Insight into the mechanism for the methanol synthesis via the hydrogenation of CO2 over a Co-modified Cu(100) surface: A DFT study.

A comprehensive density functional theory calculation was employed to investigate the reaction mechanism of methanol synthesis on a Co-modified Cu(100) surface via CO2 hydrogenation. The Cu(100) surface with embedded small Co clusters prepared experimentally was employed as a model system to explore the effects of Co dopant on the catalytic performance of Cu(100) surface towards CH3OH synthesis. The activation energy barriers and the reaction energies of 16 elementary surface reactions were determined. Our calculated results show that the most favorable reaction pathway for the hydrogenation of CO2 to CH3OH follows the sequence of CO2 → HCOO* →H2COO* →H2COOH* →H2CO* →H3CO* →H3COH*, and the OH* group hydrogenation to H2 O* is the rate-limiting step with an activation barrier of 112.3 kJ/mol. It is noted that, since the strength of Co-O bond is stronger than that of Cu-O bond, the introducing of Co dopant on the Cu surface can facilitate the formation of key intermediates for the CH3OH synthesis. Especially, the stability of the unstable dioxomethylene intermediate (H2COO*) found on the pure Cu(100) surface can be obviously enhanced on the Co-doped Cu(100) surface. As a result, with respect to the undoped surface, the productivity and selectivity towards CH3OH production on the Cu(100) surface will be improved after dispersing small Co clusters on the surface.