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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−x Sr x FeO 3−δ (x = 0, 0.2, and 0.5) and La 0.5 Sr 0.5 Fe 1−x Co x O 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 ABO 3 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.

LaFeO 3 perovskites were prepared by solution combustion method using Dextro D-(-) Levo-(þ) tartaric acid as a complexing agent. Characterization by different techniques such as X-ray diffraction, Brunauer-Emmett-Teller surface area, and scanning electron microscopy revealed relatively small crystals of perovskites. A relatively high capacity of reversible oxygen storage (3 mmol/gcat) of LaFeO 3 has been evidenced. High activity and high selectivity to synthesis gas make LaFeO 3 attractive as a catalyst and oxygen carrier for methane partial oxidation by the chemical looping process. The study of the reaction rate as function of oxygen site coverage reveals a kinetic relevant step in methane partial oxidation involving a pair of surface oxygen and oxygen vacancy. Removal of lattice oxygen generated vacancy sites which increase the reaction rate at relatively high oxygen concentrations, while the availability of surface oxygen determines the reaction rate at relatively low surface oxygen concentrations. The surface adsorbed oxygen is highly active to complete combustion while the lattice oxygen is very selective to synthesis gas.