Promoted VOC oxidation over homogeneous porous CoXNiAlO composite oxides derived from hydrotalcites: Effect of preparation method and doping

Article abstract of DOI:10.1039/c6ra08394c

Homogeneous porous and curve plated Co_xNiAlO composite metal oxide catalysts are obtained from the thermal decomposition of Co_xNiAl-layered double hydroxide (LDH) precursors, which are prepared by urea co-precipitation with surfactant, followed by a hydrothermal treatment. The as-prepared samples were characterized by XRD, BET, SEM, TEM, H₂-TPR and XPS. The Co₃AlO sample shows 90% benzene conversion (T₉₀) at 236 °C at a high space velocity (SV = 60000 mL g^-1 h^-1), and possesses much higher activity than Co₃AlO prepared with NaOH co-precipitation without surfactant, with T₉₀ = 288 °C. This is mainly correlated with the narrower pore size (2.9 vs. 17.2 nm) and lower temperature reducibility (319 vs. 360 °C). The Co₂NiAlO sample exhibits enhanced activity at T₉₀ = 227 °C with the low activation energy of 39.0 kJ mol^-1, and its lower temperature reducibility is ascribed to the larger amount of surface accessible Co³⁺. The Co₂NiAlO sample owns good reproducibility and superior reversibility and long stability with prolonged time on benzene stream in the presence of 3.5% water vapor. Moreover, a monolithic Co₂NiAlO film catalyst is fabricated by the thermal decomposition of an LDH film precursor through an in situ growth methodology, with a high reaction rate of 1.21 mmol g^-1 h^-1 under T₉₀ = 275 °C.

Full text of DOI:10.1039/c6ra08394c

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Page 1 of 27
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DOI: 10.1039/C6RA08394C
Promoted VOC oxidation over homogeneous porous CoNiAlO composited oxides derived
from hydrotalcites: effect of preparation method and doping
a
a,b
a
a
a,
Shuangde Li , Shengpeng Mo , Jiaqi Li , Haidi Liu , Yunfa Chen ∗
a
State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering,
Chinese Academy of Sciences, Beijing 100190, PR China
b
University of Chinese Academy of Sciences, Beijing 100049, PR China
Abstract
Homogeneous porous and curve plated CoxNiAlO composited metal oxides catalysts are
gained from the thermal decomposition of CoxNiAlꢀlayered double hydroxides (LDHs)
precursors, which are prepared by urea coꢀprecipitation with surfactant followed by hydrothermal
treatment. The asꢀprepared samples were characterized by XRD, BET, SEM, TEM, H ꢀTPR and
2
XPS. The Co3AlO sample shows temperature of 90% benzene conversion (T90) at 236 °C at a
−
1
−1
high space velocity (SV = 60,000 mL g h ), which owns much higher activity than Co3AlO
prepared with NaOH coꢀprecipitation without surfactant with T90 = 288 °C. This is mainly
correlated with narrower pore size (2.9 vs 17.2 nm) and lower temperature reducibility (319 vs
360°C). Co2NiAlO sample exhibits enhanced activity at T90 = 227 °C with the low activation
energy of 39.0 kJ/mol, which ascribes much lower temperature reducibility with larger surface
3
+
accessible Co . Co2NiAlO sample owns good reproducibility and superior reversibility and long
stability with prolonged time on benzene stream and 3.5% water vapor. Moreover, a monolithic
∗
Corresponding author. Tel.: +86 10 8254 4896; fax: +86 10 8254 4896.
Eꢀmail address: yfchen@ipe.ac.cn, chenyf@ipe.ac.cn.

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Co2NiAlO film catalyst is fabricated by thermal decomposition of LDH film precursor through an
−
1
−1
in situ growth methodology with high reaction rate of 1.21 mmol g
h under T90 = 275 °C.
Keywords: CoNiAlO catalysts; Layered double hydroxides; Benzene oxidation; Activation energy
1
. Introduction
The volatile organic compounds (VOCs) release of anthropogenic toxic pollutants into the
atmosphere is a worldwide threat of growing concern. VOCs may be found in nonꢀindustrial
indoor air environments, which can act as irritants to the human organism and have negative
1
2, 3
health effects, and cause bad indoor air quality. Catalytic oxidation with high efficiency is
recognized as effective method for air purification, compared with adsorption, UV photocatalytic
oxidation, nonꢀthermal plasma, plasmaꢀassisted catalysis and catalytic incineration, which have
4
, 5
been observed with potentially harmful intermediates and/or byꢀproducts. A rational control of
size and reactivity of the pore walls of metal–organic frameworks to maximize the performance of
6
capture and catalytic degradation of harmful gases are summarized. To design highꢀperformance
catalysts in terms of activity and resistance to deactivation is of great importance. Noble metal
7
8
9
catalysts over Pd/Co
3
AlO, Pt/mesoporous silica and AgꢀAu alloy exhibit high activity for VOCs
reduction, meanwhile, they are reported for their high cost, easily sintering and coking,
10
susceptibly poisoning. Non precise metal oxides as a potential alternative have attracted much
1
1
attention for their low cost, high resistance to poisoning, good reducibility. With smart design,
transitional metallic composited oxides own equivalent or even better properties than precious
1
2ꢀ14
metal because of the synergistic effect.
For example, Coꢀnanocasting synthesis of mesoporous
Cu–Mn composite oxides using siliceous temple SBAꢀ15 exhibited promoted benzene removal

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1
3
catalytic activities. To exert the synergistic effect to the maximum degree for mixed metal
oxides with high catalytic activity is still filled challenges and opportunities.
Besides, to design catalysts with small particle or pore size and hierarchical morphology
fabricated with thinner twoꢀdimensional sheets possesses more active sites and dispersion is
15
highly beneficial for outstanding catalytic activity, which is still a challenge. Zhao reported
ultrathin ZnAlꢀLDH nanosheets with coordinatively unsaturated Zn ions for their lateral size less
than 30 nm were synthesized using a facile bottomꢀup strategy, which exhibit extraordinarily high
16
activities for the photo reduction of CO
2
to CO. Li fabricated flower structure of
2 3
CoZnAlꢀMMO/Al O catalysts exhibited high dispersion of cobalt species due to wellꢀdeveloped
threeꢀdimensional flowerꢀlike CoZnAlꢀMMO platelets, which showed much higher catalytic
activity and selectivity for oxidation of ethylbenzene compared with the conventional supported
1
7
Coꢀbased catalyst prepared by incipient impregnation. Recently, many efforts proved that the
calcinations of Layered double hydroxides (LDHs) precursors may obtain well dispersed and
1
8, 19
stable catalysts with the above advantage.
Layered double hydroxides (LDHs) are a class of anion clay materials generally expressed by
2
+
3+
n−
II
III
the formula [M 1ꢀxM (OH) ](A ) ꢁ mH O, in which M and M cations disperse in an
x
2
x/n
2
n−
20, 21
ordered and uniform manner in bruciteꢀlike layers, and A is a charge compensating anion.
The specific ordered cation arrangements in the hydroxide layers of LDHs revealed by
multinuclear NMR spectroscopy could enhance the functional optimization of these materials in
20, 22ꢀ24
catalysis oxidation, photocatalysis and environmental remediation.
Therefore, the resulting
mixed oxides catalysts from a topotactic transformation of LDHs give finely dispersed mixed
II
III
25
oxides of M and M metals with a promotion of synergistic effect. Fan reviewed recent

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advances in the applications of layered double hydroxides (LDHs) with smart design in
26
heterogeneous catalysis both as directly prepared or after thermal treatment and/or reduction.
Besides, LDHs particles recently can be synthesized smaller and thinner with enhanced surface
area ranging from several micrometer to several tens nanometer choosing proper prepared method,
2
7
which will be notably favorable to the exposure of active sites. Moreover, LDHs lamellate plates
growing into film through in situ crystallization can assemble to flower, coreꢀshell, combꢀlike
structure, leading to large surface area, and the separate plate inhibits the agglomeration of active
2
5, 28, 29
components urging high activity and longꢀterm stability.
However, to our knowledge, there
is limited information on the possible cooperative effects that can exist for CoxNiAlO catalysts
synthesized by different method or varied dopant amount.
Herein, we fabricated CoxNiAlO powdered and film composited metal oxide catalysts through
the calcinations of CoxNiAlLDH precursors by urea coꢀprecipitation method followed with
hydrothermal treatment. The effect of preparation method over benzene total catalytic degradation
was evaluated through the Co3AlO samples obtained with urea and NaOH coꢀprecipitation
method. The effect of Co (or Ni) doping for CoxNiAlO samples on textural properties and
catalytic activities was further investigated.
2
. Experimental Section
2
.1 CoNiAlLDH powder and film precursor preparation
All chemicals used in this study were commercially available (from Merck) and used without
further purification. Pure aluminum substrate (purity >99.99%; thickness 0.2 mm) was purchased
from Beijing General Research Institute. CoxNiAlLDH powder precursors with varied Co content

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were prepared by a hydrothermal method (x = the molar ratio percentage of Co to Al). Briefly, a
3 2 2 3 2 2
75 mL aqueous solution containing Co(NO ) ·6H O (15, 10, 7.5, 5, 0 mmol), Ni(NO ) ·6H O
(
3 3 2
molar number of Ni = 15 mmol – molar number of Co), Al(NO ) ·9H O (5 mmol), urea (75
mmol) and sodium dodecyl sulfonate (SDS, 2.2 mmol) was delivered into a 100 mL teflon
autoclave after stirred thoroughly under 120 ºC for 6 h. Co3AlLDH precursor was prepared
3
0
through coꢀprecipitation method for comparison. Briefly, 20 mL mixed salt solution with 15
2
+
3+
mmol Co and 5 mmol Al , and a 30 mL 45 mmol NaOH solution were dropwised
simultaneously to a 180 mL 10 mmol Na CO solution keeping at constant pH 9.5 at 65 ºC with
2
3
constant stirring for 18 h, denoted as Co3AlLDHꢀRef. All the resulting suspension were
centrifuged with ethanol, deionized water several times till surfactant thoroughly removed, and
then dried at 80 °C for overnight.
The CoNiAlLDH film precursor was prepared by in situ crystallization on aluminum substrate,
which was cleaned with acetone, ethanol and deionized water in sequence before use. The Al
substrate (4×15 cm) was rolled into a tubular shape and immersed vertically in the same solution
2
+
3 2
as the preparation of Co2NiAlLDH (Co 10 mmol), for the exception of NH ·H O replacement
urea to adjust the pH = 9, then Co2NiAlLDH film (Co2NiAlLDHꢀF) was grown along their
abꢀorientation vertical to Al substrate. Afterwards, the substrate was withdrawn, rinsed with
deionized water and dried at room temperature.
2
.2 CoNiAlO powder and film catalysts preparation
The metal oxide powder and film catalysts were obtained by calcinating CoxNiAlLDH powder
−
1
and film precursors in air at 400 ºC for 4 h with a heating rate of 2 ºC min , denoted as CoxNiAlO,

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and Co2NiAlOꢀF. The detailed textural property of Co3NiAlOꢀRef shown in our previous report
30
.
2
.3 Characterization of the catalysts
Xꢀray diffraction (XRD) patterns of the catalysts were measured on a Rikagu SmartLab system
using CuꢀKa radiation in the diffraction angle (2θ) range 8º − 90º. The specific surface areas and
pore size distributions of all catalysts were obtained according to the Brunauer−Emmett−Teller
(
BET) and Barrett−Joyner−Halenda (BJH) methods, respectively, using the
N
2
adsorption–desorption method on an automatic surface analyser (ASꢀ1ꢀC TCD, Quantachrome
Cor., USA) at 77K. Before measurement, each sample was degassed at 200 ºC for 3 h. The
samples morphology was recorded on a scanning electron microscope (SEM, JEOL JSMꢀ6700F,
Japan, 15 kV, 10 mA). The microstructures of samples were obtained using transmission electron
microscopy (TEM, JEOL JEMꢀ2010F) with an accelerating voltage of 200 kV. Surface species of
the asꢀprepared catalysts were determined by Xꢀray photoelectron spectroscopy (XPS) and Xꢀray
induced Auger electron spectroscopy (XAES) using a XLESCALAB 250Xi electron spectrometer
from VG Scientific with monochromatic Al Ka radiation (1486.6 eV). Hydrogen temperature
programmed reduction (H ꢀTPR) with 30 mg catalyst (40–60 mesh) was carried out in an
2
−
1
Uꢀshaped quartz reactor under a gas flow (5% H
2
balanced with Ar, 25 mLꢁmin ). In each
procedure, the temperature was raised to 800 ºC from room temperature at a constant rate of 10
−
1
ºCꢁmin .
2
.4 Catalytic activity tests

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Performance of catalysts was evaluated in a continuousꢀfixedꢀbed quartz microreactor (i.d. 6
−
1
−1
mm) at a space velocity (SV) of 60 000 mL g h . The temperature of the reactor was controlled
using a temperature controller. Catalysts (100 mg, 40–60 mesh), mixed with 400 mg quartz sand
(40–60 mesh) were loaded in the quartz reactor with quartz wool packed at both ends of the
catalyst bed. 100 ppm benzene balanced with air was purged into the reactor at a continuous flow
−
1
1
00 mLꢁmin using mass flow controllers. For the consideration of effect of water vapour, the
mixed gas composed of a relative 3.5 % water vapour and 50 ppm benzene generated by mixing
−
1
−1
an 50 mLꢁmin air flow used for bubbling water and 50 mLꢁmin another air flow with benzene,
was purged into the reactor for catalytic tests. The concentration of benzene in the effluent gas
was analysed by a gas chromatograph (Shimadzu GCꢀ2014) equipped with a flame ionization
detector (FID) and the concentration of CO in the outlet gas was detected by another FID with a
2
2 4
methanizer furnace for converting CO to CH . To evaluate the production of benzene catalytic
degradation, the reaction gaseous production was extracted by dissolving into hexane solvent at
different reaction temperature, followed analysis by GCꢀMS (Shimadzu QP2010 Ultra, equipped
with Rxiꢀ5Sil column) with scanning mode of mass spectrometer under EI temperature at 200 ºC.
The catalytic evaluation for Co2NiAlOꢀF catalyst was performed by replacing CoxNiAlO powder
samples with film catalyst which was preꢀtailored to very small fragments. The complete
2
conversion of benzene (Wbenzene) and the yield of CO (ƞCO2) were calculated as follows:
ꢄꢅꢆꢇꢈꢆꢇꢆ,ꢉꢇꢊꢄꢅꢆꢇꢈꢆꢇꢆ,ꢋꢌꢍ
Wꢀꢁꢂꢃꢁꢂꢁ
=
× 100%
ꢄ
ꢅꢆꢇꢈꢆꢇꢆ,ꢉꢇ
ꢎ
ꢐ
ꢑꢒ ,ꢋꢌꢍ
ηꢎꢏꢐ
=
× 100%
ꢓ×ꢎꢅꢆꢇꢈꢆꢇꢆ,ꢉꢇ
where Cbenzene,in (ppm), Cbenzene,out (ppm) andCCO2,out (ppm) are the concentrations of benzene in the
inlet and outlet gas, and CO in the outlet gas, respectively.
2

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3
. Results and Discussion
3
.1 Textural study of the precursors and catalysts
The XRD patterns of CoxNiAlLDH precursors are shown in Fig. 1. In each case, the XRD
pattern exhibits the characteristic reflections of LDH materials with a series of (00l) peaks
appearing as narrow symmetric lines at a low angle with 3R packing of layers. With increased
doping of Ni, the characteristic diffraction peaks (00l) became broader than those of pure
Co3AlLDH, which could be deduced the size of LDH nanoparticles became smaller with the
effect of Ni incorporation. After calcination in air at 400°C, the XRD diffraction of CoxNiAlO
catalysts were given in Fig. 1. The strongest reflection at 2θ = 36.8 (311) for Co3AlO sample,
together with around 19.1, 31.4, 45.1, 59.5, 65.5, correspond to a Co
3
O
4
spinel phase in Fig. 1
PDF card No. 34ꢀ0425), which are the similar peaks also reported as other spinel oxide phases
Co AlO , PDF card No. 38ꢀ0814; CoAl , PDF card No.44ꢀ0160). They are hard to
(
(
2
4
2 4
O
distinguish by Xꢀray diffraction. Diffraction reflections at 2θ = 37.5, 43.6, 63.2, 75.8 and 79.5,
corresponding to the 111, 200, 220, 311 and 222, respectively, indicate the formation of NiO
phase in Fig. 1 for Ni3AlO sample (PDF card No. 47ꢀ1049). As the Ni content increased, the
intensities of the Co O peaks decrease, broader and low angle shifted. The absence of NiO
3
4
diffraction peaks reveals the formation of solid solution for CoxNiAlO samples, which will inhibit
crystal growth and is expected to bring about synergistic effect to alter their physicochemical
2 3
properties. No peak attributed to Al O can be found from the XRD patterns in all samples,
2 3
revealing that the amorphous Al O matrix in mixed oxides can play a role of support to stabilize
31, 32
and disperse Co O spinel phases,
which are also favorable to high catalytic activity.
3
4

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Fig. 1. XRD patterns of CoxNiAlLDH and CoxNiAlO.
The morphology of CoxNiAlLDH and their composited metal oxides revealed by SEM are
shown in Fig. 2. They all show uniform and randomly oriented hexagonal lamellar structure. The
30
particle size of Co3AlLDHꢀRef is ca. 300 nm. Co3AlLDH particle size is ca. 200 nm in ab plane
with 20 nm thickness in cꢀorientation, while they decreased to 120ꢀ180 nm with 10ꢀ14 nm
thickness for Co2NiAl, Co1.5NiAl, Co1NiAlLDH, which is coincided with the gradual broader
XRD peak at 2θ = 11.6° with enhanced Ni content. The result also indicated the formation of solid
solution indeed inferred from XRD, which are commonly reported can decrease the size of crystal.
The smaller size particles will generate more crystal defects which will be active for catalytic
33
reactions. Besides, for all the Niꢀrich samples, the hexagonal lamellar structures turn to curl and
gradually aggregate together to irregular flower petal. With the increased doping of Ni, the extent
of curl markedly enhanced. Ni3AlLDH shows petal morphology with even thinner platelets
around 6ꢀ8 nm. It can be deduced that there exists many stack holes through the self assembly of
LDH platelets to analogous petal structure, which may be leading the augment of surface area and
pore volume. The CoxNiAlO samples exhibit the similar morphology with their corresponding
LDHs samples, which show the metal oxide catalysts derived from the calcination of LDH
precursors can maintain the LDHs structure, keep the higher dispersion of Co O phases. The
3
4

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tendency of Co/Ni atomic ratios in the catalysts detected from SEMꢀEDX summarized in Table 1
was reasonably coincident with the initial input ratios with lower deviation. The Co/Ni ratios of
the catalysts surveyed by XPS in Table 1 exhibit lower ratios than those from EDX. The results
show that the Co/Ni ratios of the catalysts from the bulk are higher than their surface. The direct
element dispersion information, together with the various element peaks and their related
proportion for Co2NiAlO sample are shown in Fig. 3. There are very little Na and S detected from
the EDX data for Co2NiAlO, which manifested that surfactant stick on the surface of LDHs was
almost removed through washing with ethanol, following calcinations. The EDX mapping
demonstrates a uniform distribution of various elements (O, Al, Ni or Co) in the particle region.
2 3
Amorphous Al O make active elements keep very well dispersion. Well dispersion of Co and Ni
may promote their catalytic activity.
Fig. 2. SEM of CoxNiAlLDH and CoxNiAlO, all the scale bar are 200 nm.
Table 1 Atomic ratio of Co: Ni for CoxNiAlO catalysts and their BET data.
catalysts
Co/Ni atomic ratio
BET
Pore
Pore
Surface
volume size nm
Initial
EDX
XPS
2
−1
3
−1
areas m ꢁg
153.5
cm ꢁg
Co3AlOꢀRef
Co3AlO
0.34
0.34
0.58
0.60
17.2
3.0
3.1
3.6
148.6
Co2NiAlO
Co1.5NiAlO
2
1
1.47
1.02
1.28
0.66
172.7
152.4

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Co1NiAlO
0.5
0.65
0.39
178.9
193.2
127.9
119.3
0.78
0.87
0.31
0.21
3.8
4.2
23.6
5.2
Ni3AlO
Co3AlOꢀRefꢀafter test
Co2NiAlOꢀafter test
Fig. 3. SEM image, element distribution and EDX data of the Co1NiAlO sample.
The TEM images of the CoxNiAlO catalysts shown in Fig. 4 maintain the hexagonal plateꢀlike
morphology of the original LDHs precursor. Additionally, Co AlO, Co2NiAlO and Ni3AlO
3
samples in Fig. 4a, c and e all present well dispersed uniform pore embedded in the plate matrix.
The pore is around 2.2 nm for Co AlO, 2.6 nm for Ni3AlO samples, which facilitates catalysis by
3
augmenting contact between reactant and catalysts. The component of CoxNiAlO catalysts is
revealed by HRTEM (Fig. 4b, d and f). The identified fringes with lattice spacing of 0.30 and 0.21
nm are indexed to the (220) plane of Co O spinel phase for Co3AlO and (200) plane of NiO
3
4
phase for Ni3AlO with well crystallization shown in Fig. 4b and f, respectively. The lattice fringe
for Co spinel phase is clearly found, obscure for the NiO phase for Co2NiAlO in Fig 4d.
Elemental mapping of the single plate in HRTEM image for Co2NiAlO sample showed in Fig 4g,
3
O
4

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which showed well dispersion of Co and Ni meal. SAED pattern shown in Fig. 4h illustrates the
3
4
single crystalline Co2NiAlO nanostructure with hexagonal arranged spots.
Fig.4. (aꢀf) TEM and HRTEM images of the catalysts, (g, h) elemental mapping of the single plate
and SAED of Co2NiAlO.
2
Fig. 5 displays the N adsorption–desorption isotherm and the corresponding pore size
distribution curve for the CoxNiAlO catalysts and their BET and pore volume results collected in
Table 1. All the samples exhibit a typical IV isotherm with a H3ꢀtype hysteresis loop (P/P0 > 0.4).
It is noticeable that the two samples Co3AlOꢀRef and Co3AlO exhibit similar surface area and
pore volume, however their pore size distribution is quite difference, 17.2 nm for Co3AlOꢀRef and
2
.9 nm for Co3AlO samples. These results indicate that preparation method with the incorporation
of surfactant mainly leads to changes in the pore size and can make a great contribution on the

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catalytic activity for benzene oxidation. The surface properties for Ni doping into CoAlO samples
2
were also examined and show a gradually increased specific surface area from 148.5 to 193.1 m
−
1
g
0
for the exception of Co1.5NiAlO sample, increased pore volume and pore size from 0.34 to
3
−1
.87 cm g , 2.9 to 4.1 nm as the enhanced Ni content (Table 1), which are in accordance with the
different morphology for Ni doping, and will be beneficial for the disparity of the catalytic
activity.
Fig. 5. (A) N adsorption–desorption isotherms curves and (B) pore size distributions calculated
2
from the desorption branch of asꢀsynthesized CoxNiAlꢀMMO catalysts.
3
.2 X-ray photoelectron spectra
To obtain further insights into the structure–function correlations, Xꢀray photoelectron spectra
(XPS) for Co 2p, Ni 2p and O 1s were obtained for the fresh CoxNiAlO samples displayed in Fig.
6
with the reference of the residual carbon at a binding energy (BE) of 284.6 eV. Co 2p XPS
spectra was fitted assuming a theoretical value of 2 between the ratio Co 2p3/2 and 2p1/2 and a
spin–orbit splitting of 15.2 eV. Two broad and asymmetric peaks located around 780 and 796 eV
(
Fig. 6A) correspond to Co 2p3/2 and Co 2p1/2 from the spin–orbit doublet of Co
3 4
O , respectively.
3
+
The predominant peak at 780.1 eV and a small peak at 781.4 eV are attributed to Co in

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2+
3+
2+
octahedral sites and Co 2p3/2 configuration in tetrahedral sites. The Co and Co 2p1/2
3
5
components appear at 795.4 and 796.6 eV. The Co 2p3/2 shifted from 780.5 to high energy with
779.8 eV after the Ni incorporation, indicated the existence of interaction between Co and Ni,
3
6
3 4
which are also found the phenomenon for Ce doping in Co O with high energy at 774.4 eV. The
3
+
2+
surface Co /Co ratio calculated from the areas by quantitatively analyzing the XPS spectra of
the samples tended to decrease with decreasing Cobalt. The Co3AlO and Co2NiAlO samples
presents a higher ratio with 1.50 and 1.33, which are deviation from 2 corresponds to the formula
2
+
3+
2+
3+
2 4 2 4
Co (Co ) O , while the Co3AlOꢀRef sample presents the ratio of 2.13 close to Co (Co ) O .
3 4
The structural defects of the spinel Co O could play a key role in creating oxygen vacancies on
the surface, corresponding to the higher intrinsic catalytic activity. The Ni 2p spectra comprise
two regions representing the Ni 2p3/2 (850ꢀ866 eV) and Ni 2p1/2 (870ꢀ885 eV) spinꢀorbit levels.
The Ni 2p3/2 region consists of a main peak at 854.9 eV with a shoulder peak (∼1 eV above the
main peak) and a satellite peak at 861.5 eV. The Ni 2p1/2 appears at 873.1 eV with a satellite peak
3
7
(
∼7 eV above the main peak), which are consistent with the previous report on NiO. Similar
features are observed for the Ni 2p region for Coꢀcontaining samples shown in Fig. 6B.
The asymmetric O 1s peaks ranged at 528ꢀ534 eV for CoxNiAlO samples can be deconvoluted
into two contributions for their peaks at 529.8 and 531.6 eV attributed to the lattice oxygen (Olatt
)
and surface adsorbed oxygen (Oads) respectively, shown in Fig. 6C and summarized in Table 2,
which have a great impact on catalytic performance. The main peak of O 1s shifted from 530.4 eV
for Co3AlO sample to 529.8 eV for Ni doping samples for the indication of the interaction
between them. The surface Olatt/Oads molar ratio decreases faintly from 0.96 to 0.67 for increasing

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Ni incorporation. They may be due to the narrower pore size creates more vacancies and
unsaturated chemical bonds, which will lead to the increase of surface lattice oxygen ratio.
Table 2 Benzene catalytic activity, Ea and XPS results for CoxNiAlO samples.
3
+
2+
3+
2+
catalysts
Benzene conversion
Ea(kJ/ Co
Co
Co /Co
molar ratio
O
latt
O
ads
latt/ ads
O O
mol)
T
10
T
50
T
90
Co3AlOꢀRef
Co3AlO
215
160
152
167
167
186
254
208
204
213
223
292
288
236
227
243
264
>300
67.1
50.5
39.0
59.8
71.7
72.6
0.68 0.32 2.13
0.60 0.40 1.50
0.57 0.43 1.33
0.56 0.44 1.27
0.52 0.48 1.08
0.49
0.47
0.45
0.42
0.41
0.51
0.53
0.55
0.58
0.59
0.96
0.89
0.82
0.72
0.69
Co2NiAlO
Co1.5NiAlO
Co1NiAlO
Ni3AlO
Fig. 6. XPS spectra of (A) Co 2p, (B) Ni 2p and (C) O 1s of the CoxNiAlO samples.
3
.3 Temperature-programmed reduction
H
2
ꢀTPR was carried out to check the redox properties of CoxNiAlO catalysts shown in Fig. 7.
Co3AlOꢀRef sample exhibits two separate peaks, one broad low temperature peak centered at 360
ºC due to the twoꢀstep reduction of relatively large crystalline Co particles via the sequence of
3 4
O
0
38
Co O →CoO→Co , another high temperature peak at 720 ºC is ascribed to the reduction of
3
4
7
3
Co O
4
supported on Al
2
O
3
2
or CoAl O
4
. For Co3AlO sample, it is observed four separate
2
reduction peaks with the maximum rate of H consumption occurring at 319, 395, 553 and 650 °C,
respectively. The low temperature region contained two peaks corresponding with the two step
0
39
reduction of Co (III) to Co (II) and Co (II) to Co . The peaks at 553 and 650 °C ascribed to the
reduction of bulk Co O and embedded into the Al O support. The Co O reduction peak
3
4
2
3
3
4

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markedly shifted to lower temperatures than those of Co3AlOꢀRef, may be due to the quite
2
+
narrower pore size (2.9 nm vs 17.2 nm), facilitating the diffusion of Co ions. The incorporation
of Ni into the Co–Al mixed oxides presents particular effects on the H ꢀTPR profiles. It can be
2
clearly seen that the low temperature reduction region between 250−420 ºC shift gradually toward
lower temperature for the incorporation of Ni into CoxAlO systems, together with the
2
+
undiscernable reduction around the 650 ºC, implying that the enhanced substitution of Ni favors
3
+
the reducibility of Co
3
O
4
. The Co2NiAlO sample has lower reduction temperature for Co to
2
+
3+
2
Co , together with high concentration of Co observed from the maximum H consumption
occurring at 302 ºC for the largest TPR area with strong signal among CoxNiAlO samples. The
lower reduction temperatures of the Co2NiAlO sample indicate an increase of lattice oxygen
mobility on the catalyst, which will be an important prompt factor on the catalytic oxidation of
3
+
3 4
benzene. The high concentration of Co leading the structural defects of the spinel Co O lattice,
which are beneficial for more amounts of surface oxygen vacancies, improving catalytic activity
for VOCs combustion. The Co2NiAlO sample owning a larger pore volume and BET surface area
than Co3AlO, together with the incorporation of Ni could be favoured the formation of low
temperature reducibility, which is quite useful to promote catalytic oxidation. It should be noticed
2
+
that the Ni reduction peak centered at 492 ºC for Ni3AlO sample exhibited a little change for the
doping of Co. The reduction temperatures are shifted toward lower values further showing the
synergetic interaction between Co and Ni species.

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Fig. 7. Temperatureꢀprogrammed reduction profiles of CoxNiAlO catalysts.
3
.4 Evaluation of the catalytic behavior
The catalytic performances of CoxNiAlO samples were evaluated for total oxidation of
benzene as a function of the temperature shown in Fig. 8 A and B. Error bar represented the
standard deviation to the average of twice experiments with two fresh catalysts from the same
batch. The temperatures of 10% (T10), 50% (T50) and 90% (T90) benzene conversion are
2
summarized in Table 2. The benzene conversion and CO yield all increased with the rising
reaction temperature over these catalysts, while the CO yield is close to the direct conversion of
2
benzene with carbon balance nearly about 98.5%, indicating most of benzene molecules are
2 2
converted to CO and H O completely. To further evaluate the possibility of byꢀproduct, the flux
gas was abstracted with hexane for two varied reaction temperature at 200 and 240 ºC and
analysed by GCMS (Fig. 8C). There only existed benzene except the signal of hexane at T = 200
ºC, while there were only hexane detected at T = 240 ºC. The results demonstrated that there is no
byꢀproduct formed and after 240 ºC benzene has been totally degraded. Co
3
AlO sample obtaining
through surfactant method exhibited much higher activity with T90 at 236 ºC than that of

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Co AlOꢀRef sample at 288 ºC. The excellent activity of Co AlO can be attributed to the smaller
3
3
3
pore size and lower temperature reduction than those of Co AlOꢀRef proved by BET and TPR
characterization. Upon increasing addition of Ni to Co3AlO, the activity increases firstly, then
starts to decrease, even worse than that of Co3AlO. Among them, Co2NiAlO exhibited the best
−
1
−1
benzene oxidation performance at T90 = 227 ºC with the reaction rate about 0.24 mmol gcat h ,
−
1
−1
−1 −1
while Co3AlO catalyst with 0.19 mmol gcat
h
and Ni3AlO catalyst with 0.02 mmol gcat h .
The outstanding activity on the Co2NiAlO may be associated with the lower temperature
3
+
reducibility from larger surface accessible Co , together with the synergistic effect of
incorporation of Ni, inducing high surface oxygen species. The BET surface area for Co3AlOꢀRef
2
−1
and Co2NiAlO catalysts after catalytic test were reduced by ca. 30 m ꢁg , their pore volumes
were a little increase, together with increased pore size in comparison with fresh catalysts (Table
3 4
1). The activities preceded some other reported Co/Niꢀbased catalysts, like Tang reported Co O
40
nanocrystal growing from restrictive nanoreactor with T90 253 ºC for benzene degradation, Zhao
synthesized Pd, Pt, Ag–Co based spinel oxides for toluene combustion with T90 at 226, 289 and
41
3
19 ºC, respectively, Li obtained the optimal asꢀprepared CoxAlO catalysts by coꢀprecipitation
42
method with T90 at 300 ºC.
The catalytic performance can also be evaluated by comparing the activation energy (Ea) values
of different catalysts and normally the sample with lower Ea value will perform preferable
catalytic activity. The Ea values (Table 2 and Fig. 8D) could be obtained from Arrhenius equation
13
for the detail description in our previous publication. The plots of ln r versus 1/T perform
2
excellent linear relationships (the correlation coefficients (R ) were rather close to 1). The Ea
−1
−1
value of Co3AlO catalyst with 50.5 kJ mol was lower than that (67.1 kJ mol ) of Co3AlOꢀRef,

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which confirms the advantage of urea coꢀprecipitation method with surfactant. It is also observed
−
1
that the Co2NiAlO catalyst possessed the lowest Ea values (39.0 kJ mol ) among the CoxNiAlO
catalysts which confirm the promoting effect of Ni.
2
Fig. 8. (A) Benzene and (B) CO conversion as a function of reaction temperature over CoxNiAlO
−
1
−1
catalysts under benzene concentration 100 ppm in synthetic air, SV = 60 000 mL gcat h , (C)
GCꢀMS date of hexane solvent, the gaseous reaction production collected by dissolving in hexane
at reaction temperature 200 ºC and 240 ºC, respectively, mass spectrometer signal of benzene from
the gas production collected at T = 200 ºC, (D) Arrhenius plots for the oxidation of benzene over
the CoxNiAlO catalysts.
To investigate the reproducibility and reversibility of the catalysts, Co2NiAlO catalyst with
best benzene activity was selected as a model system. The identical sample was mounted and

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tested three separate times with the same temperature programming system and showed in Fig. 9
A. Satisfactorily, one batch sample essentially shows the same benzene conversion within an error
margin of < ±5 ºC, indicating a sufficiently high degree of reproducibility of the catalytic tests.
The reversibility and stability to resistance of higher temperature for benzene conversion were
monitored at three temperatures of 200, 300 and 400 ºC in sequence, and then repetition. The
catalytic activities were kept 100% benzene conversion at 400 ºC over two circle test from 200 to
400 ºC lasting 30 h, indicating that the catalysts over benzene degradation are completely
reversible and can stand up to higher temperature condition shown in Fig. 9B. The effect of water
vapor on benzene conversion for the Co2NiAlO catalyst were examined at different temperatures
(240 and 260 °C) in the absence and presence of 3.5% water vapor and shown in Fig. 9C. The
benzene catalytic activity maintained at 97.2% and 98.8% at two temperatures, with
inconspicuous variation for long timeꢀofꢀstream reaction. There was significant drop in benzene
2
conversion from 97.2% to 88.8% when 3.5% H O was introduced to the stream at 240 °C, while it
can be seen that water vapor had neglect negative effect on the catalytic activity with 98.8 %
under 260 °C. These results suggest that water vapor may competitively cover some active sites to
restrain the adsorption, mobility and activation of surface oxygen species under low temperature,
leading poor benzene oxidation activity, while surface active oxygen species, especially like Olatt
and Oads are more facial to adsorb and migrant on active sites under high temperature, leading
43
excellent catalytic activity and tolerant to the water vapor.

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Fig. 9. (A) Reproducibility and (B) reversibility for benzene conversion as a function of reaction
temperature and time over CoxNiAlO catalysts under benzene concentration 100 ppm in synthetic
air, symbol in A represented the same sample measured three times, (C) the effect of 3.5% water
vapor over Co2NiAlO catalyst at 240 and 260 °C with and lack of water vapor, SV = 60 000 mL
−
1
−1
g
cat h .
3
.5 The structure and catalytic performance of the monolithic Co2NiAlO-F catalyst
For better sake of practical application, monolithic Co2NiAlOꢀF catalyst has further been
obtained for the calcination of the Co2NiAlLDH film precursor on aluminum substrates through
in situ growth. The film catalyst recently attracted much attention for their advantages of sufficient
exposure of active sites with excellent heat conduction. Co2NiAlLDHꢀF precursor (Fig. 10A)
exhibited a series of typical hydrotalcite reflections at 2θ of 11.6º, 23.2º, 34.8ºand 60.1º, which can
be attributed to the (003), (006), (009) and (110) plane, respectively. After calcinations, the LDH
3 4
phase transform to Co O spinel phase similar identity with Co2NiAlO in Fig. 1. SEM image in
Fig.10B showed the Co2NiAlOꢀF crystallization owns thin curved hydrotalciteꢀlike platelets with
their ab plane nearly perpendicular orientation to the support. The Co2NiAlLDHꢀF on Al substrate
photographed by a camera turns to black color from light green color after calcination (Fig. 10C)
with plain surface and intense adhesion to the substrate. The catalyst growing on Al substrate was
2
nearly 1.32 mg/cm by weight. The benzene conversion evaluated in Fig. 10D manifested that the

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T
90 (275 ºC) for Co2NiAlOꢀF was reduced in comparison with the corresponding Co2NiAlO
−
1
−1
powdered catalyst at 232 ºC, while the reaction rate of Co2NiAlOꢀF with 0.31 mmol gcat
h is a
−1
−1
little higher than that of 0.24 mmol gcat
h
for Co2NiAlO at 232 ºC. The structural and
functional superiority of the film catalyst makes it an exciting efficient candidate in benzene
oxidation system.
Fig. 10. (A) XRD pattern of Co2NiAlLDH film precursor on the Al substrate (* represent the Al
substrate) and Co2NiAlOꢀF, (B) SEM images of Co2NiAlOꢀF, (C) the photograph of the
monolithic Co2NiAlLDH and Co2NiAlOꢀF catalysts on the Al substrate, (D) The comparison of
the benzene conversion over Co2NiAlO and Co2NiAlOꢀF catalysts.
4
. Conclusions
A series of mesoporous and wellꢀdispersed CoxNiAlO catalysts were fabricated via the LDHs
precursor approach. The preparation method affects remarkably their benzene catalytic activities.

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Co3AlO sample show much outstanding activity than Co3AlOꢀRef due to the small pore size and
good reducibility for the effect of surfactant when preparing. Furthermore, for different Ni doping
catalysts, Co2NiAlO sample exhibits the excellent catalytic behavior with T90 227 ºC and low
activation energy 39.0 kJ/mol, ascribe to the lower temperature reducibility from larger surface
3
+
accessible Co , together with the synergistic effect between the CoꢀNi metallic oxides solid
solution. Co2NiAlO sample displays good reproducibility and reversibility and resistance to 3.5%
−
1
−1
water vapor. The Co2NiAlOꢀF film catalyst shows higher reaction rate of 0.31 mmol gcat
h
−1
−1
than that of 0.24 mmol gcat
h for Co2NiAlO at 227 ºC.
Acknowledgments
This research described above was supported by the National Natural Science Foundation of
China (No.21401200), the strategic project of science and technology of Chinese Academy of
Sciences (No. XDB05050000), and the National Key Technology Support Program (No.
2014BAC21B).
References
1
2
3
4
. E. Gallego, F. J. Roca, J. F. Perales and X. Guardino, Build. Environ., 2013, 67, 14ꢀ25.
. L.Y. Lin and H. Bai, RSC Adv., 2016, 6, 24304ꢀ24313.
. H. Chen, Y. Yan, Y. Shao and H. Zhang, RSC Adv., 2014, 4, 55202ꢀ55209.
. M. S. Johnson, E. J. K. Nilsson, E. A. Svensson and S. Langer, Environ. Sci. Tech., 2014, 48,
8768ꢀ8776.
5
6
. L. Sivachandiran, F. Thevenet, P. Gravejat and A. Rousseau, Chem. Eng. J., 2013, 214, 17ꢀ26.
. E. Barea, C. Montoro and J. A. R. Navarro, Chem. Soc. Rev., 2014, 43, 5419ꢀ5430.

RSC Advances
Page 24 of 27
View Article Online
DOI: 10.1039/C6RA08394C
7
8
. P. Li, C. He, J. Cheng, C. Y. Ma, B. J. Dou and Z. P. Hao, Appl. Catal. B: Environ., 2011, 101,
70ꢀ579.
. S. H. Joo, J. Y. Park, C.ꢀK. Tsung, Y. Yamada, P. Yang and G. A. Somorjai, Nat Mater, 2009,
, 126ꢀ131.
5
8
9
. A. Q. Wang, C. M. Chang and C. Y. Mou, J. Phys. Chem. B, 2005, 109, 18860ꢀ18867.
0. P. O. Thevenin, A. G. Ersson, H. M. J. Kusar, P. G. Menon and S. G. Jaras, Appl. Catal. A:
Gen., 2001, 212, 189ꢀ197.
1
11. J. Deng, S. He, S. Xie, H. Yang, Y. Liu, G. Guo and H. Dai, Environ. Sci. Tech., 2015, 49,
11089ꢀ11095.
12. S. Xia, L. Zhang, X. Zhou, G. Pan and Z. Ni, Apply. Clay. Sci., 2015, 114, 577ꢀ585.
13. W. Tang, X. Wu, S. Li, X. Shan, G. Liu and Y. Chen, Appl. Catal. B: Environ., 2015, 162,
1
10ꢀ121.
4. G. Liu, J. Li, K. Yang, W. Tang, H. Liu, J. Yang, R. Yue and Y. Chen, Particuology, 2015,
9, 60ꢀ68.
1
1
1
5. Y. Sun, S. Gao, F. Lei and Y. Xie, Chem. Soc. Rev., 2015, 44, 623ꢀ636.
6. Y. Zhao, G. Chen, T. Bian, C. Zhou, G. I. Waterhouse, L. Z. Wu, C. H. Tung, L. J. Smith, D.
O'Hare and T. Zhang, Adv Mater, 2015, 27, 7824ꢀ7831.
1
17. R. Xie, G. Fan, L. Yang and F. Li, Catal. Sci. Technol., 2015, 5, 540ꢀ548.
18. X. Mei, J. Wang, R. Yang, Q. Yan and Q. Wang, RSC Adv., 2015, 5, 78061ꢀ78070.
19. R. Han, C. Nan, L. Yang, G. Fan and F. Li, RSC Adv., 2015, 5, 33199ꢀ33207.
20. J. Feng, Y. He, Y. Liu, Y. Du and D. Li, Chem. Soc. Rev., 2015, 44, 5291ꢀ5319.
21. R. Ma, J. Liang, K. Takada and T. Sasaki, J. Am. Chem. Soc., 2011, 133, 613ꢀ620.

Page 25 of 27
RSC Advances
View Article Online
DOI: 10.1039/C6RA08394C
22. P. J. Sideris, U. G. Nielsen, Z. Gan and C. P. Grey, Science, 2008, 321, 113ꢀ117.
2
3. Y. Zhao, Q. Wang, T. Bian, H. Yu, H. Fan, C. Zhou, L. Z. Wu, C. H. Tung, D. O'Hare and T.
Zhang, Nanoscale, 2015, 7, 7168ꢀ7173.
2
4. Y. Zhao, X. Jia, G. I. N. Waterhouse, L. Z. Wu, C. H. Tung, D. O'Hare and T. Zhang, Adv.
Energy Mater., 2016, 6, 1ꢀ20.
2
5. S. He, C. Li, H. Chen, D. Su, B. Zhang, X. Cao, B. Wang, M. Wei, D. G. Evans and X. Duan,
Chem. Mater., 2013, 25, 1040ꢀ1046.
2
2
2
2
6. G. Fan, F. Li, D. G. Evans and X. Duan, Chem. Soc. Rev., 2014, 43, 7040ꢀ7066.
7. Q. Wang and D. O'Hare, Chem. Rev., 2012, 112, 4124ꢀ4155.
8. S. He, Z. An, M. Wei, D. G. Evans and X. Duan, Chem. Commun., 2013, 49, 5912ꢀ5920.
9. M. Gabrovska, R. EdrevaꢀKardjieva, K. Tenchev, P. Tzvetkov, A. Spojakina and L. Petrov,
Appl. Catal. A: Gen., 2011, 399, 242ꢀ251.
3
3
3
0. S. Li, H. Wang, W. Li, X. Wu, W. Tang and Y. Chen, Appl. Catal. B: Environ., 2015,
166-167, 260ꢀ269.
1. L. He, Y. Huang, AiqingWang, XiaodongWang, X. Chen, J. J. Delgado and T. Zhang, Angew
Chem Int Ed, 2012, 51, 6191ꢀ6194.
2. M. Q. Zhao, Q. Zhang, W. Zhan, J. Q. Huang, Y. Zhang, D. S. Su and F. Wei, J. Am. Chem.
Soc., 2010, 132, 14739ꢀ14741.
3
3. W. Tang, X. Wu, S. Li, W. Li and Y. Chen, Catal. Commun., 2014, 56, 134ꢀ138.
4. Y. Han, Z.ꢀH. Liu, Z. Yang, Z. Wang, X. Tang, T. Wang, L. Fan and K. Ooi, Chem. Mater.,
3
2008, 20, 360ꢀ363.

RSC Advances
Page 26 of 27
View Article Online
DOI: 10.1039/C6RA08394C
3
3
3
3
3
5. T. Garcia, S. Agouram, J. F. SanchezꢀRoyo, R. Murillo, A. Maria Mastral, A. Aranda, I.
Vazquez, A. Dejoz and B. Solsona, Appl. Catal. A: Gen., 2010, 386, 16ꢀ27.
6. G. A. Babu, G. Ravi, T. Mahalingam, M. Navaneethan, M. Arivanandhan and Y. Hayakawa,
J. Phys. Chem. C, 2014, 118, 23335ꢀ23348.
7. V. Binni, M. V. Reddy, Z. Yanwu, C. S. Lit, T. C. Hoong, G. V. S. Rao, B. V. R. Chowdari,
A. T. S. Wee, C. T. Lim and C.ꢀH. Sow, Chem. Mater., 2008, 20, 3360ꢀ3367.
8. G. Bai, H. Dai, J. Deng, Y. Liu, F. Wang, Z. Zhao, W. Qiu and C. T. Au, Appl. Catal. A: Gen.,
2
013, 450, 42ꢀ49.
9. B. de Rivas, R. LópezꢀFonseca, C. JiménezꢀGonzález and J. I. GutiérrezꢀOrtiz, J. Catal., 2011,
81, 88ꢀ97.
2
40. W. Tang, Y. Deng, W. Li, S. Li, X. Wu and Y. Chen, Catal. Commun., 2015, 72, 165ꢀ169.
41. S. Zhao, K. Li, S. Jiang and J. Li, Appl. Catal. B: Environ., 2016, 181, 236ꢀ248.
42. D. Li, Y. Ding, X. Wei, Y. Xiao and L. Jiang, Appl. Catal. A: Gen., 2015, 507, 130ꢀ138.
43. Q. Liu, L.ꢀC. Wang, M. Chen, Y. Cao, H.ꢀY. He and K.ꢀN. Fan, J. Catal., 2009, 263, 104ꢀ113.

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Graphical Abstract
Promoted VOC oxidation over homogeneous porous CoNiAlO composited oxides derived
from hydrotalcites: effect of preparation method and doping
a
a,b
a
a
a,
Shuangde Li , Shengpeng Mo , Jiaqi Li , Haidi Liu , Yunfa Chen ∗
a
State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering,
Chinese Academy of Sciences, Beijing 100190, PR China
b
University of Chinese Academy of Sciences, Beijing 100049, PR China
Co2NiAlO powdered and film catalysts derived from layered double hydroxides precursors are
prepared with excellent catalytic activity, reproducibility, reversibility, and stability to water vapor
for benzene oxidation.
∗
Corresponding author. Tel.: +86 10 8254 4896; fax: +86 10 8254 4896.
E-mail address: yfchen@ipe.ac.cn.