Experimental and theoretical investigation for the cycloaddition of carbon dioxide to epoxides catalyzed by potassium and boron co-doped carbon nitride

Much endeavor has been devoted to efficient heterogeneous catalysts for carbon dioxide (CO2) conversion to high-value chemicals. Meanwhile, the cycloaddition of CO2 to epoxides is considered as a green and atom-economy reaction to produce cyclic carbonates. Herein, a series of K, B co-doped CN with various doping contents (K, B-CN-X) were developed by simple one-step calcination of melamine and KBH4. B was confirmed to replace the C site and KN bond was formed, which was verified by XPS (X-ray photoelectron spectroscopy) and DFT (density functional theory) calculation. Particularly, K, B-CN-4 displayed the optimal catalytic performance in the presence of Bu4NBr (tetrabutylammonium bromide) cocatalyst for the CO2 cycloaddition with propylene oxide. Besides, K, B-CN-4/Bu4NBr catalyst exhibited good substrate versatility to various epoxides and excellent recycling performance. According to the DFT calculation on CO2 adsorption and experimental results, K, B-CN-4 presented satisfactory catalytic activity due to the enhanced CO2 adsorption after K and B dopings then the possible reaction mechanism was proposed. The promising K, B-CN-X catalyst presented an attractive application due to the simple, eco-friendly synthesis route for the efficient fixation of CO2.