AlOx Coating of Ultrastable Zeolite Y: A Possible Method for Vanadium Passivation of FCC Catalysts

Abstract

AlOx coating is proposed as a possible method for vanadium passivation of the ultrastable zeolite Y (USY). Two coating methods are discussed: (i) the deposition of the [Al13O4(OH)24(H2O)12]7+ ([Al13]) complex from aqueous solutions and (ii) the anchoring of alumoxane by in situ triisobutylaluminum hydrolysis followed by calcination. The properties and the efficiency in vanadium passivation of the coated materials have been investigated with DRS, ESR, XPS, FTIR, and sorption measurements. XPS revealed for all the coated samples an enrichment in the Al content in the near-surface region and differences in Al coordination geometry. Vanadyl(IV) etioporphyrin, the major contaminant in crude oil, was used to probe the trapping efficiency of the external AlOx layer. The [Al13]-derived layer is homogeneously distributed and covers the external surface of the USY zeolite, following its topology, but without blocking its pores. About 80% of the offered vanadyl species have been preferentially trapped in this layer. The alumoxane-based method is less efficient in vanadium passivation, most probably because after calcination the aluminum species are heterogeneously distributed, both on the external surface and in the channels of USY zeolite.