Ionic Liquid Catalyzes Reactive CO2 capture

CO2 hydroxylation is the underlying reaction for a wide range of reactive CO2 capture (RCC) techniques. Despite being thermodynamically favorable, the CO2 hydroxylation kinetics are sluggish due to a higher energy barrier associated with bending the linear CO2 molecule prior to nucleophilic attack by OH-. Here, we report a previously unrecognized catalytic effect where ionic liquids (ILs) increase the rates of CO2 hydroxylation by pre-activating (or bending) CO2 locally around IL. ILs are known for their higher CO2 solubilities owing to larger void fractions; however, their role in catalyzing the CO2 hydroxylation reaction, an important step in RCC, has not been reported before. NMR, FTIR, and quantum-chemical calculations confirm bicarbonate as the dominant stable species, with carbonate converting back to bicarbonate over time. For instance, the addition of BMIM NTf₂ in KOH-ethylene glycol mixture accelerates CO2 hydroxylation by sixfold by lowering the activation energy (~35%) without chemically binding CO₂, highlighting its catalytic role. While low IL loadings enhance kinetics, higher concentrations hinder CO2 mass transfer due to reduced interfacial tension. The nature of IL cation and anion strongly influences rates, with shorter alkyl chains and I⁻/OTf⁻ anions providing the highest activity. The system demonstrates reversibility and robustness under flue gas conditions, offering a tunable pathway for efficient CO2 capture.