With the aid of the Density Functional Theory calculations, rate-determining steps were identified for the catalytic hydrogenation cycles of CO 2 and precaptured CO 2 in forms of carbamic acids. The amino ligand of Ru-MACHO® catalyst was proven initially chemically innocent but participated in concerted hydride and proton transfer reactions to produce methanol. The hydrogenation of carbamic acids were indicated more favourable in methanol production than direct CO 2 hydrogenation. • The hydrogenation of CO 2 and precaptured CO 2 by Ru-MACHO® catalyst was studied by DFT calculations. • Rate-determining steps, transition states and intermediates were confirmed by different methods. • The hydrogenation of precaptured CO 2 was proven more favourable in methanol production than CO 2 . • The amino group of catalyst did not always remain innocent but participated in methanol production. Methanol is a liquid hydrogen carrier and potential platform molecule, and significant efforts are currently devoted to hydrogenate CO 2 to methanol. In this work, hydrogenations of CO 2 and captured CO 2 (as dimethylcarbamic acid, DMCA, and methylcarbamic acid, MCA) to methanol over Ru-MACHO (pre)catalysts were studied with a Ru II -catalyst model by Density Functional Theory (DFT) calculations. For the hydrogenation of CO 2 , the concerted reaction was the rate-determining step involving a synchronous hydride transfer and proton transfer from the Ru II -catalyst to coordinatively saturated intermediate methanediol. In the hydrogenation cycles of DMCA and MCA, the first hydride transfer reactions were more difficult than the concerted hydride and proton transfer from the Ru II -catalyst to the aldehyde group of intermediate formaldehyde. These first hydride transfer reactions were identified as the rate-determining steps. The hydrogenations of DMCA and MCA were found much more favourable in methanol production than the direct CO 2 hydrogenation, however, formamides could be main intermediate products due to the easier C O breakage than C N breakage in gem diols, and during the further hydrogenation of formamides, formaldehyde could be the main intermediate due to the easier C N breakage than C O breakage in alkanolamines. In all three hydrogenation cases, the amino (NH) ligand of the Ru II -catalyst initially remained chemically innocent, and intermediates were stabilized by N H⋯O hydrogen-bonding interactions (HBIs) facilitating the continuation of catalytic hydrogenation cycles, but the NH ligand took part in multi-bond concerted reactions to produce eventually methanol.