The highly selective oxidation of cyclohexane to cyclohexanone and cyclohexanol over VAlPO4 berlinite by oxygen under atmospheric pressure

Abstract

BackgroundThe oxidation of cyclohexane under mild conditions occupies an important position in the chemical industry. A few soluble transition metals were widely used as homogeneous catalysts in the industrial oxidation of cyclohexane. Because heterogeneous catalysts are more manageable than homogeneous catalysts as regards separation and recycling, in our study, we hydrothermally synthesized and used pure berlinite (AlPO4) and vanadium-incorporated berlinite (VAlPO4) as heterogeneous catalysts in the selective oxidation of cyclohexane with molecular oxygen under atmospheric pressure. The catalysts were characterized by means of by XRD, FT-IR, XPS and SEM. Various influencing factors, such as the kind of solvents, reaction temperature, and reaction time were investigated systematically.ResultsThe XRD characterization identified a berlinite structure associated with both the AlPO4 and VAlPO4 catalysts. The FT-IR result confirmed the incorporation of vanadium into the berlinite framework for VAlPO4. The XPS measurement revealed that the oxygen ions in the VAlPO4 structure possessed a higher binding energy than those in V2O5, and as a result, the lattice oxygen was existed on the surface of the VAlPO4 catalyst. It was found that VAlPO4 catalyzed the selective oxidation of cyclohexane with molecular oxygen under atmospheric pressure, while no activity was detected on using AlPO4. Under optimum reaction conditions (i.e. a 100 mL cyclohexane, 0.1 MPa O2, 353 K, 4 h, 5 mg VAlPO4 and 20 mL acetic acid solvent), a selectivity of KA oil (both cyclohexanol and cyclohexanone) up to 97.2% (with almost 6.8% conversion of cyclohexane) was obtained. Based on these results, a possible mechanism for the selective oxidation of cyclohexane over VAlPO4 was also proposed.ConclusionsAs a heterogeneous catalyst VAlPO4 berlinite is both high active and strong stable for the selective oxidation of cyclohexane with molecular oxygen. We propose that KA oil is formed via a catalytic cycle, which involves activation of the cyclohexane by a key active intermediate species, formed from the nucleophilic addition of the lattice oxygen ion with the carbon in cyclohexane, as well as an oxygen vacancy formed at the VAlPO4 catalyst surface. Electronic supplementary materialThe online version of this article (10.1186/s13065-018-0405-6) contains supplementary material, which is available to authorized users.

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

“…31 It was reported that solvents with higher acidity can better solubilize cyclohexane, leading to the superior performance in the oxidation of cyclohexane observed in our previous work. 32 As previously reported, hydrogen bonds could be formed between the anionic groups of the ILs and hydrocarbon substrates in the oxidation with the IL as the solvent. 33,34 Therefore, these hydrogen bonds could also be generated from the interactions between the anionic groups of the ILs and cyclohexane in cyclohexane catalytic aerobic oxidation to KA oil using air as the oxidant, activating the cyclohexane and thus improving the catalytic performance of the ILs catalysts.…”

Comparative research on three types of MIL-101(Cr)-SO3H for esterification of cyclohexene with formic acid

“…Cyclohexanol is used widely to produce adipic acid, caprolactam, hexamethylene diamine and cyclohexanone. 1 The main processes for the production of cyclohexanol are based on the oxidation of cyclohexane, 2,3 the hydrogenation of phenol, 1 and the direct hydration of cyclohexene. 4 The cyclohexane oxidation process is used mainly in industry, but it is hazardous.…”

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

“…Due to the fact that molecular oxygen is more difficult to activate than H 2 O 2 or tert -butyl hydroperoxide, the cyclohexane conversion and KA oil yield in cyclohexane oxidation with molecular oxygen is generally less than 20%. The single metal oxide MnO x and other composite metal oxides such as LaCoO 3 , Mn 2 Co 3 O x , CoMoO 4, Co 3 O 4 –CeO 2 , and VAlPO 4 show catalytic activity with a KA oil yield of below 8%. ,− As the Ce 0.5 Mn 0.5 O x solid solution, it was successfully fabricated according to the structural direction of [Bmim]­[Tf 2 N], which shows excellent low-temperature catalytic activity of cyclohexane oxidation while under the synergistic effect of the acetonitrile solvent . Other transition metal immobilized catalysts, including CoFe 2 O 4 /SiO 2 , Co/SBA-15, and Co-SAPO-5-0.2 maintained the KA oil yield below 8%. ,, In addition, noble metal catalysts such as Au/SiO 2 , PdNi/KIT-6, and Cl–RhFe have improved the yield of KA oil to more than 8%, while their scarcity and expensive value limited their application. − The carbon materials o -CNT-500 displayed an inferior activity despite it can initiate the free radical to ensure the progress of the reaction .…”