To overcome the chemical inertness of CO2, the strategy consisted of pre-activating, in order to lower the reduction barrier, by preparing a carbene-CO2 compound where the CO2 is bent rather than linear. Our screening, using ionic liquids (IL) based on imidazolium cation, showed that only 1-butyl-3-methyl-imidazolium acetate (C1C4ImOAc) was capable of effectively pre-activating CO2 by chemical sorption to give a more reactive 1-butyl-3-methyl-imidazolium-2-carboxylate (C1C4ImCO2) species. Co-solvent, such as isopropanol, was used to consume the photo-generated holes (h+) but also to provide the H+ protons necessary to reduce CO2 into CO. In this paper, our data finally allowed, for the first time, to set up optimal operating conditions for the photocatalytic reduction of CO2 to CO in a bare ionic liquid medium. These results are intended to contribute to the implementation of Ionic Liquid as a medium to promote high photocatalytic CO2 transformation efficiency under mild conditions of pressure.
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