HIGH-TEMPERATURE INSITU RAMAN-SPECTROSCOPY OF WORKING OXIDATIVE COUPLING CATALYSTS

Oxidative coupling of methane is an important route to formation of ethane and ethylene. The reaction is catalyzed by a broad range of basic oxides, including lanthanum oxides, that are modified with group IA or group IIA ions. - Laser Raman spectroscopy has been used to characterize surface peroxide structures on La2O3 and Na- and Sr-modified La2O3. These surface peroxide groups are formed on these catalysts by calcination in O2 at temperatures between 500-degrees-C and 800-degrees-C. By high temperature in situ Raman spectroscopy it was possible to follow the formation of these surface peroxides and their reaction with methane. Changes in the structure and concentration of peroxide groups on the surface of the working catalysts were investigated at elevated temperatures as high as 800-degrees-C by varying the partial pressures of the reactant gases. The results provide evidence for the role of peroxide ions for the activation of methane during the oxidative coupling reaction.