10.1002/cctc.201601298
ChemCatChem
COMMUNICATION
In fact, although the ratio of adsorbed oxygen to lattice oxygen
on the surface of PdO-Co3O4 is the lowest among the four
catalysts (Table 1), sufficient superoxide species formed in the
reaction process on PdO-Co3O4 catalyst, revealed by the DRIFT
spectra, mainly contribute to an enhancement of reactivity.
more superoxide species and more oxygen vacancies on PdO-
Co3O4 could therefore bright about the exceptional activity for
methane oxidation.
Finally, the heterogeneous structure of PdO-Co3O4 catalyst
possesses large surface area, which might partially or not
straightforwardly account for the better activity than PdO/Co3O4
catalysts with relative small surface area (Figure 7).
517
562
B
CH4
A
354
778
243
510
CH4
451
190
95
0.8
A
B
CO2
H2O
0.4
0.4
Co3O4
Co3O4
CO2
H2O
140
70
0.2
1.0
PdO/Co3O4-Im
PdO/Co O -Re
PdO/Co3O4-Im
CO
H2
CO
H2
250
125
190
0.5
0.6
0.3
0.0
3
4
PdO/Co3O4-Re
PdO-Co3O4
95
0
PdO-Co3O4
200
400
600
800
200
400
600
800
Temperature (oC)
Temperature (oC)
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Relative Pressure (P/Po)
0
10
20
30
40
50
60
Pore Diameter (nm)
C
D
CH4
419
269
CH4
434
602
676
Figure 7. (A) N2 adsorption–desorption isotherms and (B) pore-size
distributions of PdO-Co3O4, PdO/Co3O4-Re, PdO/Co3O4-Im, and Co3O4
nanorods.
CO2
CO2
H2O
H2O
CO
CO
H2
H2
In summary, heterostructured PdO-Co3O4 nanorods have
been fabricated via the recrystallization process with the help of
ethylene glycol and exhibit a superior catalytic activity at low
temperature and thermal stability at high temperature to the
traditional Pd-based catalysts for methane oxidation. The
improved catalytic performance of PdO-Co3O4 catalysts is
attributed to the intimate contact of PdO and Co3O4 domains, the
formation of adequate superoxide species during the oxidation
process, and the strong redox property. Activity control catalytic
reaction and sintering resistant of catalysts by functionalizing the
two composition of catalyst should open an avenue towards the
design of advanced heterogeneous nanomaterials for small
molecule activation.
200
400
600
800
200
400
600
800
Temperature (oC)
Temperature (oC)
Figure 6. CH4-TPR profiles of (A) PdO-Co3O4 nanorods, (B) PdO/Co3O4-Re
nanorods, (C) PdO/Co3O4-Im nanorods, and (D) Co3O4 nanorods.
Besides, PdO-Co3O4 nanorods show
a strong redox
property in contrast with reference PdO/Co3O4 and Co3O4
nanorods, which could be proved by methane temperature
programmed reduction (TPR). Figure 6 shows the CH4-TPR
profiles of catalysts obtained by monitoring the formation of CO2,
CO, H2 and H2O, and the consumption of methane. For PdO-
Co3O4 nanorods (Figure 7A), the first band centered at 243 oC is
attributed to the reaction process of the PdO with CH4 from the
reduction of Pd2+ to Pd0, which can be deduced from the
species change of Pd 3d XPS (Figure S6). The broad band at
Acknowledgements
o
451 C is associated with the reaction of Co3O4 with CH4 from
We thank Dr. Andrew Haslett from ETI and Prof. Graham J.
Hutchings from Cardiff University for helpful discussions. We are
grateful for financial support by National Natural Science
Foundation of China (21273151), China ministry of science and
technology (2016YFA0202802) and Energy Technologies
Institute LLP.
the reduction of Co3+ to Co2+, which is obtained from the Co3+ to
Co2+ change of Co 2p XPS (Figure S6). It is noted that the
o
consumption peak near 517 C overlapped by the strong one at
562 C corresponds to the formation of CO2, H2O, CO, and H2,
o
which is related to reaction of CoO with CH4 from Co2+ to Co0
and the reforming of CH4 under the catalysis of Co0 or Pd0
species.[4c] The strong band at 562 oC is attributed to the
creaking of CH4 to produce H2. For two PdO/Co3O4 catalysts in
Figure 7B-C, the reduction bands of Co3+ to Co2+ shift to 354 and
Keywords: one-dimensional structure • heterostructured
catalyst • PdO-Co3O4 •methane oxidation • activity and stability
269 C, and the ones of Co2+ to Co0 move toward 510 and 434
o
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