Mesoporous Nitrogen-Doped Graphitized Carbon for Recyclable Oxidation of Cyclohexene

Through the pyrolysis of melamine–formaldehyde resin (MF) at different temperatures, the obtained mesoporous nitrogen-doped graphitized carbon (MNC) materials are detected to have different compositions of nitrogen species. With the increase in the pyrolysis temperature, the nitrogen contents decreased significantly, especially the proportion of pyridinic N and pyrrolic N species. The graphitic N dominated in NNC-1000 °C (MNC-10) with extremely low defects and a highly graphitized degree. MNC-10 could realize selective oxidation of cyclohexene with 90.1% conversion and 92.0% selectivity on the allylic α-position and can be recycled five times without obvious decline in activity and selectivity. Although MNC obtained at 900 °C (MNC-9) has comparable activity to MNC-10, the recycle experiments of MNC-9 show a considerable decline in conversion. The obvious leaching of nitrogen contents, especially the pyridinic N species in MNC-9, resulted in more defects, which are unfavorable to catalysis. The N species in the carbon layer play a positive role in the delocalized electrons promoting cyclohexene activation and tert-butyl hydroperoxide decomposition. Thereby, peroxyl radicals are formed and trigger the subsequent propagation of the radical reaction.