Investigation Of Selective Catalytic Reduction Of NO_x Over FeCu-CHA Zeolite Catalysts

With the development of economy,the problem of air pollution is also increasingly prominent.The large amount of nitrogen oxides（NOx）emission from flu gas of combustion both of the static and mobile sources needs to be eliminated.At present,using ammonia as a reductant,selective catalytic reduction（NH₃-SCR）technology is considered as one of the most effective methods to eliminate NOx in oxygen-rich conditions.In recent years,the chabazite（CHA）catalysts（including SAPO-34 and SSZ-13）received much attention due to their high activity,good selectivity and stability.In this work,the effects of the second active component Fe on the performance of Cu-SAPO-34 and Cu-SSZ-13 catalysts are investigated.The Cu-SAPO-34 catalyst is prepared by one pot method,and a series of FeCu-SAPO-34 catalysts modified with different amount of Fe loading are prepared by impregnation.These catalysts are applied in NH₃-SCR reaction.The catalysts are characterized with means of BET,XRD,ICP,SEM,UV–Vis,XPS,EPR and H₂-TPR to study the influence of the active component Fe on the catalyst’s composition,structure and performance.In addition,the FeCu-SSZ-13 catalyst is synthesized with an one pot method,and the influences of the different preparation conditions on the activity of the catalysts are investigated.The experimental results show that among the Fe_xCu-SAPO-34 catalysts,the Fe₁Cu-SAPO-34 catalyst shows the best NH₃-SCR activity above 200 ^oC.XRD and SEM results indicate that the Fe doping does not destroy the crystal structure of SAPO-34 molecular sieve.The improvement of NH₃-SCR activity at 200-350 ^oC is due to the increase of the amount of isolated Cu²⁺increased,which is verified by EPR and H₂-TPR.The addition of Fe reduces the non-selective oxidation capacity of ammonia.UV-Vis shows that isolated Fe³⁺,Fe_xO_y oligomer and Fe₂O₃ exist in Fe_xCu-SAPO-34 catalyst.The reduced ammonia oxidation ability and the existence of isolated Fe³⁺improve the NH₃-SCR activity of Fe₁Cu-SAPO-34 catalyst above 350oC.The FeCu-SSZ-13 catalyst with the amount of Fe of 2%,the Si/Al ratio of 3.7and the ion-exhange time of 8 h shows the highest activity.Compared to Cu-SSZ-13catalyst,FeCu-SSZ-13 catalyst shows better SCR activity at both low and high temperatures.The NOx conversion keeps 90%at the temperature range from 170 ^oC to 550 ^oC.In addition,the FeCu-SSZ-13 catalyst keeps good SCR activity after high temperature hydrothermal aging.UV-Vis and H₂-TPR results indicate that the addition of Fe changes the distribution of the active component Cu.The results of NO-TPD and NH₃-O₂ experiments indicate that the enhanced NO adsorption capacity and the reduced ammonia non-selective oxidation capacity are the main reasons for the improvement of the SCR activity.