Construction Of Ionic Liquid Immobilized MOF And Its Application In CO₂ Cycloaddition Reaction

Cyclic carbonates are low-toxic,degradable,high-value-added chemical products,cycloaddition reactions to afford cyclic carbonates from carbon dioxide（CO₂）and epoxides are considered to be a 100%atom-economic reaction.At present,catalytic systems that mediate the CO₂ cycloaddition reaction are usually carried out at harsh conditions such as high temperature and pressure,which limits their industrial applications.The separation and recovery of catalysts from the reaction mixture is also an ongoing challenging,therefore,the development of highly efficient,easily separable catalysts for the CO₂ cycloaddition reaction to synthesize cyclic carbonates under mild conditions has been a hot research topic.In recent years,Metal Organic Frameworks（MOFs）materials have attracted wide interests due to their diverse functional groups,adjustable organic ligands,high porosity and large specific surface area.In addition,the inherent porous physical structure of MOFs facilitates the adsorption CO₂and the diffusion of substrates.The crystallographic nature of MOFs and their diverse ligand adjustability are helpful in constructing reactive sites and understand the structure-activity relationship in the reaction mechanism.This thesis discusses the preparation of solid-supported ionic liquids using MOFs MIL-101-NH₂ which shows strong CO₂ adsorption capacity,magnetic nano-iron oxide Fe₃O₄ coated HKUST-1 and MIL-101-SO₃H that has strong epoxide activation capacity.These dual-functioning catalysts are shown to mediate the synthesis of cyclic carbonates under mild conditions.The mechanism of the reaction has been probed from the bonding interactions between ionic liquids and MOFs and through reasonable characterization methods,the structure-activity relationship between the active sites of the catalysts and the CO₂ cycloaddition reaction is also discussed.The main findings are as follows:（1）Aiming at the challenge that CO₂ is thermodynamically stable and difficult to activate.MIL-101-NH₂ that has strong CO₂ adsorption capacity is used as a solid-carrier to achieve the immobilization of a carboxylic acid functionalized imidazolium chloride ionic liquid.Through the step-by-step post-modification method of first loading and then ammoniating,the problem of inactivation of acid-base active sites is avoided.A series of experimental results show that the interaction of the Cl-Cr coordination bond between the host and the guest is used to encapsulate the ionic liquid in the nanocage of the carrier MIL-101-NH₂,this interaction is also supported by DFT calculations.Compared with the unaminated IL/MIL-101-NO₂,the presence of NH₂ functional group in MIL-101-NH₂has significantly increased the amount of CO₂adsorbed by the catalyst IL/MIL-101-NH₂.Up to 7.4 mmol/g CO₂ can be adsorbed under the condition of 1 bar CO₂.Under relatively mild conditions,the dual-functioning catalyst IL/NH₂-MIL-101 shows superior activity and reusability in the CO₂ cycloaddition reactions with epoxides,for example,91%CO₂ conversion rate is achieved,and the catalyst has been reused for 5 times in the recycling experiment,with no significant decline in the catalytic activity.（2）In order to improve the separation and recovery performance of the solid-supported ionic liquid catalyst.HKUST-1 is composited with magnetic Fe₃O₄ particles,and through the donor-acceptor interaction,the amino borofluoride ionic liquid（IL）with high epoxide activation ability is immobilized on Fe₃O₄@HKUST-1,the immobilized binding mode was verified by DFT calculations.Under relatively mild reaction conditions,the catalyst IL/Fe₃O₄@HKUST-1 exhibits superior activity in CO₂cycloaddition reactions with various substrates,the CO₂ conversion rate can reach up to 94%.In addition,the catalyst shows excellent catalytic reactivity after recovered by an external magnetic field.（3）To expand the functional magnetic composite materials,IL/MIL-101-SO₃H is synthesized by combining a magnetic functionalized ionic liquid（[TMG]Cl/2Fe Cl₃,IL）with the solids-carrier MIL-101-SO₃H.Under relatively mild reaction conditions,the CO₂conversion rate can reach 93%in the cycloaddition reaction,and the catalyst exhibits reusability after recovered by external magnetic field.Compared with previously mentioned IL/Fe₃O₄@HKUST-1 magnetic catalyst,IL/MIL-101-SO₃H maintains excellent CO₂cycloaddition reaction performance,while reducing the additional mass of the external magnetic donor,thus providing feasibility for the promotion and application of MOFs immobilized ionic liquid catalysts.