Study On The Simultaneous Removal Of Soot Particles And Nitrogen Oxides From Diesel Exhaust Catalyzed By Lanthanum-manganese Perovskite Catalysts

Due to the strong power and high fuel efficiency,diesel engines are widely used invehicles and various types of construction machinery.However,since diesel engines would emit high concentration of soot particles?PM?and nitrogen oxides?NOx?,which cause serious environmental pollution problem,it is urgent to develop efficient technology for treating these pollutions.The post-treatment catalytic technology is one of the main means to effectively solve these problems.The lanthanum manganese perovskites?La Mn O₃?catalysts are reported as the superior catalysts for the simultaneous removal of PM and NOx during this process.In current study,the catalytic performance of these catalysts was found to be further improved by doping modification at A and B positions,and the catalysts were applied to the actual diesel particulate filter?DPF?in the bench test.The main contents and conclusions are as follows:?1?For the La Mn O₃ catalyst doped with Sr and K in A site,K doping is beneficial to improve the activity of the catalyst,which is better than that of Sr-doped or undoped catalysts.In the catalytic removal of both PM and NO,the best activity sample of K-doped La_1-xK_xMn O₃(La_0.7K_0.3Mn O₃)was found,in which the combustion of soot at T₁₀,T₅₀,T₉₀were 254,336,397?,respectively.Compared with La Mn O₃,the temperature was greatly reduced 87,72 and 64?,respectively.Meanwhile,the maximum NO conversion?X??over La_0.7K_0.3Mn O₃ was 46.7%under the corresponding temperature T_??360??.The thermal stability of K-doped samples was relative lower than others,especially Sr-doped samples,which displayed a high thermal stability.Sr doping can improve the activity and maintain the thermal stability of La Mn O₃ catalyst.The activity temperature T₁₀,T₅₀,T₉₀ for soot combustion of La_0.7Sr_0.3Mn O₃ were 319,392 and 452?,respectively.Compared with La Mn O₃,the temperatures decreased by 22,16 and 9?.X?over La_0.7Sr_0.3Mn O₃ is 24.6%under the corresponding temperature T_??380??.Compared with La Mn O₃,X_?was increased by8.4%and T_?was decreased by 20?.?2?Co doping into the B site of the modified catalysts were performed.It was found that Co was beneficial to improve the activity of Sr doped catalysts and thermal stability of the K doped catalysts.Among the Sr doped samples,La_0.7Sr_0.3Mn_0.6Co_0.4O₃showed the best catalytic performance,in which 274,354,and 419?were obtained for T₁₀,T₅₀,and T₉₀,respectively.These results are significantly lower than those of La_0.7Sr_0.3Mn O₃.After Co doping into the B site of La_0.7K_0.3Mn O₃,the thermal stability of the catalyst was greatly improved.La_0.7K_0.3Mn_0.8Co_0.2O₃ displayed the low temperature(T₁₀,T₅₀,and T₉₀)of 270,346,and 408?,respectively,Meanwhile,X?and the transformation temperature did not change significantly.?3?A bench test evaluation was carried out,in which a single-cylinder diesel engine was used to provide the atmosphere of actual diesel engine exhaust.The surface coated with catalysts on DPF is the important process for its applications.It was found that the addition of nitrate components to the coating raw materials is beneficial to improve the performance of the catalyst.At the same time,if the coating amount is too large,the performance of the product will be inhibited.It might be that the surface pores of catalysts were probably blocked.The optimized parameters for the coated DPF product could be listed as follows:the mass ratio of the coating material/the catalyst is about1:4?1:5,while the coating dosage is 60?80 g/L.Furthermore,the self-made La_0.7Sr_0.3Mn_0.6Co_0.4O₃ and La_0.7K_0.3Mn_0.8Co_0.2O₃ catalyst samples were prepared and coated on the DPF under the optimized situation.It is found that the catalytic activity and stability of homemade samples La_0.7Sr_0.3Mn_0.6Co_0.4O₃are close to commercial DPF,showing a promising potential for the commercial application.