Rational design of CrOx/LaSrMnCoO6 composite catalysts with superior chlorine tolerance and stability for 1,2-dichloroethane deep destruction

Article abstract of DOI:10.1016/j.apcata.2018.11.008

1,2-dichloroethane (1,2-DCE) is a representative industrial chlorinated volatile organic compound (CVOC) making great hazardous to the environment and human health. In this work, LaSrMnCoO₆ (LSMC) double perovskite-type materials with high thermal stability and coke resistance in 1,2-DCE oxidation were prepared by a facile sol-gel method. Based on this, a series of CrO_x/LaSrMnCoO₆ catalysts (Cr/LSMC, CrO_x loading = 5 to 20 wt.%) which combine the merits of CrO_x (high activity and chlorine tolerance) and LaSrMnCoO₆ were synthesized and adopted in deep oxidation of 1,2-DCE for the first time. As expected, obvious synergistic effects between CrO_x and LSMC on 1,2-DCE destruction were observed. Amongst, 10 wt.% CrO_x/LaSrMnCoO₆ (10Cr/LSMC) shows the best catalytic activity with 90% of 1,2-DCE destructed at 400 °C. Furthermore, the outstanding catalytic durability and water resistance of 10Cr/LSMC in 1,2-DCE oxidation were also demonstrated. In addition to this, the reaction pathway of 1,2-DCE decomposition over Cr/LSMC materials was discussed based on the results of online product analysis. We found that the enhanced catalytic performance of Cr/LSMC materials can be reasonably attributed to their high reducibility, excellent 1,2-DCE adsorption capability, and large amounts of surface active lattice oxygen species. It can be anticipated that the Cr/LSMC catalysts are promising materials for CVOC elimination and the results from this work could also provide some new insights into the design of catalysts for CVOC efficient destruction.

Full text of DOI:10.1016/j.apcata.2018.11.008

Applied Catalysis A, General 570 (2019) 62–72
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
Rational design of CrO /LaSrMnCoO composite catalysts with superior
x
6
chlorine tolerance and stability for 1,2-dichloroethane deep destruction
Mingjiao Tiana,1, Yanfei Jiana,1, Mudi Ma , Chi Hea,b,⁎, Changwei Chen , Chao Liu ,
Jian-Wen Shi
a
a
a
c
d,⁎
State Key Laboratory of Multiphase Flow in Power Engineering, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, 710049, Shaanxi, PR China
National Engineering Laboratory for VOCs Pollution Control Material & Technology, University of Chinese Academy of Sciences, Beijing, 101408, PR China
Department of Environmental Engineering and Earth Sciences, Clemson University, Anderson, South Carolina, 29625, United States
Center of Nanomaterials for Renewable Energy, State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi’an Jiaotong
b
c
d
University, Xi'an, 710049, Shaanxi, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Catalytic oxidation
1,2-dichloroethane (1,2-DCE) is a representative industrial chlorinated volatile organic compound (CVOC)
making great hazardous to the environment and human health. In this work, LaSrMnCoO6 (LSMC) double
perovskite-type materials with high thermal stability and coke resistance in 1,2-DCE oxidation were prepared by
1
,2-dichloroethane
Double pervoskite-type oxides
CrO
a facile sol-gel method. Based on this, a series of CrO
0 wt.%) which combine the merits of CrO (high activity and chlorine tolerance) and LaSrMnCoO
thesized and adopted in deep oxidation of 1,2-DCE for the first time. As expected, obvious synergistic effects
between CrO and LSMC on 1,2-DCE destruction were observed. Amongst, 10 wt.% CrO /LaSrMnCoO (10Cr/
x
/LaSrMnCoO
6
catalysts (Cr/LSMC, CrO
x
loading = 5 to
x
2
x
6
were syn-
Chlorine tolerance
By-products distribution
x
x
6
LSMC) shows the best catalytic activity with 90% of 1,2-DCE destructed at 400 °C. Furthermore, the outstanding
catalytic durability and water resistance of 10Cr/LSMC in 1,2-DCE oxidation were also demonstrated. In addi-
tion to this, the reaction pathway of 1,2-DCE decomposition over Cr/LSMC materials was discussed based on the
results of online product analysis. We found that the enhanced catalytic performance of Cr/LSMC materials can
be reasonably attributed to their high reducibility, excellent 1,2-DCE adsorption capability, and large amounts of
surface active lattice oxygen species. It can be anticipated that the Cr/LSMC catalysts are promising materials for
CVOC elimination and the results from this work could also provide some new insights into the design of cat-
alysts for CVOC efficient destruction.
1. Introduction
much lower temperatures is considered as a more proper approach for
the decomposition of CVOCs [10].
1
,2-dichloroethane (1,2-DCE) regarded as one of typical chlorinated
Supported noble metal catalysts, zeolites, and transitional metal
oxides are usually studied in catalytic oxidation of CVOCs [11,12].
Noble metal-based catalysts are proved to be highly active materials in
most of catalytic oxidation reactions. However, their high cost and low
resistance to halide limit their wide applications in CVOC destruction
[13]. H-zeolites (e.g., H-ZSM-5, H-MOR, and H-BEA) were also usually
investigated as the oxidation catalysts for CVOC destruction [14], while
the Brønsted acid sites in H-zeolites usually lead to surface/structural
coke deposition and catalyst deactivation [15]. Transition metal oxides
volatile organic compounds (CVOCs) is commonly used as an industrial
solvent or an intermediate in organic synthesis process [1]. However,
its high volatility and toxicity and great contributions to the formation
of secondary pollutants and photochemical smog have caught much
attention of researchers [2]. Various control approches such as ab-
sorption, hydrodechlorination, pyrolysis and catalytic decomposition
have been investigated for CVOC destruction [3–7]. Conventional
thermal incineration requires very high temperature (> 850 °C),
leading to the formation of more toxic polychlorinated aromatic by-
products such as polychlorinated dibenzofurans (PCDFs) and dibenzo-
dioxins (PCDDs) [8,9]. In comparison, catalytic oxidation operated at
2 5 x x
(e.g., V O , CrO , and MnO ) exhibit high resistance to chlorine species
during CVOC destruction, but their catalytic activities are usually lower
than those of the noble metal-based catalysts [16–18]. Compared with
⁎
Corresponding author.
E-mail addresses: chi_he@xjtu.edu.cn (C. He), jianwen.shi@mail.xjtu.edu.cn (J.-W. Shi).
These authors are contributed equally to this work.
1
https://doi.org/10.1016/j.apcata.2018.11.008
Received 27 August 2018; Received in revised form 8 November 2018; Accepted 9 November 2018
Available online 12 November 2018
0926-860X/ © 2018 Elsevier B.V. All rights reserved.

M. Tian et al.
Applied Catalysis A, General 570 (2019) 62–72
other transition metal oxides, Cr
chlorine-tolerant catalysts for CVOC destruction [13], however, the loss
and aggregation of Cr during long-term reactions should be considered
2
O
3
is one of the most active and
of Cr/LSMC can be compared with the chemical species of metal oxides
because of the same calcinated conditions.
[
16].
In general, mixed transition metal oxides usually possess better
catalytic activity and structure stability than their single phase coun-
terparts [19–21]. Double perovskite-type oxides (DPOs; AA'BB'O
BB'O , or AA'B ) as one kind of perovskite materials have been
2.2. Catalyst characterizations
XRD measurements were performed on a powder diffractrometer
(PANalytical B.V., Netherlands) with Cu-Ka radiation in 2θ range of 20-
80° with a scanning rate of 10°/min. The tube voltage was 45 kV, and
the current was 40 mA. Fourier transform infrared spectra (FTIR) were
6
,
A
2
6
2 6
O
attracted extensive attentions in recent years due to their unique
structure and properties such as providing more expansive combination
spaces between different matching of A/A' and B/B' metals, excellent
thermal stability, and coke resistance, which make them being highly
desirable for catalytic applications [22]. Catalytic oxidation of methane
2
conducted on a Bruker Tensor 37 spectrometer. N sorption isotherms
were studied at 77 K on a Builder SSA-6000 apparatus. Before the
measurements, the samples were processed for 4 h under vacuum at
473 K. The total pore volume was measured from the amount of ni-
over Sr
2
Mg1-xFe
x
MoO6-δ was reported by Chen and co-workers [23],
0
trogen adsorbed at a relative pressure (P/P ) of ca. 0.99. The specific
and results showed that the DPOs had excellent catalytic activity at-
tributing to high contents of Fe-related surface lattice oxygen. Ding
et al. [24] found that La
intergrowth effects achieved good performance and exceptional
thermal stability for catalytic combustion of methane. La2-xSr FeCoO
oxides reported by Zhao et al. [25] were used to produce syngas and
hydrogen and the oxygen mobility of DPOs was considered to be a
potentially effective oxygen carrier for industrial applications of che-
mical looping. However, the catalytic oxidation of CVOCs over DPOs
was not reported yet. As such, the study regarding catalytic destruction
of CVOCs over DPOs may provide valuable insights for the future design
and optimization of catalysts for this reaction.
surface area and the pore size distribution were calculated using the
Brunauer-Emmett-Teller (BET) method and Barrett-Joyner-Halenda
(BJH) method, respectively. Field emission scanning electron micro-
scopy (FE-SEM) images were analyzed by the JEOL 7800 F microscope.
High resolution transmission electron microscopy (HR-TEM) images
were recorded on a FEI G2F30 microscope operating at an acceleration
voltage of 200 kV. X-ray photoelectron spectroscopy (XPS) experiments
were conducted on an AXIS ULtrabld instrument (Kratos, UK) with Mg-
Kα radiation (hν = 1253.6 eV). The X-ray anode was run at 250 W and
the high voltage was maintained at 14.0 kV with a detection angle of
54°. The pass energy was fixed at 93.90 eV to ensure sufficient resolu-
tion and sensitivity. The base pressure of the analyzer chamber was
2 6
MnNiO -MgO composite oxides with biphasic
x
6
–8
In the present work, CrO
x
/LaSrMnCoO
6
catalysts (Cr/LSMC) with
approximately 5 × 10 Pa. The spectra of all elements were recorded
with extremely high resolution by using a RBD 147 interface (RBD
Enterprises, USA) through the XPS Peak 4.1 software. The containment
carbon (C 1s = 284.8 eV) was used as the calibrated binding energies.
CrO loadings varied from 5 to 20 wt.% were prepared by a wet im-
x
pregnation protocol. The effects of structural, textural, and surface
chemical properties of synthesized samples on their activity, product
yield, and reaction durability in catalytic destruction of 1,2-DCE were
investigated. In addition to this, the influence of water vapor on the
oxidation of 1,2-DCE over prepared catalysts was also studied.
Moreover, the reaction products distribution of 1,2-DCE destruction
over Cr/LSMC were further explored. We believe that the CrO
LaSrMnCoO catalysts are potential and promising materials for CVOC
removal and the results from the present work could also provide new
insights into the design of efficient catalysts for CVOC destruction.
H
2
-TPR experiments were performed on a TP-5080 (Xianquan, China)
equipped with a thermal conductivity detector (TCD). In each test,
50 mg of catalyst was pretreated in a N flow (30 mL/min) from 30 to
500 °C and kept at 500 °C for 1 h, then cooled down to the ambient
temperature. The sample was reduced in a 5% vol.% H /Ar flow
(30 mL/min) from 30 to 800 °C with a heating rate of 10 °C/min.
Temperature programmed desorption of O (O -TPD) and 1,2-DCE (1,2-
DCE-TPD) were investigated on the same equipment as H -TPR. 100 mg
of catalyst was pretreated in a N flow (30 mL/min) from 30 to 400 °C
and kept at 400 °C for 1 h and then cooled to the room temperature
prior to adsorption of O or 1,2-DCE (500 ppm) for 2 h. After being
saturated with O or 1,2-DCE, the catalyst was treated in a pure N flow
2
30 mL/min) for 1 h at room temperature. The desorption profiles of O -
2
x
/
2
6
2
2
2
2
2. Experimental
2
2.1. Catalyst preparation
2
2
(
LaSrMnCoO
gel method. Stoichiometric amount of La(NO
CH COO) ·0.5H O, Mn(CH COO) ·4H O, and Co(NO
firstly dissolved in 10 mL of deionized water and stirred at room tem-
perature for 30 min. Then, a certain amount of critic acid (1.5 times of
total metal ions) was added to the above transparent solution. After
stirring for 1 h, the mixture was heated to 70 °C and maintained under
continuous stirring until a sol was formed. Then, the obtained sol was
dried at 100 °C for 24 h to obtain a dried gel. Finally, the resulting
powder was calcined at 500 °C for 3 h and 1100 °C for 3 h in sequence
6
double perovskite-type oxide was prepared by the sol-
·6H O, Sr
·6H was
TPD or 1,2-DCE-TPD were recorded online from 30 to 700 °C with a
heating rate of 10 °C/min. Thermogravimetric analysis (TG) of the aged
catalysts was studied on an HCT-2TGA/DSC-1analyzer (Beijing
Permanent, China) in temperature range of 35–700 °C with a heating
rate of 10 °C/min under a continuous air flow of 50 mL/min.
3
)
3
2
(
3
2
2
3
3
2
3
)
2
2
O
2.3. Catalytic activity
All catalytic activity tests were performed in a continuous-flow
fixed-bed reactor, which consists of a quartz tube that was filled with
the prepared catalyst. The 1,2-DCE-contained gas was produced by
bubbling air through a VOC (volatile organic compound) saturator, and
then further diluted with another air stream (1000 ppm of 1,2-DCE).
Temperatures of the fixed-bed and tubular electric furnace were mon-
itored automatically by temperature programmed controller. In each
test, 50 mg of catalyst (40–60 mesh) was putted into the tube reactor
and the total gas flow rate was kept at 400 mL/min (gas hourly space
velocity (GHSV) of ca. 48,000 mL/(g·h)). Besides, the temperature of
catalyst bed was firstly raised to 100 °C with the 1,2-DCE feed stream
passing and stabilized for 30 min, followed by a second temperature
ramp of 5 °C/min up to 550 °C. The 1,2-DCE, Cl-contained by-products,
under air atmosphere to obtain the LaSrMnCoO
LSMC).
6
support (denoted as
CrO
LSMC with the solution of Cr(NO
dried at 80 °C for 12 h and then calcinated at 500 °C for 5 h. CrO
catalysts with CrO loadings of 5, 10, 15, and 20 wt.% (calculated as the
x
/LSMC catalysts were prepared by impregnation of synthesized
·9H O. The impregnated solids were
/LSMC
3
)
3
2
x
x
weight percent of chromium on LSMC; the practical Cr loading mea-
sured by XRF analysis is shown in Table S2) are named as 5Cr/LSMC,
1
0Cr/LSMC, 15Cr/LSMC, and 20Cr/LSMC, respectively. For compar-
ison, pure CrO , MnO , and CoO oxides were also prepared by calci-
nation the corresponding metal precursors at 500 °C for 5 h. It’s worth
noting that the active content CrO introduced into the LSMC was also
calcinated at 500 °C for 5 h. Therefore, the physicochemical properties
x
x
x
x
CO, and CO
2
in outlet gas were analyzed online by gas chromatograph
(GC9890B, China) equipped with an electron capture detector (ECD)
63

M. Tian et al.
Applied Catalysis A, General 570 (2019) 62–72
and a flame ionization detector (FID) coupled with an Ni-converter.
Other by-products were identified by online mass spectrometer
(
SHP8400PMS, China).
The conversion of 1,2-DCE (X1,2-DCE) was calculated by Eq. (1):
C
in − Cout
X
1,2‐DCE
=
× 100%
C
in
(1)
where Cin and Cout are the inlet and outlet concentrations of 1,2-DCE,
respectively.
The yields of CO, CO
2
, HCl, and Cl
2
(respectively denoted as YCO
,
Y
CO2, YHCl, and YCl2) were calculated by Eqs. (2)–(5), respectively:
Cco
Yco =
× 100%
× 100%
× 100%
× 100%
2
Cin × X1,2‐DCE
(2)
(3)
(4)
(5)
Cco
2
Yco
=
2
2
Cin × X1,2‐DCE
CHCl
YHCl =
2
Cin × X1,2‐DCE
2CCl
2
YCl =
2
2
Cin × X1,2‐DCE
where CCO, CCO2, CHCl, and CCl2 are the outlet concentrations of CO,
CO
2
, HCl, and Cl
2
, respectively. Stability test was carried out at 550 °C
after a heating processing for 1,2-DCE combustion. To investigate the
effect of water vapor on catalytic activity, the time-on-stream 1,2-DCE
oxidation experiments were carried out in the presence and absence of
2
vol.%, 3 vol.%, and 5 vol.% of water vapor, which were introduced by
automatic sample injector through pretreatment processor at 100 °C.
Activity test was performed under the condition of 1,2-DCE of
1
5
000 ppm, GHSV of 48,000 mL/(g·h), and reaction temperature of
50 °C.
3. Results and discussion
Fig. 1. (A) Catalytic activity of the synthesized catalysts for 1,2-DCE oxidation;
(
B) 1,2-DCE oxidation rates at 250 °C.
3
3
.1. Catalytic performance of synthesized samples
.1.1. Catalytic activity
3.1.2. Reaction product distribution
Catalytic activity of all prepared samples for 1,2-DCE oxidation is
The reaction products of prepared catalysts in the oxidation of 1,2-
DCE are analyzed by online gas chromatography and online MS. The
relationship between chlorinated by-products distribution and reaction
temperature is shown in Figs. 2 and S4. As shown in Fig. 2, several Cl-
containing by-products (1,1,2-trichloroethane, trichloroethene, and
perchloroethylene) can be found in reaction process. 1,1,2-tri-
chloroethane was firstly detected at about 200 °C. The concentration of
1,1,2-trichloroethane increases with the increasing of temperature and
reaches the maximum value at about 500 °C, and then decreases with
the further increasing of temperature. LSMC owns the smallest amount
of 1,1,2-trichloroethane, which is associated with its low catalytic ac-
tivity. The concentration of 1,1,2-trichloroethane over Cr/LSMC sam-
ples is higher than that of LSMC and follows the order of 5Cr/
LSMC > 10Cr/LSMC > 15Cr/LSMC > 20Cr/LSMC, indicating that the
displayed in Fig. 1A. All CrO
x
supported catalysts possess much higher
1
,2-DCE oxidation activity (T90 = 400–537 °C) than that of LSMC sup-
port (T90 > 550 °C). Amongst, 10Cr/LSMC shows the best oxidation
activity with 90% of 1,2-DCE converted at 400 °C, much better than
some typical catalysts for 1,2-DCE oxidation reported in the literature,
such as rod-like Co
90 = 460 °C), and 10Ba/Al2O3 (T90 = 460 °C) [18,26,27]. Pure CrO
oxide also shows good catalytic activity in 1,2-DCE oxidation
3
O
4
(T90 = 420 °C), Co/hydroxyapatite
(
T
x
(
(
T
T
90 = 463 °C) compared with that of MnO
x x
(T90 = 494 °C) and CoO
90 = 516 °C). By comparing with T90 values, the activity of all syn-
thesized catalysts is in order of 10Cr/LSMC (400 °C) > CrO
x
x
(
(
463 °C) > MnO
516 °C) > 20Cr/LSMC (525 °C) > 5Cr/LSMC (537 °C).
The oxidation of 1,2-DCE over perovskite-type oxides and transition
metal oxides obeys a first-order reaction mechanism with respect to 1,2-
DCE concentration (c): r = -kc = (-A exp(-E /RT))c, where r, k, A, E
x
(494 °C) > 15Cr/LSMC
(510 °C) > CoO
x
incorporation of CrO enhances the catalytic activity of LSMC and fa-
cilitates the oxidation of 1,2-DCE. Small amounts of trichloroethene and
perchloroethylene species are also detected in the reaction, which is
ascribed to the dehydrochlorination of 1,1,2-trichloroethane (Fig. 2).
Additionally, the formation of trichloroethene and perchloroethylene is
attributed to the chlorination reaction and the generation of hydrogen
chloride at high temperature.
The by-products distribution over 10Cr/LSMC was also analyzed by
online MS, as shown in Fig. S4. The mass peaks of main fragment ions
were determined based on the National Institute of Standards and
Technology (NIST) chemistry database, and the mass ions of m/z = 62,
a
a
−
1
are the reaction rate (mol/s), rate constant (s ), pre-exponential
factor, and apparent activation energy (kJ/mol), respectively [28,29].
The reaction rates of 1,2-DCE over composite catalysts at 250 °C are
displayed in Fig. 1B. It can be observed that the reaction rates over
-11
catalysts are in sequence of 10Cr/LSMC (2.73 × 10 mmol/(g⋅s)) >
-
11
-11
2
0Cr/LSMC (2.50 × 10
mmol/(g⋅s)) > 15Cr/LSMC (2.44 × 10
mmol/(g⋅s)) > LSMC
(1.96 × 10-
1.88 × 10 mmol/(g⋅s)). Results reveal that the reaction rates of 1,2-
DCE over 10Cr/LSMC are obviously higher than that of LSMC catalyst,
11
mmol/(g⋅s)) > 5Cr/LSMC
-
11
(
27, 44, 36, 70, and 29 represent for 1,2-DCE, vinyl chloride, CO
Cl , and acetaldehyde, respectively. As revealed in Fig. S4 (left part),
the concentrations of vinyl chloride and 1,2-DCE show a decline trend
2
, HCl,
which indicates that the introduction of CrO
oxidation.
x
is favorable for 1,2-DCE
2
64

M. Tian et al.
Applied Catalysis A, General 570 (2019) 62–72
2
Fig. 2. Distribution of reaction by-products and yield of CO and CO during 1,2-DCE oxidation.
2
the forming of Cl can be considered to follow direct decomposition of
1,2-DCE and the Deacon reaction in reaction process.
CO and CO
Fig. 2). The CO
2
can be also detected during the oxidation process
2
yield of samples enhances with the increasing of re-
(
action temperature and reaches at around 90% at 550 °C, while the CO
yield shows an opposite tendency at the temperature range of
4
00–550 °C (CO yield < 20% at 550 °C), indicating that the produced
CO is oxidized to CO at temperature higher than 400 °C. Both HCl and
Cl are considered as the deep oxidation products of 1,2-DCE, and Cl is
mainly formed through the Deacon reaction at high temperatures
2
2
2
(
(
> 350 °C). The chlorine balance of LSMC (102.88) and 10Cr/LSMC
99.71) is shown in Table S3. Fig. 2 shows that the CO yield of LSMC
catalysts (86%) are less than that of 10Cr/
LSMC (87%) at 550 °C, suggesting that the introduction of CrO im-
proves catalytic performance of LSMC and enhances the oxidation of
2
support (82%) and CrO
x
x
1,2-DCE over the materials.
3
.1.3. Stability and coke formation
It is of great importance to study the stability of a catalyst for cat-
x
Fig. 3. Stability of 10Cr/LSMC and CrO for 1,2-DCE oxidation.
alytic oxidation of CVOCs due to chlorine poisoning and/or coke de-
position, especially for industrial applications. The reaction stability of
with the increasing of reaction temperature, suggesting that the dehy-
drochlorination process is the first step in 1,2-DCE destruction, similar
to previous report [13]. Besides, a fragment ion signal corresponding to
acetaldehyde can be detected in the whole temperature range for ac-
tivity test (the maximum concentration of acetaldehyde occurred at
two active catalysts (10Cr/LSMC and CrO
displayed in Fig. 3. It can be found that the long-term stability of 10Cr/
LSMC catalyst is much better than that of CrO . The conversion of 1,2-
DCE over 10Cr/LSMC can keep at around 99% in the first 2 h, and then
slowly decreases and keeps at about 80% in the following 98 h. CrO
x
) was evaluated at 550 °C, as
x
5
00 °C), illustrating the occurrence of oxidation processes, as shown in
Fig. S4 (right part). CO, CO , HCl, and Cl as the main products were
also observed during 1,2-DCE oxidation, and it is worth noting that the
signal of Cl obviously enlarges at temperature higher than 350 °C,
indicating that the Deacon reaction (HCl + O →H O + Cl de-
termined by the high catalytic activity is proceeded [30]. Consequently,
x
2
2
oxide shows an obvious activity loss and deactivation in the whole test
period, over which the conversion of 1,2-DCE sharply decreases to
about 70% after 7 h and then further reduces to around 40% after 12 h.
Above results demonstrate that Cr/LSMC catalysts possess excellent
reaction durability for the destruction of 1,2-DCE attributed to the
2
2
2
2
)
65

M. Tian et al.
Applied Catalysis A, General 570 (2019) 62–72
x
Fig. 4. TG profiles of 10Cr/LSMC and CrO materials.
synergistic effect of perovskite-type oxides (good thermal stability) and
CrO active sites (excellent activity).
x
The amount of coke deposited on the used catalyst (after 100 h of
stability reaction) was investigated by TG technology. Fig. 4 shows the
detailed TG profiles of 10Cr/LSMC and CrO
loss (0.15 wt.%) at around 280 °C, which is mainly associated with the
adsorbed species (CO , H O, or chlorinated species). No coke deposition
that can be decomposed above 400 °C over 10Cr/LSMC is detected [31].
As depicted in Fig. 4, CrO has three weight loss processes. The weight
x
. 10Cr/LSMC has weight
2
2
x
losses of the materials at the temperature lower than 200 °C including
two stages are attributed to the physically adsorbed molecular water
[
32]. The weight loss of coke and adsorbed species disintegration over
CrO (about 0.66 wt.%) at the temperature of 375 °C is higher than that
x
of 10Cr/LSMC, indicating that the 10Cr/LSMC has better resistance to
coke deposition. The TG profiles of all the catalysts are displayed in Fig.
S5. It can be observed that all the catalysts except 10Cr/LSMC own
2 2
three weight loss stages. The desorbed of CO , H O, or chlorinated
species can result in the weight losses of the materials at the tem-
perature lower than 200 °C. The weight losses of the materials at tem-
perature above 400 °C are associated with the decomposed of coke
deposition.
Fig. 5. Effect of water feeding concentration on 1,2-DCE oxidation over 10Cr/
LSMC catalyst.
atmosphere and the recovered 1,2-DCE conversion can be contributed
to the covered active components is totally exposed to 1,2-DCE when
turn off the feeding water.
3
.1.4. Effect of water vapor
Water vapor is a common component in industrial tail gas. In most
cases, the water molecular in catalytic oxidation reactions is char-
acterized as a competitive role, which can take up the active sites over
catalysts [33,34]. Herein, the effect of water with different inlet con-
centrations varied from 2 to 5 vol.% on 10Cr/LSMC catalyst was in-
vestigated, as shown in Fig. 5. The conversion of 1,2-DCE is obviously
inhibited when water vapor injected into the reaction system, and the
activity of 10Cr/LSMC catalyst decreases continuously in the first 2.5 h
with the increasing of water vapor concentration, especially when the
water content increases from 3 to 5.0 vol.%. Then, the conversion of
3.2. Catalyst characterizations
3.2.1. Structural and textural properties
Crystal structure of all prepared catalysts was characterized by XRD,
as shown in Fig. 6. The peaks centered at 35.0° and 40.7° over MnO
be assigned to the diffraction of MnO (PDF No.: 01-089-2804) and the
other peaks over MnO can be attributed to the diffraction of Mn
(PDF No.: 01-075-1560) (Fig. 6g). Similarly, two different oxide phases
(Cr (PDF No.: 01-084-0315) and CrO (PDF No.: 01-071-0869)) can
be found in CrO oxide (Fig. 6f). However, CoO oxide just has narrow
3 4
and intensive diffraction peaks attributing to the presence of Co O
x
can
x
3 4
O
1,2-DCE respectively stabilizes at around 95%, 92%, and 87% in the
2
O
3
2
presence of 2, 3, and 5 vol.% of water vapor. Remarkably, the 1,2-DCE
conversion rates are obvious recovered in all cases when shutting down
the water vapor, suggesting that the 10Cr/LSMC catalyst possesses su-
perior water-resistance in catalytic oxidation of 1,2-DCE. It's surprised
to observe that the most active 10Cr/LSMC sample deactivates from
x
x
phase (PDF No.: 00-042-1467) (Fig. 6h). All Cr/LSMC catalysts have
similar diffraction peaks at 2θ = 23.0°, 32.8°, 40.5°, 46.6°, 58.6°, and
68.9°, corresponding to the typical diffraction peaks of DPOs (Fig. 6a-e)
[24,35]. There are some small diffraction peaks appeared over Cr/
1
00% to 80% of 1,2-DCE conversion at 550 °C in dry atmosphere during
durability test just after 350 min (Fig. 3), but 1,2-DCE conversion over
0Cr/LSMC just decreases from 100% to 87%–95% in humid atmo-
LSMC catalysts when CrO
The diffraction peaks at 28.0° and 38.4° can be assigned to the Mn
phase, and weak diffraction peaks at 2θ of 26.0° and 71.7° can be re-
spectively attributed to the existence of CrO (PDF No.: 3-065-1388)
and Cr , indicating that the highly dispersed chromium oxides are
successfully introduced to LSMC. The appearance of Mn peaks in the
LSMC samples can be contributed to the interaction between CrO and
LSMC, which results in the exposure of the Mn crystal phase. FTIR
x
loading is higher than 5 wt.% (Fig. 6c-e).
1
3 4
O
sphere during durability test. Different results obtained in dry and
humid atmospheres are owing to that the chlorinated species attack
results in the inactivation of partial active sites on 10Cr/LSMC in dry
atmosphere (Fig. 3), but the competitive adsorption of water molecule
on the active content decreases the exposure ratio of active components
resulting in the decreasing catalytic activity of 10Cr/LSMC in humid
3
2 3
O
3 4
O
x
3 4
O
66

M. Tian et al.
Applied Catalysis A, General 570 (2019) 62–72
3.2.2. Catalyst morphology
FE-SEM micrographs of the synthesized materials are presented in
Fig. 7. It is shown that LSMC has shaggy surfaces with irregular
morphologies, composed of heterogeneous particles with different
diameters (50–200 nm), and some particle aggregates can be found
(
Fig. 7a). Comparatively, 5Cr/LSMC (Fig. 7b) and 10Cr/LSMC (Fig. 7c)
display more shaggy morphologies composed of small and regular ball-
like particles with average diameter around 150 nm. However, the
particles of 15Cr/LSMC (Fig. 7d) and 20Cr/LSMC (Fig. 7e) are ob-
viously aggregated. CrO
average diameter of about 500 nm (Fig. 7f). The morphology of cata-
lysts after stability tests (10Cr/LSMC-used and CrO -used) was further
investigated, as shown in Fig. 7g and h. Comparing with the fresh CrO
the particles of CrO -used catalyst are severely sintered and lots of large
x
mainly consists of bar-like particles with
x
x
,
x
aggregates can be found, leading to an obvious activity loss. In contrast,
the 10Cr/LSMC-used catalyst possesses a shaggy morphology and no
obvious particle aggregate can be observed even after 100 h of con-
tinuous reaction at 550 °C, which indicates the excellent durability of
10Cr/LSMC catalyst.
Fig. 6. XRD patterns of (a) LSMC, (b) 5Cr/LSMC, (c) 10Cr/LSMC, (d) 15Cr/
As shown in Fig. 7i, two types of lattice distances (0.288 and
x x x
LSMC, (e) 20Cr/LSMC, (f) CrO , (g) MnO , and (h) CoO .
3 4
0.257 nm) respectively assigned to the (200) plane of Mn O (main
crystal plane) and (111) plane of MnO can be distinguished in LSMC,
indicating the co-existence of Mn3+ and Mn . Three different lattice
planes can be found in 10Cr/LSMC, as displayed in Fig. 7k. (200) and
was also used to prove the formation of doped oxides as the vibration
2+
frequencies of metal-oxygen bonds are sensitive to be detected [36]. As
displayed in Fig. S1, the broad band at around 600 cm–1 is assigned to
(
122) planes with lattice distance of 0.287 and 0.196 nm can be as-
signed to the CrO phase, and (104) plane with lattice distance of
0.264 nm belongs to the Cr phase, in accordance with the XRD re-
sults (Fig. 6). However, just two kinds of lattice fringes with distance of
3 4
.287 nm ((200) plane of CrO ) and 0.276 nm ((103) plane of Mn O )
the stretching vibration of Oe C]O functional group in plane and out
3
of plane bending modes [37]. The band corresponding to CreO in the
framework is observed at 933 cm–1, confirming the incorporation of Cr
2 3
O
−1
in LSMC [38]. The band at 1383 cm is associated with the stretching
vibration of CeOH or bending vibrations of −OH [39].
0
3
can be observed in 20Cr/LSMC (Fig. 7l). Above results suggest that the
crystal structure of Cr/LSMC catalysts can be obviously changed when
alter the CrO loading.
x
Results of specific surface area and pore structure of synthesized
x
catalysts are illustrated in Table 1. CrO has the largest specific surface
2
3
area (24.4 m /g) and pore volume (0.14 cm /g), while the related
2
3
2
parameters of MnO
.09 cm /g) are much smaller. All Cr/LSMC catalysts possess larger
specific surface area (5.5-8.7 m /g) and pore diameter (14.4–27.2 nm)
than those of LSMC (< 1.0 m /g and 12.7 nm), which are favorable for
x
(6.2 m /g and 0.05 cm /g) and CoO
x
(4.9 m /g and
3
3.2.3. Surface status
0
2
Deconvolution of La 3d, Sr 3d, Mn 2p, Co 2p, Cr 2p, and O 1 s, was
performed by fitting a Gaussian-Lorentzian (GL) function with a Shirley
background, as shown in Fig. 8. The results from deconvolution are
presented in Tables 2 and 3. As shown in Fig. 8, both La 3d3/2 and La
2
the diffusion of reactant molecules and further accelerate the oxidation
rate. As listed in Table 1, the specific surface area of Cr/LSMC decreases
3
8
d
5/2 display doublet peaks for 10Cr/LSMC (La 3d3/2: 854.5 and
with the increasing of Cr content when CrO
x
loading is lower than
51.1 eV; La 3d5/2: 838.2 and 834.8 eV) and LSMC (La 3d3/2: 854.4 and
1
5 wt.%. However, 5Cr/LSMC and 20Cr/LSMC samples are character-
2
850.7 eV; La 3d5/2: 837.5 and 834.1 eV), suggesting the presence of
ized with very close specific surface area values of 8.7 and 8.3 m /g,
respectively. 5Cr/LSMC sample owns higher specific surface area
compared to 10Cr/LSMC and 15Cr/LSMC catalysts attributed to the
3+
La
[24,40]. The Sr 3d XPS spectra of 10Cr/LSMC and LSMC can be
divided into three peaks. The peaks at 131.8 and 134.0 eV are respec-
2
+
tively associated with the bulk Sr
3
and surface-bound SrCO species,
highly dispersion of CrO
x
on the surface of LSMC. 20Cr/LSMC also has a
indicating the presence of Sr2+ in the formation of perovskite phase
[41]. The bonding energy (BE) measured at 133.2, 134.6, and 134.8 eV
are ascribed to the presence of SrO [42]. The BE of Sr 3d at 136.1 eV is
2
large specific surface area of 8.3 m /g due to the large specific surface
2
x
area of CrO (24.4 m /g) although the 20Cr/LSMC sample is obviously
agglomerated compared with 5Cr/LSMC.
3
related to the existence of SrCO , and the formation of which is due to
the influence of susceptible surface of the oxide system [42,43]. As
shown in Fig. 8, Sr element in LSMC and 10Cr/LSMC samples exists as
2+
Sr . Table 3 exhibits the BE positions of Sr 3d XPS spectra. In addition,
the distributions of Mn and Co species are also analyzed by XPS
Table 1
Physicochemical properties and catalytic performance of synthesized catalysts.
(
Table 2), and the results suggest that the ratio of Mn and Co species is
0.92 and 0.93 (molar ratio of Mn and Co is 1 : 1), respectively, de-
monstrating that the sample (LaSrMnCoO ) is successfully synthesized.
a
b
c
d
d
Samples
S
(
BET
2
D
v
D
p
T
50
T
90
3
m /g)
(cm /g)
(nm)
(°C)
(°C)
6
5
1
1
2
Cr/LSMC
8.7
7.0
5.5
8.3
0.12
0.08
0.07
0.10
0.07
0.14
0.05
0.09
27.2
17.7
24.8
14.4
12.7
7.2
441
315
378
400
478
362
383
336
537
400
510
525
> 550
463
494
Mn 2p3/2 XPS spectra of LSMC and 10Cr/LSMC are displayed in
Fig. 8. The Mn 2p3/2 can be divided into two peaks centered at 643.0
and 641.4 eV, corresponding to Mn and Mn , respectively [44]. The
Mn /Mn
that of LSMC (0.96), and redox capability of CrO
enhanced by the large numbers of high valence Mn
0Cr/LSMC
5Cr/LSMC
0Cr/LSMC
4+
3+
4+
3+
LSMC
CrO
MnO
CoO
< 1.0
24.4
6.2
ratio on the surface of 10Cr/LSMC (1.13) is higher than
x
x
sites can be strongly
4+
x
9.4
5.1
cations on the
x
4.9
516
surface of LSMC [45]. The chemical state of Co is also examined by XPS.
As the Co 2p3/2 binding energy of Co2+ and Co closes to each other,
the spin-orbit splitting of Co 2p peaks (ΔE = E (Co 2p1/2) – E (Co 2p3/
3+
Note: a BET specific surface area calculated at P/P
= 0.99; c BJH pore diameter calculated from the
volume estimated at P/P
absorption branch; Temperatures at which 50% and 90% conversion of 1,2-
DCE.
= 0.05-0.30; b Total pore
0
0
d
2
)) is usually used to correlate with the cobalt oxidation state [46,47].
2 3
The ΔE values of 16.0, 15.0, and 15.2 eV stand for CoO, Co O , and
67

M. Tian et al.
Applied Catalysis A, General 570 (2019) 62–72
Fig. 7. FE-SEM images of (a) LSMC, (b) 5Cr/LSMC, (c) 10Cr/LSMC, (d) 15Cr/LSMC, (e) 20Cr/LSMC, (f) CrO
images of (i) LSMC, (j,k) 10Cr/LSMC, and (l) 20Cr/LSMC.
x x
, (g) 10Cr/LSMC-used, and (h) CrO -used; HR-TEM
Co
3
O
4
, respectively [48,49]. In this work, the spin-orbit values of LSMC
distribution over 10Cr/LSMC, CrO
vestigated, as documented in Table 2. The ratio of O
catalysts is in sequence of 10Cr/LSMC (0.67) > CrO (0.35) > LSMC
x
, and LSMC catalysts are in-
and 10Cr/LSMC are 15.4 and 15.6 eV, respectively, indicating that the
cobalt state in these catalysts are mainly present as Co
α
/O in above
β
3
+
.
x
It has been reported that Cr ions exist in various oxidation states in
(0.06), in accordance with the activity of catalysts and indicates that
surface lattice oxygen species play a significant role in the oxidation of
1,2-DCE. The effects of surface lattice oxygen species in oxidation
process can be concluded that the lattice oxygen species of catalyst
firstly oxidize the VOC leaving behind oxygen vacancies on catalyst
3
+
6+
supported Cr materials and Cr cations (Cr and Cr ) play important
roles in redox processes [50]. The Cr 2p3/2 XPS peaks with BE at around
3
+
6+
5
[
77 and 580 eV can be respectively assigned to Cr and Cr species
43,51–53]. Fig. 8 displays that the Cr element in CrO oxide is primary
x
3
+
3+
existed in the form of Cr
with BE of 576.4 eV, while both Cr
and
2
surface, and then the adsorption of O at vacancies is produced.
6
+
Cr
79.6 eV can be observed in 10Cr/LSMC, indicating the co-existence of
Cr and CrO , in agreement with the results of XRD (Fig. 6). The
percentage of Cr
according to the corresponding XPS peak areas (Table 2), and the
species with BE values respectively centered at 576.5 and
Whereafter, the O-atom produced by the dissociation of O
the vacancies in the process [58].
2
to replenish
5
2
O
3
3
The surface property of catalysts after stability tests (10Cr/LSMC-
used and CrO -used) were further characterized by XPS. The Cl 2p
6
+
3+
and Cr
is about 85% and 15% in 10Cr/LSMC
x
spectra and related results from deconvolution are respectively dis-
played in Fig. 9 and Table 3. Both Cl 2p XPS spectra can be further
decomposed into two sub-peaks centered at 198.5/198.7 and 200.1/
200.2 eV, respectively. The binding energy at 198.5/198.7 eV can be
6
+
presence of large amounts of high-valent Cr
tion ability of catalyst [54,55].
can enhance the oxida-
The fitted O 1 s spectra display three major oxygen contributions
with the corresponding peaks centered at BE of 528.8–530.1,
2
ascribed to the adsorption of HCl and/or Cl from the decomposition of
5
31.3–532.0, and ∼533.3 eV, attributed to the surface lattice oxygen
), surface adsorbed oxygen (O ), and carbonates/adsorbed mole-
cular water (O ), respectively (Fig. 8) [56,57]. The oxygen species
1,2-DCE, and the binding energy at 200.1/200.2 eV can be attributed to
the adsorption of 1,2-DCE on catalyst surface [51]. Results from Table 3
reveal that 1,2-DCE, HCl and/or Cl species can be detected both on the
2
(
O
α
β
γ
68

M. Tian et al.
Applied Catalysis A, General 570 (2019) 62–72
Fig. 8. La 3d, Sr 3d, Mn 2p, Co 2p, Cr 2p, and O1 s XPS spectra of synthesized catalysts.
Table 2
XPS results of Cr 2p, Mn 2p, Co 2p and O 1 s.
Samples
Cr 2p3/2
Cr3+
Mn 2p3/2
Mn4+
Mn
Co
O 1 s
/
Cr6+
Cr6+/(Cr3+ + Cr6+
)
Mn3+
Mn4+/Mn3+
O
a
O
b
O
c
α
β
γ
α β
O /O
1
CrO
LSMC
0Cr/LSMC
533.9
32598.7
/
3056.6
/
/
0.85
/
/
1048.9
/
5190.2
926.2
/
4991.7
1.13
/
0.96
0.92
/
0.93
19941.3
14154.9
1536.8
29714.5
40938.6
25849.3
20076.5
9285.3
30801.9
0.67
0.35
0.06
x
Note: a
α β γ
O O O is carbonates/adsorbed molecular water species.
is surface lattice oxygen; b is surface adsorbed oxygen species; c
69

M. Tian et al.
Applied Catalysis A, General 570 (2019) 62–72
Table 3
XPS results of Sr 3d and Cl 2p.
[47,60], and the reduction signal between 400 and 500 °C (with a small
2
+
shoulder at 480 °C) can be assigned to the reduction of Co species to
metallic cobalt [20]. As shown in Fig. 10A, all DPOs (LSMC and Cr/
LSMC) exhibit similar reduction profiles with two different reduction
regions of 414–474 and 643–664 °C (Fig. 10a-e), which is similar to the
previous work [24]. The metal elements at A-site of DPOs usually have
stable valence (e.g., La3+ and Sr ) and are hard to be reduced [61].
And the catalytic activities of the perovskites are mainly determined by
the B site element properties [62]. Therefore, the changes of metallic
valence states at B-site of DPOs have a crucial effect in the redox pro-
cess. As shown in Fig. 10A, the first reduction region corresponds to the
Samples
Sr 3d
SrCO
Cl 2p
3
(eV) SrO (eV)
Sr2+ (eV) 1,2-DCE (eV)
HCl/Cl
eV)
2
(
2+
1
0Cr/LSMC 134.0
134.8
/
133.2/
136.1
/
131.8
200.2
200.1
/
198.7
198.5
/
CrO
x
/
/
LSMC
1
34.6
6
+
3+
4+
3+
overlapping reduction of Cr
Co /Co
to Cr , Mn /Mn
to MnO, and
3+
2+
to Co° [14,15,20]. The second reduction region can be
3
+
2+
assigned to the reduction of Mn to Mn [20]. Compared with LSMC,
all reduction peaks of Cr/LSMC catalysts shift towards lower tempera-
x
tures, indicating the interaction between CrO and LSMC enhances the
reducibility of catalysts. Amongst, 10Cr/LSMC possesses the best low-
temperature reducibility with reduction peaks centered at 414 and
6
43 °C, endowing the superior activity of 10Cr/LSMC.
Fig. 10B shows the reducibility of the used CrO
materials. No obvious reduction peak over the used CrO
tected, indicating the active contents of single-metal oxides CrO
almost used up but incomplete recovery after 100 h of 1,2-DCE oxida-
tion due to the deposition of chlorinated species or coke. The H con-
sumption peak of the used 10Cr/LSMC catalyst appears at higher
temperature (centered at 564 °C) and owns a smaller amount of H
x
and 10Cr/LSMC
can be de-
are
x
x
2
2
consumption compared to fresh 10Cr/LSMC catalyst, which suggests
that the catalytic active sites (Cr6+, Mn , and Co ) take part in 1,2-
4+
3+
DCE oxidation reaction and are consumed in the oxidation process.
Compared to used CrO
x
, a larger amount of H
2
consumption of used
10Cr/LSMC demonstrates the interaction and existence of electron
Fig. 9. Cl 2p XPS spectra of the used 10Cr/LSMC and CrO
x
catalysts.
x
transfer between CrO and LSMC.
surface of CrO
active sites, leading to the decrease of catalytic activity.
x
and 10Cr/LSMC, which could occupy and block the
3
.2.5. Oxygen mobility
In general, the oxygen desorption peaks below 400 °C can be at-
tributed to the surface adsorbed oxygen (O ), while the peaks appearing
α
above 400 °C are due to the desorption of surface lattice oxygen (O )
β
3
.2.4. Reducibility
Reducibility of all prepared catalysts was studied, as displayed in
Figs. 10A and S2. As shown in Fig. S2, the reduction of CrO begins at
about 250 °C, and its reduction profile is characterized by a single H
consumption peak centered at 335 °C, assigning to the reduction of
[63]. The oxygen desorption peaks below 200 °C are considered to be
physically adsorbed oxygen species bound to the surface of the catalysts
[64], and the chemically adsorbed oxygen (O
orbs between 200 and 400 °C [65]. Despite the similarity of the systems,
differences in the desorbed oxygen can be found obviously. As shown in
Fig. 11, very weak peaks corresponding to the desorption of lattice
oxygen can be observed over LSMC (Fig. 11a), suggesting the presence
of a small amount of surface lattice oxygen, in accordance with the XPS
results (Fig. 8 and Table 2). Among Cr/LSMC catalysts, the desorption
x
−
2
−
2
and O species) des-
6
+
3+
Cr to Cr species [52,53]. For MnO
assigned to the reduction of Mn to MnO and the temperature over
06 °C is corresponding to the reduction of MnO to metallic Mn in
spinel oxides [20,44,59]. The H consumption peaks at 359 °C over
CoO can be attributed to the reduction of Co
x
, the reduction peak at 449 °C is
3 4
O
5
2
2
+
x
3
O
4
to Co
species
Fig. 10. (A) H
2 2 x
-TPR profiles of (a) LSMC, (b) 5Cr/LSMC, (c) 10Cr/LSMC, (d) 15Cr/LSMC and (e) 20Cr/LSMC; (B) H -TPR profiles of the fresh and used CrO , and
10Cr/LSMC samples.
70

M. Tian et al.
Applied Catalysis A, General 570 (2019) 62–72
are one type of promising materials for industrial CVOC destruction.
Acknowledgements
This work was financially supported by the National Natural Science
Foundation of China (21477095, 21677114, 21876139) and the
National Key Research and Development Program (2016YFC0204201),
and the Fundamental Research Funds for the Central Universities
(
xjj2017170). The valuable comments from the editor and anonymous
reviewers are much appreciated.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.apcata.2018.11.008.
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