Effects of Oxygen Mobility in La–Fe-Based Perovskites on the Catalytic Activity and Selectivity of Methane Oxidation

The mechanism and structure requirements of selective and total oxidation of methane in a chemical looping process are both experimentally and theoretically examined on La_1–xSr_xFeO_3−δ (x = 0, 0.2, and 0.5) and La_0.5Sr_0.5Fe_1–xCo_xO_3−δ (x = 0.5 and 1) perovskites. The oxygen mobility in the perovskites described by the formation energy of oxygen vacancy is found to have a pronounced effect on the catalytic activity and selectivity. In particular, the selectivity is controlled largely by the surface oxygen concentration or the oxygen vacancy concentration on perovskites, which depends strongly on the bulk oxygen concentration and the relative rate of the lattice oxygen diffusion with respect to the surface reaction. The substitution of Sr for La at the A site and the substitution of Co for Fe at the B site of the ABO₃ perovskites dramatically increase the oxygen mobility. A higher oxygen diffusion rate, and hence enrichment of oxygen on the surface, would improve the catalyst selectivity toward total oxidation.