Mesoporous carbon nitride grafted with n-bromobutane: a high-performance heterogeneous catalyst for the solvent-free cycloaddition of CO2 to propylene carbonate

Abstract

A new type of mesoporous-C₄N₄-based catalyst (n-butBr/mp-C₃N₄) was prepared by simple grafting of n-bromobutane. The N₂ adsorption–desorption and X-ray diffraction characterizations indicate that, in comparison with the parent mp-C₃N₄, the textual and structural properties have been well retained by n-butBr/mp-C₃N₄. In the cycloaddition of CO₂ with propylene epoxide, the n-butBr/mp-C₃N₄ exhibits high catalytic conversion as well as a high selectivity to propylene carbonate. The maximum TOF value obtained over n-butBr/mp-C₃N₄ is 10.7 h⁻¹ at 6 h under 140 °C, which compares favorably to other reported C₃N₄-based catalysts. In addition to n-bromobutane, mp-C₃N₄ materials grafted with other alkyl halides also provide high catalytic activities. According to the Fourier transform infrared and X-ray photoelectron spectroscopy measurements, it is speculated that the catalytic active sites of n-butBr/mp-C₃N₄ are uncondensed amines and Br anions which originate from the reaction between n-bromobutane and the N-containing heterocycles of mp-C₃N₄.