SrFeO3-δ perovskite oxides:: Chemical features and performance for methane combustion

Oxygen-deficient SrFeO3-delta (0.02 < delta < 0.26) perovskites were prepared by soft-chemistry procedures, followed by annealing under different conditions, including high oxygen pressure. These materials contain Fe cations in the mixed Fe3--Fe4+ valence state. The samples were characterized by X-ray and neutron powder diffraction, thermal analysis under reducing conditions, temperature-programmed reduction and desorption, specific surface area measurements, and XPS. The most deficient oxide, SrFeO2.74, shows a complex neutron diffraction diagram corresponding to a superstructure of perovskite in which half of the Fe cations are pentacoordinated to oxide anions in a pyramidal configuration. By contrast, the other half are octahedrally coordinated. The materials were tested as catalysts for methane oxidation. At moderate temperatures, a significantly higher catalytic activity was observed for the most oxygen-deficient sample, which is consistent with the oxygen desorption ability exhibited by this material, containing a large number of oxygen vacancies in its crystal structure.