Metal organic framework-derived Co3O4 microcubes and their catalytic applications in CO oxidation

Article abstract of DOI:10.1039/c6nj02507b

Metal-organic framework (MOFs)-derived metal oxides with diverse morphologies and microporous structures have shown potential applications in heterogeneous catalysis. In this study, two types of porous Co₃O₄ catalysts, Co₃O₄-MA and Co₃O₄-DMA (MA = methylamine and DMA = dimethylamine), were successfully synthesized via a one-step pyrolysis of Co-based metal-formate frameworks, [Amine][Co(HCOO)₃] (Amine = methylamine, dimethylamine), in air. The obtained porous Co₃O₄ catalysts were systematically characterized by XRD, SEM, TEM, XPS, H₂-TPR, and N₂ adsorption-desorption analysis. The results show that the obtained porous Co₃O₄ catalysts are composed of nanoparticles and inherit the morphology from the precursor [Amine][Co(HCOO)₃]. Co₃O₄-MA and Co₃O₄-DMA exhibit an excellent catalytic activity for CO oxidation, with both of them reaching a 100% CO conversion at 170 °C.

Full text of DOI:10.1039/c6nj02507b

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Metal organic frameworks-derived Co O microcubes and
3
4
catalytic application in CO oxidation
Received 00th January 20xx,
Accepted 00th January 20xx
Chi Zhang, Li Zhang,* GuanꢀCheng Xu, Xin Ma, YingꢀHai Li, ChuꢀYang Zhang, DianꢀZeng Jia*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Metalꢀorganic frameworks (MOFs) derived metal oxides with diverse morphologies and microporous
structures have shown potential application in heterogeneous catalysis. In this paper, two kinds of porous
Co O catalysts, Co O ꢀMA and Co O ꢀDMA (MA = methylamine and DMA = dimethylamine), have been
3
4
3
4
3
4
successfully synthesized via oneꢀstep pyrolysis of Coꢀbased metal-formate frameworks [Amine][Co(HCOO)3]
Amine = methylamine dimethylamine ) under air. The obtained porous Co O catalysts were systematically
(
,
3
4
characterized by XRD, SEM, TEM, XPS, H ꢀTPR and N adsorptionꢀdesorption analysis. The results show
2
2
that the obtained porous Co O catalysts are composed of nanoparticles and inherit the morphology from the
3
4
precursors [Amine][Co(HCOO) ]. The Co O ꢀMA and Co O ꢀDMA exhibit excellent catalytic activity for CO
3
3
4
3
4
o
oxidation, both of them reach 100% of CO conversion at 170 C.
5,6
and the unprecedented properties. Owing to their open channels,
permanent cavities and order crystalline lattice, MOFs have been
used as hosts for the synthesis of the metalꢀoxide nanoparticles. For
1
. Introduction
7
Reducing CO concentration in the air by active catalysts and
reaching the allowed concentration levels according to
environmental regulations has become a top priority. So the CO
oxidation heterogeneous catalysis is an important research area
which attracted more and more attention.
example, Wang et al. employed ZIFꢀ8 (Zn(MeIM) , MeIM=2ꢀ
2
methylimidazole) as a host to prepare neat Co O nanoparticles,
3
4
1
ꢀ
1
ꢀ1
o
which exhibit high specific rate 12.8 mmol g
h
at 70 C, good
8
cycling stability and longꢀterm stability in CO oxidation. Tan et al.
used MILꢀ53(Al) with high thermal stability as a support material of
9
As the CO oxidation catalysts, noble metals possess high activity
and desirable thermal stability, but the disadvantages of high cost
and low availability make them compulsion to consider transition
a copper catalyst for CO oxidation. Moreover, owing to their
uniform and tridimensional structures within inorganic clusters
1
0
connected by organic moieties,
candidates in chemical sensors,
which make MOFs good
lithium ion batteries,
2
11
12
metal catalyst as an alternative. Among the transition metal oxides,
1
3
14
cobalt oxide is considered to be one of the most important transition
metal catalysts which possesses excellent CO oxidation activity both
supercapacitor, catalysis, and so forth, various MOFꢀderived
metal oxides and composites were synthesized and utilized as
catalysts for CO oxidation which exhibit excellent catalytic activity.
Recently, Zhang et al. employed Cuꢀbased MOFs to prepare
o
3
at ambient temperature and lower temperature as ꢀ77 C. Much
effort has been devoted to research the influence of the particle size
and shape effect with regard to CO oxidation. Recent scientific
CuO/Cu O porous composites with adjustable composition and
2
researches have shown that the physical and chemical properties of
various morphologies, and the porous composites reach 100% of CO
conversion at 240~260 C. Qin et al. prepared AO /CuO /C (A = Sr,
x y
4
o
15
Co O are closely associated with the morphology and porosity.
3
4
Therefore, it is fundamental and technological interest to develop
facile and efficient synthetic approaches for the preparation of
La, Ce, Al) composites by using AꢀCuꢀBTC as precursor, and one of
CuO /C showed the promising catalysts in selective catalytic
y
16
specific porous and morphologyꢀcontrolled Co O .
3
4
reduction of NO with CO. Yan et al. synthesized rattleꢀtype
Co O @SiO nanoparticles via thermal decomposition of
Co [Co(CN) ] @SiO core–shell nanocubes, which reaches 100% of
Since the last decade, metalꢀorganic frameworks (MOFs) has
attracted wide attention of researchers because of their potentialities
3
4
2
3
6 2
2
o
17
CO conversion at 150 C. Wang et al. synthesized nanoscale Co/C
by simple pyrolysis of a Coꢀcontaining metalꢀorganic framework
(
ZIFꢀ67) at 600 °C, which exhibited high catalytic activity for CO
Key Laboratory of Energy Materials Chemistry (Xinjiang University), Ministry of
Education. Key Laboratory of Advanced Functional Materials, Autonomous Region.
Institute of Applied Chemistry, Xinjiang University, Urumqi, 830046, Xinjiang, P. R.
China.
*Corresponding author. E-mail: zhanglixju@163.com, jdz0991@gmail.com
Tel./Fax: +86-991-8580586
18
oxidation even at a temperature as low as ꢀ30 °C. Pang et al.
calcined the corresponding nanostructured Coꢀ8ꢀhydroxyquinoline
coordination precursor in air and then obtained Co O which can
3
4
19
catalyze the oxidization of nearly 100% of CO to CO at 100 °C.
2
However, facile and controlled synthesis of nanostructured porous
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ARTICLE
Journal Name
3
Co O
4
catalysts derived from the thermolysis of Coꢀbased MOFs is spectroscopy (XPS) was performed on an Escalab 250 Xi from
still in its infancy.
Thermo Fisher Scientific. H
(H ꢀTPR) analysis was performed by using a
2
2
temperatureꢀprogrammed reduction
Micromeritics
Herein, we report a facile strategy to prepare porous Co
3
O
4
Chemisorb 2920 apparatus. For each analysis, accurate amounts of
calcined sample (60~65 mg) were purged in a flow of pure argon at
catalysts by calcining formateꢀbased metalꢀorganic frameworks. As
various structure and shapes of metalꢀformate frameworks can be
o
o
20
2
00 C for 120 min to remove traces water (heating rate 10 C /min).
After cooling to room temperature, H ꢀTPR experiments were
performed using a 10 vol% H /Ar mixture at a flow rate of 50
mL/min. The sample was heated from ambient temperature to 800
controlled to achieve by using ammonium cation templates, the
porous Co were prepared via simple solidꢀstate thermolysis of the
Coꢀbased metalꢀformate frameworks. The asꢀmade Co remain the
shape of the precursors very well, and show excellent catalytic for
3
O
4
2
3
O
4
2
o
o
3
+
C at heating rate of 10 C /min and H
2
consumption was detected by
CO oxidation. The results indicates the synergy of O
sites is considered to be the main effect on catalytic activity of
Co for CO oxidation and the specific surface area seemed
v c
, O and Co
a thermal conductivity detector (TCD).
3
O
4
2
.4 Catalytic performance test
less important. This method is also applicable to the preparation of
other metal oxides with a number of potential applications.
50 mg catalysts were put in a quartz glass reaction tube without any
preꢀtreatment. The reaction temperature was monitored by a
thermocouple placed in the middle of the catalyst bed. A mixture of
2
. Experimental details
1
vol % CO and 20 vol % O balanced by N was introduced as the
2 2
All the chemical reagents were purchased commercially and used
without further purification.
−
1
reactants. The total flow rate was 50 mL min , corresponding to a
space velocity of 60000 mL g h . Online analysis of CO and CO2
was performed at each temperature after a stabilization time of about
−
1
−1
3 3
2.1 Synthesis of [Amine][Co(HCOO) ] (Amine = NH CH3,
2
0 min with Agilent GC7890 gas chromatograph. The CO
(
CH NH
3
)
2
2
)
conversion was calculated based on the change in CO concentrations
of the inlet and outlet gases as follow:
In a typical synthesis, 2.38 g of CoCl
dissolved in 20 mL of methanol in a beaker. 3.106 g of methylamine
water solution (NH CH , 40%), 2.7618 g of formic acid (HCOOH,
8%) and 1 g of PVP were dissolved in 20 mL of methanol. Then the
2 2
• 6H O and 1 g of PVP were
2
3



CO OUT




8

RCO = 1−
×100%
cobalt chloride solution was dropped into the ligand solution. The
mixture was stirred at room temperature for 30 minutes and aged for
CO IN
30 minutes. The resulting pink precipitates were collected by
centrifugationꢀredispersion cycles to remove any possible residual
reactants, and finally dried under vacuum at 40 C for 5 h.
3
. Results and discussion
o
Metalꢀformate frameworks were used as precursors in this work.
Templated by ammonium cations, two metalꢀformate frameworks
In the preparation of [(CH
water solution were replaced by 5.464 g dimethylamine water
solution ((CH NH, 33%) and similar procedure was used.
.2 Synthesis of porous Co catalysts
Co catalysts were obtained
Amine][Co(HCOO) ]. Thermal decomposition was achieved under
air in a muffle furnace with a heating rate of 1 K min up to 500 C
and maintained for 2 h. The two samples were named as Co ꢀMA
and Co ꢀDMA, respectively.
For purposes of comparison, commercial Co
Co ꢀC, was purchased from a commercially available source
Tianjin Kwangfu).
.3 Material characterizations
3 2 2 3
) NH ][Co(HCOO) ], methylamine
[
Amine][Co(HCOO)
3
]
(Amine
3 3 3 2 2
= NH CH , (CH ) NH ) were
3 2
)
2
1, 22
formed.
A modified precipitation method was used in this work
2
3 4
O
to obtain the microcrystals of two metalꢀformate frameworks. Cobalt
chloride, formic acid neutralized by amines frameworks. Cobalt
3
O
4
from
calcination
of
[
3
ꢀ
1
o
3
O
4
3
O
4
3
4
O , donated as
3
O
4
(
2
Thermogravimetric analyses (TGA) were performed on a Netzsch
SDT449F3 thermal analyzer in air atmosphere at a scan rate of 10 K
ꢀ
1
min . Scanning electron microscope (SEM) images were taken
using Hitachi Sꢀ4800 microscope. Transmission electron
a
microscopy (TEM) images were obtained with a Hitachi H600
microscope. Powder Xꢀray diffraction (XRD) data were recorded on
a Bruker D8 advance diffractometer at 40 KV and 40 mA using Cu
o
Kα radiation (λ = 0.15405 nm) radiation, with a step size of 0.02 in
2
2θ. The surface area and N adsorptionꢀdesorption isotherm
measurement were carried out on a Micromeritics ASAP 2020
analyzer at 77 K. Prior to the measurement, the sample was degassed
at 120 C for 6 h in the vacuum line. Xꢀray photoelectron
Fig. 1 XRD patterns (a, b) and SEM (c, d) images of [NH
(CH NH ][Co(HCOO) ] (b, d).
3 3 3
CH ][Co(HCOO) ] (a, c), and
[
3
)
2
2
3
o
2
| J. Name., 2012, 00, 1-3
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chloride, formic acid neutralized by amines and PVP were used
as the reactants, and the whole synthesizing process was run
mildly at ambient temperature. The polymer PVP was added as
an additive in the crystallization to tune the size of the resulting
crystals. XRD patterns of the asꢀprepared samples, as shown in
2
1, 22
Fig. 1aꢀb, match well with the simulated XRD patterns,
indicating the formation of pure phase [NH CH ][Co(HCOO)
and [(CH NH ][Co(HCOO) ]. SEM images (Fig. 1cꢀd) show
that the as prepared [NH CH ][Co(HCOO) and
(CH NH ][Co(HCOO) ] are consisted of microcubes, and the
3
3
3
]
3
)
2
2
3
3
3
3
]
[
3
)
2
2
3
size distribution are about 5 ꢁm and 7 ꢁm, respectively.
The thermal behaviour of the [Amine][Co(HCOO)
3
] in air
are shown in Fig. 2a. The curves indicate twoꢀstep weightꢀloss
patterns of the compounds. The first weight losses are ascribed
to the removal of amine and one formate molecule per formula
unit. The second losses are attributed to the decomposition of
remaining organic components. The final residues were found
to be 35.9% and 36.3%, which are close to the calculated values
Fig. 3 Adsorption and desorption isotherms for nitrogen (at 77 K) of the Co
3
O
4
-MA
-DMA (red). Inset shows the corresponding Barrett-Joyner-Halenda
BJH) pore size distribution.
(
(
3 4
black) and Co O
of 35.4% and 33.5%, estimated as Co
NH CH ][Co(HCOO) and [(CH
respectively. Based on the TG results, we predicted that Co
could be formed by pyrolyzation of [NH CH ][Co(HCOO)
and [(CH NH ][Co(HCOO)
C. Therefore, the asꢀprepared [NH
(CH NH ][Co(HCOO) ] were annealed at 500 C for 2 h, and
ꢀMA and Co ꢀDMA were obtained. XRD results of
ꢀMA and Co ꢀDMA are shown in Fig. 2b. The peaks at
3
O
NH
4
produced from
(
1
400), (422), (511), and (440) reflections of Co
003), respectively. Moreover, the sharp diffraction peaks confirm
the high crystallinity of Co ꢀMA and Co ꢀDMA. More
structural information was revealed by SEM and TEM. SEM images
(Fig. 2cꢀf) show that the obtained Co ꢀMA and Co ꢀDMA
retain the geometries of the precursors with smaller size about 3 ꢁm
and 5 ꢁm, respectively. Moreover, the Co ꢀMA and Co ꢀDMA
3 4
O (JCPDS No. 43ꢀ
[
3
3
3
]
3
)
2
2
][Co(HCOO) ],
3
3
O
4
3
O
4
3 4
O
3
3
3
]
3
)
2
2
3
] at temperature higher than 350
CH ][Co(HCOO) ] and
o
3
O
4
3 4
O
3
3
3
o
[
Co
Co
3
)
2
2
3
3
O
4
3 4
O
3
O
O
4
4
3 4
O
microcubes are composed of nanoparticles with size distributions
about 35 ~ 42 nm and 45 ~ 70 nm, respectively. There are a lot of
pores distributed on the surface of cobalt oxides. In addition, the
3
3 4
O
2θ = 18.9°, 31.2°, 36.8°, 38.5°, 44.8°, 55.3°, 59.3°, and 65.2°
correspond well to the characteristic (111), (220), (311), (222),
3 4 3 4
interior structure of Co O ꢀMA and Co O ꢀDMA was further studied
by TEM. TEM images, as shown in Fig. 2cꢀf insets, reveal that the
interior structures are composed of nanoparticles and abundant pores,
which might ascribed to the gas released during the process of
thermal decomposition of the precursors.
The N
2
adsorption−desorption isotherm curves are shown in Fig.
3
. It can be seen that both of the samples exhibit typeꢀIV adsorption
isotherms with a clear hysteresis loop, indicating the presence of
mesoporous structure in the samples. The BarrettꢀJoynerꢀHalenda
(
BJH) pore size distribution curves in the inset of Fig. 3 shows the
pore size distributions of Co ꢀMA and Co ꢀDMA are in the
similarity mesoporous range (2.3~5 nm). The specific surface areas
of Co ꢀMA and Co ꢀDMA calculated through Brunauer–
3
O
4
3 4
O
3
O
4
3 4
O
2
2
EmmettꢀTeller (BET) method were 6.77 m /g and 9.37 m /g,
respectively. The comparatively low specific surface areas might be
due to the excessive pyrolysis make the particles aggregating.
Attempts were made to investigate the catalytic activities of the
3 4
asꢀobtained Co O catalysts for CO oxidation. The reactions were
carried out in a fixedꢀbed flow reactor with 50 mg catalysts and with
ꢀ
1
ꢀ1
a gas flow mixed of CO (0.5 ml min ), O
(
2
(10 ml min ), and N
39.5 ml min ). The catalytic activity for CO oxidation as a function
of the temperature is shown in Fig. 4a. Apparently, the synthesized
Co ꢀDMA catalyst exhibits the best catalytic activity for CO
oxidation. The T50 (the temperature of 50% conversion) for Co
2
ꢀ
1
3
O
4
3
4
O ꢀ
ꢀMA
o
o
DMA is 160 C, which is 3 C lower than that of Co
50=163 C). The temperatures for 100% CO conversion of Co
MA and Co O ꢀDMA are both at 170 C. In contrast, Co O ꢀC
3 4 3 4
3
O
4
Fig.
(CH
products obtained from calcination of the as-prepared precursors in air; SEM images
with insets showing TEM images of (c, d) Co -MA and (e, f) Co -DMA.
2
(a) TGA curves of the as-synthesized [NH
3
CH
3
][Co(HCOO)
3
]
and
o
(
T
3 4
O ꢀ
[
3
)
2
NH
2
][Co(HCOO) ] microcrystals in air flow; (b) XRD patterns of the Co
3
O
3 4
o
shows poor CO oxidation activity with T50 at 230 °C and only 75%
J. Name., 2013, 00, 1-3 | 3
O
3 4
3 4
O
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o
CO conversion was obtained even when the temperature reaches Co ꢀDMA exhibits
3
O
4
ꢀMA and Co
3
O
4
ꢀDMA started at 200 C. Co
3
O
4
o
highly at 320 °C. These results demonstrate that the porous Co only one peak at 375 C, while Co O ꢀMA presents two peaks at
prepared in this work can effectively catalyze the CO oxidation at a 391 C and 448 C, assigned to the chemisorbed/dissociated oxygen
lower temperature, and the full CO conversion temperature is much and bulkꢀphase lattice oxygen, respectively. This observation can be
3
O
4
3 4
o
o
lower than that of Co
MA and Co ꢀDMA might be attributed to their small particles and of Co
porous structures, which offer a larger contact area with CO. The In addition, Co
Arrhenius plots of CO oxidation over the two samples are shown in higher hydrogen consumption between 200
3
O
4
ꢀC. The better catalytic properties of Co
3
O
4
ꢀ
explained by the particle size of Co
ꢀDMA are usually reduced to metallic cobalt in one step.
ꢀDMA shows lower reduction temperature and
3 4
O , of which the larger particles
24
3
O
4
3 4
O
3
O
4
o
o
C
and 350 C,
−1
Fig. 4b. The apparent activation energy (kJ mol ) was calculated suggesting that Co O ꢀDMA is more likely to be reduced than
3 4
o
o
using conversion data between 130 C and 170 C. The apparent Co
activation energy of CO oxidation over Co ꢀMA and Co ꢀDMA Many works have been done to study the mechanisms of catalytic
are 155.4 kJ mol and 113.2 kJ mol , respectively. Thus, Co
DMA shows a better catalytic activity than Co ꢀMA due to its oxidation could proceed as below:
lower value of activation energy of CO oxidation. Furthermore, 1/2 O + X ↔ O · X
cycling tests were performed to study the stability of Co ꢀMA and
Co ꢀDMA, as shown in Fig. 4cꢀd, and no significant deactivations
were observed in the second run. Moreover, the catalytic durability
3
O
4
ꢀMA.
3
O
4
3 4
O
−
1
−1
3,25ꢀ27
3
O
4
ꢀ
activity of Co
3
O
4
for CO oxidation.
The mechanism of CO
3
O
4
2
(1)
(2)
(3)
3
O
4
CO + O · X ↔ CO
2
· X
3
O
4
o
CO · X ↔ CO + X
2
2
of Co
the similar conditions (Fig. 4e). It is found that there is no decay of
CO conversion even after 20 h. Therefore, the two porous Co
catalysts, Co ꢀMA and Co ꢀDMA, prepared via oneꢀstep
3 4 3 4
O ꢀMA and Co O ꢀDMA was also evaluated at 180 C under
where “X” denotes the active site. The adsorption of oxygen occurs
at the active site (Eq. (1)) and the CO is oxidized by chemisorbed
and dissociated oxygen species (Eq. (2)). CO and surface O
molecules chemisorbs preferably at a surfaceꢀexposed Co site, and
then the CO is oxidized by surface oxygen resulting oxygen vacancy
3
O
4
3
O
4
3 4
O
26
2
pyrolysis of Coꢀbased metal-organic frameworks, exhibit good
3
+
cycling and longꢀterm stability of CO oxidation.
3
,27
subsequently.
Therefore, the active site is widely considered to
As the CO oxidation is always dependent on the redox properties
be the major factor of the catalytic activity in CO oxidation. In
addition, the chemisorbed oxygen and oxygen vacancies may also
be active for oxygen exchange and CO oxidation.
of catalysts, H
2
ꢀTPR analyses were performed to investigate the
follows
→ CoO → Co. Both of the reduction of
redox behavior. As shown in Fig. 4f, the reduction of Co
3
O
4
2
3
3 4
the following steps: Co O
As can be seen from above the results, both of the two catalysts
are with small BET surface areas, but exhibit excellent CO
oxidation performance. We predict that the BET surface area does
not play the leading role in CO oxidation in this study. Therefore,
the probable catalytic mechanisms should be further discussed. XPS
analysis was performed to investigate the chemical state of the
3 4 3 4
elements present in Co O ꢀMA and Co O ꢀDMA as well as to
3
+
understand the influence of the Co and oxygen components. As
shown in Fig. 5aꢀb, the sharp peaks at 780.1, 530.4, 284.9 eV
correspond to the characteristic peaks of Co 2p, O 1s, and C 1s,
Fig. 4 (a) CO conversion curves of Co
plots for the rate of CO oxidation over Co
Co -MA for CO conversion; (d) Cycling test of Co
conversion of Co
profiles of Co -MA and Co
3
O
4
-MA, Co
-MA and Co
-DMA for CO conversion; (e) CO
3
O
4
-DMA and Co
3 4
O -C; (b) Arrhenius
3 4
O
3 4
O -DMA; (c) Cycling test of
O
3 4
3 4
O
o
Fig. 5 XPS survey of wide scan for (a) Co -MA and (b) Co
3
O
4
3 4
O -DMA; XPS spectra of (c)
3 4
O
-MA and Co
3 4 2
O -DMA at 180 C with reaction time; (f) H -TPR
Co 2p and (d) O 1s in Co -MA and Co O -DMA.
3
O
4
3 4
3 4
O
3 4
O -DMA.
4
| J. Name., 2012, 00, 1-3
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3 4
Table 1 Results of curve fitting of Co 2p and O 1s XPS spectra of the different Co O
Acknowledgements
samples
This work was financially supported by Key Laboratory Open
Research Fund (No. 2016D03008), National Science Foundation of
China (No. 21661029, U1203292, 21161020, 21301146), Natural
Science Fund for Distinguished Young Scholars of Xinjiang Uygur
Autonomous Region (No. 2013711008) and Technological
Innovation Youth Training Project of Xinjiang Autonomous Region
Catalyst samples
Relative percentage (%)
3
+
2+
Co
a
b
c
C
Co
O
L
O
V
O
2
H O
Co
3
O
4
-MA
33.7
35.7
32.2
18.6
20.3
16.4
21.9
27.5
25.6
37.5
3 4
Co O -DMA
26.8
39.3
a
b
c
O
L
= lattice oxygen. O
V
= oxygen vacancies. O
C
= chemisorbed and dissociated
(
No. 2013721017).
oxygen.
Notes and references
respectively, indicating the existence of cobalt, oxygen, and carbon
3 4
elements in Co ꢀMA and Co O ꢀDMA. The Co 2p XPS spectra 1 A. Alvarez, S. Ivanova, M.A. Centeno, J.A. Odriozola, Appl. Catal. A: Gen., 2012,
3
O
4
profiles (Fig. 5c) are composed of two main peaks at about 780.9 eV 431ꢀ432, 9ꢀ17.
2
V.M. Rao, V. Shankar, J. Chem. Tech. Biotechnol., 1988, 42, 183ꢀ196.
and 796.5 eV, respectively, corresponding to the Co 2p1/2 and Co
2
+
3 X. Xie, Y. Li, Z.Q. Liu, M. Haruta, W. Shen, Nature, 2009, 458, 746ꢀ749.
2p
3/2 spinꢀorbit peaks of Co
3 4
O . The satellite shakeꢀups of Co are
4
5
K.K. Lee, W.S. Chin, C.H. Sow, J. Mater. Chem. A, 2014, 2, 17212ꢀ17248.
G. Ferey, Chem. Soc. Rev., 2008, 37, 191ꢀ214.
3
+
located at 781.3 and 796.6 eV, and satellite shakeꢀups of Co are
located at 779.9 and 795.0 eV. The relative percentage of the 6 J.L.C. Rowsell, O.M. Yaghi, Micropro. Mesopor. Mater., 2004, 73 (1ꢀ2), 3ꢀ14.
3
+
surfaceꢀexposed Co sites of Co
than that of Co ꢀDMA (26.8 %), as summarized in Table 1.
Unexpectedly, Co ꢀMA exhibits lower catalytic activity than
Co ꢀDMA in spite of the higher superficial fraction of the Co
3 4
O
ꢀMA is 33.7 %, which is higher 7 J. Liu, L. Chen, H. Cui, J. Zhang, L. Zhang, C.Y. Su, Chem Soc Rev., 2014, 43, 6011ꢀ
6
8
9
2
061.
3
O
4
W. Wang, Y. Li, R. Zhang, D. He, H. Liu, S. Liao, Catal. Commun., 2011, 12, 875ꢀ879.
Z. D. Tan, H. Y. Tan, X. Y. Shi, J. Zhuan, Y. F. Yan, Z. Yin, Inorg. Chem. Commun.,
015, 61, 128ꢀ131.
3
O
4
3
+
3
O
4
sites. So the components of oxygen might have effects on the 10 J. K. Sun, Q. Xu, Energy Environ. Sci., 2014, 7, 2071ꢀ2100.
catalytic reaction. Each asymmetric O 1s peak can be coherently 11 Y. Lu, W. Zhan, Y. He, Y. Wang, X. Kong, Q. Kuang, Z. Xie, L. Zheng, ACS Appl.
Mater. Inter., 2014, 6, 4186ꢀ4195.
L
fitted by four components, as shown in Fig. 5d. O component of O
1
2 K.J. Lee, T. H. Kim, T. K. Kim, J. H. Lee, H. K. Song, H. R. Moon, J. Mater. Chem.
A, 2014, 2, 14393ꢀ14400.
3 D.Y. Lee, S. J. Yoon, N. K. Shrestha, S. H. Lee, H. Ahn, S. H. Han, Micropor.
3 4
1s spectra centred at 530 ± 0.2 eV, is the lattice oxygen in the Co O
V
phase. O component, centred at 531 ± 0.1 eV, is oxygen vacancies
1
2
‑
which are associated with O ions in oxygenꢀdeficient regions Mesopor. Mater., 2012, 153, 163ꢀ165.
within the matrix of Co
and dissociated oxygen species (O
component, which is centred at around 532 ± 0.2 eV.
3
O
4
. O
C
is usually attributed to chemisorbed 14 J. Y. Ye, C. J. Liu, Chem. Comm, 2011, 47, 2167ꢀ2169.
−
2−
−
−
15 S. Zhang, H. Liu, C. Sun, P. Liu, L. Li, Z. Yang, X. Feng, F. Huo, X. Lu, J. Mater.
2
, O , or O ) and OH
2
8, 29
Chem. A, 2015, 3, 5294ꢀ5298.
The peaks
1
1
6 Y. H. Qin, L. Huang, D. L. Zhang, L. G. Sun, Inorg Chem Commun, 2016, 66, 64ꢀ68.
7 N. Yan, Q. Chen, F. Wang, Y. Wang, H. Zhong, L. Hu, J. Mater. Chem. A, 2013, 1,
at around 533 ± 0.2 eV are usually attributed to adsorbed water.
Owing to lower binding energy of O in Co
in Co ꢀDMA become more labile than that in Co
this might be responsible for the easier generation of O
L
3 4
O ꢀDMA (Fig. 5d), the 637ꢀ643.
O
L
3
O
4
3
O
4
ꢀMA, and 18 X. Wang, W. Zhong, Y. Li, Catal. Sci. Technol., 2015, 5, 1014ꢀ1020.
9 H. Pang, F. Gao, Q. Chen, R. Liu, Q. Lu, Dalton. Trans, 2012, 41, 5862ꢀ5868.
20 K. L. Hu, M. Kurmoo, Z. M. Wang, S. Gao, Chem.- A Eur. J., 2009, 15, 12050ꢀ
1
V
in the
in Co
ꢀMA (Fig. 5d), and this might
molecules more easily adsorbed or desorbed in O
3
0
Co
DMA is lower than that in Co
cause O
resulting in more active for CO oxidation of Co
relative percentage of O in Co ꢀDMA (27.5%) is higher than that
in Co ꢀMA (21.9%), as shown in Table 1, also suggesting that
Co
one could conclude that the synergy of O
major possibility responsible for the high activity in CO oxidation of
Co
3
O
4
ꢀDMA. Furthermore, the binding energy of O
V
3 4
O ꢀ
1
2
2064.
3 4
O
1 Z. M. Wang, B. Zhang, T. Otsuka, K. Inoue, H. Kobayashi, M. Kurmoo, Dalton.
2
V
sites, Trans., 2004, 2209ꢀ2216.
3
1
3
O
4
ꢀDMA. The 22 Z. M. Wang, K. L. Hu, S. Gao, H. Kobayashi, Adv Mater, 2010, 22, 1526ꢀ1533.
2
4
3 B. Meng, Z. Zhao, X. Wang, J. Liang, J. Qiu, Appl. Catal. B: Environ., 2013, 129,
C
3 4
O
91ꢀ500.
3
O
4
2
4 J. Luo, M. Meng, X. Li, X. Li, Y. Zha, T. Hu, Y. Xie, J. Zhang, J. Catal., 2008, 254,
O
4
ꢀDMA exhibit more active catalytic performance. In this work, 310ꢀ324.
3
3
+
2
5 F. Wang, X. Wang, D. Liu, J. Zhen, J. Li, Y. Wang, H. Zhang, ACS Appl. Mater.
V
C
, O and Co sites is the
Inter., 2014, 6, 22216ꢀ22223.
2
2
2
6 H. Zhang, X. Hu, Sep. Purif. Technol., 2004, 34, 105ꢀ108.
7 Y. B. Yu, T. Takei, H. Ohashi, H. He, X. L. Zhang and M. Haruta, J. Catal., 2009,
67, 121ꢀ128.
3
4
O .
4
. Conclusion
In summary, we have demonstrated a novel method which employs
metalꢀformate frameworks as precursors to prepare Co catalysts.
Asꢀsynthesized Co ꢀMA and Co
28 Z. Wu, R. Jin, Y. Liu, H. Wang, Catal. Commun. 2008, 9, 2217ꢀ2220.
2
3
1
9 M. Kang, E. D. Park, J. M. Kim, J. E. Yie, Appl. Catal. A: Gen., 2007, 327, 261ꢀ269.
0 P. Sudarsanam, B. Mallesham, D. N. Durgasri, B.M. Reddy, RSC Advances, 2014, 4,
1322ꢀ11330.
3
O
4
3
O
4
3 4
O
ꢀDMA with porous structures 31 W. Song, A.S. Poyraz, Y. Meng, Z. Ren, S.ꢀY. Chen, S.L. Suib, Chem. Mater.,
014,26, 4629ꢀ4639.
2
in cubic shape exhibit high activities in CO oxidation, thus display
potential applications in the environmental protection. More
importantly, the present work shows that pyrolysis of metalꢀformate
frameworks is an effective and mild synthetic approaches to
fabricate transition metal oxides with novel morphology and
structure. The synthetic strategy can also be extended to synthesize
polymetallic oxides with various mesostructures, which might
possess better catalytic performance than single metal.
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