Possible mechanisms for organic carbonates from CO₂ capture.

Post-combustion carbon capture appears a necessary part of CO₂ abatement. The economy thereof can be improved by subsequent utilization of the captured carbon in a Carbon Capture and Utilization (CCU) approach. A challenge in CCU is the large amount of energy normally needed to functionalize CO₂, due to its thermodynamic stability. This challenge may be met by reacting the gas to something in which the oxidation number of carbon is unchanged at +4. A possibility involves reactions between CO₂ and alcohols to organic carbonates. Based on experimental insight a mechanism for amine-catalyzed formation of organic carbonates from CO₂ and alcohols was suggested (1). We here report quantum chemical results for such a mechanism and an analysis of the factors governing reactivity. Our results indicate that the presence of an additional molecule as co-catalyst is required to obtain energetically feasible pathways. Calculations were carried out using NWChem/ B3LYP/aug-cc-PVDZ (2,3,4), including Grimme D3 for dispersion corrections (5) and COSMO with acetonitrile for solvent effects (6).