Metallic monolith supported LaMnO3 perovskite-based catalysts in methane combustion

Metallic monolith supported LaMnO3 perovskite-based catalysts are characterized by a high activity in methane combustion (95.5% conversion at 745 degrees C) and by a high thermal resistance. The activity of the catalysts depends on the duration and temperature of LaMnO3 calcination. The same relation holds for the chemical composition of the catalyst surfaces when they are determined by the XPS method. The shortening of the time of LaMnO3 perovskite calcination from 12.5 h to 8 h (700 degrees C) reduces the conversion of methane over a fresh catalyst. This is attributable to the lower amount of manganese (Mn:La=0.48) on the surface of this catalyst compared to the catalyst whose perovskite was calcined for 12.5 h (Mn:La=1.8). The extension of calcination time from 8 h to 12.5 h (at 700 degrees C) brings about a decrease in the specific surface area (SSA) from about 13.7 m(2)/g to 9.4 m(2)/g. After approximately 6 h on stream, the activities of the two catalysts become comparable. Aging of the catalyst with an LaMnO3 active layer at 920 degrees C for 24 h reduces methane combustion to 82.5% (at 745 degrees C). The aging process changes the catalyst surface, where Al and C content increases and the Mn:La ratio decreases. The activity of the monolithic LaMnO3 catalyst rises with the increase in the amount of the active layer from 11.5% to 17.8%. Methane conversion is greater over catalysts with an LaMnO3 than with an LaCoO3 active layer, but the LaMnO3 catalysts show a lower resistance to thermal shocks.