La, Ca and Fe oxide perovskites: preparation, characterization and catalytic properties for methane combustion

La1−xCaxFeO3 (x=0.1, 0.2, 0.3, 0.4, 0.5) perovskites prepared by citrate method and calcined at 1073 K have been investigated as catalysts for methane combustion. The formation of the perovskite structure has been shown by X-ray diffraction (XRD) for all samples. The surface area (SA) values are in the range 3–6 m2 g−1 for the samples up to x=0.4, whereas SA is 0.7 m2 g−1 for the specimen with x=0.5. The atomic susceptibility increases with increasing in Ca content. The Fe4+/Fetotal ratio has been determined by both redox titration and TPR analysis. The amount of Fe4+ enhances with Ca substitution but the Fe4+/Ca2+ ratio is quite constant giving rise to an increasing formation of oxygen vacancies to preserve charge neutrality. All perovskites show a similar intrinsic activity in CH4 combustion with activation energy, Ea, of about 23 kcal mol−1. A slightly lower value of Ea is shown by LaFeO3 which, in contrast with Ca substituted samples, exhibits a small cationic defectivity. Methane reaction order lower than one was found for all catalysts.