UiO-66 porous liquids with synergistic catalytic effects for promoting efficient CO₂ conversion

Metal-organic frameworks (MOFs) and ionic liquids (ILs) have been extensively investigated for CO₂ catalytic conversion, but their individual application is largely limited by harsh reaction conditions and low catalytic activity. Combining ILs with MOFs to construct porous liquids (PLs) with both fluidity and permanent porosity enables favorable synergistic effects in theory, which can promote CO₂ selective adsorption, mass transfer and activation processes, thus, markedly boosting the conversion efficiency. However, how the synergistic effect influences the efficiency of CO₂ catalytic conversion and its mechanism remains unclear. Herein, various Type III PLs using UiO-66 with different surface groups (UiO-66, UiO-66-NH₂ and UiO-66-OH) as porous hosts and imidazolium bromide ILs as sterically hindered solvents were synthesized for CO₂ catalytic conversion to verify the synergistic effect, respectively. The resulting PLs have been demonstrated excellent room-temperature fluidity, uniform stability, and permanent porosity. As expected, by integrating accessible pores with mobile Lewis-acid and Lewis-base sites, the as-prepared PLs could catalyze the CO₂-propylene oxide (PO) cycloaddition reaction under mild conditions (90 °C, 1.0 MPa, 8 h) without co-catalysts, yielding up to 84.89% with 99% selectivity. Furthermore, the effectiveness and high efficiency of the synergistic effect between the porous host and the sterically hindered solvent in converting CO₂ to cyclic carbonates have been demonstrated through both experimental studies and molecular simulations. More importantly, given the virtually limitless combinations arising from the diversity of MOFs as porous hosts and ILs as sterically hindered solvents, the significance of our work lays a foundation for the rational design of high-performance PLs for CO₂ conversion in practical chemical processes.