Reaction activities of several developed catalysts for NO oxidation and NOx (NO + NO2) reduction have been determined in a fixed bed differential reactor. Among all the catalysts tested, CO3O4 based catalysts are the most active ones for both NO oxidation and NO, reduction reactions even at high space velocity (SV) and low temperature in the fast selective catalytic reduction (SCR) process. Over Co3O4 catalyst, the effects of calcination temperatures, SO2 concentration, optimum SV for 50% conversion of NO to NO2 were determined. Also, CO3O4 based catalysts (Co3O4-WO3) exhibit significantly higher conversion than all the developed DeNO(x) catalysts (supported/unsupported) having maximum conversion of NOx even at lower temperature and higher SV since the mixed oxide Co-W nanocomposite is formed. In case of the fast SCR, N2O formation over Co3O4-WO3 catalyst is far less than that over the other catalysts but the standard SCR produces high concentration of N2O over all the catalysts. The effect of SO2 concentration on NO, reduction is found to be almost negligible may be due to the presence of WO3 that resists SO2 oxidation. (c) 2007 Elsevier B.V. All rights reserved.