Studies of High-temperature Catalytic Combustion over Mixed Metal Oxide Catalysts

Abstract

Catalytic combustion of methane was performed over monolithic honeycomb catalysts composed of mixed metal oxides. Since perovskite catalysts were significantly deactivated due to sintering into agglomerates and reaction with cordierite at high temperature (Figs.5 and 6), the complete combustion was not achieved at a high flow rate. In contrast, a single phase honeycomb composed of Mn-substituted hexaaluminate was successfully demonstrated for the high-efficiency catalytic combustion (Fig.4). The temperature of the catalyst bed was constantly maintained at 1200°C during the operation. Manganese-substituted hexaaluminate had excellent heat resistance in maintaining the large surface area over 20 m²/g after calcination at 1300°C. The large surface area was very effective in stabilizing and promoting the fuel-lean homogeneous combustion which occurs in a catalyst bed. It also became evident that the formation of thermal NO^x in the combustion process is greatly suppressed by the use of the Mn-substituted hexaaluminate catalysts (Fig.7).