Molecular insights into the carbon dioxide–carboxylate anion interactions and implications for carbon capture

In this work, we analyze the interaction of carbon dioxide with different carboxylate anion derivatives in the gas phase at the ab initio CCSD(T)//MP2 level using the aug-cc-pVTZ basis set. The systems considered here include the formate, acetate, propionate, bicarbonate, carbamate and glycinate anions. The study is relevant to get a better understanding of the interactions involved in novel carbon capture processes through either ionic liquids or amino acid salts. We describe the formation of covalent and non-covalent adducts and show that the formation energies are significantly larger than those previously reported for amines, which are used in conventional carbon capture processes. The nature of the interactions is analyzed using the natural bond orbitals methodology. The binding energy in the non-covalent processes does not depend much on the derivative, but covalent adducts display a rough correlation with nucleophilic/electrophilic indices provided distortion effects on the monomers are taken into account. In the case of glycinate, interactions with the amino and carboxylic moieties involve comparable energetics and the existence of several minima in the potential energy surface might be a factor contributing to the good CO2 capture capacity exhibited by this species in recent experimental studies.