Oxide aerogel catalysts

Aerogels and xerogels of TiO₂, V₂O₅, ZrO₂, and Al₂O₃ with and without additives were prepared by hydrolysis of metal alkoxide. The aerogels and the xerogels were obtained by supercritical drying of the wet gels in ethanol and by drying at 90°C for 24 h in air. Catalyst activity of the gels for NO reduction with C₃H₆ were determined at 200-600°C in a fixed bed flow reactor. The highest NO conversion to N₂ was obtained with Al₂O₃ aerogel catalysts, about 80% at 500°C. Al₂O₃-ZrO₂ and ZrO₂ have higher activities at lower temperatures. TiO₂ and V₂O₅ have low activities although they have high oxidation activities. Catalyst activity of aerogels is higher than that of xerogels because of the higher effective diffusivity of reaction gas attributed to the high porosity and larger pore size.