In Situ Synthesis Of Metal Modified SAPO-34 Zeolite And Study Of Catalytic Performance

Silicon aluminum phosphorus zeolite（SAPO-n）has been widely used in adsorption and catalysis as its unique three-dimensional pore structure,large surface area,adjustable acidity,and high thermal stability.However,due to the limitations of thermodynamic stability,the acidity of zeolite is difficult to be adjusted in a wide range if we only change the Si content in.To solve this problem,heteroatoms are introduced into the framework of zeolite to disturbing the distribution of acid sites in SAPO-34.Then the obtained zeolite with high concentration of acid site was applied in CO₂ cycloaddition reaction.The specific work content is as follows:（1）Firstly,the optimal raw material ratio for hydrothermal synthesis of SAPO-34 was explored by adjusting the ratio between Si and Al in the initial gel.Then,based on the optimal raw material ratio,a one-step hydrothermal method was used to in-situ grow Cu into the framework of SAPO-34.The structural characterization results obtained based on BET,XRD,and UV-vis showed that Cu atoms were successfully doped into the SAPO-34framework,but the introduction of Cu led to a decrease in the crystallinity.According to the quantitative results of acidity,we concluded that with the increase of Cu addition,the acidity of Cu APSO-34 first increased and then decreased.The catalytic performance of Cu APSO-34 was evaluated by CO₂ cycloaddition reaction.Under the optimal reaction conditions,the yield of styrene oxide was 42%.Due to the increase in total acid content generated by Cu modification,its performance is superior to that of SAPO-34.However,Cu_0.05APSO-34 has poor cyclic stability due to the poor hydrothermal stability.（2）In order to obtain a CO₂ cycloaddition catalyst with high activity stability,Zn atoms were introduced into SAPO-34 using the same preparation method.Based on structural characterization such as XRD,BET,and UV-vis,it was determined that Zn atoms were successfully incorporated into the structure of Zn APSO-34 through in-situ growth,and the crystallinity was significantly improved.According to the NH₃-TPD results,the acid content of Zn APSO-34 shows a volcanic trend with the increasing Zn content.When Zn_0.05APSO-34 was applied to the CO₂ cycloaddition reaction,the conversion of styrene oxide can reach74%,which was much higher than the performance of Cu_0.05APSO-34 with the same Cu content.After 10 cycles,the product yield unchanged and has good stability.In conclusion,and the metal isomorphous substituted Me APSO-34 zeolite was successfully prepared by one-step hydrothermal method.The acid amount of SAPO-34 was significantly increased by using heteroatom.The metal isomorphous substituted Me APSO-34 showed high activity and stability for CO₂ cycloaddition.This work provides a guidance for the controllable preparation of high acid zeolite catalyst.