Surface composition and catalytic activity of La-Fe mixed oxides for methane oxidation

Abstract Four La-Fe oxide samples with La/Fe atomic ratio y = 1.02 ∼ 0.68 (denoted as LayFe) were prepared by the citrate method. The samples had a decreased specific surface area with the La/Fe atomic ratio decreasing. XRD pattern proved that the sample La0.94Fe is single phase perovskite La0.94FeO3−d. Phase composition of the samples was estimated by the Rietveld refinement method. XPS analyses indicate that La3+ ions are enriched on surface of crystallites for all the samples, and surface carbonate ions are relatively abundant on the samples La1.02Fe and La0.94Fe. Catalytic activity for methane oxidation per unit surface area of the samples is in the order of La0.68Fe > La0.76Fe > La0.94Fe > La1.02Fe both in the presence and in the absence of gaseous oxygen. A reason for this order would be the higher concentration of Fe3+ ion on the surface of the samples La0.68Fe and La0.76Fe.