Ion-island induced spatially separated active sites in poly(ionic liquid)s for efficient CO2 fixation into cyclic carbonates

Abstract

Carbon dioxide (CO₂) conversion into carbonates via cycloaddition with epoxides represents a promising approach for achieving carbon neutrality and advancing clean energy technologies. However, it remains challenging to design efficient heterogeneous catalysts that achieve high catalytic activity comparable to homogeneous components with minimal dosage under mild conditions. From the perspective of maintaining intrinsic activity while realizing sufficient exposure of active sites, this work presents a new strategy to construct efficient heterogeneous catalysts based on ion-island induced spatially separated active sites in hyper cross-linked poly(ionic liquid)s (HPILs). By optimizing the Friedel-Crafts alkylation and ionization in specific directions, we synthesized a series of HPILs featuring ion-island architectures with spatially separated active sites. Intriguingly, it was discovered that the electron-withdrawing ionic liquids induced unidirectional polymerization into ion-islands, and the electron-rich triphenylphosphine (PPh₃) tended to cross-link multidirectional forming networks, which co-regulated the distributions of ion-islands and therein inter-ion interaction. Remarkably, HPIL-3 with peripherally distributed ion-islands demonstrated exceptional catalytic efficiency (TOF = 1451.1 h⁻¹) for CO₂ and propylene oxide (PO) at 90 °C with 0.05 mol% Br^- (relative to PO). Combining EPS and in-situ DRIFTS analysis revealed that the quaternary phosphine cations (P⁺) and Br^- synergistically activated both CO₂ and PO molecules, thereby accelerating the cycloaddition process.