Supported Vanadium Oxide Catalysts: Quantitative Spectroscopy, Preferential Adsorption of V^4+/5+, and Al₂O₃ Coating of Zeolite Y

Abstract

A series of supported vanadium oxide catalysts were prepared by the incipient wetness method as a function of the support composition (Al 2 O 3, SiO 2, 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 V 4+ and V 5+ and to unravel their coordination geometries. These spectroscopic fingerprints have been used to study the preferential adsorption of V 4+/5+ ions on SiO 2, Al 2 O 3, and USY. Both V 4+ and V 5+ were preferentially adsorbed on Al 2 O 3 and showed a much smaller preference for USY and SiO 2 . 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 Al 2 O 3 . The method is based on the deposition of USY with the so-called Keggin ion, [Al 13 O 4 (OH) 24 (H 2 O) 12 ] 7+, which is too big to enter the USY channels or pores. The obtained Al 2 O 3 /USY material showed a preferential adsorption of V 4+ onto the Al 2 O 3 film, suggesting that this method could be useful for vanadium passivation of FCC catalysts.