Coordination-Unsaturated Co–O Structure Mediated by a Fluorination Strategy to Trigger C–H Bond Activation

The exploitation of efficient catalysts for the selective oxidation of alkylbenzenes continues to be a daunting challenge. Herein, we report that F-doped Co3O4 (F-OV-Co3O4), prepared by sequential liquid-phase reduction treatment and F-doping modification, promotes the solvent-free oxidation of ethylbenzene (EB) to acetophenone (AP) with molecular oxygen. Both experimental findings and theoretical calculations substantiate that the proper reduction/fluorination treatment can promote more electrons filled into the antibonding orbitals, modulating the electronic structure and atomic coordination environment of Co sites in Co3O4. The coordination-unsaturated Co-O structure facilitates C-H bond activation, boosting the intrinsic activity of EB oxidation. Under the optimal reaction conditions, the conversion of EB can achieve 80.2% (ri = 0.206 mol gcat-1 h-1), accompanied by 92.4% selectivity of AP, surpassing that of the current Co3O4-based catalysts under similar reaction conditions. This work provides a paradigm to boost the aerobic oxidation of alkylbenzenes using cheap and readily available transitional metal oxide catalysts, which can be accomplished by regulating the coordination environment of active sites.