Study of the Parameters Impacting the Photocatalytic Reduction of Carbon Dioxide in Ionic Liquids
Yulan Peng, Kaï C. Szeto, Catherine C. Santini, Stéphane Daniele
Abstract
Abstract To overcome the chemical inertness of CO 2 , one strategy consists of pre‐activating or destabilizing it, to lower the reduction barrier, by preparing a carbene‐CO 2 compound where the CO 2 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 (C 1 C 4 ImOAc) was capable of effectively pre‐activating CO 2 by chemical sorption to give a more reactive 1‐butyl‐3‐methyl‐imidazolium‐2‐carboxylate (C 1 C 4 ImCO 2 ) species. A co‐solvent can be used to consume the photo‐generated holes in Pd/g‐C 3 N 4 as a sacrificial agent but also to provide the protons necessary to reduce CO 2 . In this study, the influence of several type of co‐solvents such as H 2 O, isopropanol (iPrOH), and 1‐(2‐hydroxyethyl)‐3‐methyl imidazolium bis(trifluoromethanesulfonyl)imide [C 1 C 2 (OH)ImNTf 2 ], has been tested on the activation of CO 2 in C 1 C 4 ImOAc. We first defined the optimal molar ratio of co‐solvent to be used in order not to compromise CO 2 pre‐activation for subsequent application in CO 2 transformation. Photocatalytic reductions of CO 2 to CO on Pd/g‐C 3 N 4 by varying different parameters demonstrated that CO 2 pre‐activation in a mixture of C 1 C 4 ImOAc and isopropanol was the most efficient to consider a prospective strategy of CO 2 photoreduction in an IL medium.