Experiment of Cu-ZSM-5 catalytic decomposition of NO in coal-fired flue gas

The denitration method of direct catalytic decomposition of NO avoids the disadvantages of air preheater blockage and catalyst poisoning caused by the use of NH₃ in SCR.It is a new denitrification method worth studying.The Cu ion-exchanged ZSM-5 zeolite exhibits high NO decomposition activity.A series of Cu-ZSM-5 catalysts was prepared by ion exchange method and used for the direct catalytic decomposition of NO in flue gas.The effects of preparation conditions such as the silicon-aluminum ratio of ZSM-5 zeolite, Cu ion concentration of exchange liquid, exchange temperature and reaction conditions such as reaction temperature, space velocity, O₂ concentration on the catalytic performance of Cu-ZSM-5 catalytic decomposition NO were compared.Considering the catalytic efficiency, catalyst processing capacity, and the actual flue gas environment of coal-fired power plants, the optimum preparation conditions of the catalyst were obtained as follows: the silicon-aluminum ratio is 25,Cu ion concentration is 0.01 mol/L,and exchange temperature is 40 ℃.The optimal reaction conditions were reaction temperature 550 ℃,space velocity 1 200 h^-1,and O₂ concentration 5%.The result showed that the decomposing conversion rate of NO was close to 50% under the optimum conditions.ICP-OES,XRD,BET,SEM,TEM,O₂-TPD were applied to the characterization and analysis of these catalysts, and the effect mechanisms of reaction conditions and preparation conditions on the performance of Cu-ZSM-5 in catalytic decomposition NO were obtained.The zeolite silicon-aluminum ratio determines the exchangeable copper species content, and a lower silicon-aluminum ratio can provide more exchange sites.The Cu²⁺ concentration indirectly changes the exchange degree of Cu-ZSM-5 by affecting the content of the hydrolyzed product Cu(OH)⁺.The lower exchange temperature is not conducive to the hydrolysis of Cu²⁺ to form the active center precursor Cu(OH)⁺.Higher exchange temperature will cause the hydrolysis process to move to the two-step hydrolysis direction, forming inactive CuO.Increasing the reaction temperature can increase the reaction rate and accelerate the separation of O₂ from the active center.The lower the space velocity, the longer the contact time between the catalyst and the reactant.The lower the O₂ concentration, the stronger the deoxygenation cycle regeneration performance of the active center Cu²⁺-O_2--Cu²⁺²⁺,and the higher the catalytic activity.