MnO2 as efficient and robust catalyst for halogen-free synthesis of cyclic carbonate from CO2 and epoxides

Cyclic carbonate is an important fine chemical/intermediate and their synthesis from CO₂ and epoxides is economical and green pathway, however, it is still a challenge to develop a efficient and robust catalyst for halogen-free synthesis of cyclic carbonate. Herein, we successfully prepared large-scale MnO₂ catalysts by microfluidics method, and the MnO₂ especially δ-MnO₂ showed >99.9 % propylene carbonate yield under 393 K, 3 MPa CO₂ and DMF solvent. Moreover, the initial TOF value over δ-MnO₂ on the basis of total catalyst amount was 5.80 h⁻¹, which was the maximum among all the reported heterogeneous metallic oxide catalysts for halogen-free synthesis of propylene carbonate from CO₂ and epoxides, and the superior catalytic performance can be ascribed to the abundant moderate acidic–basic active sites on the δ-MnO₂ surface and the synergistic effect of δ-MnO₂ and DMF. Furthermore, the δ-MnO₂ can be reused at least 4 times and exhibited wide substrate applicability.