Support effects on the dispersion and interaction of Ce and W species for NH3-SCR

Abstract

The purpose of this study is to investigate the interaction of Ce and W species with TiO2, Al2O3 and SiO2 supports, so as to illustrate the influence of supports and distribution of Ce, W species on SCR reaction. It is found that low-temperature activity followed the order of CeW > CeWTi > CeWAl > CeWSi. The reasons for the various activity of the catalyst were investigated by a series of characterization. The low-temperature NH3-SCR activity is associated with the surface concentrations of Ce3+, oxygen vacancies and active oxygen species, which are dominated by the dispersion and interactions of Ce/W species with the supports. Arising from interactions of Ti4+ with high-density electron cloud, finely dispersed Ce and W species facilitate the W-Ce synergism and produce more active oxygen. All these contribute toTiO2 can make Ce and W species in an ideal distribution, so the corresponding catalyst shows excellent NOx conversion of CeWTi catalyst at 200–350 °C. The reaction process observed by in situ DRIFT indicated that the NH3-SCR reaction on CeO2-WO3 containing catalysts mainly follow Langmuir-Hinshelwood (L-H) mechanism at low temperature. Based on the analysis of the characterization and reaction process, it is concluded that the control step of NH3-SCR reaction at low temperature over CeO2-WO3 containing catalysts is the adsorption and activation of NOx.