High-Performance and Recyclable Multisite Catalytic System for CO₂ Fixation Using Crown Ether-Linked Schiff Base and Alkali Halides

The development of efficient and sustainable catalytic systems for CO₂ fixation is crucial for carbon-neutral chemical processes. We now report a high-performance and recyclable multisite catalytic system based on a crown ether-linked Schiff base in combination with alkali halides for the synthesis of cyclic carbonates from epoxides and CO₂. The designed catalyst features multiple active sites, including a Lewis acidic alkali ion center and a nucleophilic iodide source, enabling the efficient activation of epoxides under solvent-free conditions with atmospheric pressure. Systematic studies on the effects of cations and calcium salts revealed that the multi-activation mechanism plays a critical role in enhancing the catalytic performance. The catalyst exhibited a high selectivity and activity, achieving up to a 97% yield of cyclic carbonates at atmospheric CO₂ pressure and 70 °C. The simulated post-combustion exhaust gas (CO₂: 7.5%, N₂: 92.5%, relative humidity: 90%) was concentrated to 97% and used as the material for the reaction to yield 90% of styrene carbonate from styrene oxide. Furthermore, the catalyst was easily recovered and reused for multiple cycles without any significant loss of activity. This study provides a practical and environmentally-friendly approach for CO₂ utilization, contributing to the advancement of sustainable catalytic processes.