Study On Anti-poisoning And Modification Of SCR Reaction Mechanism Based On Cu/SAPO-34 Molecular Sieve Catalyst

NO_x emitted from diesel exhaust can cause pollution such as photochemical smog,and controlling NO_x emissions from diesel engines can effectively reduce air pollution.Diesel exhaust gas treatment technology often uses a selective catalyst reduction（SCR）system,in which the catalyst is the technical core of the SCR system.Conventional vanadium-based SCR catalysts are not able to meet increasingly stringent emission standards,and research on more efficient molecular sieve catalysts is essential.In this paper,a molecular sieve was used as a carrier,and a Cu/SAPO-34 powder catalyst sample was prepared by impregnation method,and a Cu/SAPO-34 monolith catalyst sample was prepared by a one-step impregnation method.By studying the catalytic activity,surface morphology,crystal and pore structure,desorption and reduction properties of powder catalyst samples and monolith catalyst samples,it was found that the monolithic catalyst samples prepared by one-step impregnation method retained the original catalytic activity.The monolithic catalyst with binder and dispersant has higher high temperature activity,and the catalyst has better dispersibility on the surface of cordierite and larger specific surface area,indicating that the monolith catalyst prepared by adding binder and dispersant has better performance,has good practical application potential.Through the Fourier in situ diffuse reflectance infrared（In Suit DRIFTS）characterization method,the similarities and differences of the reaction mechanism between the powder sample and the whole sample were compared.It was found that both of them used Bronsted acid as the main acid site,and the reaction satisfies NH₃ strong adsorption,NO and O₂ weak adsorption,followed the Eley-Rideal mechanism,the main difference is that other nitrate and nitrite intermediates appear in the whole catalyst reaction process due to the dispersion effect,but have little effect on the overall catalytic effect.The anti-hydrothermal aging performance and sulfur resistance of Cu/SAPO-34 molecular sieve catalyst were studied.The high temperature and low temperature water vapor conditions of diesel engine were simulated.The hydrothermal aging resistance of the catalyst was investigated.It was found that Cu/SAPO-34 catalyst was rich in water vapor at 700°C.Under the condition of aging for 24 h,it also showed good performance.However,after aging for 24 h at 75°C,the reactivity is seriously degraded.It is found by XRD,BET and SEM that low temperature hydrothermal aging will destroy the molecular sieve structure and lead to activity reduce.Finally,the sulfur resistance of Cu/SAPO-34catalyst was tested.It was found that the reaction activity seriously decreased when the concentration of 200 ppm SO₂ was passed into the SCR reaction at 300°C,indicating that its sulfur resistance was poor.It is mixed with a V-W-Ti catalyst in a solid phase ball mill at a 1:1 mass ratio.It is found that the denitration efficiency of the modified sample can reach more than 90%under the same conditions,and the sulfur resistance is obviously improved.