Preparation and catalytic activity for methane oxidation of perovskite-type La(0.8)Sr(0.2)MO(3) (M=Co, Mn) with high surface area

Perovskite-type La(0.8)Sr(0.2)MO(3) (M = Co, Mn) compounds were prepared by malic acid-aided (MAL) and reverse homogeneous precipitation (RHP) methods and their catalytic activities for the total oxidation of methane were examined. Monophasic perovskites could be prepared by both methods at 823 K, which was lower by 300 K than the conventional nitrate decomposition (NIT) method. The lowering of the calcination temperature resulted in an increase in specific surface area. It appears that precursors with homogeneously dispersed constituent metal cations are formed by complexing metal cations with malic acid in the MAL method or by rapid and homogeneous precipitation as metal hydroxides in the RHP method, and therefore the formation of the perovskite phase at lower temperatures is facilitated. High surface-area oxides prepared by the MAL and RHP methods showed higher catalytic activity for methane oxidation than oxides prepared by the NIT method, though promotion of weight-normalized activity by the increased surface area was more prominent in La0.8Sr0.2MnO3 than in La0.8Sr0.2CoO3. These results clearly indicate that MAL and RHP methods are very useful for preparing highly active perovskite catalysts.