Novel Carbon Nitride/Metal Oxide Nanocomposites as Efficient and Robust Catalysts for Coupling of CO₂and Epoxides

Several environmentally benign graphitic carbon nitride (g-C3N4)-based nanocomposites with Lewis acid-base dual functionalities were developed through the pyrolysis of deep-eutectic solvents (DESs). They were used as heterogeneous catalysts for cycloaddition of CO2 to epoxides. The catalysts' structures and different process conditions were optimized, and a comparison of the catalytic activity was made with reported heterogeneous catalysts. Moreover, the catalyst reusability and applicability to different epoxides were examined. The results showed that the 2.0Zn@g-C3N4-550 combining with tetrabutylammonium bromide (TBAB) could efficiently and selectively convert CO2 into the desired products under the conditions of 90 °C, 1.5 MPa CO2 for 3.0 h. In addition, no obvious deactivation was observed after the catalyst was reused for five cycles. Based on the experimental results, a possible synergistic catalytic mechanism was finally proposed.