AlOx coating of ultrastable zeolite Y: A possible method for vanadium passivation of FCC catalysts

AlOx coating is proposed as a possible method for vanadium passivation of t he ultrastable zeolite Y (USY). Two coating methods are discussed: (i) the deposition of the [Al13O4(OH)(24)(H2O)(12)](7+) ([Al-13]) complex from aque ous solutions and (ii) the anchoring of alumoxane by in situ triisobutylalu minum hydrolysis followed by calcination. The properties and the efficiency in vanadium passivation of the coated materials have been investigated wit h 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 a nd differences in Al coordination geometry. Vanadyl(IV) etioporphyrin,the m ajor contaminant in crude oil, was used to probe the trapping efficiency of the external AlOx layer. The [Al-13]-derived layer is homogeneously distri buted and covers the external surface of the USY zeolite, following its top ology, but without blocking its pores. About 80% of the offered vanadyl spe cies have been preferentially trapped in this layer. The alumoxane-based me thod 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.