Cobalt-based catalysts supported on titania and zirconia for the oxidation of nitric oxide to nitrogen dioxide

Cobalt-based catalysts supported on TiO 2 and ZrO 2 were studied for the oxidation of NO to NO 2 in excess oxygen. NO oxidation was studied as the first step in a two-step catalytic scheme where NO is oxidized to NO 2 and in turn NO 2 is reduced with CH 4 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/ZrO 2 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 Co 3O 4 also showed significant NO oxidation activity.