Study On Modified Preparation And Catalytic Performance Of Wide Temperature C₃H₆-SCR Molecular Sieve Catalyst

With the rapid development of mobile sources（motor vehicles）,the problem of environmental pollution caused by nitrogen oxides in their exhaust gas is also very prominent.Therefore,how to efficiently remove nitrogen oxides from mobile source exhaust gas is the focus of many researchers.Through literature research,selective catalytic reduction（SCR）is one of the best denitrification technologies in many mobile sources.A large amount of C₃H₆ and NOx coexist in the mobile source tail gas.Therefore,C₃H₆ as a reducing agent can not only effectively remove NOx,but also realize the co-removal of hydrocarbon pollutants.Molecular sieve catalysts have many advantages,including large specific surface area and good catalytic performance,so they are widely used in SCR reaction.However,in the conventional preparation method,the conventional calcination requires a lot of time and cost,and the high activity operating temperature window of the catalyst is still narrow.Therefore,in this paper,through the development of new molecular sieve catalyst and its formula,supplemented by plasma technology for enhanced preparation,so as to enhance the interaction between active components and support,enhance the catalytic activity and broaden the high activity operating temperature window.In this paper,the simulated automobile exhaust was taken as the research object,C3H6 and no were used as raw materials for SCR denitrification,and Mn was used as the active component of the catalyst.Low temperature plasma technology was used to enhance the treatment.The catalytic performance and stability of the optimal Mn based molecular sieve catalyst formula and the influence of different plasma conditions on the SCR denitrification effect were investigated,XPS,TG,SEM,XRD,FT-IR and other physical methods were used to qualitatively analyze the effect of catalyst structure on denitration performance.The experimental results are as follows（1）The catalysts with different active components,promoter metals and contents were synthesized by conventional impregnation method combined with low temperature plasma enhanced treatment.The catalytic performance of different catalysts was tested,and the Mn based molecular sieve catalyst with the best catalytic performance was selected.The structure of Mn based molecular sieve catalyst was analyzed by characterization technology.The results show that the no conversion of10%Mn-5%Zr-2.5%Bi-ZSM-5-p zeolite catalyst is about 93.8%at 250℃,and the operating temperature window T50 is 175-460℃;compared with the 10%Mn-5%Zr-ZSM-5-p zeolite catalyst without doping Bi,the no conversion is increased by 8.3%,and the operating temperature window T50 is widened by 30℃;compared with the10%Mn-5%Zr-ZSM-5-p zeolite catalyst without doping Bi,the no conversion is increased by 10.3%For Mn-ZSM-5-p zeolite catalyst,the no conversion was increased by 16.5%,and the operating temperature window T50 was widened by 40℃.XRD characterization showed that the doped metal oxide was amorphous on the surface of zeolite support,and the doped catalyst still maintained the microporous structure of ZSM-5.TG characterization results show that the doping metal can improve the thermal stability of Mn based zeolite catalyst.SEM results show that the doped metal has been successfully loaded on the surface of molecular sieve support,but it still causes some damage to the structure of the catalyst and reduces its relative crystallinity.The FT-IR results showed that the doped metal existed and gathered around ZSM-5 through coordination bond.XPS analysis showed that Mn Ox existed mainly in the form of Mn₂O₃ on the surface of three different catalysts,and the doping promoter enhanced the interaction between metal components and ZSM-5.（2）Based on the optimal formula of Mn based molecular sieve catalyst,the stability of Mn based molecular sieve catalyst prepared by conventional impregnation method combined with conventional calcination and low temperature plasma treatment in C₃H₆-SCR was investigated.The results show that the Mn based molecular sieve catalyst treated by plasma has better stability than that by conventional calcination,and the stability of Mn based molecular sieve catalyst is gradually improved with the doping of promoter metal.（3）The optimal Mn based zeolite catalysts were prepared by conventional impregnation method combined with glow discharge plasma and dielectric barrier discharge plasma treatment,and the SCR denitrification performance of the catalysts was tested.The results show that the no conversion of 10%Mn-5%Zr-2.5%Bi-ZSM-5-GD treated by glow discharge plasma is about 93.8%at 250℃and the operating temperature window is 175-460℃;the no conversion of 10%Mn-5%Zr-2.5%Bi-ZSM-5-DBD treated by dielectric barrier discharge plasma is about 97%at 250℃and the operating temperature window is T50℃It is 155-430℃.The physical analysis of DBD treated catalyst is as follows:XRD analysis shows that the doped metal oxides are mainly amorphous,and the catalyst still maintains the MFI structure of ZSM-5;TG characterization results show that metal doping can enhance the thermal stability of zeolite catalyst;SEM characterization results show that a large number of doped metals are loaded on the surface of ZSM-5 support,and the crystal structure of ZSM-5 is affected The results of FT-IR showed that the metal species of the catalyst had coordination bonds with ZSM-5 molecular sieves while maintaining the original characteristic skeleton peak of ZSM-5,resulting in the appearance of new characteristic peaks;XPS showed that the Mn Ox on the surface of the catalyst mainly existed in the form of Mn₂O₃,and the introduction of promoters enhanced the interaction between metal components and ZSM-5 The amount of lattice oxygen on the surface of the catalyst doped with promoters was significantly increased and the amount of adsorbed oxygen on the surface of the catalyst was decreased after the catalyst was treated with DBD.