The effect of the calcination temperature of LaFeO3 precursors on the properties and catalytic activity of perovskite in methane oxidation

In the synthesis of perovskite-type LaFeO3 oxides iron and lanthanum nitrates were used as a precursors. The nitrates were dissolved in water, evaporated, crushed and calcined in temperature range of 650-850 degrees C. The obtained perovskites were applied as an active layer on monolithic catalysts for the oxidation of methane. The increase in the calcination temperature of the perovskite precursors from 650 degrees to 850 degrees C results in a reduction in the surface area of the powders from 10.1 to 4.2 m(2)/g. XRD studies revealed that calcination at 800-850 degrees C caused the formation of an almost homogeneous LaFeO3 perovskite phase. A decrease in the La/Fe surface ratio from 12 to 5.2 with the rise in calcination temperature from 650 degrees to 800 degrees C was detected by XPS. EDX results confirmed that at 750-850 degrees C, the La/Fe ratio in the perovskite layer is close to the stoichiometric and amount to 1.01-1.03. The highest activity in methane oxidation was achieved when the LaFeO3 perovskite was calcined at 700 degrees C. A further slight increase in the activity was noticed after H-2 treatment. As the calcination temperature of the perovskites is increased, the catalyst activity decreases due to a reduction in the specific surface area, despite the more complete LaFeO3 perovskite phase formation.