Study On MnO_x@ZSM-5 Catalyst For NH₃-SCR At Low Temperature

Nitrogen oxides(NO and NO2)remain a major source for air pollution,which contribute to photochemical smog,acid rain,ozone depletion and greenhouse effect.They not only destroy the environment,but also harm human health.Selective catalytic reduction of NO,with NH3 is a well-established technology to remove NO,,particularly that from the flue gases of coal-fired power plants and industrial boilers.It is a great interest to develop active SCR catalysts with high SCR activity and N2 selectivity.In this paper,MnO,was adopted as active component and ZSM-5 as a carrier,MnOx was confined into the channels of ZSM-5 by impregnation to prepare MnO,@ZSM-5 catalyst.Furthermore,its SCR catalytic performance was studied.The main research results are as follows:(1)The effect of preparation temperature on the dispersion of MnOx on the carrier was studied.XRD,BET and TEM results showed that MnOx is located inside the ZSM-5 channels at the preparation temperature of 20?,when the preparation temperature is increased,MnOx is mainly located outside surface of ZSM-5 which is easy to agglomerate.XPS,H2-TPR and Raman results showed that Mn species existed mainly in the form of Mn4+.SCR test results showed that MnOx confined in the channels of ZSM-5 is showed to be good activity at mid-high temperature,and the NOx conversion reached 90%at the temperature of 275-350?,MnOx loaded on the outside surface of ZSM-5 showed good activity at low temperature.(2)The effect of H-ZSM-5 modification on catalytic performance was studied.The results showed that modifying H-ZSM-5 by different ions can significantly affect the distribution of MnOx on the support,thus having a greater influence on catalytic performance,especially the T90 and the operating temperature window.The characterization results showed that some Na particles can occupy the internal sites of ZSM-5 channels after NaCl modified,making it difficult for MnOx to disperse in ZSM-5 channels;When H-ZSM-5 was modified by NH4NO3,the presence of NH4+ groups may make it easier for MnOx to locate outside surface of carrier.(3)The effect of preparation volume,ultrasonic treatment,solvent,precursors and drying method on catalytic performance were further studied.The results showed that when preparation volume is 200 mL,without ultrasonic treatment,ethanol as solvent,Mn(NO3)2 is used as the precursor and the concentration is 0.2 mol/L,dry after filtration,this can optimize catalytic performance.