THE ROLE OF THE DEFECT STRUCTURE OF OXIDE CATALYSTS FOR THE OXIDATIVE COUPLING OF METHANE - THE ACTIVATION OF THE OXIDANT

Based on analysis of the catalytic properties and defect structure of oxide catalysts, the new systematization of catalysts for the oxidative coupling of methane (OCM) reaction has been proposed. The oxygen defects (anion vacancies for SrO and Li/Bi2O3 (0.1 at.%)) and impurity defects (transition metal ions for Li/CaO, Na/CaO) was proposed to play the important role for the process of N2O activation in OCM. The addition of O-2 in CH4-N2O reaction mixture decreased the rate of N2O decomposition over SrO and Li/Bi2O3, while for M/CaO catalysts such effect was not observed. It was explained by the fact that the activation of O-2 and N2O in OCM process occurs on the same centres for the first group of catalysts and different centres for the second group of catalysts. Two temperature ranges of proceeding of OCM reaction over SrO was established. The mechanism in which CO2 is a poison for active oxygen species was proposed.