Study On Anti-poisoning Mechanism Of Cu-ZSM-5 Based On NO Decomposition

Direct catalytic decomposition of NO is the most environmentally friendly and economical denitration technology.ZSM-5 molecular sieve provides a stable reaction site for the catalytic decomposition of NO due to its unique silicon-aluminum tetrahedral structure and arrangement,but there are still problems such as water vapor and SO₂ interference.In this thesis,the rare earth element La is used to dope and modify Cu-ZSM-5 to suppress the damage of water vapor to the active sites and framework aluminum.CeO₂ oxide film is used to wrap the catalyst particles to prevent the active sites from contacting with water vapor or SO₂.In the effective working range of Cu-ZSM-5（350-600℃）,the effect of water vapor and SO₂ on the catalyst activity was studied.Using XRD,BET,SEM,UV-vis,IR,NO-TPD,H₂-TPR and XPS characterizations,analysis of Cu-ZSM-5 water vapor and SO₂ poisoning mechanism,the mechanism of La doping modification resistance to water vapor poisoning,and the mechanism of CeO₂ oxide film resistance to water vapor and SO₂ poisoning.The main results of this thesis are as follows:（1）When NO concentration is 0.1%and NO concentration is 5%,the best NO conversion of Cu-ZSM-5 is 55.2%.5%,10%and 15%water vapor reduce NO conversion by 0.3%,2.2%,5.2%,0.25%,0.5%and 0.75%SO₂ reduce NO conversion by 0.7%,2.3%,4.1%.When stopping the water vapor and SO₂,NO conversion partially restored.The effect of water vapor on the stability of NO conversion is higher than that of SO₂.La₂-Cu-ZSM-5 prepared with0.0025 mol/L lanthanum nitrate has the best water vapor resistance,and NO conversion reaches57.9%.Cu-ZSM-5@Ce₂ prepared with 0.001 mol/L cerium nitrate has the best resistance to water vapor and SO₂,and NO conversion reaches 58.2%.（2）High-temperature water vapor（450-600℃）impacts the catalyst framework,causing the framework aluminum to fall off,and the four-membered ring and the five-membered ring are severely broken.The crystallinity of the catalyst is reduced,the number of micropores is reduced,and the particle surface is eroded to form cavities.10%water vapor reduce NO adsorption capacity in[Cu-O-Cu]²⁺active sites by 18.1%,the active sites ratio decreases by45.4%,and the side reaction produces Cu O by water vapor with the active sites.The completeness of the catalyst particles under the effect of SO₂ is reduced,the flakes are increased,the pores of the ten-membered ring are severely fractured,and the mesopores increase.0.5%of SO₂ reduces the amount of NO adsorption in the active sites by 15.6%,and SO₂ reacts with active sites and free Cu²⁺to form Cu SO₄.（3）La doping does not change the crystallinity of Cu-ZSM-5,the specific surface area of the micropores and the pore diameter.The more the load of La,the stronger the protective ability of the skeleton.0.0025 mol/L lanthanum nitrate increase Cu loading by 0.23%.After the action of water vapor,the proportion of active sites only decrease by 2.5%.[La-O-La]⁴⁺is preferentially combined with water molecules to prevent high-temperature water vapor from directly impacting the catalyst framework and inhibit the hydrolysis reaction of the active sites.（4）Cu-ZSM-5@Ce₂ catalyst prepared by 0.001 mol/L cerium nitrate has a CeO₂ oxide film is moderate,uniform element distribution,and good crystallinity and pore structure.CeO₂oxide film contains a large amount of highly active Ce⁴⁺and O_β,which accelerates the release step of Cu-ZSM-5 catalytic decomposition of oxygen.And CeO₂ promotes the conversion of free Cu²⁺on the surface of the catalyst to the active sites,increasing its quantity.CeO₂ oxide film wraps on the outer surface of Cu-ZSM-5 particles,preventing the contact of water vapor or SO₂ with the active sites.