Abstract
The clay mineral-based catalyst assisted with zinc halides was explored for cycloaddition of CO2, which was fabricated by modifying tetramethylguanidine (TMG) on palygorskite (Pal). More activated sites and oxygen vacancies were generated in Pal particles, and were found to be favorable for loading TMG after thermal/acid treatment. The composite TMG@P-Pal in combination with ZnBr2 showed excellent catalytic performance, and the conversion reached 99.0% (selectively >99.0%) for coupling gaseous CO2 with various epoxides. The kinetics indicated that the catalysis followed a reaction order of one, and the apparent activation energy (Ea = 76.93 kJ·mol−1) was derived by the Arrhenius equation. The catalytic activity of zinc halides was confirmed to follow the order of ZnBr2 > ZnCl2 > ZnI2 in producing cyclic carbonates. Both TMG molecules and Pal were found to activate CO2 based on the DFT calculations. This study elucidates the layer-chain structured palygorskite loaded with ZnBr2 can be a promising material for catalyzing CO2 cycloaddition with aid of guanidine molecules.
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