Theoretical evidence of the CO2 reduction by a Mo-based complex: a DFT study based on the reaction force decomposed into four components

Context: The conversion of carbon dioxide into methanoic acid through direct hydrogenation with H2 in the gas phase implies overcoming a high activation energy (more than 60 kcal mol -1) that makes the process kinetically infeasible. In this study, the use of the [(PY5Me2)Mo(III)(H)(OH)]+ complex instead of H2 lowered the activation energy of the hydrogenation by 98.5%. Reaction mechanism in the presence and absence of the Mo-based complex is analyzed through the reaction force, its components, and their respective reaction works. It was found that the high activation energy for the direct hydrogenation of CO2 with H2 is a consequence of a predominance of three types of reaction force components acting as retarding forces while a fourth type of reaction force component is acting as a driving force from the reactant state until the transition state. On the contrary, the low activation energy for the hydrogenation of CO2 assisted by the Molybdenum-based complex is a consequence of opposing types of force components balancing each other, where two act as retarding forces against two reaction force components acting as driving forces. Method: Quantum chemistry calculations were performed through DFT methods with the BP86 density functional along with MWB28 pseudopotentials including a proper basis set for Mo and 6-31+G(d,p) basis set for the remaining atoms implemented in Gaussian 16. AOMix post-SCF software was employed to determine bond orders on stationary points. The reaction force analysis focused on the reaction mechanisms of both chemical reactions using numerical differentiation of energy profiles with OriginPro 2020.