The Heptazine-Based Materials through Intrinsically Modification for the Cycloaddition of CO2 and Bisepoxides

For the efficient utilization of CO2 into valuable product, the attractive carbon nitride catalysts have been widely studied. In this work, heptazine-related materials with varying degree of polymerization were designed by an intrinsically modification strategy and employed in the cycloaddition of CO2 with the bisepoxide 1, 4-butanediol diglycidyl ether (BDODGE). We initially figured out that the sample prepared at 450 °C contained more melem hydrate, exhibiting the best performance. The epoxides conversion and corresponding cyclic carbonates selectivity could achieve 93.1 % and 99.3 % at 140 °C for 20 h without any cocatalyst and solvent, respectively. Results of the catalytic tests suggested that the high catalytic activity was dependent on big size porous structure and the synergetic effect of active amino groups and -OH groups. The role of water in maintaining the specific structure and providing active site has been proved. Moreover, the CN-450-W catalyst exhibited outstanding recycling stability. And finally, a plausible reaction mechanism was proposed.

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.