Selective liquid phase oxidation of cyclohexane over Pt/CeO₂–ZrO₂–SnO₂/SiO₂ catalysts with molecular oxygen

Partial oxidation of cyclohexane into cyclohexanone and cyclohexanol (KA-oil) is an industrially significant reaction for producing precursors for the synthesis of ε-caprolactam and adipic acid, which are the building blocks of nylon. However, to date, the cyclohexane conversion ratio has usually been limited to less than 6% to prevent further oxidation of the cyclohexanol and cyclohexanone targets. In this study, we report that Pt/CeO₂–ZrO₂–SnO₂/SiO₂, in which CeO₂–ZrO₂–SnO₂ provide reactive oxygen molecules from inside the bulk, can act as efficient catalysts. Optimization of the catalyst composition and reaction conditions provided a cyclohexane conversion ratio of 24.1% and a total selectivity for cyclohexanol and cyclohexanone of 83.4% at 130 ℃ in 0.5 MPa (4.9 atm) air for 7 h over a 5wt%Pt/16wt%Ce_0.68Zr_0.17Sn_0.15O_2.0/SiO₂ catalyst. This catalyst has significant advantages over conventional catalysts because the reaction proceeds at a lower pressure, and there is no need for toxic radical initiators or free-radical scavengers.