Abstract

Density functional theory (M06-L-D3) calculations have been employed to theoretically study the CO2 cycloaddition to propylene oxide (PO) on the copper-doped graphene with a di-vacancy defect (Cu-DV) and the Cu-N4 moiety embedded into graphene (Cu-NG). A CO2 molecule is adsorbed on the Cu active site of two catalysts with the adsorption energies of about −5.5 kcal/mol. PO adsorbs strongly on the coordinatively-unsaturated Cu site with adsorption energies of −10.0 (Cu-DV) and −11.3 (Cu-NG) kcal/mol. The catalytic generation of cyclic carbonate from CO2 and PO by Cu-DV and Cu-NG is predicted to follow a similar multistep mechanism. The first step is the ring-opening of the adsorbed PO by nucleophilic attack of bromide. The second step is the insertion of CO2 into the CuO bond of alkoxide intermediate to form the linear carbonate intermediate. The third step is the transformation of linear carbonate via intramolecular cyclic SN2-type reaction to form the corresponding cyclic carbonate. Mechanism explorations reveal that the rate-limiting step lies in the formation of cyclic carbonate with activation barriers of 14.8 and 14.9 kcal/mol for the catalytic process over Cu-DV and Cu-NG, respectively. Therefore, our theoretical study suggests that Cu-DV and Cu-NG could possess catalytic activity for CO2 cycloaddition to PO as comparable to that of potential catalysts.

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