Protic ionic liquids tailored by different cationic structures for efficient chemical fixation of diluted and waste CO2 into cyclic carbonates

Environment-friendly approaches to directly convert atmospheric or flue gas CO2 to high-value chemicals is of great significance yet challenging. Protic ionic liquid catalysts with excellent properties are showing potential for the chemical fixation of CO2. In this work, a series of protic ionic liquids with different cationic structures have been synthesized, which bear hydrogen-bond interactions between unique N+–H bonds and the O atoms of epoxides and they are highly active catalytic sites. It was found that [AlTMG]Br shows obviously high/good catalytic activity for converting epoxides into cyclic carbonates with CO2 in the atmosphere or at even lower pressures (15% CO2 and 85% N2), outperforming the corresponding homogeneous catalyst analogues and superior to the known solvent- and metal-free catalytic systems. The results showed that under mild homogeneous catalytic reaction conditions, low-pressure CO2 can directly react with epoxides to give cyclic carbonates with excellent yields, without any co-catalysts such as metals, solvents and additives. In addition, the best catalyst [AlTMG]Br was proved to be robust with remarkable reusability, and displaying great potential for pollution reduction and industrial applications for the chemical conversion of atmospheric CO2.