Oxalamide-derived ionic polymer/carbon nanotube composites: Highly active heterogeneous catalyst for promoting cycloaddition of carbon dioxide to epoxides

Abstract

Ionic polymers functionalized with hydrogen bond donors (HBDs) exhibit immense potential in the green chemical fixation of carbon dioxide (CO₂); however, achieving high catalytic activity remains a significant challenge. In this study, we synthesized oxalamide-based ionic polymers and their composites with carbon nanotubes using a straightforward ball-milling method. The incorporation of oxalamide notably enhanced the catalytic activity of the ionic polymers by activating the C-O bond of the epoxide via HBD interaction. Furthermore, compositing with carbon nanotubes enhanced the catalytic performance of the composite materials via improving the accessibility of active sites. As a result, the optimized composite catalyst, P(PyOA-BBr₃)@CNT-3, demonstrated exceptional catalytic efficiency in the cycloaddition reaction between CO₂ and epichlorohydrin, achieving an outstanding initial turnover frequency (TOF) of 1360 h⁻¹ and a 68 % yield of epichlorohydrin carbonate at 140 °C. This makes our solid organocatalyst one of the most efficient metal-free solid catalytic systems reported to date. Moreover, P(PyOA-BBr₃)@CNT-3 exhibited good substrate compatibility and could be easily recycled and used for at least six cycles. This study not only introduces an efficient HBD for designing bifunctional catalysts, but also presents a feasible and environmentally friendly approach for constructing highly active ionic polymer-based composite catalysts for CO₂ fixation.