Revealing the Mechanism of Converting CO2 into Methanol by the Cu2O and Oxygen Vacancy on MgO: Experiments and Density Functional Theory.

Given the great significance of defect and Cu compounds for the reduction of CO2 as well as the few reaction mechanisms of converting CO2 into different hydrocarbons, the effects of oxygen vacancies and Cu2O on the reduction of CO2 were thoroughly investigated, and possible mechanisms were also proposed. A series of Cu2O/Ov-MgO catalysts were synthesized for photothermal catalytic reduction of CO2 to methanol under visible-light irradiation, among which the 7%Cu2O/Ov-MgO composite exhibited the best reduction activity and the yield of methanol was 19.78 μmol·g-1·h-1. The successful composite of Cu2O and Ov-MgO can yield a loose and porous nanosheet, uniform distribution, favorable absorbance and photoelectric performance, and increased specific surface area and adsorption ability of CO2, which are all vital to the adsorption and conversion of CO2. The introduction of oxygen vacancy and Cu2O not only promotes the adsorption of CO2 but also provides more electron-triggered CO2 activation. Density functional theory (DFT) calculation was also performed to reveal the reaction mechanism for effective enhanced CO2 reduction to ethanol or methanol by the comparison of CuO/MgO and Cu2O/Ov-MgO composites, illustrating the reaction pathways of different products. By comparing the key steps in determining the selectivity of C1 or C2, the kinetic barriers of obtaining CH3OH for the Cu2O/Ov-MgO composite with CH3OH as the main product were found to be lower than those of generating CH2*, while the opposite is true for CuO/MgO composites, whereby it may be easier to obtain more C2 products. These insights into the reaction mechanism of converting CO2 into different hydrocarbons are expected to provide guidance for the further design of high-performance photothermal catalytic CO2 reduction catalysts.