Preparation Of ZIF-67@CeO₂ Composite Material And Study On Its Catalysis Of CO₂ Cycloaddition Reaction

Zeolitic imidazolate frameworks（ZIFs）are a new type of nanoporous crystal materials,which have huge specific surface area,ultra-high porosity,tunable properties and function,high thermal stability.Therefore,ZIFs have shown broad application prospects in the fields of adsorption,gas storage,drug delivery,separation,and photoelectricity.In addition,ZIFs have unsaturated metal centers and organic functional groups on the imidazole ring,can provide catalytic active centers for catalytic reactions.So,they have received great attention in the field of catalysis.In particular,ZIFs have shown great application potential in the cycloaddition reaction of CO₂ and epoxides.This is because the Lewis acid sites on the ZIFs skeleton can activate the epoxides,while the Lewis base sites on the imidazole ligands can adsorb and activate CO₂,and exhibit a high CO₂ adsorption rate in the CO₂ cycloaddition reaction.However,traditional ZIFs as catalysts still have disadvantages such as low catalytic activity and poor recyclability.Therefore,the development of functional ZIFs materials have gradually become a research hotspot in the field of ZIFs synthesis and application,and ZIFs composite materials with a core-shell structure have also emerged.Compared with traditional ZIFs materials,ZIFs composites with a core-shell structure have the excellent characteristics of ZIFs and other materials,and exhibit different properties in terms of specific surface area,pore structure,and acid-base properties,and have enhanced catalytic performance.Based on the previous work,this paper designs and synthesizes the ZIFs composite material with a core-shell structure,uses experimental characterization techniques to study its structure and properties,and investigates its catalytic performance in the cycloaddition reaction of CO₂ and epoxides.In this paper,ZIF-67@Ce O₂ composite material was prepared in ethanol solvent with ZIF-67 as the seed and cerium nitrate as the reaction substrate.ZIF-67@Ce O₂ were characterized by PXRD,FE-SEM,TEM,XPS,N₂ isothermal adsorption and desorption,TPD,TG,elemental analysis and ICP-OES.The results showed that the ZIF-67@Ce O₂ had a unique core-shell structure and maintained high specific surface area,high pore volume and good thermal stability of ZIF-67.The ZIF-67@Ce O₂ was used to catalyze a series of cycloaddition reactions of epoxides and CO₂,and compared with single ZIF-67 and Ce O₂.The results were found that ZIF-67@Ce O₂-33.3%（33.3%=Ce（NO₃）₃.6H₂O/（ZIF-67+Ce（NO₃）₃.6H₂O））showed different acid-base properties from ZIF-67 and Ce O₂,and had more acid-base sites.The ZIF-67@Ce O₂-33.3%showed enhanced catalytic activity in the cycloaddition reaction of CO₂ and styrene oxide,and the conversion rate of styrene oxide can reach 100.00%,indicating that it had good applicability in reactions involving complex epoxides.The catalytic conversion rate of ZIF-67@Ce O₂-33.3%remained at 100.00%when it was reused for the fourth time,indicating its excellent recyclability.