Acid-base bifunctional catalyst: Carboxyl ionic liquid immobilized on MIL-101-NH₂ for rapid synthesis of propylene carbonate from CO₂ and propylene oxide under facile solvent-free conditions

In terms of ‘green chemistry’ and ‘atom economy’, the cycloaddition of CO₂ to yield cyclic carbonate without any additive is an eco-friendly way to utilize CO₂. Unfortunately, the low CO₂ capture quantity of common catalysts limited its catalytic efficiency. Herein, a novel acid-base bifunctional catalyst was successfully prepared by immobilizing ionic liquid on MIL-101-NH₂ (IL/MIL-101-NH₂) and tested for propylene carbonate (PC) rapid and facile synthesis from CO₂ and propylene oxide (PO). The synergetic interaction between Lewis base with strong CO₂ chemical capture capacity and Brønsted acid with strong hydrogen bond donor leads to the high catalytic efficiency of IL/MIL-101-NH₂ for carbonate synthesis from CO₂ and PO without any additive. The immobilization mode between MIL-101-NH₂ and IL is energetically supported by the density functional theory (DFT) calculations. This design idea of specific catalyst and the acid-base synergetic strategy provides new insights into the design of powerful catalyst systems for the CO₂ conversion.