CO₂ hydrogenation to methanol is an important route for the resource utilization of greenhouse gases. Conventional gas-phase CO₂ hydrogenation to methanol suffers from low single-pass CO₂ conversion and limited methanol space-time yield at low temperatures. Most existing studies on alcohol-assisted CO₂ hydrogenation to methanol are based on liquid-phase processes, which are difficult to industrialize owing to the challenges in product separation, and the microscopic reaction mechanism and kinetic characteristics of such processes remain unclear. In this work, starting from reaction-pathway regulation, we constructed a gas-phase methanol-assisted CO₂ hydrogenation to methanol reaction system, in which a Ga-modified CuZn-based catalyst achieved a methanol space-time yield of 2.54 g g_Cu^-1 h^-1 at a low reaction temperature of 200 °C. This alcohol-assisted strategy exhibits good universality. Besides methanol, ethanol, n-propanol, and iso-propanol can all enhance catalytic performance, and the promoting effect has also been verified in CuZnAl and CuZnZr catalyst systems. Kinetic analysis revealed that the rate constants for the direct hydrogenation of formate species adsorbed on Cu and ZnO were as low as 0.012 and 0.017 min^-1, respectively. Upon the introduction of methanol, the rate constants of formate species were significantly enhanced to 0.421 and 0.464 min^-1, confirming that methanol addition markedly accelerates the consumption of formate intermediates. Combined with isotope-tracing experiments, physicochemical characterization, and density functional theory (DFT) calculations, it was confirmed that methyl formate is a key intermediate of the alcohol-assisted pathway. Methyl formate exhibits higher low-temperature hydrogenation rate than formate species and is preferentially hydrogenated to methanol rather than decomposed to CO. Ga doping further lowers the activation-energy barrier of the rate-determining step. Kinetic order tests showed that the reaction order with respect to H₂ increases under the methanol-assisted system, indicating that methanol formation rate is more sensitive to the hydrogen partial pressure. This work reveals the promotion mechanism of gas-phase alcohol assistance from both experimental kinetics and theoretical perspectives, providing theoretical support for the development of low-temperature, highly efficient CO₂ hydrogenation to methanol processes.

Alcohol-assisted methanol synthesis, CO2 hydrogenation, Reaction route regulation, Ga modified Cu-based catalyst