Heterogeneous Photocatalytic Systems Formed by Compound [Zr6O4(OH)4(C6H5COO)8(H2O)8][SiW12O40] in Combination with Inorganic Cocatalysts for the CO2 Reduction to Alcohols in Water.

The photoreduction of CO2 to methanol and ethanol is a highly sought-after reaction due to the economic and environmental implications of these products. Both methanol and ethanol are versatile chemical feedstock and renewable fuels. The ionic hybrid compound [Zr6O4(OH)4(C6H5COO)8(H2O)8][SiW12O40] (Zr6W12) provides effective separation of the generated electron-hole pair during exposure to UV radiation through a Z-scheme disposition of the HOMO-LUMO levels of each discrete ionic entity. However, this compound does not promote the CO2 reduction. In contrast, the incorporation of selected inorganic cocatalysts, such as AgI, Bi2O3, CeO2, CuI, CuO, Cu2O, In2O3, PbO, Sb2O3, SnO, TiO2 or ZnO, to the photocatalytic system can enable the activation and reduction of CO2, leveraging their electronic properties and interactions with Zr6W12. Some of these heterogeneous photocatalytic systems perform well for the photoreduction of CO2 into methanol and/or ethanol in water and without the need of any sacrificial chemical reagent, achieving maximum production levels of 163 μg g-1 h-1 and 144 μg g-1 h-1 for methanol and ethanol, respectively, for the Zr6W12/CuI photocatalytic mixture. Theoretical calculations have been conducted to determine how the relative disposition of the HOMO/LUMO energy levels of Zr6W12 and the band structure of the inorganic cocatalysts impact on the CO2 photocatalytic reduction to alcohols.