Cobalt-based catalysts supported on TiO2 and ZrO2 were studied for the oxidation of NO to NO2 in excess oxygen. NO oxidation was studied as the first step in a two-step catalytic scheme where NO is oxidized to NO,? and in turn NO2 is reduced with CH4 to N-2 under lean conditions. Catalysts were prepared by sol-gel (SG) and incipient-wetness impregnation (IWI) techniques and characterized by temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), laser Raman spectroscopy (LRS), and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). It was found the nature of the support, the synthesis technique, and the pretreatment conditions affect the catalytic activity. 10% Co/ZrO2 catalysts prepared by IWI were found to be most active among the catalysts tested, giving the highest NO uptake capacity and the highest turnover frequency (TOF) based on NO adsorption sites. Tests with bulk Co3O4 also showed significant NO oxidation activity. (C) 2007 Elsevier Inc. All rights reserved.