Study On The Preparation And Catalytic Carbon Oxide Conversion Performance Of Functionalized Metal-organic Framework-based Materials

The rapid accumulation of atmospheric carbon dioxide（CO₂）has caused a number of environmental problems such as the greenhouse effect.On the other hand,CO₂,as a non-toxic,abundant and renewable C1 raw material,can be converted into various high-value chemicals.Therefore,the effective capture and resource utilization of CO₂ is conducive to mitigating atmospheric CO₂ concentrations,realizing the artificial carbon cycle process,as well as helping to alleviating mankind’s dependence on traditional energy materials.Among many CO₂ catalytic conversion reactions,the cycloaddition of CO₂ with epoxy compounds is a type of CO₂ chemical fixation reaction with 100%atomic utilization,and its product,cyclic carbonate,is a high-value chemical that is widely used in many fields such as plastics,batteries,and fine chemicals.Unlike conventional catalytic materials,metal organic frameworks（MOFs）are a class of crystalline porous materials constructed from metal ions or metal clusters with organic ligands through coordination bonds.Due to their reasonable structural design,controllable pore size,high surface area and permanent porosity,MOFs have received much attention in recent years as potential systems for gas storage,separation and multiphase catalysis.As for CO₂ capture and conversion,MOFs also show great potential.However,simple MOF materials for CO₂ cycloaddition reactions still face many problems,such as the requirement of high temperature and pressure and other reaction conditions,and the limited active site species.In this context synthesized several composite porous materials with high stability and catalytic performance based on structural advantages of MOF materials,and functionalized them by pyrolysis,material composite and other post-synthesis means to realize the adjustment of pore size and the introduction of new catalytic sites.As a result,several multifunctional MOF-based catalysts were formed for efficient catalysis of CO₂ cycloaddition,thus improving the catalytic efficiency of the reaction under mild conditions,the reuse rate of the catalyst,and their practical application potential.The main research contents are as follows:1.In the CO₂ cycloaddition reaction,Lewis acid and Lewis base sites can be used as the catalytically active sites.Therefore,this work designed a lanthanide（Ⅲ）complex with1-vinylimidazole（Vim）and immobilized it with an aluminum-based MOF,DUT-5,by reaction of polymerization to obtain a porous composite catalyst La-Vim/DUT-5.The high oxyphilicity and Lewis acidity of lanthanide complexes and the Lewis basicity of imidazole N make them promising candidates for the catalytic conversion of carbon dioxide.The density of catalytic active sites can be efficiently tuned to significantly improve the catalytic performance of the coupled CO₂ and epoxide.Specifically,La-Vim/DUT-5 can efficiently convert epichlorohydrin to the corresponding product in up to 94%yield under mild solvent-free conditions（60°C,1 bar CO₂）.Moreover,the yield of cyclic carbonate La-Vim/DUT-5 remained essentially unchanged after 9 cycles.La-Vim/DUT-5 showed good catalytic performance even in low CO₂ concentration or humid environment.2.Although Lewis acid site has good catalytic performance for CO₂ cycloaddition reaction,it is easy to be inactivated under humid conditions,which is not conducive to the capture and utilization of CO₂ in physical environment.Therefore,this work designed an acetic acid-assisted polyhydroxy acid modification method for the preparation of a series of UiO-66-GA-X（X=400,800,1200 or 1600）catalysts containing both Lewis acid and hydrogen bond donor（HBDs）.The effects of the amount of acetic acid and D-gluconic acid,as well as the synergistic interaction between catalytic sites,on the activity of these UiO-66-based catalysts were investigated.Using the competitive fit between the modulator（acetic acid）and the polyhydroxy acid（D-gluconic acid）,HBD can be successfully incorporated into the UiO-66 framework.Benefiting from the presence of D-gluconic acid and the synergy between the Lewis acid and HBD sites,the optimized UiO-66-GA-1200 showed remarkable activity and cyclic stability for the coupling reaction of CO₂ and epoxide under mild reaction conditions（60°C,1 bar CO₂）.Notably,UiO-66-GA-1200 exhibited excellent catalytic performance（yield:92-94%）over the primordial UiO-66 catalyst even when exposed to humid conditions or under dilute CO₂（15%）.This work provides a practicable approach to obtain solid catalysts with HBDs,as well as to promote the chemical immobilization of CO₂ in real feasibility.3.In the above two works,powder materials inevitably face the problem of catalyst separation.Therefore,this work synthesized bimetallic Co/Zn-ZIF-8 by grinding method,and calcined it in argon atmosphere,and finally obtained a porous carbon material with magnetic properties.Mechanical synthesis is an environmentally friendly method for MOF production,which can ensure the minimum amount of solvent used and the effective separation of unreacted metal ions and ligands without heating.The resulting composite catalyst exhibits significant activity for the cycloaddition reaction of CO₂ with epoxide under mild reaction conditions（60℃,1 bar CO₂）.In addition,NPC-900 can be easily removed from the catalytic system in the presence of an external magnetic field.There was no significant loss of product yield after 10repetitions.In addition,the catalytic performance of NPC-900 remained good even when exposed to a humid environment（100%relative humidity,RH）or diluted CO₂（15%）,demonstrating its great potential for practical CO₂ catalytic conversion.In addition,NPC-900 has also been used in solar-driven CO₂ catalytic conversion,and the results also show satisfactory CO₂ catalytic performance.