1Institute of Applied Synthetic Chemistry, Vienna, Austria
Opposites attract: The combination of sub- or supercritical CO2 (scCO2) and ionic liquids offer unique opportunities for process intensification. In general, the solubility of CO2 in ionic liquids increases with increasing pressure, which leads to intense investigations for the use in capture techniques, often enhanced by chemisorption. On the other hand, ionic liquids are virtually insoluble in scCO2, which renders them ideally suited for forming biphasic systems with scCO2 for multiphase catalysis.
Supercritical CO2 can be employed as a carrier for reactants and gases into the ionic liquid phase while efficiently extracting valuable products. This is particularly important for CO2 reductions since products such as CO produced during catalysis are distributed into the CO2 phase, thus preventing a build-up of CO around the catalyst. Furthermore, the benefits of ionic liquids are not limited to facilitated reaction engineering in biphasic catalytic systems. Eventually, ionic liquids may act as catalysts or cooperative media for catalysis, while CO2 can simultaneously serve as the solvent and C1 building block for fine chemicals.
This presentation will highlight different applications for combining ionic liquids and sub- or supercritical CO2 in catalysis. Examples will include waste biomass valorization in ionic liquid/scCO2 biphasic systems and catalytic processes with supported ionic liquids as catalysts. Ultimately, we will discuss the photocatalytic reduction of CO2, where ionic liquids as cooperative media play a triple role as co-catalyst activating CO2 towards reduction but also immobilize the involved catalysts and increase the solubility of CO2 compared to conventional solvents.