Novel Cu-Based Zeolites:Preparation And Application For Removal Of NOx

Selective catalytic reduction technology is the most effective deNO_x method,which can not only relieve the demage of NO_x to the environment,but also protect human health.The key is the design and preparation of catalysts.Zeolites have the advantages of high specific surface area,large adsorption capacity and good hydrothermal stability,zeolites containing Cu and Fe are considered as the deNO_x materials which most likely to replace commercial V-W-Ti catalysts,and are also the current research hotspots.In this paper,Cu based zeolite catalysts’NH₃-SCR performance was studied on the basis of the reaction characteristics.XRD,NH₃-TPD,solid-state NMR,In-situ FTIR are used to characterize the physicochemical properties of different samples and to explore the relationship between them and catalytic performance.The following results were obtained:In the first part,Cu-ZSM-5 was prepared by dual-template method,the copper-amine complex formed by ethylenediamine and Cu（NO₃）₂ was added in the synthesis process in order to prepare Cu-ZSM-5 by one-step,and the subsequent steps of ion exchange treatment were avoided and the experimental process was simplified.At the same time,the Si/Al ratio and copper content could be simply controlled by changing the addition quantity of copper amine and aluminium source.Compared with Cu-ZSM-5-C prepared by ion exchange impregnation method,Cu-ZSM-5-D prepared by double template method showed better catalytic activity.The results showed that Cu-ZSM-5-D synthesized by double template method has more acidic sites to adsorb more NH₃ and better NO adsorption capacity,which is the main reason for the better catalytic activity of Cu-ZSM-5-D.In the second part,hierarchical ZSM-5 was prepared by one-step hydrothermal synthesis,amphiphilic long chain organic molecule was used as template in the synthsis process.The conventional ZSM-5 was prepared for comparison.Cu species was introduced by ion exchange impregnation method and used for NH₃-SCR.Hierarchical Cu-ZSM-5-meso had better catalytic activity than conventional Cu-ZSM-5-C at low temperature,the apparent activation energies of Cu-ZSM-5-meso and Cu-ZSM-5-C calculated by Arrhenius formula were equivalent,which indicates that the better mass transfer ability of multistage pore structure is the important reason for the better low-temperature acitivity of Cu-ZSM-5-meso.In addition,larger specific surface area,more acidic sites and better NO adsorption capacity are also benefit to NH₃-SCR reaction.It was found that Cu-ZSM-5-meso had good hydrothermal stability,and it could inhibit the formation of nitrate species,and showed better sulfur resistance in 250-300°C.In the third part,hierarchical SSZ-13 was prepared by one-step hydrothermal method with dual-template,Cu species was introduced by ion exchange and then used for NH₃-SCR.It was found that hierarchical Cu-SSZ-13-meso exhibited better catalytic performance than conventional Cu-SSZ-13-C at 100-550°C,wider temperature window and better water and sulfur resistance.The multistage porous structure of Cu-SSZ-13-meso can promote mass transfer,and Cu-SSZ-13-meso had more acidic sites and better redox ability.In addition,Cu-SSZ-13-meso exhibited good hydrothermal stability,which showed good catalytic performance even after hydrothermal aging treatment at 800°C for 16 h.