Bottom-up fabrication of DABCO-based bicationic ionic liquid-grafted MIL-101(Cr): Facilitating simultaneous activation of CO₂ and epoxides for cyclic carbonate synthesis

Efficient activation of substrates as an orthogonal pathway for facilitating CO₂ fixation into cyclic carbonates, poses ongoing challenges for the ingenious design and development of heterogeneous cooperative catalysts. Herein, a bottom-up strategy was employed to stepwise graft chloromethyl, triethylenediamine (DABCO), and chloroethylamine onto the organic linkers, forming bicationic ionic liquid tethered to MIL-101(Cr). The introduced –NH₂ and quaternary ammonium groups dangling within the micro-mesopores ensured the fast enrichment and polarization of CO₂ molecules, while the inherent unsaturated Cr³⁺ sites bonded with the epoxides to promote the simultaneous activation. The ample Cl^- counter-anions further nucleophilically attacked to proceed the ring opening process, triggering an upgradation in catalytic performance for cycloaddition. After optimized by the response surface methodology (RSM), a chloropropene carbonate (CPC) yield of 97.8 % with a selectivity of 99.3 % were attained over the developed Cl[TNH₂]Cl@MIL-101(Cr) at mild conditions (104.5 °C, 1.07 MPa, 3.75 wt% of catalyst, 1.91 h) in the absence of any solvent or co-catalyst. Furthermore, Cl[TNH₂]Cl@MIL-101(Cr) displayed good durability, universality, and recyclability. The synergy of multiple sites was testified by the in-situ DRIFTS spectra and DFT calculations, and thus the potential catalytic mechanism was deduced. The implement of this work could shed some lights on the rational assembling of robust IL@MOFs nanocomposites and offered novel avenues for the fabrication of high-efficiency catalysts for practical CO₂ conversion.