Biomass-derived phosphorus-doped carbon materials as efficient metal-free catalysts for selective aerobic oxidation of alcohols

Abstract

Heteroatom-doped carbon materials (HDCMs) with abundant active functional groups and stable structural characteristics are promising catalysts for eco-friendly metal-free catalysis. In this work, phosphorus-doped carbon materials with a highly porous structure and extremely high surface area (>1600 m² g⁻¹) were successfully prepared via a convenient and scalable strategy using easily available soluble starch and phosphoric acid, which are expected to show good performance in mass-transfer and thus promote the catalytic process. As expected, the as-prepared PC-700 catalyst showed remarkable catalytic performance in aerobic oxidation of benzyl alcohol with a higher TOF value than other previously reported heteroatom-doped carbon catalysts. It also exhibited great tolerance for various substrates, including aromatic, alicyclic, heterocyclic, and aliphatic alcohols. On the basis of the related characterization studies and experimental results, it was proved that the P–O–C species and the defects caused by P–O species doping in the PC-700 catalyst are the active sites for aerobic oxidation. A unique mechanism was proposed for the catalytic process, which is different from that of N-doped graphene and graphene oxide catalyzed reactions that follow a free radical mechanism. In addition, the recycling test and characterization of the reused catalyst indicate that the PC-700 shows extraordinary performance in terms of both recyclability and stability and retains high reactivity even after eight cycles.