Preparation of La 2 Zr 2 O 7 composite oxides with fluorite/pyrochlore phases by excluding element influences for catalyzing oxidative coupling of methane.

To elucidate the effect of the ABO phase on the oxidative coupling of methane (OCM) while excluding elemental influences, LaZrO compounds with a disordered defect fluorite (LaZrO-F) structure and an ordered pyrochlore phase (LaZrO-P) have been synthesized. Irrespective of their element composition, the catalytic performance of LaZrO-F exceeds that of LaZrO-P. Furthermore, the LaZrO-F surface has more oxygen vacancies/defects than the LaZrO surface because LaZrO-F exhibits a higher lattice disorder degree and lower B-O bond strength, which leads to the formation of more reactive oxygen anions (O and O) and basic sites for OCM. Isotopic exchange results have testified that surface-active oxygen sites are generated due to the gaseous O adsorption/activation occurring on the surface vacancies both simple and multiple hetero-exchange mechanisms. In conclusion, crystal structure is the primary factor that governs the catalytic performance of ABO compounds, with the disordered defect fluorite phase being the most optimal structure for OCM.