Catalytic oxidative dehydrogenation of propane in the presence of O 2 and N 2O—the role of vanadia distribution and oxidant activation

Abstract

For the oxidative dehydrogenation of propane (ODP), the initial rates of products formation over differently-loaded VO x /γ-Al 2O 3 catalytic materials (0.5–9.5 wt.% of vanadium) were derived from near differential degree of conversion for two different oxidants, i.e. O 2 and N 2O. By replacement of O 2 with N 2O, overall activity decreased, while the selectivity towards propene formation increased for the same degree of propane conversion. The fundamental insights into phase composition, reduction, structure and dispersion of vanadium sites as well as electronic properties of VO x /γ-Al 2O 3 were derived from characterisation of the materials by XRD, TPR, EPR, UV–VIS diffuse reflectance spectroscopies (UV–VIS-DRS), contact potential difference (CPD) and electrical conductivity measurements. UV–VIS and conductivity measurements were applied for in situ studies. As a result of the characterisation studies, the following relationships between catalytic performance and solid-material properties were obtained. Isolated sites are beneficial for propene selectivity but they do not completely cover the support surface, on which propene can be adsorbed and further oxidised to CO x . A high selectivity to propene can be achieved by covering the support fully by well-dispersed vanadia species. Since N 2O decomposition, over the studied materials, is less favourable than O 2 activation, a decrease in the steady-state concentration of active sites and an increase of the propene selectivity is achieved.