A series of supported vanadium oxide catalysts were prepared by the incipient wetness method as a function of the support composition (Al2O3, SiO2, and USY), the metal oxide loading (0-1 wt %), and the impregnation salt (vanadyl sulfate and ammonium vanadate). These catalysts have been studied by combined DRS-ESR spectroscopies in order to quantify the amount of V4+ and V5+ and to unravel their coordination geometries. These spectroscopic fingerprints have been used to study the preferential adsorption of V4+/5+ ions on SiO2, Al2O3, and USY. Both V4+ and V5+ were preferentially adsorbed on Al2O3 and showed a much smaller preference for USY and SiO2. The observed preference orders are discussed in relation with the properties of the support. In addition, a novel method is proposed to coat the external surface of USY with a thin film of Al2O3 The method is based on the deposition of USY with the so-called Keggin ion, [Al13O4(OH)(24)(H2O)(12)](7+), which is too big to enter the USY channels or pores. The obtained Al2O3/USY material showed a preferential adsorption of V4+ Onto the Al2O3 film, suggesting that this method could be useful for vanadium passivation of FCC catalysts.