Synthesis of Zn Modified Carbon Nitrides Heterogeneous Catalyst for the Cycloaddition of CO₂ to Epoxides

Various Zn modified carbon nitride (Zn-C₃N₄) were facilely prepared by one-step thermal polymerization method, and were successfully used for the chemical fixation of CO₂ to epoxides producing cyclic carbonates in the presence of KI co-catalyst. The combination of binary heterogeneous Zn-C₃N₄ and KI exhibited efficient catalysis for the coupling of CO₂ and epoxides. The effects of different reaction parameters, including reaction temperature, CO₂ pressure, reaction time, and catalyst loading on activities were discussed. The yield of propylene carbonate (PC) could reach 99% under the optimized reaction conditions (130 ^oC, 2 MPa, 5 h) without additional solvent used, and the selectivity was above 99%. The catalysts showed good recycle performance and versatility for the cycloaddition of CO₂ to various epoxides. The possible reaction mechanism over Zn-C₃N₄/KI catalytic system was proposed. The developed Zn-C₃N₄/KI catalysts exhibited attractive application as simple, effective and ecofriendly alternative catalysts for CO₂ effective utilization.