Oxidative dehydrogenation of propane over rare-earth orthovanadates

High-purity rare-earth orthovanadates (R_EVO₄), PrVO₄) GdVO₄, DyVO₄, HoVO₄, ErVO₄, NdVO₄, TbVO₄ and LuVO₄, have been prepared by the citrate method. XRD, FTIR, LRS, UV-VIS diffuse reflectance, TPR and EPR techniques have been employed to characterize them. The catalytic performances of PrVO₄, ErVO₄, GdVO₄, DyVO₄ and NdVO₄ in the oxidative dehydrogenation of propane can compete with that of Mg₃V₂O₈. The selectivity of propene over TbVO₄, LuVO₄ and HoVO₄ was relatively low. TPR results showed that the more easily the catalyst is reduced, the higher the propene selectivity. EPR and in situ Raman experiments confirmed the presence of low-valence vanadates at the catalyst surface in the reaction process. We observed that ¹⁸O₂-isotope exchange occurred over the catalysts via a double-step single exchange process and the activity of the catalysts increased with an increase of isotope exchange rate.