Mechanism Of Selective Catalytic Reduction Of NO_x At Low-temperature And Preparation Of Mn-Zr-Ti Catalyst

Nitrogen oxides(NOx)is one of the major air pollutants.The technology of selective catalytic reduction(SCR)at low-temperature(LT)is expected to deplete NOx efficiently.Mn-based catalysts have attracted attention for their superior activity at LT.However,it generally shows low N2 selectivity and poor resistance towards H2O and SO2.Mn-based catalysts has not been applied to industry yet,which could be primarily ascribed to the imprecision of the mechanism of deNOx.Therefore,it is significant to clarify the mechanism and develop novel LT SCR catalysts.For the problems above,the reaction mechanism over Mn-based catalyst,the effect of H2O and SO2 on the reaction routes as well as the deactivation mechanism were studied in this work.The prepared Mn-Zr-Ti catalyst shows superior catalytic activity,N2 selectivity and resistance to H2O and SO2.The investigation on honeycomb monolith catalyst facilitates its industrial application.The major research contents and results are as follows:Ⅰ.NOx is reduced by absorbed NH3 in the form of bidentate nitrato and monodentate nitrito species.Oxygen is the vital intermediate in the SCR process,including electron transfer from N to Mn,the adsorption of NO,the activation of NH3 by depriving a hydrogen,etc.The Oxygen-intermediate mechanism is first proposed.Ⅱ.The active sites could be occupied by H2O,which results in the decrease of activity.SO2 give rise to the deactivation of catalysts by generating the deposition of ammonium salts and the formation of metal sulfates.The salinization deactivation mechanism is first proposed.Ⅲ.The adsorption of H2O and SO2 can transform the Lewis acid sites into Br(?)nsted acid sites,resulting the decrease of catalytically oxidizing ability and adsorption capacity for NO,as well as the increase of adsorption capacity for NH3.These suppress the formation of N2O via Langmuir-Hinshelwood mechanism.IV.The prepared Mn-Zr-Ti shows the NO conversion>99%and N2 selectivity>97%at 160-280℃.The incorporation of Co improves the catalytic performance and resistance towards SO2 by increasing the concentration of Lewis acid sites,surface adsorbed oxygen and Mn4+.The prepared honeycomb monolith Mn-Zr-Ti catalyst shows the NO conversion>96%at 160-280℃.The evaluation of monolith catalyst facilitates the industrial application of Mn-based catalysts.