Structures and Catalytic Properties of Cr–Cu Embedded CeO2 Surfaces with Different Cr/Cu Ratios

Abstract

The effects of the Cr/Cu ratios of Cr–Cu-embedded CeO2 surfaces (0.065 wt % Cu loading) on their local structures and catalytic activities were studied using experimental and theoretical approaches. The sample with a weight ratio of Cr/Cu = 1, which was prepared by wet impregnation followed by subsequent thermal aging at 900 °C for 25 h, showed catalytic activity higher than that of the Cu/CeO2 sample in both CO–O2 and CO–NO reactions. The activity of the catalyst was enhanced by increasing the Cr/Cu ratio. The highest activity occurred for a Cr/Cu ratio of around 3, and after it had been thermally aged, its activity was superior to that of Rh/CeO2. Having more Cr than Cu increases the surface concentration of the Cu+ sites, which promotes CO adsorption and its reaction with surface O atoms. As-formed surface O vacancies are filled by the dissociative adsorption of O2 and/or NO. At the optimum composition, almost all of the Ce sites on the outermost layer are replaced by Cr and Cu, and oxidative chemisorp...