Studies on crystalline microporous vanadium silicates III. Selective oxidation of n-alkanes and cyclohexane over VS-2

Abstract

The oxyfunctionalization of n-alkanes (C6, C7, and C8) and cyclohexane over vanadium silicates (VS-2) with Si/V = 79, 122, and 161 in presence of aqueous H2O2 yields corresponding alcohols and carbonyl compounds at 373 K. Unlike titanium silicates, VS-2 is able to activate the primary carbon atoms of n-alkanes, giving rise to primary alcohols and aldehydes in addition to secondary alcohols and ketones. The latter are, however, the preferred products of oxidation. The oxidative conversions and the H2O2 selectivities decreased in the order, n C6 > n C7 > n C8 > cyclohexane, consistent with the decrease in the diffusivity of these alkanes in the zeolites. Solvents have considerable influence on the conversion, CH3CN being the most suitable. The formation of a radical-type intermediate has been confirmed by ESR spectral observations. A possible mechanism for the oxidation through a peroxo radical intermediate has been proposed