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.

Efficient Inhibition of Deep Conversion of Partial Oxidation Products in C-H Bonds’ Functionalization Utilizing O2 via Relay Catalysis of Dual Metalloporphyrins on Surface of Hybrid Silica Possessing Capacity for Product Exclusion

“…To explore in greater detail the radical species in this work, electron paramagnetic resonance (EPR) measurement was also carried out utilizing 5,5-dimethyl-1-pyrroline N-Oxide (DMPO) as a radical capture reagent. It is demonstrated in Figure 12 that when cyclohexane was utilized as a model substrate possessing C-H bonds, the main radical species were carbon-centered radicals (cyclohexyl radical, C 6 H 11 •), peroxide-centered radicals (cyclohexyl peroxide radical, C 6 H 11 OO•), and oxygen-centered radicals (cyclohexyl oxygen radical, C 6 H 11 O• and hydroxyl HO•), which is in good agreement with the radical species reported in relevant documents [1,11,22,66,67]. Secondly, in the determination of the major radical species, the activation of O 2 and the corresponding key intermediates were explored and verified, too.…”

Roles of Oxygen Vacancies in CeO2 Nanostructures for Catalytic Aerobic Cyclohexane Oxidation

“…The oxidation of hydrocarbons into value-added chemical products, especially alkanes that are much more difficult to utilize without active functional groups, is of great importance in the chemical industry. − Cyclohexane oxidation is a typical hydrocarbon resource high-value utilization process, and in this process, the oxidation products including cyclohexanol, cyclohexanone (referred to as KA oil), and adipic acid are important organic intermediates for nylon-6 and nylon-66 in the nylon industry. ,− For the details of cyclohexane oxidation, the widely accepted oxidation process of cyclohexane includes the activation of cyclohexane to a cyclohexyl radical, the transition to KA oil, the further oxidation to adipic acid, and the over oxidation to glutaric acid, succinic acid, and other byproducts, as described in Scheme (b). − As a complex radical oxidation reaction, it is a great challenge to activate the C–H bond and to generate active radicals under proper conditions due to the strong and inert C–H bonds, and on the other hand, it is also an important issue to investigate in order to control the oxidation process to realize the production of target products under high selectivity and avoid over oxidations. − …”