Double perovskite oxides A2FeMoO6-δ (A = Ca, Sr and Ba) as catalysts for methane combustion

Double perovskites of composition A(2)FeMoO(6-delta) (A, alkali earths) have been prepared by soft-chemistry procedures, followed by annealing under reducing conditions (H-2/N-2 flow). These materials are half metallic ferromagnets, well known for their colossal magnetoresistance properties. The samples have been characterized by X-ray diffraction; temperature-programmed oxidation, specific surface measurements and XPS. The Sr compound, of tetragonal symmetry, exhibits a significant amount of oxygen vacancies, as assessed by TPO. The materials have been tested as catalysts for methane oxidation. At moderate temperatures, a significantly higher catalytic activity is observed for the Sr double perovskite, for which a 80% of conversion is reached at 800 K; by contrast the Ca and Ba materials are found to display much poorer characteristics, hardly achieving 50% of conversion rate at 1000 K. The much superior characteristics of Sr2FeMoO6-delta are believed to be related to the presence of oxygen vacancies in the crystal structure. (C) 2004 Elsevier B.V. All rights reserved.