Highly efficient cobalt-doped carbon nitride polymers for solvent-free selective oxidation of cyclohexane

Selective oxidation of saturated hydrocarbons with molecular oxygen has been of great interest in catalysis, and the development of highly efficient catalysts for this process is a crucial challenge. A new kind of heterogeneous catalyst, cobalt-doped carbon nitride polymer (g-C₃N₄), was harnessed for the selective oxidation of cyclohexane. X-ray diffraction, Fourier transform infrared spectra and high resolution transmission electron microscope revealed that Co species were highly dispersed in g-C₃N₄ matrix and the characteristic structure of polymeric g-C₃N₄ can be retained after Co-doping, although Co-doping caused the incomplete polymerization to some extent. Ultraviolet–visible, Raman and X-ray photoelectron spectroscopy further proved the successful Co doping in g-C₃N₄ matrix as the form of Co(II)N bonds. For the selective oxidation of cyclohexane, Co-doping can markedly promote the catalytic performance of g-C₃N₄ catalyst due to the synergistic effect of Co species and g-C₃N₄ hybrid. Furthermore, the content of Co largely affected the activity of Co-doped g-C₃N₄ catalysts, among which the catalyst with 9.0 wt% Co content exhibited the highest yield (9.0%) of cyclohexanone and cyclohexanol, as well as a high stability. Meanwhile, the reaction mechanism over Co-doped g-C₃N₄ catalysts was elaborated.