Soot And Nox Purification Catalyst Surface Of Reactive Oxygen Mechanism

With the development of economy and increase in the number of vehicle, environmental pollution is becoming more and more severe. Diesel has focused much more attention from many countries around the world due to its high efficiency and low fuel consumption. In this dissertation, exhausts compositions, harm and its control technologies including fore-engine, internal-engine and after-treatment are summarized. The types of diesel exhaust purification catalysts are classified and introduced, and research advance of superficial active oxygen is also summed up.Catalysts investigated in our research are divided into two systems: 1) Lanthanum-Cobalt perovskite-type catalysts, including doped Ce, Zr, Mn. 2) Ceria-Zirconia solid solution catalysts, including doped La, Co, Mn.A series of technologies such as Temperature programmed oxidation (TPO), BET, X-ray diffraction (XRD), Fourier transformation infrared spectrometry (FT-IR), Temperature programmed Reduction (H₂-TPR), Temperature programmed desorption (O₂-TPD)and in situ diffuse reflection infared Fourier transformed (in situ DRIFT), X-ray Photoelectron Spectroscopy (XPS) were used to determine the catalysts. The performance of surface active oxygen species on different sestem catalysts were investigated. On the basis of the experimental results of in situ DRIFT, a reaction mechanism was proposed, which can preferably explain the reaction process of simultaneous removal of PM and NO_x over 30%Mn/Ce_0.7Zr_0.3O₂.Results obtained in this dissertation are followed:1) It was revealed the activity of LaCoO₃ catalyst was significant with citric acid complex combustion. The catalysts were prepared by partly substituted LaCoO₃ with Ce, Zr, Mn. Substituted with small amount of transition metals can promote the catalytic activity of perovskite and does not affect the crystalline structure of perovskite. The activity of LaCo_0.95Mn_0.05O₃ catalyst was best, its Ti and Tm respectively downed to 306℃and 505℃, and the conversion of NO achieved to 27.1%.2) Ceria-Zirconia solid solution with different the ratio of ceria-zirconia were prepared by complex combustion method. It determined the best ratio of ceria-zirconia through structure characterization and activity evaluation. The catalysts which prepared by doped Ce_0.7Zr_0.3O₂ with La, Co, Mn formed the ternary solid solution. Doped with moderate transition metals can promote the catalytic activity of solid solution catalysts. The activity of 30%Mn/Ce_0.7Zr_0.3O₂ catalyst was best, its Ti and Tm respectively downed to 298℃and 504℃, and the conversion of NO achieved to 30.6%.3) During partly Mn-substituted LaCo_1-xMn_xO₃ catalysts, small amount of Mn-doped was good for the defects, increased the concentration of Oˉ, improved the activity of perovakite.4) Among x%Mn/Ce_0.7Zr_0.3O₂ with different doping of Mn, Moderate Mn-doped can increase the concentration of O₂- on the surface of catalysts, improved the activity of solid solutions for simultaneous removal of PM and NO_x.5) The catalytic performance of 30%Mn/Ce_0.7Zr_0.3O₂ was directly related to the superoxide species ( O₂- ) and nitrate species ( NO₃^- ) which adsorbed on the surface of 30%Mn/Ce_0.7Zr_0.3O₂. They were active species during the reaction of PM and NO_x, and further, the formation of the isocyanate species ( -NCO ) was clarified.