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

Abstract Alumina gels are known to be good catalysts for the selective reduction of NO x 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% Ga 2 O 3 were prepared by hydrolyzing Al( sec -C 4 H 9 O) 3 (ASB) in an ethanol solution, adding Ga(NO 3 ) 3 dissolved in H 2 O, followed by supercritical drying. The catalytic activity of aerogel catalysts containing 38–51 wt% Ga 2 O 3 was higher than pure alumina at low temperatures, 450–550°C, but decreased when the Ga 2 O 3 content was 66 wt%. The amount of desorbed NH 3 , which is related to the catalytic activity, increased with increasing Ga 2 O 3 content, but the fraction of mesopores, 20–30 nm in diameter, decreased when Ga 2 O 3 content >60 wt%. These results show that changes in the gel microstructure caused by Ga 2 O 3 addiction affect the catalytic activity.