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

摘要

A series of supported vanadium oxide catalysts were prepared by the incipient wetness method as a functionudof the support composition (Al2O3, SiO2, and USY), the metal oxide loading (0-1 wt %), and the impregnationudsalt (vanadyl sulfate and ammonium vanadate). These catalysts have been studied by combined DRS-ESRudspectroscopies in order to quantify the amount of V^4+ and V^5+ and to unravel their coordination geometries.udThese spectroscopic fingerprints have been used to study the preferential adsorption of V^4+/5+ ions on SiO2,udAl2O3, and USY. Both V^4+ and V^5+ were preferentially adsorbed on Al2O3 and showed a much smaller pref-erenceudfor USY and SiO2. The observed preference orders are discussed in relation with the properties of theudsupport. In addition, a novel method is proposed to coat the external surface of USY with a thin film ofudAl2O3. The method is based on the deposition of USY with the so-called Keggin ion, [Al13O4(OH)24(H2O)12]7+ ,udwhich is too big to enter the USY channels or pores. The obtained Al2O3/USY material showed a preferentialudadsorption of V^4+ onto the Al2O3 film, suggesting that this method could be useful for vanadium passivationudof FCC catalysts.