Influence of superacid sites in USY zeolites on gasoil cracking

Most petroleum refineries are using high octane cracking catalysts based on ultrastable Y zeolite (USY). Ultrastabilization is achieved by increasing the framework Si/Al ratio of the zeolite by either stream chemical treatments or a combination of both. If a partial dealumination of the Y zeolite is carried out during the manufacture of the catalyst, the ulterior dealumination in the FCC unit becomes slower, and more crystallinity is retained. If partially NH{sub 4}{sup +} exchanged NH{sub 4}NaY zeolite is steam calcined, a slow framework dealumination occurs while silicon migration to stabilize the defects sites takes place. Following this procedure, the extraframework aluminum (EFAL) remains in the zeolite and its exact nature and therefore its catalytic role depends on the method and conditions used for its formation. In a previous paper the authors have shown that by an adequate treatment of steam dealuminated Y zeolites with (NH{sub 4})SiF{sub 6} it is possible to remove the EFAL selectivity. The physicochemical characterization of these samples shows that the presence of EFAL is responsible for the formation of superacid sites, as well as for the neutralization of a part of framework hydroxyls. In this work, they have studied the effect of remotion of the EFALmore » on the gasoil cracking behavior of the zeolites, as well as the influence of the presence of EFAL on the thermal stability of the samples.« less