Alumina aerogel catalysts prepared by two supercritical drying methods used in methane combustion

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Abstract
Palladium-supported alumina aerogels were prepared by two different supercritical drying methods. In one method, an alumina wet gel was dried under supercritical conditions of ethanol in an autoclave. In the other, the aerogel was supercritically dried by extracting ethanol using carbon dioxide in an extractor. The Pd-supported alumina aerogel prepared in the autoclave exhibited a high specific surface area of 112.8 m2/g after firing at 1200 °C for 5 h, while the other had a specific surface area of only 5.2 m2/g due to α-alumina transformation. Their catalytic properties for methane combustion were measured. The Pd-supported alumina aerogel prepared in the autoclave combusts methane perfectly at 50–60 °C lower temperature than the other. Palladium particles on the alumina aerogel prepared in the autoclave contained palladium oxide, while those prepared in the CO2 extractor contained only palladium metal.