]. Recently, transition-metal oxides catalysts
(
such as Mn, Co, Fe, Cr and Cu) and rare earth metal oxides catalysts (such as Ce, La)
were alternative options and used as catalysts for combustion of VOCs [16-19]. Cobalt
oxide (Co O ) exhibits excellent performance in catalytic combustion of VOCs [20-22].
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The catalytic performances of singular oxide catalysts were mostly lower than that of
noble-metals catalysts. However, the mixture of two or more non-noble metal
elements was an effective method to improve catalytic activities due to their various
synergistic effects. Tang et al. [23] proved that the Mn-Co mixed oxide showed higher
catalytic removal of VOCs because of higher surface area, richer porous construction
and lower temperature reducibility. Pu et al. [24] revealed that ZrO -modified Co O
2
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catalysts could increase the catalytic oxidation of VOCs due to the improvement of
Co2+ concentrations and O /O ratios. Liotta et al. [25] found that the excellent
ads latt
activity of Co Ce in catalytic oxidation of VOCs was attributed to higher mobility of
x
lattice oxygen. Besides, it was reported that the insertion of iron into the spinel of
cobalt oxide could increase of the thermal stability and selectivity of CO , and then
2
enhanced VOCs conversion [26]. In addition, researcher proved that there was more
abundant surface Oads species on LaCoO than on single CoO and LaO , and the
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x

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increased of Oads species contributed to the improvement of low-temperature
reducibility [27]. It could be seen that bimetallic synergy could lead to the enhancement
of active species, resulting in a dramatically increased in catalytic performance. Based
on the above discussion, the interaction between Co and other metal species played an
important role in the catalytic oxidation of VOCs. Meanwhile, the role of bimetallic
synergy over Co-based catalysts was still in dispute. Thereby, the effect of oxygen
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species and active species on CoO modified by different transition metals/rare earth
x
metals in catalytic oxidation of toluene still needs to be further clarified.
A series of Co-M (M = La, Mn, Zr and Ni) mixed oxides catalysts were
synthesized by co-precipitation method and used in catalytic combustion of toluene
(
C H ). Our goal was to clarify the effect of structure, redox ability and surface active
7 8
species over Co-M on the catalytic performance, revealing the structure-activity
relationship. Meanwhile, the catalysts were characterized by a numerous of
techniques, including N2 adsorption/desorption, X-ray diffraction (XRD), H2
temperature programmed reduction (H -TPR), O temperature programmed
2
2
desorption (O -TPD) and X-ray photoelectron spectroscopy (XPS).
2
2
. Experimental
2
.1. Catalyst preparation
All chemical reagents in the synthesis process were of analytical grade, and all
reagents were directly used without any further purification. Co-M (M = La, Mn, Zr
and Ni) oxide was prepared by a traditional co-precipitation method with 8.82 g
Co(NO ) ·6H O and 2.72 g La(NO ) ·xH O were used as precursor and dissolved into
3
3
2
3 3
2
100 mL distilled water to form an aqueous solution at room temperature and stirred
until complete dissolution on magnetic stirrer. Ammonia solution was gradually
added stirred until the pH value reached 10. The resulting precipitates was aged
overnight at room temperature, filtered and washed by distilled water and then dried
at 105 °C overnight in air oven. Finally, the dried precipitates were calcined at 550 °C
in air atmosphere for 5 h. The obtained products are denoted as Co-La.
Other catalysts were prepared by the same preparation method and marked as
Co-Zr, Co-Ni and Co-Mn, respectively. Different metal M loaded was 20 wt.%,

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respectively.
.2 Catalysts Characterization
XRD patterns of the samples were recorded on a Bruker D8 Advance powder
diffractometer using Cu Ka radiation. The patterns were collected in the 2θ range of
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0-80 °C with a constant 2θ step size of 0.02° and per step time of 2 s.
The specific surface areas (SBET) of the catalysts were calculated by N2
adsorption at liquid nitrogen temperature (-196 °C), meanwhile total pore volume
D ) and average pore diameter (D ) were measured, using a physical adsorption
(
V
P
instrument (Beijing Builder Electronic Technology Company, SSA-6000).
Raman measurements of the samples were recorded on a Renishaw-2000 Raman
-1
microscope at a resolution of 2 cm . The excitation source was the 514.5 nm line of
+
Ar laser.
XPS spectra were gained on a An ESCALAB 250 photoelectron spectrometer
(Thermo Fisher Scientific, USA) by using a monochromatized micro focused Al Ka
X-ray as the excitation source. The binding energy (BE) scale was corrected for
charging of samples by use of the C1s peak of adventitious carbon as reference at
284.6 eV.
H -TPR measured on a chemisorption instrument (Beijing Builder Electronic
2
Technology Company, PCA-1200). 20 mg of the catalyst was placed in a U-type
quartz tube and pretreatment in pure N stream. The temperature was rised to 300 °C
2
with rate of 10 °C/min and maintained for 60 min, and then decrease to 100 °C.
Following samples was reduced via Ar gas mixture with 5% H , and total flow rate
2
was 30 mL/min. The H consumption was measured by a thermal conductivity
2
detector (TCD), while the temperature was gradually increased to 900 °C.
O -TPD was carried out by the chemisorption instrument (Beijing Builder
2
Electronic Technology Company, PCA-1200). 200 mg samples was measured with
U-shaped quartz tube and pre-treated in a pure He stream at 300 °C for 60 min, then
samples were cooled down to 50 °C in He atmosphere mixture with 20 vol.% O2
stream at a rate of 30 mL/min. Finally, the sample was heated at the 10 °C/min to
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00 °C with pure He atmosphere.

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2
.3. Catalytic activity measurement
Catalytic combustion reactions performance of toluene was determined in a fixed
bed reactor (i.d. = 8 mm, o.d. = 10 mm). 0.1 mL of catalysts (40-60 mesh) was placed
at the bed of the reactor. In the tests, the volume composition of the feed gas was the
concentration of C H 500 ppm, 20 vol.% O and N mixture stream. The total flow
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rate of the feed stream is 100 mL/min. The concentration of toluene in the import and
exit gases were analyzed by an on-line gas chromatography via using FULI 9790Ⅱ
equipped with FID detectors. The conversion rate X (%) of toluene was estimation by
the following equation (Eq. (1)):
Cin -Cout
X =
× 100%
(1)
Cin
In this equation, C refers to the import concentration of toluene, C is the exit
in
out
concentration of toluene at different temperatures.
The toluene oxidation was also characterized by selectivity of CO , the CO
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generation rate following equation (Eq. (2)):
C
CO2 generation rate =
× 100%
(2)
CCO2
In this equation, CCO2 is the concentration of CO when toluene is oxidized
2
completely and C is the concentration of CO at different temperatures.
2
3. Results and discussion
3
.1. XRD
XRD technique was the main method to study the phase and crystal structure of
materials. The XRD patterns of Co-M (M = La, Mn, Zr and Ni) samples were
displayed in Fig. 1. From the XRD spectrum, it was detected that the diffraction peaks
2
θ = 19.1, 31.3, 36.9, 38.6, 44.9, 55.7, 59.4, 65.4 and 77.4° over the samples, which
were corresponded to (111), (220), (311), (400), (422), (511), (440) and (533) planes
of Co O spinel structure (JCPDS PDF # 73-1701), respectively. Furthermore, ZrO
2
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(
JCPDS PDF # 89-9069) phase over Co-Zr was detected, indicating the ZrO phase
2
was separated. However, no MnO and NiO species were observed, which indicated
x
x
that the Mn or Ni species were incorporated into the cobalt oxides lattice to form the
solid solution or it was dispersed uniformly on the surface of Co O . Noticeably,
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Co-La catalyst was observed several peaks appear at 23.1, 33.0, 40.7, 47.5 and 69.4°,
respectively, which were assigned to the characteristic of LaCoO perovskite phase
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(
JCPDS PDF # 75-0279). The form reason of perovskite-type (ABO ) might be
3
explained by the tolerance factor [28], t:
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RA + RO
t =
2
B O
(R + R )
Where R represents the ionic radius of the A, B or the oxide ion. The perovskite
structure could be formed when the tolerance factor falls between 0.8 and 1.0 [29-30]
.
3+
2+
Considering Co and Co both high and low spin configurations possible, the ionic
radius values were 0.53 (low spin) 0.61 (high spin) and 0.57 (low spin) 0.74 (high
spin), La ionic radius values was 1.32 Å. The obtained tolerance factors could vary
from 0.90 to 0.98 for Co-La, thus perovskite-type structures could be formed. It was
reported that the perovsike-type oxides was active toward oxidation of CO and VOCs
[27,31-32]
. Besides, minor peaks of La O were detected at 29.6°, which indicated that
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the agglomeration of excess La O oxides formed. The formation of pure LaCoO
3
2
3
perovskite was related to the preparation method, the content ratio of Co/La and the
roasting temperature. Therefore, Co O phase and LaCoO perovskite crystal phase
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3
were formed on the Co-La catalyst. For the composite oxide Co-Mn and Co-La, the
diffraction peaks intensity of Co O crystalline phase was obviously decreased
3
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compared with Co-Zr and Co-Ni catalysts, which revealed that Co-Mn and Co-La
possessed smaller crystal size. Besides, the average crystalline size of the catalysts
was calculated with Scherrer equation applied for Co O and the results were listed in
3
4
Table 1. The particle size (P ) of Co-La, Co-Mn, Co-Zr and Co-Ni was 11, 10, 26 and
S
2
5 nm, respectively. It was reported that the smaller size particles could create more
crystal defects, which would be beneficial to catalytic activity [23].

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Fig. 1. XRD patterns of Co-La, Co-Mn, Co-Zr and Co-Ni samples.
3.2. N adsorption-desorption
2
N adsorption-desorption isotherms and pore-size distributions of Co-M (M =
2
La, Mn, Zr and Ni) catalysts were shown in Fig. 2a and Fig. 2b, respectively. The
SBET, DV and DP were listed in Table 1. As shown in Fig. 2a, the N2
adsorption-desorption isotherms of each sample belong to type IV characteristics with
a type H hysteresis loop at high relative pressure [31]. Particularly, the adsorption
3
intensity of Co-La catalysts was higher than that of other samples, indicating the
formation of abundant mesopores over Co-La. Mesoporous structures owned many
unique characteristics, which was beneficial to the inherent performance of solid
materials [33-34]. From the Fig. 2b, it was found that the pore size of Co-La was mainly
distributed in the range 5-41 nm. While the pore distribution sizes scope of Co-Mn,
Co-Zr and Co-Ni samples were located in 12.3-68.7, 3.2-21.9 and 2.2-69.6 nm,
respectively. The catalysts exhibited affluent porous structure, which could promote
the adsorption and diffusion of reactant, and then decreased limitations of interphase
mass transfer, resulting in the improvement of catalytic activities [23]. As seen in Table
1
, Co-La sample possessed largest specific surface area and the highest pore volume
2
-1
3 -1
with values of 41 m g and 0.36 cm g , respectively, which could be attributed to
remarkable contribution of existence of vast mesoporous structures. The ranking in
terms of SBET values over these mixed oxides decreased as follows: Co-La > Co-Mn >
Co-Zr > Co-Ni. Higher specific surface area was able to provide more available active
sites, which was beneficial for the boost of catalytic activity [31]. Therefore, the

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catalyst owned rich mesoporous structure and larger specific surface area would be
beneficial for the improvement in toluene combustion activity.
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4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Fig. 2. (a) N adsorption-desorption isotherms and (b) pore-size distributions of Co-La, Co-Mn,
2
Co-Zr and Co-Ni samples
Table 1. Physical properties of Co-La , Co-Mn, Co-Zr and Co-Ni catalysts.
2
-1
3 -1
Samples
Co-La
Co-Mn
Co-Zr
SBET (m g )
D (cm g )
D (nm)
PS (nm)
11
V
P
41
34
25
12
0.36
0.21
0.10
0.12
27.9
22.3
12.2
39.9
10
26
Co-Ni
25
3.3. Raman
As shown in Fig. 3, the Raman spectrum of Co-M (M = La, Mn, Zr and Ni)
catalysts were investigated. All samples exhibited five Raman-active modes at 190,
-1
4
80, 520, 610 and 682 cm . The positions of these bands were in good agreement
[24,35-36]
-1
with the reported values for Co O spinel
. The band at 190 cm corresponded
3
4
to the characteristic of tetrahedral sites (CoO ), which was attributed to the F (3)
4
2g
-1
symmetry. The Raman band with medium intensity at 480 and 520 cm was ascribed
to the E and F (2) symmetry, respectively. Another the weak band at approximately
g
2g
-1
-1
6
10 cm corresponded to the F (1) symmetry. Whereas the band at 682 cm was
2g
attributed to the vibrations of the octahedral sites (CoO ), which was assigned to the
6
A symmetry of the O spectroscopic [37]. No others impuritie vibrational modes was
7
1
g
h

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observed, revealing that the metal M species were well dispersed on the surface of
catalysts. Compared with Co-Zr and Co-Ni samples, the raman bands of Co-La and
Co-Mn shifted toward lower wavenumbers. Meanwhile, the peak intensity become
weak and a slight increase in half peak width, indicating the structural disorder was
increased and the Co-O bond strengths (force constants) was decreased, and then
increased the lattice oxygen activity [38]. The consequence implied that the addition of
0
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different metal species into CoO could affect the crystal structure. However, the
x
addition of LaO and MnO could more obvious affect the crystal structure.
x
x
Fig. 3. Raman spectra of Co-La, Co-Mn, Co-Zr and Co-Ni samples
3
.4. XPS
To investigate the detailed information of the surface chemical composition and
oxidation state of the catalyst, XPS spectra of Co2p and O1s electronic levels were
displayed in Fig. 4a and Fig. 4b. As shown in Fig. 4a, the asymmetrical Co2p3/2 XPS
spectrum of all catalysts could be decompose into two components with a BE at
3+
7
79.6±0.3 eV corresponds to Co , while the peak with a BE at 781.1±0.3 eV was
related to Co2+ [39]. The presence of these peaks demonstrated the existence of both
3+
2+
Co and Co species in all the catalysts. In order to determine the atomic and molar
ratios of surface species, the integration of the corresponding peaks was carried out
(
Figure S1) and the results were summarized in Table 2. As shown in Table 2, the
3
+
2+
Co /Co concentration ratio increased in the sequence of Co-Ni < Co-Zr < Co-Mn <
3
+
Co-La. It was reported that the more concentration surface Co in Co-based catalyst
would be beneficial for the enhancement of oxidation performance [40-41]. Xie et al.

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found that the Co3+ over Co O catalyst was mainly the active site for VOCs
DOI: 10.1039/C9NJ01783F
3
4
oxidation, which could contribute to the improvement of catalytic performance and
CO selectivity for VOCs catalytic oxidation [40]. Thereby, the introduction of
2
3
+
different metal oxides into CoO could change the Co ratios, and then affected the
x
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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catalytic performance.
The O1s spectra for the Co-La, Co-Mn, Co-Zr and Co-Ni catalysts were
de-convoluted into two parts, as observed in Fig. 4b. The one with a BE at
2−
5
29.5-530.1 eV was attributed to the lattice oxygen (O , expressed as O ), and the
latt
-
other with a BE at 530.8-531.6 eV was assigned to surface-adsorbed oxygen (O or
2
−
[42]
O , denoted as O ) . The area ratio of O /O was listed in Table 2, it could be
ads
ads latt
seen that the O /O ratio decreased in the order of Co-Ni > Co-La > Co-Zr >
ads latt
Co-Mn. It was reported that the Oads was important for physical property of the
catalyst, which was beneficial to the Mars-van-Krevelen mechanism for VOCs
oxidation [43]. It was well known that the adsorbed oxygen species concentration was
related to the oxygen vacancies density. Hence, higher O /O value implied the
ads latt
presence of more oxygen vacancies on the catalyst surface [24], which meant that the
catalyst would own more active sites.
Table 2. XPS analysis of Co-La, Co-Mn, Co-Zr and Co-Ni catalysts.
3
+
2+
Catalysts
Co-La
Co (at. %)
13.6
O (at. %)
50.2
M (at. %)
11.0 (La)
10.0 (Mn)
6.3 (Zr)
Co /Co
O /O
ads latt
2.33
0.95
0.31
0.75
0.99
Co-Mn
Co-Zr
14.5
43.3
1.27
22.2
50.8
1.08
Co-Ni
27.3
50.4
1.4 (Ni)
0.79

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Fig. 4. (a) Co2p3/2 and (b) O1s XPS spectra of Co-La, Co-Mn, Co-Zr and Co-Ni samples
3.5. H -TPR
2
H -TPR was an ideal technique to examine the redox ability of catalysts. Fig. 5
2
illustrates the H -TPR profile of all samples. The Co-Ni and Co-Zr samples mainly
2
exhibited two reduction peaks with could be resolve into two components, and the
reduction peaks in the range of 250-450 °C, which was attributable to the reduction of
Co O to CoO and CoO to Co [44], respectively. For the Co-Mn catalyst, there were
0
3
4
three reduction peaks centered at 240, 343 and 536 °C. The first weak peak could be
attributed to the reduction of Mn O to Mn O [45], while a second peak was probably
2
3
3
4
3
+
2+
due to the combination of Mn O (MnO ) to Mn O and Co to Co . The third broad
2
3
2
3
4
0
3+
peak corresponded to the synergistic reduction peak of CoO into Co and Mn into
Mn2+ [38]. The Co-La sample exhibited the lowest initiate reduction temperature over
the all samples. There were three mainly reduction peaks were observed at 196, 331
and 480 °C with a shoulder at 597 °C. The first weak peak at 196 °C originated from
the reaction between H and chemisorbed oxygen, which could be ascribed to the
2
depletion of highly reactive oxygen species [46]. According to O -TPD results (see
2
latter), however, the Co-La catalyst possessed the most chemically adsorbed oxygen
species was observed at 312 °C. The physicsorbed and/or chemisorbed oxygen
species could be readily removed at relatively low temperature. The similar results
were proved by Zhang and Cai et al. [31,38]. Whereas, the second and third peaks might
3
+
2+
2+
0
be attributed to the reduction of Co into Co and Co into Co , respectively. The
Co-La catalyst showed optimal reducing property, which was probably due to the

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formation of the perovskite-type structure, and then enhanced the low-temperature
reducibility. The shoulder at 597 °C in the Co-La sample could be ascribed to the
partial reduction of LaCoO perovskite. The perovskite reduction process included the
3
formation of a spinel structure (La CoO ), the reduction of the B cation (CoO to Co)
2
4
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
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2
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and finally La O and metallic Co [28]:
2
3
2
LaCoO → La CoO + CoO + 1/2O
3 2 4 2
CoO → Co + 1/2O2
La CoO → La O + Co + 1/2O
2
2
4
2
3
Obviously, as shown in Fig. 5, all samples of the low temperature reducibility
decreased in the order of Co-La > Co-Mn > Co-Zr > Co-Ni, which could be attributed
to the formation of the Co-O-M (Mn, Zr and Ni) solid solution in Co O spinel
3
4
structure, thus resulted in the a decrease in reducibility [47]. It was worth mentioned
that the Co-Mn sample exhibited the higher low-temperature reduction capacity,
which could be contributed to the strong synergistic effect between Mn and Co
species in the mixed oxides [23]
.
Fig. 5. H -TPR profiles of Co-La, Co-Mn, Co-Zr and Co-Ni samples
2
3
.6. O -TPD
2
The O -TPD measurements was carried out in order to investigate the desorption
2
of oxygen species of the samples, and the profiles were depicted in Fig. 6. Apparently,
only one desorption peak of all the samples at 877 °C could be observed except for
the Co-La. Whereas the Co-La exhibited three clearly desorption regions, which were
in the temperature range of 226-372 °C, 625-772 °C and 772-855 °C, respectively.

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The oxygen species desorbed at low-temperature (< 400 °C) were attributed to the
weakest molecular physicsorbed or chemisorbed oxygen denoted as O . Whereas,
ads
the desorption peaks appearing at high temperatures (> 400 °C) were ascribed to the
-
-
bulk lattice oxygen species (O ). The chemically adsorbed oxygen O /O and
latt
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2
-
physically adsorbed oxygen O species were much easier to desorb than the lattice O
2
species [48]. As shown in Fig. 6 (a), for the Co-La, there was a weak and evident low
temperature oxygen desorption peak at 312 °C, suggesting that a small amount of
chemically adsorbed oxygen species formed on the surface of Co-La. These results
could be inferred that Co-La mixed oxide possessed outstanding oxygen storage
capacity. The oxygen species desorbed in 625-772 °C region, which could be
associated with over-stoichiometric oxygen of the perovskite-type oxides, it might be
formulated by the following equation [31]
:
2
Co3 + + O2 - (□) → 2Co2 + + O2
Where the extra oxygen charges were compensated by cation vacancies (□). The
phenomenon suggested that more over-stoichiometric oxygen presence could promote
redox reaction. Additionally, it was found that the Co-La sample exhibited the lowest
temperature (741 °C) of Olatt desorption among the samples, indicated that the Olatt
species of the Co-La sample were more mobile. The higher mobility of lattice oxygen
species might be accelerated the oxygen transfer from bulk to surface, which favored
oxidation reactions [1]. The O -TPD results demonstrated that the Co-La sample
2
possessed more available adsorbed oxygen and excellent oxygen mobility, which
could facilitate the interaction with reactants at low temperature, thus improving the
catalytic performance, which was closely related to the formation of perovskite-type
structures over Co-La.

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Fig. 6. O -TPD profiles over Co-La, Co-Mn, Co-Zr and Co-Ni samples
2
3.7. Catalytic performance
The conversion of toluene and the CO selectivity as a function of reaction
2
temperature were shown in Fig. 7. It could be observed that the toluene conversion
increased with the increasing of temperature. The Co-La catalyst exhibited the
optimal activity with T50 and T90 (the reaction temperature of 50% and 90% toluene
conversion, respectively) was 233 °C and 243 °C, respectively. However, the T50 and
T90 of Co-Ni catalyst was 272 °C and 279 °C, respectively. It could be seen that the
descended sequence of activity for all the catalysts was as follows: Co-La > Co-Mn >
Co-Zr > Co-Ni. The result might be related to the intrinsic property of each
adulteration metal oxide and its interaction with Co O . Combined with H -TPR and
3
4
2
XPS results, Co-Mn with the superior redox ability but showed lower catalytic
performance in comparsion with Co-La, which might be the fact that the
perovskite-type structures of Co-La was responsible for the superior catalytic activity.
Fig. 7b exhibited the CO selectivity over the samples, and the temperature of
2
completely converted to CO and H O were listed in Table 3. Generally speaking, the
2
2
desired products from the oxidation of VOCs were CO and H O. However, some
2
2
intermediate products, such as CO and unwanted organic compounds were often
generated in the process of oxidation. Hence, it was necessary to investigate CO2
selectivity to the desired products when explored a catalytic oxidation process. As
shown in Fig. 7b, the CO selectivity was gradually rise with increasing temperature
2
for all samples, until the CO yield was close to the direct conversion of toluene,
2

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suggested that VOCs molecules were completely converted to CO and H O
2
2
completely. The increased order of completely transform to CO for all the catalysts
2
was as follows: Co-Mn < Co-Ni < Co-Zr < Co-La. Apparently, the Co-La catalyst
possessed the greatest CO selectivity, and the selectivity to CO was approximately
2
2
0
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5
0% and 100% at 234 and 267 °C, respectively. It was worth noting that the Co-La,
Co-Zr and Co-Ni catalysts completely generated to CO temperature were in
2
accordance with the toluene absolutely conversion temperature, indicating that the
complete oxidation of toluene generated to CO and H O over the catalysts. However,
2
2
for the Co-Mn catalyst, compare with the activity temperature (275 °C), the CO2
selectivity temperature (301 °C) had a significant lag, which could be attributed to the
poor deep oxidation capability and the formation of the intermediate, such as benzyl
alcohol or benzoic acid species [49]
.
For ABO type perovskite, it possessed excellent catalytic performance for
3
VOCs oxidation at high temperatures [50]. However, for the CO selectivity, which
2
was ascribed to the deep oxidation of CO at higher-temperatures. Thus, the
distinguished catalytic activity of Co-La sample was related to the LaCoO perovskite
3
structure. Otherwise, above the results, it could be observed that the order of catalytic
performance was completely consistent with the result of H -TPR and O -TPD.
2
2
Therefore, it could be concluded that the difference in catalytic performance and CO2
selectivity were correlated to the surface active oxygen species and low-temperature
reducibility.
Obviously, at the low temperatures range of 220-240 °C, the CO selectivity
2
lagged the toluene conversion over all samples, which could be attributed to the
toluene was first decomposed into C H intermediates, and then further oxidized to
x
y
[
51]
CO with the temperature rising. According to the situ FTIR results, Luo et al.
2
found that the characteristic peaks of benzene ring and benzoic acid were observed
over MOF-Mn1Co1 catalyst at low temperature. When the temperature was increased
up to 300 °C, the species of toluene and partially oxidized intermediates gradually
descend; meanwhile, the peak of adsorped water was presented, implying the further
deep oxidation. Feng et al. proposed reaction mechanism about the oxidation of

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toluene over Co/Sr-CeO . It was found that toluene was first broken down into methyl
2
and phenyl groups [1]. The similar phenomena were also proved by Chen et al. [52]
.
Therefore, compared with toluene conversion rate, the CO selectivity shown a lag.
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
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8
9
0
1
2
3
4
5
6
7
8
9
0
Fig. 7. The light-off curves as a function of reaction temperature for (a) toluene conversion and (b)
CO selectivity over samples
2
4
. Discussions
It was well known that there were several mainly factors influenced the catalytic
combustion activity of catalysts for VOCs oxidation, such as structural
characterization, porosity, specific surface area, surface active species (i.e. surface
oxygen species (Oads and O )) and redox ability [53], which resulted from the nature
latt
of different metals loaded on the Co O .
3
4
4
.1 Structure-activity relationship over Co-M (M = La, Mn, Zr and Ni) catalysts
In this study, the Co-M (M = La, Mn, Zr and Ni) catalyst exhibited the same
typical Co O spinel crystalline structures but different crystalline sizes, the catalytic
3
4
performances were varied. As for the Co-La, the LaCoO and La O were detected.
3
2
3
Notably, compared with Co-Mn, Co-Zr and Co-Ni catalysts, Co-La possessed smaller
lattice size, highest specific surface area and largest pore volume, which was
beneficial to facilitate the diffusion and adsorption of reactant, resulting in the
improvement of catalytic activity [54]. From the pore size distribution result, the Co-La
exhibited the largest mesoporous distribution compared with others three catalysts,
which was related to the aggregation of LaCoO perovskite [55]. From the Raman
3
result, the peak of Co-La was the weakest and broadest, indicating that the

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crystallinity was the lowest. Generally, the lower crystallinity was beneficial to the
catalytic activity. These results implied that the introduction of La ions into Co O
3
4
could affect the microstructure of the catalyst, and then influenced the catalytic
performance. Chen [52] and Zhang [31] proved that the improvement of the surface area
of catalysts resulted in better performance in catalytic combustion of VOCs. Thereby,
in order to further investigate the structure-activity relationship for the Co-based
catalysts, an intuitionistic analysis was carried out based on the correlated profiles of
T90, and the specific surface area (Fig. 8a) was selected as arguments for the
estimation of the catalytic combustion activity over all catalysts. As shown in Fig. 8a,
the T90 values for the catalysts gradually decreased with an evident increase in the
specific surface area. It could be seen that the order of T90 for the catalysts was as
follows: Co-La > Co-Mn > Co-Zr > Co-Ni. The present results demonstrated that the
catalytic activity of catalysts was affected by the specific surface area, and the favored
pore structure could promote the catalytic oxidation of toluence.
0
1
2
3
4
5
6
7
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9
0
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4.2 Effect of the surface species on the catalytic activity
For the Co-based catalyst, the Co3+ and Oads were main active species for
catalytic oxidation of toluene [43,56]. Generally, the C H molecules were adsorbed and
7
8
3
+
reacted with the adsorbed oxygen species on the Co-based catalysts, partial Co were
2
+
reduced to Co . Thereby, CO and H O was produced. Then, the dissipative surface
2
2
adsorbed oxygen was regenerated mainly from the migration of the bulk lattice
oxygen and the supplement of the gaseous O . Finally, the reduced states were
2
oxidized and returned to initial oxidation state (i.e. Co2+ to Co3+) [56]. The whole
reaction obeyed to the two irreversible steps of the MVK (Mars-van Krevelen)
mechanism [57]. To gain insights into the relationship of surface Co and Oads with
catalytic activity, the correlated profiles of T90 was selected an intuitive analysis.
As shown in Fig. 8b, T90 monotonically increased with the decrease of
3+
Co /Co ratio, indicating that Co3+ played a crucial role for toluene combustion,
which was well in agreement with previous research [51]. More Co cations provided
sufficient active sites for VOCs adsorption, which could improve the catalytic
performance. From the MVK mechanism, the catalytic activity could be enhanced
3
+
2+
3+

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3
+
when the Co were reduced at a lower temperature. According to the H -TPR results,
2
it was clearly found that the Co-La sample possessed optimal low-temperature
reducibility. For cobalt oxides, the low temperature was assigned to the reduction of
3
+
2+
Co to Co , whereas the high temperature could be attributed to the reduction of
Co2+ to Co0 [58-60]. Thus, it could be inferred that the abundant Co3+ species could
improve the low-temperature reducibility. Ngamou and Bahlawane reported that the
edge-connected octahedrally coordinated Co3+ possessed the higher reducibility,
1
1
1
1
1
1
1
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1
1
2
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0
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0
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0
which was responsible for the superior activity of cobalt oxides toward the deep
oxidation of VOCs [61]. Meanwhile, the presence of more Co3+ could rapidly
3+
2-
2+
supplement the dissipative active oxygen (2Co + O
→ 2Co +O ). Hence, the
2
latt
3+
existence of abundant and easily reduced surface Co was crucial for the catalytic
combustion of toluene.
Surface adsorbed oxygen as the active species was another important influence
factor over the catalytic oxidation of VOCs [31]. Normally, catalytic combustion of
VOCs on the Co-based catalysts included the reduction of O2-latt, the generation of
oxygen vacancies and re-oxidation of active oxygen species, the equilibrium of Olatt
[1]
2-
↔ 2O- + V ↔ O
-
and Oads was followed the reaction process : O
↔ O2ads
2 ads
latt
ads
O
↔ O2gas. Moreover, the breaking of C-H and C-C bond and insertion of oxygen in
C-H was different oxygen species, respectively. Because the bond energy of C-C
bond (332 KJ/mol) was lower than the C-H bond (414 KJ/mol). The cleavage of C-C
bonds were broken by electrophilic oxygen species (O- and O - ) [62], which was a
ads
2 ads
critical step in the reaction rate. It was proved that toluene would preferentially react
with adsorbed oxygen (O ) by Feng and Zhao et al. [1,63]. Thereby, Co-La possessed
ads
the best low-temperature catalytic activity due to the amounts of adsorbed oxygen.
As indicated the Fig. 8c, the T90 versus O /O ratio was plotted. It was
ads latt
obvious that the Co-Ni sample owned the highest O /O ratio, but it exhibited the
ads latt
lowest catalytic performance. However, the Co-La sample exhibited optimal catalytic
oxidation of activity. The phenomenon suggested that the O /O ratio of the
ads latt
catalysts was not the only factors affecting the catalytic oxidation of toluence.
Because the toluene would preferentially react with adsorbed oxygen, from the Fig.

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7
a, at the 220 °C, it could be seen that the catalytic activity of Co-La and Co-Ni was
similar, which was ascribed to the similar ratio of O /O (Co-La:0.95; Co-Ni:0.99).
ads latt
However, with the increase of temperature, the catalytic activity of Co-Ni obvious
became worse, which could be attributed to the least Co3+ over Co-Ni, and the
consumed adsorbed oxygen could not timely be supplemented. To sum up, the Co-La
possessed the optimal catalytic activity, which was attributed to the abundant surface
0
1
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9
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+
active species (Co and O ).
ads
Additionally, according to the Table 2, for Co-Ni and Co-Zr catalysts, the atomic
ratios of Ni (1.4%) and Zr (6.3%) were lower than the Mn (10.0%) and La (11.0%),
which indicated that Ni and Zr were good dispersed on the catalyst surface. It was
reported that the excellent dispersion could significantly improve the catalytic
performance [64,65]. However, according to the diagram of the Co /Co and O /O
3+
2+
ads latt
with the activity, Co-Mn and Co-La exhibited the better catalytic performance.
3
+
Therefore, it could be also inferred that the Co and O played an important role in
ads
improving catalytic activity.
3
+
2+
Table 3. The results for T50, T90, CO selectivity and T90 with Co /Co
2
3
+
2+
Samples
Co-La
Co-Mn
Co-Zr
T50 (°C)
233
T90 (°C)
243
CO selectivity (°C)
T90 with Co /Co (°C)
2
267
301
280
280
243 (2.33)
253
265
266 (1.27)
271
278
278 (1.08)
Co-Ni
272
279
279 (0.79)
.

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0
3+
2+
Fig. 8. The correlation of T90 with the (a) specific surface area, (b) surface Co /Co ratio and (c)
O /O ratio over Co-M catalysts.
ads latt
5
. Conclusions
A series of Co-M (M = La, Mn, Zr and Ni) composite oxides catalysts were
prepared by co-precipitation method. The catalytic performances were evaluated via
catalytic oxidation of toluene over all catalysts. Results showed that the Co-M
samples could be achieved at below 300 °C for the complete conversion of toluene.
Among all, Co-La exhibited optimal catalytic activity and CO selectivity for toluene
2
oxidation. XRD and Raman analyses showed that the introduction of La into Co O
3
4
spinel structure led to an obvious transformation of the microstructure, which was the
formation of LaCoO perovskite and owed the weakest Co-O bond strengths, resulted
3
in the largest specific surface areas and pore volumes. Moreover, the XPS result
3
+
showed the Co-La possessed the most Co and higher O /O ratio. It was found
ads latt
that the more Co3+ could improve the low-temperature reducibility. The O -TPD
2
result revealed that the Co-La exhibited the excellent oxygen storage capacity, which

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could afford the enough adsorbed oxygen species for reaction process. According to
the thorough analysis of specific surface area and surface active species with the
activity relationship, it could be concluded that the superior catalytic activity of the
Co-M (M = La, Mn, Zr and Ni) catalysts were basically associated with the higher
0
1
2
3
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9
0
1
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0
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0
3
+
specific surface area, more abundances of surface Co and adsorbed oxygen species.
6
. Acknowledgements
This work is supported by the National Natural Science Foundation of China (No.
1872096) and Doctoral Research Start-up Project of Henan University of Urban
2
Construction (No. 990/Q2017011).
References
[
1] X. Feng, J. Guo, X. Wen, M. Xu, Y. Chu, S. Yuan, Appl. Surf. Sci., 2018, 445,
1
45-153.
[
2] S. Zhao, K. Li, S. Jiang, J. Li, Appl. Catal. B, Environ., 2016, 181, 236-248.
3] A. Rokicińska, M. Drozdek, B. Dudek, B. Gil, P. Michorczyk, D. Brouri, S.
Dzwigaj, P. Kuśtrowski, Appl. Catal. B, Environ., 2017, 212, 59-67.
[
[
4] S.C. Kim, W.G. Shim, Appl. Catal. B, Environ., 2010, 98, 180-185.
5] F. Wang, H. Dai, J. Deng, G. Bai, K. Ji, Y. Liu, Environ. Sci. Technol., 2012, 46,
[
4
034-4041.
[
6] F.N. Aguero, B.P. Barbero, L. Gambaro, L.E. Cadús, Appl. Catal. B, Environ.,
2009, 91, 108-112.
[
7] G. Li, C. Zhang, Z. Wang, H. Huang, H. Peng, X. Li, Appl. Catal. A, Gen., 2018,
5
50, 67-76.
[
8] S. Zuo, Q. Huang, R. Zhou, Catal. Today, 2008, 139, 88-93.
9] H.S. Kim, T.W. Kim, H.L. Koh, S.H. Lee, B.R. Min, Appl. Catal. A, Gen., 2005,
280, 125-131.
[

Page 23 of 28
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ01783F
[10]B. Solsona, E. Aylón, R. Murillo, A.M. Mastral, A. Monzonís, S. Agouram, T.E.
Davies, S.H. Taylor, T. Garcia, J. Hazard. Mater., 2011, 187, 544-552.
[
11]N. Li, F. Gaillard, A. Boréave, Catal. Commun., 2008, 9, 1439-1442.
[12]T.H. Lim, S.J. Cho, H.S. Yang, M.H. Engelhard, D.H. Kim, Appl. Catal. A, Gen.,
015, 505, 62-69.
[13]Z. Pu, H. Zhou, Y. Zheng, W. Huang, X. Li, Appl. Surf. Sci., 2017, 410, 14-21.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
[
14]J. Chen, W. Shi, J. Li, Catal. Today, 2011, 175, 216-222.
15]H. Li, G. Lu, D. Qiao, Y. Wang, Y. Guo, Y. Guo, Catal. Lett., 2011, 141,
452-458.
[
[
16]C. Chen, J.J. Pignatello, Appl. Catal. B, Environ., 2013, 142, 785-794.
[17]Y. Wang, W. Deng, Y. Wang, L. Guo, T. Ishihara, Mol. Catal., 2018, 459, 61-70.
18]S. Lin, G. Su, M. Zheng, D. Ji, M. Jia, Y. Liu, Appl. Catal. B, Environ., 2012,
23, 440-447.
[19]W. Si, Y. Wang, S. Zhao, F. Hu, J. Li, Environ. Sci. Technol., 2016, 50,
572-4578.
[20]J. Mei, S. Zhao, H. Xu, Z. Qu, N. Yan, RSC Advances, 2016, 6, 31181-31190.
21]Y. Zheng, Y. Liu, H. Zhou, W. Huang, Z. Pu, J. Alloys Compd., 2017, 734,
12-120.
[22]Y. Ren, Z. Ma, L. Qian, S. Dai, H.Y. He, P.G. Bruce, Catal. Lett., 2009, 131,
46-154.
[23]W. Tang, X. Wu, S. Li, W. Li, Y. Chen, Catal. Commun., 2014, 56, 134-138.
24]Z. Pu, Y. Liu, H. Zhou, W. Huang, Y. Zheng, X. Li, Appl. Surf. Sci., 2017, 422,
[
1
4
[
1
1
[

New Journal of Chemistry
Page 24 of 28
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/C9NJ01783F
85-93.
[
25]L.F. Liotta, M. Ousmane, G.D. Carlo, G. Pantaleo, G. Deganello, G. Marcì, L.
Retailleau, A.G. Fendler, Appl. Catal. A, Gen., 2008, 347, 81-88.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
[26]N. Bahlawane, P.H.T. Ngamou, V. Vannier, T. Kottke, J. Heberle, K.K.
Höinghaus, Phys. Chem. Chem. Phys., 2009, 11, 9224.
[27]Y. Liu, H. Dai, J. Deng, L. Zhang, Z. Zhao, X. Li, Y. Wang, S. Xie, H. Yang, G.
Guo, Inorg. Chem., 2013, 52, 8665-8676.
[
28]X. Chen, S.A.C. Carabineiro, P.B. Tavares, J.J.M. Órfão, M.F.R. Pereira, J.L.
Figueiredo, J. Environ. Chem. Eng., 2014, 2, 344-355.
[
29]L.G. Tejuca, J.L.G. Fierro, J.M.D. Tascón, Adv. Catal., 1989, 36, 237-328.
[30]L.G. Tejuca, J.L.G. Fierro, Properties and applications of perovskite-type oxides,
Marcel Dekker, New York, 1993.
[
[
[
31]C. Zhang, Y. Guo, Y. Guo, G. Lu, A. Boreave, L. Retailleau, A. Baylet, A.G.
Fendler, Appl. Catal. B, Environ., 2014, 148, 490-498.
32]R. Spinicci, M. Faticanti, P. Marini, S.D. Rossi, P. Porta, J. Mol. Catal., A, 2003,
197, 147-155.
33]A.S. Poyraz1, C.H. Kuo, S. Biswas, C.K. King’ondu, S.L. Suib, Nat. Commun.,
2
013, 4, 2952.
[34]P. Zhang, H. Zhu, S. Dai, ChemCatChem, 2015, 7, 2788-2805.
35]C.W. Tang, C.B. Wang, S.H. Chien, Thermochim. Acta, 2008, 473, 68-73.
[36]S.K. Tripathy, M. Christy, N.H. Park, E.K. Suh, S. Anand, Y.T. Yu, Mater. Lett.,
008, 62, 1006-1009.
[
2

Page 25 of 28
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ01783F
[37]V.G. Hadjiev, M.N. Iliev, I.V. Vergilov, J. Phys. C: Solid State Phys., 1988, 21,
L199.
[
38]T. Cai, H. Huang, W. Deng, Q. Dai, W. Liu, X. Wang, Appl. Catal. B, Environ.,
2015, 166, 393-405.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
[
39]J. Kan, L. Deng, B. Li, Q. Huang, S. Zhu, S. Shen, Y. Chen, Appl. Catal. A, Gen.,
2016, 530, 21-29.
[
40]X. Xie, Y. Li, Z.Q. Liu, M. Haruta, W. Shen, Nat. lett., 2009, 458, 746-749.
41]Y. Luo, K. Wang, J. Zuo, Q. Qian, Y. Xu, X. Liu, H. Xue, Q. Chen, Catal. Sci.
Technol., 2017, 7, 496-501.
[
[
42]S. Xie, Y. Liu, J. Deng, J. Yang, X. Zhao, Z. Han, K. Zhang, H. Dai, J. Catal.,
2017, 352, 282-292.
[
43]Y. Wang, L. Zhang, L. Guo, ACS Appl. Nano Mater., 2018, 1, 1066-1075.
44]L.F. Liotta, H. Wu, G. Pantaleo, A.M. Venezia, Catal. Sci. Technol, 2013, 3,
3085.
[
[
45]Q. Liang, K. Chen, W. Hou, Q. Yan, Appl. Catal. A, Gen., 1998, 166, 191-199.
[46]W. Song, A.S. Poyraz, Y. Meng, Z. Ren, S.Y. Chen, S.L. Suib, Chem. Mater.,
014, 26, 4629-4639.
2
[
[
[
47]F.C. Vallejo, N.G. Inoglu, H.Y. Su, J.I. Martínez, I.C. Man, M.T.M. Koper, J.R.
Kitchinb, J. Rossmeislc, Chem. Sci., 2013, 4, 1245-1249.
48]P. Li, C. He, J. Cheng, C.Y. Ma, B.J. Dou, Z.P. Hao, Appl. Catal. B, Environ.,
2011, 101, 570-579.
49]Y. Liao, X. Zhang, R. Peng, M. Zhao, D. Ye, Appl. Surf. Sci., 2017, 405, 20-28.

New Journal of Chemistry
Page 26 of 28
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/C9NJ01783F
[50]S. Varma, B.N. Wani, N.M. Gupta, Appl. Catal. A, Gen., 2001, 205, 295-304.
[
51]Y. Luo, Y. Zheng, J. Zuo, X. Feng, X. Wang, T. Zhang, K. Zhang, L. Jiang, J.
Hazard. Mater., 2018, 349, 119-127.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
[52]J. Chen, X. Chen, X. Chen, W. Xu, Z. Xu, H. Jia, J. Chen, Appl. Catal. B,
Environ., 2018, 224, 825-835.
[53]G. Zhou, X. He, S. Liu, H. Xie, M. Fu, J. Ind. Eng. Chem., 2015, 21, 932-941.
[
54]H. Tüysüz, M. Comotti, F. Schüth, Chem. Commun., 2008, 34, 4022-4024.
55]Y. Wang, S. Xie, J. Deng, S. Deng, H. Wang, H. Yan, H. Dai, ACS Appl. Mater.
Interfaces, 2014, 6, 17394-17401.
[
[
56]Q. Wang, Y. Peng, J. Fu, G.Z. Kyzas, S.M.R. Billah, S. An, Appl. Catal. B,
Environ., 2015, 168, 42-50.
[
57]N. Bahlawane, Appl. Catal. B, Environ., 2006, 67, 168-176.
58]B.De. Rivas, R.L. Fonseca, C.J. González, J.I.G. Ortiz, J. Catal., 2011, 281,
88-97.
[
[
59]P.G. Harrison, I.K. Ball, W. Daniell, P. Lukinskas, M. Céspedes, E.E. Miró, M.A.
Ulla, Chem. Eng. J., 2003, 95, 47-55.
[
60]J.Y. Yan, M.C. Kung, W.M.H. Sachtler, H.H. Kung, J. Catal., 1997, 172,
1
78-186.
[61]P.H. Tchoua, N.N. Bahlawane, Chem. Mater., 2010, 22, 4158-4165.
62]V.D. Sokolovskii, Catal. Rev., 1990, 32, 1-49.
[63]J.H. Zhao, Z.C. Tang, F. Dong, J.Y. Zhang, Molecular Catalysis, 2019, 463,
7-86.
[
7

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2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ01783F
[64]S.C. Kim, W.G. Shim, Appl. Catal. B, Environ., 2009, 92, 429-436.
[
65]L. Ma, C.Y. Seo, X.Y. Chen, K. Sun, J.W. Schwank, Appl. Catal. B, Environ.,
2
017, 222, 44-58.
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The effect of different metal oxides on catalytic activity of the Co O4
3
catalyst for toluene combustion: Importance of structure-property
and surface active species
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a
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b, *
a
a
Xuejun Zhang , Min Zhao , Zhongxian Song , Heng Zhao , Wei Liu , Jinggang
a
a
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Zhao , Zi’ang Ma , Yun Xing
a
College of Environmental and Safety Engineering, Shenyang University of
Chemical Technology, Shenyang 110142, People’s Republic of China
b
Faculty of Environmental and Municipal Engineering, Henan Key Laboratory of
Water Pollution Control and Rehabilitation Technology, Henan University of Urban
Construction, Pingdingshan, 467036, People’s Republic of China
Corresponding Authors:
*Z. X. Song: email, songzhongxian@126.com, Tel., (+86)-375-2089031
The Co-based catalysts were used to the catalytic oxidation of toluene. The
LaCoO perovskite was detected over Co-La sample, which could improve the
3
catalytic oxidation of toluene. The abundance of Co3+ and active oxygen species
contributed synergistically to the redox cycle reaction, resulting in the enhancement of
catalytic activity of toluene combustion.