Abstract
Partial oxidation of cyclohexane into cyclohexanone and cyclohexanol (KA-oil) is an industrially significant reaction for producing precursors for the synthesis of ɛ-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 °C in 0.5 MPa (4.9 atm) air for 7 h over a 5wt%Pt/16wt%Ce0.68Zr0.17Sn0.15O2.0/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.
Highlights
The selective oxidation of cyclohexane (CyH) to cyclohexanone (Cy=O, denoted as “K”) and cyclohexanol (CyOH, denoted as “A”), which is a radical chain reaction, is a significant process in the chemical industry, because these are important intermediates for the manufacture of nylon-6 and nylon-6,6 [1]
KA-oil is produced by this method with 70%–85% selectivity; the CyH conversion ratio is usually limited to less than 6% to prevent further oxidation of the target KA-oil
A number of alternative processes that employ heterogeneous catalysts have been proposed for selective CyH oxidation using molecular oxygen with a particular focus on improving the CyH conversion ratio without a significant decrease in the selectivity for KA-oil
Summary
The selective oxidation of cyclohexane (CyH) to cyclohexanone (Cy=O, denoted as “K”) and cyclohexanol (CyOH, denoted as “A”), which is a radical chain reaction, is a significant process in the chemical industry, because these are important intermediates for the manufacture of nylon-6 and nylon-6,6 [1]. We have previously prepared novel catalysts to realize the complete oxidation of volatile organic compounds under moderate conditions [10,11] These catalysts involved a combination of platinum and a solid promoter to supply reactive oxygen molecules, which was important in order to allow oxidation of hydrocarbons in the gas phase [11,12]. We have designed advanced catalysts that are optimized for CyH oxidation to KA-oil in the liquid phase without the need for radical initiators or free-radical scavengers To realize such advanced catalysts, we have focused on a combination of Pt, Ce0.68Zr0.17Sn0.15O2.0, and SiO2 (silica gel). The catalyst composition was optimized to simultaneously realize high activity and high selectivity
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