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

Abstract

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 imidazolium 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.

Thermo‐ and Photocatalytic Activation of CO2 in Ionic Liquids Nanodomains

“…Peng an co-workers screened the influence of several co-solvents (H 2 O, iPrOH, and EM-(OH)Im•NTf 2 ) on the activation of CO 2 by Pd/g-C 3 N 4 catalyst in BMIm•OAc IL. [118] A high rate of CO (70.82 μmol g À 1 h À 1 ) with a selectivity of 100 % was found in iPrOH/BMIm•OAc reaction media. Recently, modified ZnSe quantum dots with thiol functionalized imidazoliumbased IL (3-(2-mercaptoethyl)-1-methyl-imidazolium tetrafluoroborate (MEMIm•BF 4 )) were prepared and generated up to 2.4 mmol CO g ZnSe À 1 in aqueous ascorbate solution.…”

“…The authors concluded that the presence of citrazinate anion is the key factor that provided multiple sites for CO 2 absorption and acted as a photosensitizer. Peng an co‐workers screened the influence of several co‐solvents (H 2 O, iPrOH, and EM(OH)Im⋅NTf 2 ) on the activation of CO 2 by Pd/g‐C 3 N 4 catalyst in BMIm⋅OAc IL [118] . A high rate of CO (70.82 μmol g −1 h −1 ) with a selectivity of 100 % was found in iPrOH/BMIm⋅OAc reaction media.…”