Catalyst activity of alumina-galia aerogels for selective reduction of NO_x

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% 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.