Synergistic Catalysis By Hydroxyl For Fixation Of CO₂into Cyclic Carbonate

Carbon dioxide is a main greenhouse gas. It is also a cheap, nontoxic, andabundant carbon source. Hence, development of green, efficient and inexpensive wayto fix carbon dioxide into useful chemical products has attracted widespread attentionin recent years. It was recently reported that, one of the most effective method ofchemical fixation of CO₂is the coupling reaction of epoxide and CO₂to generatecyclic carbonates. Considering the problems in cycloaddition of CO₂and epoxide toproduce cyclic carbonate, the main work and innovative results for this dissertationare summarized as follows:1A series of hydroxyl-functionalized quaternary ammonium salts with differentnumber of hydroxyl group in the cation were synthesized. Their activity andreusability toward the coupling of epoxide and CO₂without any additional co-catalystand organic solvent were investigated thereafter. Although the synergistic effect ofhydroxyl group is preferable to accelerate the reaction, interestingly, the number ofhydroxyl groups in the cation of the salts did not play a positive effect on the reaction.As a result, highest activity and selectivity were achieved in the presence of threehydroxyl groups functionalized quaternary ammonium salts. The relationship betweenthe higher catalytic reactivity and OH-functional group was proposed.2A catalytic system composed of triethanolamine and potassium iodide wasproved to be efficient for the chemical fixation of CO₂with epoxide under the mildconditions. Effects of parameters such as catalyst molar ratio and amount, reactiontime, pressure, and temperature were studied systematically. It was found that a91%conversion of propylene oxide as well as99%propylene carbonate selectivity couldbe achieved in the presence of triethanolamine/KI （molar ratio=l:1） at110℃,2MPa,1h without any organic solvents. Moreover, the catalyst could be reused for five timeswithout loss of activity.and was found to be applicable to other terminal epoxides. Theeffect of the catalytic system with different number of hydroxyl group on the reactionwas systematically investigated.3ordered mesoporous carbon CMK-3modified imidazoles ionic liquid catalystwere synthesized and applied to the synthesis of cyclic carbonate. The samples werecharacterized by X-ray powder diffraction （XRD）, nitrogen adsorption-desorption,transmission electron microscopy （TEM） and elemental analysis.