Modification of Cu/ZSM-5 catalyst with CeO2 for selective catalytic reduction of NOx with ammonia

Abstract

Cu/ZSM-5 and CeO2-modified Cu/ZSM-5 catalysts were prepared by a wetness impregnation method. The addition of CeO2 was found to enhance the NOx selective catalytic reduction (SCR) activity of the catalyst at low temperatures, but the high-temperature activity was weakened. The catalysts were characterized by X-ray diffraction (XRD), nitrogen physisorption, inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), H2 temperature-programmed reduction (TPR) and NH3 temperature-programmed desorption (TPD). The results showed that more CuO clusters instead of isolated Cu2+ species were obtained on the modified catalyst. These active CuO clusters, as well as the Cu-Ce synergistic effect, improved the redox property of the catalyst and low-temperatures SCR activity via promoting the oxidation of NO to NO2 and fast SCR reaction. The loss in high-temperatures activity was attributed to the enhanced competitive oxidation of NH3 by O2 and decreased surface acidity of the catalyst.