Oxidative dehydrogenation of propane over differently structured vanadia-based catalysts in the presence of O 2 and N 2O

Abstract

The effect of the nature and distribution of VO x species over amorphous and well-ordered (MCM-41) SiO 2 as well as over γ-Al 2O 3 on their performance in the oxidative dehydrogenation of propane with O 2 and N 2O was studied using in situ UV–vis, ex situ XRD and H 2-TPR analysis in combination with steady-state catalytic tests. As compared to the alumina support, differently structured SiO 2 supports stabilise highly dispersed surface VO x species at higher vanadium loading. These species are more selective over the latter materials than over V/γ-Al 2O 3 catalysts. This finding was explained by the difference in acidic properties of silica- and alumina-based supports. C 3H 6 selectivity over V/γ-Al 2O 3 materials is improved by covering the support fully with well-dispersed VO x species. Additionally, C 3H 6 selectivity over all materials studied can be tuned by using an alternative oxidising agent (N 2O). The improving effect of N 2O on C 3H 6 selectivity is related to the lower ability of N 2O for catalyst reoxidation resulting in an increase in the degree of catalyst reduction, i.e. spatial separation of active lattice oxygen in surface VO x species. Such separation favours selective oxidation over CO x formation.