ON THE PECULIARITIES OF REOXIDATION BY CARBON-DIOXIDE OF CATALYSTS WITH VARYING COMPOSITIONS IN THE METHANE OXIDATIVE COUPLING REACTION

Catalytic properties of the La-Cu-O and La-Na-Mn-O systems reoxidized by carbon dioxide and oxygen were studied in the methane oxidative coupling reaction under non-steady-state conditions. Reoxidation of the La-Cu-O composition by carbon dioxide is accompanied by the reduction of CO2 to CO. In the course of the reaction, bulk-to-surface oxygen diffusion occurs, which results in a sharp increase in the total oxidation rate and in the poisoning of sites responsible for oxidative coupling. The presence of CO2 is found to have an effect on catalyst reoxidation by oxygen. In the La-Na-Mn-O system exhibiting high selectivity to C-2-hydrocarbon production (70 - 100%), oxygen diffusion is observed only after deep reduction and prolonged ''relaxation'' of the catalyst in an inert atmosphere. During the reoxidation of this catalyst by carbon dioxide, the formation of carbonate fragments stable at high temperatures occurs. They decompose to yield C-2-hydrocarbons and CO2 under the catalytic reaction conditions.