| Selective catalytic reduction with NH3（NH3-SCR）is currently an efficient and promising technology for removing nitrogen oxides（NOx）from stationary source flue gas,and the key to this technique is the choice of an excellent catalyst.In recent years,researches on NH3-SCR catalysts have mostly focused on improving catalytic activity at low temperature and SO2 resistance.Especially,Mn-based zeolite catalysts,which utilize the variable valence state of Mn as active center and zeolites with large specific surface and good hydrothermal stability as catalyst carrier,exhibit excellent catalytic performance for NH3-SCR at low reaction temperature,and their practical application are promising.However,the biggest issue of Mn-based zeolite catalysts is that active center Mn is more favorable to react with SO2 to generate manganese sulfate,leading to catalyst deactivation,which limits its practical application.Therefore,the development of a Mn-based zeolite catalyst with good denitrification performance at low temperature and good SO2 resistance is of great significance for industrial applications.In this thesis,the best denitration supported catalyst was prepared with Mn as the active component.A number of techniques have been employed to decouple the interdependence between physicochemical properties of catalysts with different Mn loadings and catalytic activity.Based on the best denitration catalyst,two research strategies,second metal modification method for constructing sacrificial sites and the addition of protective layer,were performed to promote the SO2 resistance of catalyst.The obtained findings are as follows:（1）The Mn-based ZSM-5 catalyst prepared by solvent evaporation method has the best catalytic activity,especially when the Mn loading is 20 wt.%.The NOx conversion rate is almost 100%at 150℃.After characterization and analysis,it was found that the loading of Mn did not destroy the topology structure of ZSM-5,and most of Mn Ox located in the micropore channels of zeolite.The introduction of Mn first located in the bridging hydroxyl position of zeolite.With the increase of Mn loading,Mn ions gradually grew up into small particles of oxide.Compared with bulk manganese oxide or oxide-based manganese oxide catalysts,these small manganese oxide particles with electropositivity may be one of the reasons for the high denitration activity.Based on the results of XPS and H2-TPR,it was showed that the high proportion of Mn4+and Mn3+with high catalytic activity was also the reason for the high denitration activity of the catalyst.（2）Using ZSM-5-20%Mn with good catalytic activity as the matrix to study the SO2resistance of Mn-based catalysts,it was found that a feasible catalyst filling method was proposed over tandem catalysts,through which Ce-modified Ti O2 and ZSM-5-20%Mn were efficiently coupled.The two-layer catalyst filling method can effectively protect the main denitration catalyst（ZSM-5-20%Mn）from SO2 poisoning.Under reaction condition at 200℃,100 ppm SO2 and the space velocity 31500 h-1（calculated based on the main catalyst）,the denitration performance of the catalyst maintains at a high level（about 90%）for almost 122hours as the mass ratio of the main catalyst to the protective agent 1:2.After characterization and analysis of the used up-layer of catalyst Ce-modifed Ti O2,ammonium sulfate was generated and deposited on the surface of Ce-modifed Ti O2,due to the strong interaction between Ti O2 and SO2.After calcination,the deposited ammonium sulfate salts could decompose and Ce-modifed Ti O2 can be recycled as up-layer of tandem catalyst to inhibit SO2 poisoning of low-layer of catalyst（ZSM-5-20%Mn）. |
