Research On Direct Decomposition Of NO Over Ion-doping Cu-ZSM-5 Zeolite Catalyst

As far as we know, Cu-ZSM-5 zeolites are the best catalysts for NO direct decomposition (De-NO) in medium temperature. In this paper, the improved zeolites catalysts M-Cu-zsm-5(M=Ce, La, Ag) were characterized .By XRD, ICP, SEM, IR and NO-TPD. By studying the influence of ion-exchange condition, promoter addition, reaction temperature, GHSV and O₂ concentration on the activity of catalysts in a fixed bed micro-reactor, the optimum preparation conditions and the reaction conditions were determined, and the NO decomposition reaction kinetics was analyzed.In the preparation process, the optimum concentration of Cu ion-exchange solution is found to be 0.011 mol/L. The loading of Cu is increased with the exchange times increase. The NO removal rate of the 1st and 3rd ion-exchanged Cu-ZSM-5 achieved its maximum value under oxygen-free condition at 600℃, with the former 5% higher than the latter.The addition of Ag⁺ or Ce³⁺ can both increase the activity of catalyst and reduce reaction temperature. Ion-exchange is the best loading method comparing with blending method and impregnation method. The optimum ion-exchange sequence of Ag-Cu-ZSM-5 is loading Ag⁺ first, and then Cu²⁺, which the NO removel could reach 60% at 320℃within 5% of O₂. But when adding Ce to the catalyst, Ce³⁺ and Cu²⁺ should be loaded at the same time, which the NO removel could reach 61% at 330℃. The doping of Ce and La can strengthen the oxygen resistance and widen the activiy temperature interval. Under the O₂ content of 5% at 320℃-350℃, the NO removal rate could maintain more than 62% for 30h on Cu-Ce-La-ZSM-5, indicating that Ce,La compete for O₂ absorption in the reaction region, which solving the oxygen-repressed problem. The addition of CaH₂(10% wt.) into Cu-Ce-La-ZSM-5 can greatly promote the NO removel, which could reach 83% at 340℃,. The SEM result showes that CaH₂ improve pore structure of the catalyst, which facilitaing the surface area increasement and catalytic activity promotion.The conclusion of macrokinetics analysis is followed as: the De-NO reaction order is 2, the apparent velocity constant was 1.21×10⁵m³Â·s^-1·mol^-1, and the apparent activation energy is 37kJ/mol.