Photo-assisted oxidation of 2-methylpropane over Rb+-modified V2O5/SiO2. Formation of 2-methylpropane-2-ol from 2-methylpropane and O2

Abstract

The reactivity of the surface species interacting with Rb ions in the photo-oxidation of 2-methylpropane at room temperature has been investigated to clarify the mechanism of photo-oxidation of alkanes. (Propane is oxidized into oxygenates over photo-irradiated V2O5/SiO2. The addition of alkali metal ions to V2O5/SiO2 greatly enhances the catalytic activity as well as the selectivity to propanone. This is due to the formation of new kinds of surface-active species by interaction between vanadium ions and alkali metal ions. The interaction affects the exciting wavelength of vanadate effective for the oxidation, λ > 400 nm.) The activity of the species is considerably high. Propanone and C4-compounds were formed. The most striking point is the formation of 2-methylpropan-2-ol over the Rb+-modified catalyst. The reaction path of the formation of 2-methylpropan-2-ol has been studied by analysing the products of the reactions with various sole reactants. The results suggest that the formation of 2-methylpropan-2-ol is not formed via 2-methylpropene. A tracer study with 18O2 showed that oxygen atoms incorporated into 2-methylpropan-2-ol were from gaseous oxygen, whereas propanone contained 16O which originated from the lattice oxygen in the catalyst. It is likely that 2-methylpropan-2-ol is formed by mono-oxygenation as found in the enzyme system from 2-methylpropane and gaseous oxygen.