Acta Phys. -Chim. Sin. ›› 1993, Vol. 9 ›› Issue (06): 746-751.doi: 10.3866/PKU.WHXB19930606

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The Study of Adsorbed Oxygen Species on the Surface of a Series of Na2SnO3 Catalysts by epr Experiments

Luo Xiao-Ming; Han Qiao-Feng; Chen Yi; Han Shi-Ying; Jin Tong-Zheng; Sui Yun-Xia   

  1. Chemistry Department, Nanjing University, Nanjing 210008; Centre of Materials Analysis, Nanjing University, Nanjing 210008
  • Received:1992-05-15 Revised:1992-07-27 Published:1993-12-15
  • Contact: Luo Xiao-Ming

Abstract: According to the results of investigation in a series of Na_2SnO_3 catalysts for oxidative coupling of methane, a sample (5 mol%Li_2 SO_4-Na_2SnO_3) with good catalytic properties was selected as the main research object. By using electron paramagentic resonance(EPR) method, the form of surface adsorbed oxygen has been investigated. The EPR results confirm that a signal with g value of 2.013 is from the species of surface adsorbed oxygen, and that it can be assigned to adsorbed superoxide species O_2~-. At 300 ℃ or the above this type of oxygen species can form on that catalyst sample.
The species O_2~- is stable under conditions of room temperature and vacuum of 1.33×10~(-2) Pa. But at 700 ℃ the reaction between O_2~- and CH_4 occured, and at the same time the intensity of O_2~- signal considerably decreased. The resuls show that the surface species O_2~- might play an important role in activating CH_4 molecules in the oxidative coupling reaction of methane.

Key words: Superoxide ion, Oxidative coupling of methane, Na2SnO3