Thermally stable alumina–gallia aerogel as a catalyst for NO reduction with C3H6 in the presence of excess oxygen

Abstract

In order to improve thermal stability, an alumina–gallia aerogel was prepared and the catalyst performance for NO reduction with C₃H₆ was compared with that of an alumina–gallia xerogel. Basically, both were prepared by a sol–gel method with supercritical drying for the former, while with oven drying for the latter. Upon heating at 800, 900, and 1000 °C, the aerogel exhibited higher NO conversion than the xerogel at reaction temperature <400 °C, while NO conversion was lower on the former than on the latter at >500 °C. At 450 °C, NO conversion was almost the same for these two catalysts. A marked difference was observed upon heating them at 1100 °C: the aerogel still maintained quite a high activity, while the xerogel greatly lost it. After heating the aerogel at 1100 °C, γ-phase alumina remained untransformed with its surface area of 80 m²/g, while the xerogel was completely transformed to α-alumina with its surface area of 6 m²/g. The high activity remaining on the aerogel heated at 1100 °C was ascribed to its large surface area.