A novel and efficient catalyst system composed of detonation nanodiamond and potassium iodide for chemical fixation of carbon dioxide

In this paper, we report a novel, unusual catalytic system that can efficiently catalyze the cycloaddition of CO2 with propylene oxide to form propylene carbonate in a mild solvent-free condition based on the combination of detonation nanodiamond (DND) and potassium iodide (KI). When the reaction was carried out at 0.8 MPa pressure and 90 degrees C for 6 h, the reaction catalyzed by DND-KI (e.g. 1.0 mol% KI relative to propylene oxide(PO), DND: KI = 0.8:1 wt/wt) has a yield as high as 96.4%, which is much higher than that catalyzed by DND with other substances such as potassium bromide, potassium chloride, tetrabutylammonium iodide, and 1-butyl-3-methylimidazolium iodide. DND-KI also shows a higher catalytic reaction yield than the catalyst systems from other carbon nanomaterials such as graphene, carbon nanotube and nanodiamond prepared by a high-pressure high-temperature method. The DND-KI has an excellent service life. After ten cycles of reaction, it has almost no loss in catalytic activity. DND-KI is also applicable to the cycloaddition of CO2 with other epoxides. We further show that the excellent catalysis capability of DND-KI originates from the special subsidiary functional groups (e. g. hydroxyl and carboxyl groups) that the DND possesses and a synergetic effect between those functional groups and KI during the reaction. The large specific surface area and porous structure also facilitate the reaction.