The entire reaction mechanism for the gas-phase CO2-CO conversion by early transition metal ions, La+, Hf+, and Ta+, are studied using density functional theory (DFT). The results indicate that the lowest energy path corresponds to the eta(2)-O coordination of CO2 followed by the insertion of M+ into the C-O bond. The reactions are all exothermic due to the participation of the metal ions, to be compared with the strong endothermic process of the unimolecular CO2 decomposition. Crossing points (CPs) are localized, and possible spin inversion processes are discussed by means of the intrinsic reaction coordinate (IRC) approach. (c) 2006 Published by Elsevier B.V.