Studies on active species for selective catalytic reduction of NO on alumina-supported cobalt oxide catalysts

Alumina-supported cobalt oxide catalysts were prepared by three different methods: The impregnation and sol/gel methods using either an acid or a base as a precipitant. The catalysts prepared by sol/gel methods, followed by calcination at 773 K, exhibited a significant activity for the selective catalytic reduction (SCR) of NO with propene as a reductant. The catalyst prepared by impregnation showed poor activity when it was calcined at 773 K, but exhibited enhanced activity when calcined at 1073 K. This is attributed to tiny CoAl2O4 crystallites formed during calcination of the catalyst at 1073 K. However, in sol/gel catalysts, finely-divided CoAl2O4 crystallites were formed during calcination, even at 773 K, because of the high dispersion of Co ions in the alumina support. Thus, the active species of alumina-supported cobalt oxide catalysts for SCR of NO with propene were concluded to be tiny CoAl2O4 crystallites dispersed on alumina.