Preparation Of Rare Earth-modified Iron-based Catalysts And Basic Research On Its Application In NH₃-SCR

Our coal resources are very rich,so the energy structure is dominated by coal,and this structure will not change for a long time.However,the combustion of coal produces large amounts of NO_x and SO_x,causing serious environmental pollution.Therefore,it is urgent to control the emission of nitrogen oxides.The selective catalytic reduction of NO by NH₃?NH₃-SCR?technology has become the mainstream technology for fixed primary denitration due to its high NO conversion efficiency and good N₂ selectivity.China uses wet desulfurization technology for coal.The flue gas from coal combustion after desulfurization still contains a large amount of water and a small amount of SO_x.Therefore,the water and sulfur resistance of the catalyst is important for determining whether it can be a successful low temperature NH₃-SCR catalyst.Based on the above status quo,this paper focuses on the reaction mechanism of rare earth metal lanthanum,lanthanum doped Fe₂O₃ based composite oxide catalyst in NH₃-SCR and the water and sulfur resistance of the catalyst.The specific research is as follows:?1?The Fe-Sm composite oxide catalyst was prepared by the citric acid method.Compared with pure Fe₂O₃ and pure Sm₂O₃,the catalyst exhibited better activity and N₂ selectivity in the NH₃-SCR reaction.By XRD,NH₃-TPD,H₂-TPR and in situ DRIFTS,the reasons for the good activity and selectivity of the catalyst are proposed.It can be seen from XPS and H₂-TPR that after doping Sm,the surface adsorbed oxygen content of the catalyst is significantly increased,which is beneficial to the NH₃-SCR reaction,thereby facilitating the improvement of activity.In addition,after doping Sm,the number of various acid sites on the surface of the catalyst has increased significantly,especially the medium-strength acid sites,and the order of the numbers is consistent with the order of the catalyst activity,thereby demonstrating the medium-strength acid sites.The increase in the amount is another important reason for the increase in catalyst activity.?2?The effects of different preparation methods and different calcination temperatures on the activity of the catalyst were investigated.As the calcination temperature increases,the activity of the catalyst first rises and then decreases.At the calcination temperature of 500^oC,the catalyst exhibits the optimal activity.The catalyst was prepared by different preparation methods,and the catalyst activity was optimized by the citric acid method.?3?In-depth discussion of the Fe-Sm composite oxide catalyst has good resistance to water and sulfur,Fe₂O₃ itself has good resistance to water and sulfur.It can be seen from the EPR that the doping of Sm causes the catalyst to generate more surface oxygen defects,thereby improving the redox property.?4?The effect of Ce doping on the performance of the catalyst was studied systematically when the Fe-based catalyst was synthesized by citric acid method.The physical and chemical properties of the catalyst were characterized by XRD,NH₃-TPD,H₂-TPR,etc.,and the reaction mechanism of the catalyst was further studied by in situ DRIFTS technology.The relationship between catalyst activity and its texture properties,surface composition and chemical state was investigated.The following conclusions can be drawn:After doping Ce,the redox property of the Fe-based catalyst and the surface acidity of the catalyst can be improved,and the balance between the two can be achieved,which is beneficial to the NH₃-SCR reaction and the catalyst activity is significantly improved.