Study On The Catalysts For Selective Catalytic Reduction Of NO_x With NH₃for Diesel Exhaust

With the high air-fuel ratio and fuel-economy, the diesel vehicles’ possesion is increasing yearly, however, the environment pollution which is from the diesel exhaust emissions has become more and more serious. The Selective Catalytic Reduction (SCR) with NH3is the most effective technology for removal of NOx in diesel exhaust, the development of effective SCR catalyst is the core of this technology. The purpose of this study was to develop a catalyst with high catalytic activity, wide active temperature window, strong and stable sulfur resistance and high durability.Firstly, Mn-Ce-Zr/ZSM-5was prepared by impregnation method. Among these catalysts, Mn6-Ce1-Zr2/ZSM-5sample showed the highest activity, the NOX conversions exceeds90%at160～330℃; The catalystic properties were characterized with TEM、XRD、H2-TPR、NH3-TPD. The results indicated that Mn6-Ce1-Zr2/ZSM-5sample’rich weak acid and strong ability of redox ability was the main reason of the high catalytic activity; The addition of Zr greatly enhanced the dispersion of active phases on the support surface. Moreover, Mn6-Ce1-Zr2/ZSM-5exhibited superior sulfur resistance.Secondly, in order to research a catalyst with more wide temperature window, excellent sulfur resistance, and has good thermal stability at high temperature, we prepared a series of Fe-V/TiO2catalysts. The samples were characterized by thermogravimetric analysis, X-ray diffraction, H2temperature programmed reduction, NH3temperature-programmed desorption and Raman spectra. It was found that the addition of Fe could obviously decrease the losing of V2O5at high temperature, which greatly decreased the toxicity of the vanadium-based catalysts in mobile sources. Among the synthesized catalysts, the Fe1-V1/TiO2showed the highest activity with the NOx conversion efficiency over90%between220℃and420℃due to formation of FeVO4active sites. Fe1-V1/TiO2exhibited excellent thermal stability at high temperature and sulfur resistance in the presence of SO2, but the activity and sulfur resistance stability of this catalyst in the presence of water vapor decreased more obviously. Moreover, we also prepared Fe1-V1/TiO2/cordierites by in-situ hydrothermal synthesis and impregnation. The monolithic catalysts exhibited the similar high catalystic activity and sulfur resisitance stability as the powder catalysts. Accordingly, this catalyst is expected to be applied in practice.