Crystalline structure refinements and properties of Ni/TiO2 and Ni/TiO2-Ce catalysts and application to catalytic reaction of “CO + NO”

Abstract

Catalysts containing 7wt% Ni were prepared by impregnation of anatase-phase TiO2 and Ce-doped TiO2 that were synthesized by sol–gel techniques. The catalysts were extensively characterized by a variety of methods including BET surface area measurements, temperature programmed H2 reduction (H2-TPR), scanning transmission electron microscopy (STEM), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) for CO adsorption. The crystallography, crystallite size, microstrain in the crystalline structure and concentration of all phases in the catalysts were determined by X-ray diffraction and refinement of the crystalline structure with the Rietveld method. As catalytic probe reaction, the stoichiometric oxidation of CO by NO was used. Doping with ceria affected the crystallography of the anatase-phase titania, increased the structural defects, and decreased the anatase crystallite size. This, in turn, led to more extensive contact of nickel particles with the support facilitating the reduction of nickel and of the surface of the Ce-doped TiO2. Among the various catalysts investigated, the Ce-doped Ni/TiO2 catalyst with a Ce/(Ce+Ti) ratio of 0.1 was found to be the most active for CO oxidation by NO.