Design of composite based on UiO-66 and ionic liquid for the CO2 conversion into cyclocarbonate

Exploiting an effective catalyst for CO 2 conversion into value-added chemicals under mild circumstances still remains a challenge. Herein, UiO-66 decorated with ionic liquids (ILs) (denoted as UiO-66-ILs) were facilely synthesized by the mixed ligands of 1,4-benzene dicarboxylic acid and pyridyl-containing mono-carboxylic acid isomer (including nicotinic acid (NA), isonicotinic acid (INA), and 2-pyridine carboxylic acid (PCA)), followed by the further modification with different bromoalkanes. Among various UiO-66-ILs, UiO-66 derivative containing the ILs composed of PCA and bromoethane (named as UiO-66-ILs(PCA-EtBr)) displayed superior catalytic performance on CO 2 -epichlorohydrin cycloaddition into chloropropene carbonate, with a high yield of 90 % under 0.1 MPa CO 2 at 110 °C without the addition of any solvent and cocatalyst. Whereas, UiO-66-ILs(NA-EtBr) and UiO-66-ILs(INA-EtBr) as analogues of UiO-66-ILs(PCA-EtBr) presented a low yield of 77 % and 67 %, respectively, unveiling that the orientation of carboxyl at monocarboxyl pyridine ligand played a great influence on the catalytic activity. The excellent activity of UiO-66-ILs(PCA-EtBr) was attributed to the synergetic effect of Lewis acidity from MOF nodes for activating C–O bond of epoxide, CO 2 absorption by pyridyl moiety, and nucleophilicity of ILs decoration. In addition, UiO-66-ILs(PCA-EtBr) exhibited a broad scope of epoxide substrate, as well as a great recyclability. Moreover, a possible catalytic mechanism was proposed for CO 2 conversion into cyclocarbonate.