USY Zeolite Properties

USY (Ultra-Stable Y) is dealuminated Y zeolite catalyst engineered for maximum hydrothermal stability. Three properties make it the dominant FCC catalyst for supplier evaluation: steam stability, tunable acidity through unit cell size control, and secondary mesoporosity.

Hydrothermal Stability

Dealumination removes the most hydrolysis-susceptible framework Al atoms, stabilising the remaining lattice. USY survives hundreds of FCC regenerator cycles at 700 to 800 C in steam. This is the property that makes USY commercially viable — non-dealuminated HY would collapse within hours under these conditions.

Controlled Acidity via UCS

Unit cell size (24.24 to 24.55 A) is the primary QC parameter linking framework Si/Al to performance. Lower UCS means higher framework Si/Al, fewer but more isolated acid sites, less hydrogen transfer, and higher gasoline selectivity. Higher UCS means more total acidity and higher initial conversion.

Mesoporosity

Dealumination creates secondary pores (20 to 500 A) that improve diffusion of heavy feed molecules to acid sites. Mesopore volumes of 0.10 to 0.35 cm3/g enhance bottoms conversion and metals tolerance in resid FCC. This mesoporosity is absent in the parent Y zeolite.

See HY vs USY and the USY product hub.