High-purity rare-earth orthovanadates (R(E)VO(4)). 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 PrVO,, ErVO,, GdVO,, DyVO, and NdVO, 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. mie observed that O-18(2)-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.
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