Guanidyl-implanted UiO-66 as an efficient catalyst for the enhanced conversion of carbon dioxide into cyclic carbonates.

The development of heterogeneous catalysts for promoting epoxide cycloaddition with carbon dioxide is highly desirable for recycling CO 2 and achieving the goal of carbon neutrality. Herein, we designed and synthesized Zr-based metal organic frameworks (MOFs) by implanting functional guanidyl into the framework via mixing different molar ratios of 4-guanidinobenzoic acid (Gua) with 1,4-benzenedicarboxylic acid (BDC). Consequently, a small sized Zr-MOF (∼350 nm) can be prepared by implanting Gua with 20% molar ligands, denoted as UiO-66-Gua 0.2 ( s ). Compared to large sized and different guanidyl Zr-MOFs, UiO-66-Gua 0.2 ( s ) exhibited an optimal activity on catalyzing epoxide cycloaddition with CO 2 in the presence of the Bu 4 NBr cocatalyst. A yield of 97% for the product of chloropropene carbonate was achieved at 90 °C under 1 atm CO 2 . The great performance of UiO-66-Gua 0.2 ( s ) might be attributed to the synergistic effect of guanidyl groups as hydrogen-bond donors and Zr centers acting as Lewis-acidic sites. In addition, the heterogeneous catalyst of UiO-66-Gua 0.2 ( s ) exhibited a great versatility towards converting other epoxides and a satisfactory recyclability for five consecutive runs. Moreover, a plausible reaction mechanism has been proposed for UiO-66-Gua 0.2 ( s ) in promoting CO 2 epoxide cycloaddition reactions.