Ionic liquids self-assemble to construct triazine-based heterogeneous catalysts for synergistically catalyzing the cycloaddition reaction of CO2

Abstract

Developing catalysts for the cycloaddition reaction between carbon dioxide and epoxides under mild conditions is an important approach to achieve carbon dioxide fixation. In this study, we utilized NH₃-ethanol solution at room temperature to promote the self-assembly of ionic liquids into a triazine structure, thereby avoiding environmental issues such as acid pollution associated with traditional methods. In addition, by controlling the amount of vinylbenzene used, the pore size distribution of hyper poly(ionic liquid)s (HPILs) can be concentrated (13.38 nm). It is worth noting that the catalyst exhibits excellent catalytic performance with a TOF as high as 185.7 h⁻¹. It is 2–3 times greater than in previous studies. Through a series of characterization techniques, including X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption–desorption isotherms (BET), it was proven that the catalyst constructed uniformly distributed synergistic catalytic sites (ILs-triazine). The triazine structure activates CO₂ by bending its bond angle through π-conjugation interactions, while the Lewis basic sites in ILs polarize the C–O bond to form alkyl halides. These two effects work synergistically to catalyze the cycloaddition reaction. Density functional theory (DFT) calculations clarified the reaction mechanism, laying the foundation for the development of metal-free multi-phase ring addition reaction catalysts.