Comparing BaZrO 3 Perovskite and La 2 Zr 2 O 7 Pyrochlore for Oxidative Coupling of Methane (OCM): The Importance of Basic Sites vs Oxygen Vacancies.

La 2 Zr 2 O 7 pyrochlore with intrinsic oxygen vacancies and BaZrO 3 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 BaZrO 3 are higher than that of La 2 Zr 2 O 7 under the reaction condition. This is because BaZrO 3 possesses more basic sites than La 2 Zr 2 O 7 , 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.