Study of the Parameters Impacting the Photocatalytic Reduction of Carbon Dioxide in Ionic Liquids

摘要

To overcome the chemical inertness of CO2, one strategy consists of pre-activating or destabilizing it, to lower the reduction barrier, by preparing a carbene-CO2 compound where the CO2 is bent rather than linear. This pre-activation has been studied in ionic liquids (IL) based on imidazolium as a cation with different anions under conditions of mild pressure, room temperature and UV/Vis light. This screening 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. A co-solvent can be used to consume the photo-generated holes in Pd/g-C3N4 as a sacrificial agent but also to provide the protons necessary to reduce CO2. In this study, the influence of several type of co-solvents such as H2O, isopropanol (iPrOH), and 1-(2-hydroxyethyl)-3-methyl imidazo- lium bis(trifluoromethanesulfonyl)imide [C1C2(OH)ImNTf2], has been tested on the activation of CO2 in C1C4ImOAc. We first defined the optimal molar ratio of co-solvent to be used in order not to compromise CO2 pre-activation for subsequent application in CO2 transformation. Photocatalytic reductions of CO2 to CO on Pd/g-C3N4 by varying different parameters demonstrated that CO2 pre-activation in a mixture of C1C4ImOAc and isopropanol was the most efficient to consider a prospective strategy of CO2 photoreduction in an IL medium.