THE STUDY OF ADSORBED OXYGEN SPECIES ON THE SURFACE OF A SERIES OF Na2SnO3 CATALYSTS BY EPR EXPERIMENTS

According to the results of investigation in a series of Na2SnO3 catalysts for oxidative coupling of methane, a sample (5mol%Li-2 SO (4)-Na2SnO3) 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 0(2)(-). At 300 degrees C 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 1.33x10(-2) Pa. But at 700 degrees C the reaction between O-2(-) and CH4 occured, and at the same time the intensity of O-2(-) signal considerably decreased. The results show that the surface species o(2)(-) might play an important role in activating CH4 molecules in the oxidative coupling reaction of methane.