Dicyano-functionalized indium framework as a heterogeneous catalyst for CO2 fixation in the absence of solvent and co-catalyst

Abstract

Catalytic carbon dioxide (CO₂) transformation into valuable products is of great interest, especially the development of innovative methods for CO₂ fixation reactions. In this paper, we report the porous cyanide-functionalized MIL-68(In) metal–organic framework as a novel Lewis acid–base bifunctional catalyst. The MIL-68(In) framework was modified with different cyanide functional groups, such as 1,3-phenylene diacetonitrile and malononitrile, for the catalytic CO₂ fixation reaction into cyclic carbonates. The properties of the synthesized catalysts were fully characterized using different techniques, including PXRD, FTIR, N₂ adsorption, BET, SEM, XPS, TGA, NH₃-TPD, and CO₂-TPD. Under the optimized conditions (30 mg catalyst, 1 MPa CO₂ pressure, 20 mmol epichlorohydrin, 100 °C, 10 h), MIL-68(In) functionalized with 1,3-phenylene diacetonitrile was found to afford a remarkable heterogeneous catalyst with selectivity (100%) and high conversion (99%) for the coupling reaction between CO₂ and the epoxide without any co-catalyst or solvent. Moreover, the functionalized MIL-68(In) MOF also revealed applicability to other large epoxides. The enhanced activity of functionalized MIL-68(In) results from the collaboration between the unsaturated Lewis acidic indium centers and cyanide functional groups as nucleophilic sites. Furthermore, the reusability tests demonstrated that the modified MIL-68(In) was easily recycled by filtration and reusable for at least five runs with no loss in catalytic ability.