Alumina gels are known to be good catalysts for the selective reduction of
NO, using hydrocarbon under an oxidizing atmosphere. The effects of galia-a
ddition on the microstructure and catalytic activity of alumina aerogels we
re investigated. Aerogels containing 0-66 wt% Ga2O3 were prepared by hydrol
yzing Al(sec-C4H9O)(3) (ASB) in an ethanol solution, adding Ga(NO3)(3) diss
olved in H2O, followed by supercritical drying. The catalytic activity of a
erogel catalysts containing 38-51 wt% Ga2O3 was higher than pure alumina at
low temperatures, 450-550 degreesC, but decreased when the Ga2O3 content w
as 66 wt%. The amount of desorbed NH3, which is related to the catalytic ac
tivity, increased with increasing Ga2O3 content, but the fraction of mesopo
res, 20-30 nm in diameter, decreased when Ga2O3 content > 60 wt%. These res
ults show that changes in the gel microstructure caused by Ga2O3 addiction
affect the catalytic activity. (C) 2001 Elsevier Science B.V. All rights re
served.