Effects of Ni loading on the physicochemical properties of NiOx/CeO2 catalysts and catalytic activity for NO reduction by CO

Abstract

Transition metal oxide catalysts have been investigated extensively because of their relatively low cost and high activity in many chemical reactions. In this work, a series of NiO_x/CeO₂ catalysts (0.5–30 wt% Ni) were prepared using the incipient wetness impregnation method. These catalysts were tested with various characterization techniques, including Brunauer–Emmett–Teller (BET) theory, Raman spectroscopy, X-ray powder diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and gas chromatography (GC) for their physicochemical properties, surface properties, reduction properties and catalytic activities in the NO reduction by CO reaction. The increase in Ni loading of the catalyst (up to 5% NiO_x/CeO₂) led to the decrease in specific surface area, formation of NiO_x crystalline structures on the CeO₂ surface, easier reduction of the catalyst compared to bulk NiO_x and bulk CeO₂, and increase in catalytic activity in the NO reduction by CO reaction. From these results, the surface dispersion of NiO_x and the formation of monolayer NiO_x coverage of the catalysts were believed to affect the catalytic activity greatly. The results provided insights into the structure–activity relationship of NiO_x/CeO₂ catalysts for the NO reduction by CO reaction.