Selectivity effects of a new aluminum species in strongly dealuminated USY containing FCC catalysts

We have hydrothermally prepared and characterized a catalytically active tetrahedral aluminum species in faujasite distinct from the normal framework aluminum. The new tetrahedral species is formed after a severe steam dealummation at 830°C and is characterized by a²⁷A1 MASNMR shift of about 53 ppm compared to the 60 ppm shift observed for framework tetrahedral aluminum. DRIFTS experiments show that the 53 ppm species is associated with a Lewis rather than a protonic site. This species is associated with strong acidity and poor cracking selectivity compared to a conventional dealuminated faujasite at the same unit cell size. This site is very active and makes large amounts of gas and coke with poor gasoline selectivity compared to typical commercial FCC catalysts. After an appropriate sequence of hydrothermal dealumination and controlled pH washing steps, the 53 ppm species is the only species observed by NMR.