Homogeneous dispersions and small size of deposited high-content cobalt on alumina were achieved by the co-precipitation method and were well maintained on the cobalt-based binary alumina catalysts with Zn, Ag, Fe, Cu or Ni as modifiers. The component and concentration of deposited cobalt species were characterized by UV-vis, EDX and XPS spectra and found to be greatly related to the Co loading, calcination temperatures and the type of additive metals. The optimal Co loading of 8 wt% and calcination temperatures of 800 degrees C were demonstrated. With respect to the single cobalt-based alumina catalyst, the surface concentration of Co2+ on the binary catalysts with addition of Fe, Cu, Ag or Ni was all reduced and accompanying with part conversion of Co2+ to Co3O4 on the Fe and Ni-modified catalysts. A slight enhanced surface Co2+ concentration was only achieved on the Zn-promoted catalyst. It was also demonstrated that for the case of Cu and Fe the additive metals themselves participated in the activation of propene. The octahedral and tetrahedral Co2+ ions were suggested as the common active sites. A maximum deNOx activity of 96% was observed on the 8Co4ZnA800 catalyst at the reaction temperatures of 450 T, and the catalytic performance on the cobalt-based binary alumina catalysts can be described as fellows: CoZn > CoAg, CoNi > Co Cu > CoFe. Based on the in situ DRIFT spectra, different reaction intermediates R-ONO and -NCO besides -NO2 were formed on the 8Co4ZnA800 and 8Co4FeA800 samples, respectively, demonstrating their dissimilar reaction mechanisms. (c) 2007 Elsevier B.V. All rights reserved.