Nano‐Confined NHC–Al Interfaces for Efficient CO ₂ Chemical Fixation

Nano‐confined interfacial NHC‐Al sites in Al 2 O 3 ‐supported ionic liquid phases (SILPs) act as engineered catalysts for selective CO 2 fixation into epoxides, with NHC‐Al adduct formation confirmed by solid‐state nuclear magnetic resonance (NMR) and X‐ray photoelectron spectroscopy (XPS). The synergistic combination of NHC‐Al adducts and IL moieties generates membrane‐like nano‐confined environments at the solid–liquid interface. These confined environments regulate substrate access and product diffusion during CO 2 absorption and fixation, which exhibit a high affinity for CO 2 capture under mild reaction conditions. Size‐selective transport within the nano‐confined SILP architecture favors small‐sized epoxides over bulky ones, leading to enhanced reaction rates and selectivity. The NHC@SILP‐PMImAl 2 O 3 catalyst, containing a lower fraction of NHC‐Al adduct (15%) and a high proportion of imidazolium‐chloride ion pairs, exhibited the highest activity, achieving a turnover frequency of 16.09 h −1 for epichlorohydrin at 1‐bar CO 2 and 70°C. In contrast, the NHC‐Al SILPs with a high NHC‐Al adduct (41%) showed a significantly reduced performance (59.1 TONs). This comparison highlights that catalytic efficiency is governed by a balance between NHC‐Al formation and the availability of nucleophilic chloride species within the nano‐confined environment. Chloride‐assisted CO 2 cycloaddition in SILPs proceeds via Al 2 O 3 surface hydroxyl‐mediated epoxide activation rather than imidazolium C2‐H pathways typical of neat ionic liquids, as supported by density functional theory.