Ionic Liquid-Modified Co/ZSM-5 Catalyzed the Aerobic Oxidation of Cyclohexane: Toward Improving the Activity and Selectivity

Abstract

Ionic liquid (IL)-modified metal/ZSM-5 composites served as heterogeneous catalysts toward cyclohexane aerobic oxidation, demonstrating excellent KA oil (cyclohexanol and cyclohexanone) selectivity with improved activity. The effects of the different functional groups of the IL on the oxidation were further systematically investigated. The catalytic activity of the catalyst was closely related to the anionic group of the IL, whereas the cationic group had no obvious effects. The cyclohexane conversion and selectivity of KA oil reached 9.7 and 92.2%, respectively, using the optimized catalyst C6mimHSO4-Co/ZSM-5. This favorable catalytic performance was mainly attributed to the activation of the cyclohexane by the anionic group of the IL, whereas the excellent selectivity was ascribed to the superior solubility of KA oil in the IL while avoiding overoxidation. Based on the results of in situ electron paramagnetic resonance spectra, a catalytic mechanism involving a free-radical process was also proposed.

Supported Fe Ions on Different Zr-Based Metal–Organic Frameworks for Alkane Oxidation

“…Based on the above evidence, the catalytic cycle of the oxidation of cyclohexane was proposed (Figure ). − After excitation of MIL140-BPDC-Fe by visible light, Cl • radicals were generated by the LMCT process and abstracted an H atom from cyclohexane to produce an alkyl radical (R • ). Then ROO • radicals were produced in the presence of oxygen, and cyclohexanol and cyclohexanone were obtained in an approximately 1:1 ratio via a Russell fragmentation reaction between two molecules of ROO • .…”

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

“…1541 [C 6 C 1 Im][HSO 4 ]/Co/ ZSM-5 composites served as heterogeneous catalysts toward cyclohexane aerobic oxidation to cyclohexanol and cyclohexanone with almost 10% conversion. 1542 There is a synergetic effect on the oxidation of benzylic C− H bonds by Ni-MOF and [C 4 C 1 Im][Br] using tert-butyl hydroperoxide as oxidant. 1543 Oligomeric ILs (OILs) contain-ing six Im cores associated with phosphomolybdic anion catalyze the oxidation of cyclohexane to cyclohexanone in moderate yields.…”

“…The cis -dioxidomolybdenum­(VI) complex in [C 4 C 1 Im]­[PF 6 ]/scCO 2 is a very highly selective catalyst for the oxidation of cyclohexane to cyclohexanol . [C 6 C 1 Im]­[HSO 4 ]/Co/ZSM-5 composites served as heterogeneous catalysts toward cyclohexane aerobic oxidation to cyclohexanol and cyclohexanone with almost 10% conversion …”

Efficient and Selective Oxygenation of Cycloalkanes and Alkyl Aromatics with Oxygen through Synergistic Catalysis of Bimetallic Active Centers in Two-Dimensional Metal-Organic Frameworks Based on Metalloporphyrins

“…However, due to the inertness of O=O double bonds in molecular oxygen (bond dissociation energy is about 498 kJ/mol), and C–H bonds in hydrocarbons (bond dissociation energy is about 420 kJ/mol) [ 1 , 21 , 22 , 23 , 24 ], severe conditions, such as high temperatures, powerful oxidants, and corrosive additives, are normally required. For instance, in the commercial production of KA oil (cyclohexanone and cyclohexanone), the reaction temperature must approach 160–170 °C under a pressure of 1.0–2.0 MPa [ 25 , 26 , 27 , 28 ]. Another example is toluene and its derivatives, which must be oxidized using hazardous bromide additives and caustic acidic circumstances [ 29 , 30 , 31 ].…”

“…Thus, the hydrocarbon conversion is generally kept at a lower level to achieve a decent selectivity toward partly oxygenated products, resulting in low reaction efficiency. In commercial cyclohexane oxygenation, conversion is generally regulated at around 5% to offer a higher selectivity (75–85%) towards KA oil [ 26 , 32 , 33 , 34 ]. It is a critical necessity to minimize deep oxygenation and selectivity loss with conversion growth in commercial cycloalkane oxygenation and alkyl aromatic oxygenation with oxygen.…”