Methanol synthesis by CO and CO2 hydrogenation on Cu/γ-Al2O3 surface in liquid paraffin solution

Methanol synthesis by CO and CO2 hydrogenation over Cu-based γ-Al2O3 catalysts has been extensively studied. However, the reaction mechanism of this synthesis on Cu/γ-Al2O3 in liquid paraffin solution is still unclear at the microscopic level. This work investigated the synthesis of methanol by CO and CO2 hydrogenation and water-gas-shift reaction on Cu/γ-Al2O3 in liquid paraffin solution using density functional theory calculations. In CO hydrogenation, methanol was synthesized through the intermediates CHO, CH2O, and CH3O; the rate-limiting step was CHO hydrogenation. In CO2 hydrogenation, methanol was synthesized through the intermediates CHOO, CH2OO, CH2O, and CH3O; the rate-limiting step was CHOO hydrogenation. A comparison of the activation energies of the rate-limiting steps in CO and CO2 hydrogenation (1.37 and 1.10 eV, respectively) at typical catalytic conditions (e.g., 573 K) revealed that the reaction rate of direct CO2 hydrogenation was faster than that of direct CO hydrogenation. This finding indicated that methanol was mainly produced by CO2 hydrogenation. The calculated results were consistent with the experimental ones.