A series of CoOx/Al2O3 catalysts was prepared, characterized, and applied for the selective catalytic reduction (SCR) of NO by C3H8. The results of XRD, UV-vis, IR, Far-IR and ESR characterizations of the catalysts suggest that the predominant oxidation state of cobalt species is +2 for the catalysts with low cobalt loading (<= 2 mol%) and for the catalysts with 4 mol% cobalt loading prepared by sol-gel and co-precipitation. CO3O4 crystallites or agglomerates are the predominant species in the catalysts with high cobalt loading prepared by incipient wetness impregnation and solid dispersion. An optimized CoOx/Al2O3 catalyst shows high activity in SCR of NO by C3H8 (100% conversion of NO at 723 K, GHSV: 10,000 h(-1)). The activity of the selective catalytic reduction of NO by C3H8 increases with the increase of cobalt-alumina interactions in the catalysts. The influences of cobalt loading and catalyst preparation method on the catalytic performance suggest that tiny CoAl2O4 crystallites highly dispersed on alumina are responsible for the efficient catalytic reduction of NO, whereas Co3O4 crystallites catalyze the combustion of C3H8 only. (c) 2007 Elsevier B.V. All rights reserved.