Catalytic oxidative dehydrogenation of propane in the presence of O2 and N2O -: the role of vanadia distribution and oxidant activation

For the oxidative dehydrogenation of propane (ODP), the initial rates of products formation over differently-loaded VOx/gamma-Al2O3 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 N2O. By replacement of O-2 with N2O, 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 VOx/gamma-Al2O3 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 COx.(.) A high selectivity to propene can be achieved by covering the support fully by well-dispersed vanadia species. Since N2O 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. (C) 2001 Elsevier Science B.V. All rights reserved.