154
T. Li et al. / Applied Catalysis A: General 398 (2011) 150–154
H+
4. Conclusion
MN+
CH3
H
MN+
CH3
+
Over the catalyst system of nano-gold (Au/SiO2) and IL, the pro-
cess of methane to methanol was investigated. The results showed
that IL acted as a dissolution medium for the nano-Au/SiO2, while
in the meantime played a key role in promoting the reactivity
of gold, and rendered a reaction with high selectivity. The sys-
tem of nano-Au/SiO2 and IL could be recycled, and conversion
of methane in the recycled system still remained at a high level.
This process of methane oxidation did not use concentrated sul-
furic acid and heavy-metal catalysts, thus we can eliminate the
impacts on the environment. A reaction mechanism was pro-
posed, which indicated that molecular oxygen was consumed in
the oxidation–reduction cycle. Consequently, methane oxidation
to methanol can be achieved as a green chemical process. The sys-
tem can also be used in other green chemical processes of liquid
phase or gas phase oxidation.
Nu: -
OX
M(N-2)+
CH3
+
N
Fig. 6. The mechanism of electrophilic substitution.
2Au+/IL + 2KHSO4
CF3COOCH3
2H+ +2e-
2Au/IL + 2H+ + K2S2O8
CH4 + CF3COOH
2Au+/IL + 2e-
1
2
+
3
2Au/IL
Fig. 7. Mechanism of methane oxidation over nano-gold catalysts in ionic liquid.
Acknowledgement
catalyst system (nano-gold and ionic liquid) not only can meet
the requirements of green chemistry, but can also lower operation
costs, save resources, and reduce waste emissions. Therefore, it is
an environmentally friendly process.
We acknowledge support from the State Key Projects for Basic
Research & Development, China, through Grant No. 2005CB221406.
We thank X. Hou and Dr. L.G. Wei for supporting.
Appendix A. Supplementary data
3.5. Discussion on reaction mechanism
Supplementary data associated with this article can be found, in
Methane can be activated and oxidized by means of three
modes: (1) via formation of a methyl radical, (2) via oxidative addi-
tion, (3) via electrophilic substitution. Presently, the mechanism
of electrophilic substitution is widely accepted, which is shown in
Fig. 6.
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