Selective oxidation of benzene by an iron oxide carbonaceous nanocatalyst prepared from iron perchlorate salts and hydrogen peroxide in benzene and acetonitrile

Direct benzene hydroxylation under mild conditions using hydrogen peroxide can be essential in producing phenol. A new iron oxide-carbonaceous nanocatalyst (Fe-oxide CNC) is prepared in situ using a precursor of Fe(ClO₄)₂ and H₂O₂ in benzene and CH₃CN. The obtained Fe-oxide CNC can efficiently catalyze benzene oxidation to phenol using H₂O_2(aq) in CH₃CN. The highest phenol production was achieved with the turnover number (TON) of 122 in unit iron content and selectivity of 96% at 60 °C. The catalyst was characterized by SEM, TEM, XAS, XPS, Raman, XRD, BET, and TGA techniques. Interestingly, materials identification and characterization of the Fe-oxide CNC provided evidence to support the presence of Fe₂O₃. In addition, the carbonaceous moieties mainly consisted of branched aliphatic hydrocarbons on the iron oxide surface, which enhance the catalytic performance for benzene oxidation to phenol. The Fe-oxide CNC can be recycled three times with comparable catalytic efficiency. Using H₂¹⁸O₂ as an oxidant, the phenol product with highly enriched ¹⁸O-atom indicates that the reactive oxygen species (ROS) activated by H₂O_2(aq) is crucial for aromatic oxidation. Time-resolved spin trapping experiments displayed the formation of the intermediate adducts consisting of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and reactive oxygenated radicals. For 3‒24 h durations, higher steady-state concentrations of the oxygenated intermediates observed at 25 °C than 60 °C indicate that the catalytic oxidation of benzene mediated by Fe-oxide CNC performs much faster kinetics at 60 °C than the ambient condition.