Synthesis Of Zinc MOFs Derived Materials For CO₂ Adsorption And Conversion

CO₂,as a major greenhouse gas,which emissions have a significant impact on the ecology of the planet.Moreover,CO₂ is a very cheap,and non-toxic C1 resource that can be processed and converted into high-value chemicals using a variety of organic compounds,which made efficiently CO₂utilization technology very meaningful.One of the numerous conversion pathways is cycloaddition between CO₂ and epoxides to produces cyclic carbonates,which has 100%atomic economy,meets the requirements of environment friendly,and has broad application prospects.However,many obstacles still exist in applied catalysts,such as low catalytic activity or separation difficultion.Therefore,with the demands of efficient and stable catalyst for cycloaddition reaction,three multiple active sites cooperated MOF materials are designed and synthesized.The main research contents are as follows:（1）A series of new porous supported catalysts（ZIF-PVIB）were prepared by introducing hydrogen bond donor groups and nucleophilic groups into the catalyst structure by radical polymerization and post-modification using zinc-based metal-organic framework material ZIF-8 as the carrier and 1-vinylimidazole as the monomer.The structure of ZIF-PVIB catalyst was characterized by FT-IR,PXRD and other characterization methods.The effect of the ratio of support to monomer on the pore structure and specific surface area of the catalyst was studied.The prepared ZIF-PVIB was applied to catalyze the conversion of CO₂ into cyclic carbonate,and the effects of different catalyst structure,reaction conditions and other factors on the catalytic activity were systematically studied,and the results showed that the ZIF-PVIB-3 catalyst with a ratio of support to monomer mass of 1:3 could catalyze 98%of the product yield at130℃,2 MPa,6 h.The catalyst can maintain good catalytic activity after 5 cycles,and has good universal applicability to the cycloaddition reaction of different epoxy substrates.Finally,combined with the experimental results,the mechanism of ZIF-PVIB catalyzed CO₂ cycloaddition reaction is proposed.（2）In order to simplify the preparation process of the catalyst and further improve the catalytic performance of the catalyst for cycloaddition reaction,bisimidazolyl ionic liquid monomers were designed and synthesized to perform radical polymerization on the surface of ZIF-8 to prepare a core-shell double-active site composite（ZIF-PDB）with high specific surface area.The structure of ZIF-PDB catalyst was investigated by FT-IR,PXRD and other characterization methods.The effect of different polyionic liquid loading on catalyst activity was systematically studied by taking CO₂ and propylene oxide cycloaddition to propylene carbonate as a model,and the optimal loading amount was obtained through comparative experiments.After optimizing the process conditions,it was found that the ZIF-PDB-2 catalyst could obtain 97%product yield with 5 wt%catalyst dosage at 120℃,2 MPa,and 5 h,and the selectivity was greater than 99%.In addition,ZIF-PDB-2 showed good universality to other epoxides investigated,and could be recycled 10 times and maintained good catalytic activity.Finally,combined with experimental research and density functional theory calculation,the mechanism of CO₂cycloaddition reaction under catalytic system is revealed.（3）In order to further introduce the multi-Lewis base group,using ZIF-8 material as the carrier,amino functionalized ionic liquid and vinyl imidazolium salt were selected as monomers,and a series of novel ZIF-8 matrix composites（ZIF-VAImBr）were prepared and characterized by two-component radical polymerization.The effects of ionic liquid species on pore structure,specific surface area and stability of catalysts were systematically investigated.The structure,morphology and catalytic site of ZIF-VAImBr catalyst were investigated by FT-IR,PXRD and other characterization methods.The ZIF-VAImBr catalyst was applied to the heterogeneous catalytic CO₂ cycloaddition reaction,and the reaction temperature,reaction time,reaction pressure and other conditions were optimized.The results show that ZIF-VAImBr catalyst can efficiently convert CO₂ into target cyclic carbonate products at 100℃,2 MPa,5 h,solvent-free and co-catalyst-free,and the catalytic activity is not significantly reduced after 10 cycles.At the same time,combined with the experimental research and characterization results,the mechanism of Lewis acid-base and nucleophilic site synergistic catalyzed CO₂cycloaddition reaction was proposed.