Mechanistic study of oxidative coupling of methane over Mn2O3Na2WO4SiO2 catalyst》.pdfVIP

ELSEVIER Applied Catalysis A: General 124 ( 1995) 9-18 Mechanistic study of oxidative coupling of methane over Mn,O,-Na2W0,/ SiOz catalyst Jingang Wu, Shuben Li *, Jianzhong Niu, Xueping Fang State Key Laboratory of 0x0 Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences. Lanzhou 730000, People’s Republic of China Received 6 April 1994; revised 5 August 1994; accepted 19 September 1994 Abstract EPR and Raman spectroscopies have been used to characterize the active oxygen species on Mn#- Na2W04/Si02 catalyst. The results show that the lattice oxygen 02- ISresponsible for the activation of methane. F-centers with an EPR parameter g = 2.0046 form when gas-phase oxygen is admitted at room temperature onto the catalyst reduced with methane at 800°C. Molecular oxygen plays an inducing role in the two-electrons transfer from W4+ to the oxygen ion vacancy which is produced by methane reduction. The EPR peak at g = 2.0046 disappears with increasing temperature. Raman spectra give further information about the production of 02- from molecular oxygen. For the catalyst reduced with methane, no Raman lines are observed, because the top W-O bonds are broken by the reduction, W-O-Si species are slightly ionic, and they are Raman inactive. When the temperature is increased to 80°C in the presence of gas-phase oxygen, Raman lines are obtained which are the same as those of the catalyst before reduction. N