Implanting multi-functional ionic liquids into MOF nodes for boosting CO2 cycloaddition under solventless and cocatalyst-free conditions

Abstract

It is critical to design an effective catalyst for CO2 conversion into cyclocarbonate to achieve the carbon neutrality. Herein, MIL-101(Cr) tethered by hydrogen bond donors (HBD)-containing ionic liquids (denoted as MIL-101-ILs(R), R = OH, NH2, and COOH) were synthesized through the implantation of 4,4′-bipyridine into MOF nodes via the post-synthetic modification, followed by the decoration with bromoalkanes including bromoethanol, bromoethylamine, and bromoacetic acid. Their catalytic performance were evaluated by the epoxide cycloaddition reaction under 1.0 MPa CO2 and 80 ℃ for 6 h in the absence of solvent and cocatalyst. Compared to MIL-101-ILs without HBD, MIL-101-ILs(OH) and MIL-101-ILs(NH2) demonstrated the more chloropropene carbonate (CPC) yield of 88 % and 83 %, respectively. Notably, MIL-101-ILs(COOH) exhibited an uppermost activity with a CPC yield of 96 %, attributed to the cooperativity of Lewis acidity originating from Cr3O clusters, hydrogen-bond interaction afforded by carboxyl groups, and the strong nucleophilicity offered by Br- ions of ILs. Moreover, MIL-101-ILs(COOH) presented excellent recyclability. A potential catalytic mechanism for epoxide cycloaddition with CO2 into cyclic carbonate has been proposed.