Preparation of imidazole ligand zirconium-based UiO-66 and its application in the direct synthesis of dimethyl carbonate from CO2 and methanol

Abstract

In this study, imidazole carboxylate was introduced into the structure of UiO-66 as a secondary ligand. Subsequently, a novel imidazole ligand zirconium-based UiO-66-Im-X material was prepared, which was used to catalyze the direct synthesis of dimethyl carbonate (DMC) from carbon dioxide (CO₂) and methanol. The influence of imidazole carboxylate content on the physicochemical properties and catalytic performance of the UiO-66-Im-X catalyst was studied. The results showed the addition of imidazole carboxylate increased the number of ligand defects in the Zr₆ formula unit, which significantly enhanced the α-acidic sites of the UiO-66-Im-X catalyst. UiO-66-Im-0.2 with a good crystal structure exhibited the highest surface area, pore volume, and acidic sites and demonstrated the best catalytic activity. At 3.5 MPa, 140 °C, and a reaction time of 8 h, the DMC yield reached 0.9335 %. In addition, the catalytic effect of UiO-66-Im-0.2 exceeded 90 % after four recycling iterations, demonstrating excellent reusability. The in-situ infrared spectroscopy results and density functional theory (DFT) calculations demonstrated that the incorporation of the imidazole ring significantly enhanced the adsorption capacity of CO₂ molecules and reduced its adsorption energy on the UiO-66-Im-0.2 catalyst.