Study On The Physical & Chemical Characteristics And Catalytic Properties Of The Modified Zeolite SCR Catalyst On Diesel Engines

Vehicle emissions have become a major source of the city air pollution. NOx removal is an important aspect of automobile exhaust purification. Among many NOx removal technology ways, NH₃-SCR is suitable for China and can meet EuroⅣand even more stringent emission regulations. Combined with XRD, SEM, TEM, FT-IR, UV-vis and N₂ adsorption-desorption isotherms, the performance and physic-chemical properties of metal modified ZSM-5 zeolite catalysts are evaluated in this paper, and the conclusions are as follows:1. In the self-designed catalyst performance system, the copper, manganese and nickel modified ZSM-5 zeolite catalysts had the better performance than cerium, strontium, iron, lanthanum and cobalt modified ones in the condition of a space velocity of 60000 h^-1 and ammonia-nitrogen ratio of 1:1.2. When the metal loading was low, the active species in the copper, manganese and nickel modified ZSM-5 zeolite catalysts dispersed equally. As the loading increasing copper and nickel modified ZSM-5 zeolite catalysts would precipitate, while the manganese kept dispersion well. At lower metal contents, Cu/ZSM-5, Mn/ZSM-5 and Ni/ZSM-5 all showed double peaks in the NOx reduction profiles; as the metal contents increased, the low temperature and high temperature peak combined into one unit.3. In the Copper, manganese and nickel modified ZSM-5 zeolite catalysts, metallic oxides as active phases enriched on the surface of zeolites, as the loading increased the contents in the surface increase rapidly. The three catalysts had the activity order: Cu/ZSM-5 > Mn/ZSM-5 > Ni/ZSM-5. There was a strong interaction between the copper and ZSM-5 zeolite, which changed the electronic properties of the active component and resulted in higher active; while there was a weak interaction between the nickel and ZSM-5 zeolite, the ZSM-5 only played a supportive role as a carrier, Ni/ZSM-5 had lower active.4. When Cu, Mn, Ni loadings were 2.2%, 3.1% and 14.6%, the Cu/ZSM-5, Mn/ZSM-5 and Ni/ZSM-5 reached the best active. The metal active species presented in the zeolite in the form of metal cation or lower congregate metal oxides.5. Most of the copper species in the Cu/ZSM-5 were Cu⁺, which were the active species. Most of the manganese species in the Mn/ZSM-5 were Mn²⁺, which were the active species, while some of the manganese species were Mn³⁺. All of the nickel species in the Ni/ZSM-5 were Ni²⁺, which were the active species clearly.