Catalyst activity of alumina–galia aerogels for selective reduction of NOx

Alumina gels are known to be good catalysts for the selective reduction of NOx using hydrocarbon under an oxidizing atmosphere. The effects of galia-addition on the microstructure and catalytic activity of alumina aerogels were investigated. Aerogels containing 0–66 wt% Ga2O3 were prepared by hydrolyzing Al(sec-C4H9O)3 (ASB) in an ethanol solution, adding Ga(NO3)3 dissolved in H2O, followed by supercritical drying. The catalytic activity of aerogel catalysts containing 38–51 wt% Ga2O3 was higher than pure alumina at low temperatures, 450–550°C, but decreased when the Ga2O3 content was 66 wt%. The amount of desorbed NH3, which is related to the catalytic activity, increased with increasing Ga2O3 content, but the fraction of mesopores, 20–30 nm in diameter, decreased when Ga2O3 content >60 wt%. These results show that changes in the gel microstructure caused by Ga2O3 addiction affect the catalytic activity.