Constructing Defective Co3V2O8 Hexagonal Prism for Solvent-free Selective Oxidation of Cyclohexane: Strategy of Ionic Liquid Mediation

Abstract

Oxygen vacancies (OVs) engineering is essential in the regulation of the structure and properties of the catalysts for selective oxidation. In this work, the strategy of ionic liquid (IL) mediation was successfully developed in constructing the OV-rich defective Co3V2O8 (CVO), exhibiting excellent performance in cyclohexane oxidation. Coupling the prepotency of the heating treatment, ILs constructed optimal [Bmim][Ac]-CVO-700 possesses the highest OV concentration and catalytic activity with 12.7% cyclohexane conversion accompanied by 89.6% KA oil (cyclohexanol and cyclohexanone) selectivity. Experimental investigation reveals that ILs not only regulates the morphology structure as structure-directing agents but also benefits the formation of OVs through coordination with the Co2+ and V5+. The redox cycle between Co3+/Co2+ and V5+/V4+ was accelerated via the constructed OVs, enhancing the activation of substrates and the transfer of electrons. The distinguished performance is attributed to the rich OVs, porous structure, and synergistic effect between the active metals. The structure–activity relationship between OVs concentration and cyclohexane conversion further indicated that OVs facilitate the essential steps for the generation of targeted products. The possible reaction pathway of cyclohexane oxidation over the OV-rich CVO catalyst was also suggested regarding the radical trapping experiment. This design not only presents a facile and effective strategy for constructing OVs using ILs but also provides an in-depth insight into OV-rich mixed metal oxides in selective oxidation.