Combined Cyclohexene Dehydrogenation and Oxygenation over VO x /CeO2 with O2 and Vaporized H2O2 as Oxidants

Selective oxidation of hydrocarbons over metal oxide catalysts frequently invokes Mars-van Krevelen (MvK) mechanisms involving lattice oxygens. At typical reaction temperatures, oxidative dehydrogenation reactions predominate and compete with total oxidation; the production of more useful oxygenates is challenging. However, because the regeneration of lattice oxygens has been previously hypothesized to involve the transient formation of surface hydroperoxides or peroxides, MvK cycles should be capable of forming products derived from both lattice oxygen and surface (hydro)peroxide species under certain conditions. In this report, we study the low-temperature reaction of cyclohexene with O-2 over CeO2-supported VOx catalysts. Below 150 degrees C and for higher VOx loading, cyclohexene converts to benzene and trans-1,2-cyclohexanediol with no appreciable CO2 formation. Control experiments show similar behavior in other supported vanadia catalysts. Conversely, using vaporized H2O2 as the oxidant exclusively gives 1,2-cyclohexanedione, suggesting that MvK reoxidation cycles do not directly involve H2O2. These findings contribute to the current understanding of selective oxidation mechanisms and demonstrate routes to the formation of industrially useful oxygenates with O-2 or vaporized H2O2 over metal oxide catalysts.