Enhancing the coupling reaction between CO2 and epoxides over amino-functionalized defective-UiO-66

Abstract

Metal-organic frameworks (MOFs) exhibit promising catalytic potential for various reactions owing to their unique structure composed of designable metal-oxo clusters bridged by organic linkers, modifiable frameworks, and intrinsic porosity. Currently, defective MOFs are gaining considerable attention due to their accessible Lewis acid sites, tunable ligands, and superior performance compared with pristine MOFs. In this work, we have developed an amino-functionalized UiO-66 with ligand defects, denoted as UiO-66-DABAx (where x represents the molar percentage of 3,4-diaminobenzoic acid (DABA) relative to the total linker content), which enables an efficient pathway for the cycloaddition reaction of CO2 with epoxides under mild conditions. The increased density of Lewis acid sites and the presence of amino-functionalized ligands synergistically facilitate the ring-opening of epoxides and CO2 adsorption. Compared with pristine UiO-66, UiO-66-DABAx exhibits a stronger affinity for CO2. More importantly, UiO-66 modified with 20 mol% DABA (UiO-66-DABA20) exhibits optimal catalytic activity in the CO2 cycloaddition reaction, yielding a cyclic carbonate of 95%. This study paves a promising strategy for the chemical fixation of CO2 into cyclic carbonates using amino-functionalized defective UiO-66 as a potential heterogeneous catalyst under mild reaction conditions.