Comparing BaZrO3 Perovskite and La2Zr2O7 Pyrochlore for Oxidative Coupling of Methane (OCM): The Importance of Basic Sites vs Oxygen Vacancies.

La2Zr2O7 pyrochlore with intrinsic oxygen vacancies and BaZrO3 perovskite without intrinsic oxygen vacancies were synthesized for the OCM reaction. It has been revealed that the OCM performance and surface selective oxygen species of BaZrO3 are higher than that of La2Zr2O7 under the reaction condition. This is because BaZrO3 possesses more basic sites than La2Zr2O7, and thus it can stabilize the OCM reactive oxygen species better at elevated temperature. In the structure, the A-O bond lattice oxygen of the two compounds mainly provides basic sites, but the B-O bond lattice oxygen mainly promotes deep oxidation of methane and the generated hydrocarbons. The types of the OCM reactive oxygen species are prone to be associated with the properties of the A-site metal oxides.