Revealing the Mechanism of Converting CO 2 into Methanol by the Cu 2 O and Oxygen Vacancy on MgO: Experiments and Density Functional Theory.

Given the great significance of defect and Cu compounds for the reduction of CO ₂ as well as the few reaction mechanisms of converting CO ₂ into different hydrocarbons, the effects of oxygen vacancies and Cu ₂ O on the reduction of CO ₂ were thoroughly investigated, and possible mechanisms were also proposed. A series of Cu ₂ O/O _v -MgO catalysts were synthesized for photothermal catalytic reduction of CO ₂ to methanol under visible-light irradiation, among which the 7%Cu ₂ O/O _v -MgO composite exhibited the best reduction activity and the yield of methanol was 19.78 μmol·g ^-1 ·h ^-1 . The successful composite of Cu ₂ O and O _v -MgO can yield a loose and porous nanosheet, uniform distribution, favorable absorbance and photoelectric performance, and increased specific surface area and adsorption ability of CO ₂ , which are all vital to the adsorption and conversion of CO ₂ . The introduction of oxygen vacancy and Cu ₂ O not only promotes the adsorption of CO ₂ but also provides more electron-triggered CO ₂ activation. Density functional theory (DFT) calculation was also performed to reveal the reaction mechanism for effective enhanced CO ₂ reduction to ethanol or methanol by the comparison of CuO/MgO and Cu ₂ O/O _v -MgO composites, illustrating the reaction pathways of different products. By comparing the key steps in determining the selectivity of C ₁ or C ₂ , the kinetic barriers of obtaining CH ₃ OH for the Cu ₂ O/O _v -MgO composite with CH ₃ OH as the main product were found to be lower than those of generating CH ₂ *, while the opposite is true for CuO/MgO composites, whereby it may be easier to obtain more C ₂ products. These insights into the reaction mechanism of converting CO ₂ into different hydrocarbons are expected to provide guidance for the further design of high-performance photothermal catalytic CO ₂ reduction catalysts.