Research On Simultaneous Catalytic Removal Of NO_x And Soot By La-Mn Perovskite Catalyst

Catalytic purification is the core of the post-treatment technology of diesel engine pollutant purification.It is of great significance to carry out research in this area for environmental protection.In this paper,a series of La-Mn perovskite composite oxide catalysts were synthesized by citric acid complex combustion method and the performance of catalyst for simultaneous removal of nitrogen oxides and soot particles were studyed.Firstly,LaMnO₃ catalyst was synthesized,and the La_0.9A_0.1MnO₃?A=K,Sr,Pr?series catalysts were prepared by substituting K,Sr and Pr for La.The samples with the best substitution performance were selected and La_1-xA_xMnO₃?x=0.1,0.2,0.3?series catalysts were prepared and the effect of different content of A-site substituted elements on the catalytic activity was investigated.Then,the Mn of B site was replaced by V,Ti and Co to prepare LaMn_0.95B_0.05O₃?B=V,Ti,Co?series catalysts and the elements with the best substitution performance were selected.Based on the above studies,the LaMnO₃ perovskite catalysts were simultaneously substituted with AB sites to prepare La_0.8K_0.2Mn_1-yCo_yO₃?y=0.05,0.15,0.25,0.35?series of catalysts,and further investigated the influence of simultaneous substitution of AB sites on the performance of LaMnO₃ catalyst.The catalytic activity of the catalyst for the simultaneous removal of nitrogen oxides and soot was tested by the catalyst activity evaluation.The reaction performance of the catalyst was tested by H₂-TPR,O₂-TPD,Soot-TPR,NO-TPD and CO₂-TPD.The structural features of the catalyst were characterized by XRD,BET,SEM,FT-IR and XPS.The results of XRD and FT-IR show that all the samples have formed perovskite structure,indicating that the substituted elements can enter the perovskite structure well within a certain range.But K₂Mn₄O₈ is formed when the K content is 0.3 and La₄Co₃O₁₀ is formed when the Co content is 0.35,indicating that excess element substitution will form heterogenous phase.SEM results show that the LaMnO₃ perovskite catalyst has fluffy long and short cotton flocs.BET results show that the prepared samples were calcined at a high temperature of 800°C with a small specific surface area of 11-15 m²/g.The results of XPS showed that the ratio of Mn⁴⁺/Mn³⁺and O_ads/O_lat first increased and then decreased when LaMnO₃ was substituted by both K and Co,reaching its maximum when the content of Co was 0.25.The increase of Mn⁴⁺and O_ads content is helpful to improve the ability of catalyst to remove NOx and soot.The catalyst activity evaluation results show that the LaMnO₃ perovskite catalyst enhance the ability of removing NOx and soot after being substituted,and the effect of simultaneous substitution of A and B positions is better.When the content of Co is 0.25,the catalyst has the best catalytic effect:the initial combustion temperature and maximum combustion temperature of soot is 260°C and 365°C,respectively,the rate of NO conversion reach 61.08%.The results of H₂-TPR,O₂-TPD,Soot-TPR,NO-TPD and CO₂-TPD indicate that the reduction temperature is reduced at low temperature?except for V and Ti?,the number of surface chemically adsorbed oxygen increases and the ability to adsorb NO is enhanced after the LaMnO₃ perovskite catalyst substituted.In addition,the CO₂ can adsorb on the catalyst surface at low temperature,thus inhibiting the combustion of soot.