ORIGIN OF THE OPTIMUM IN CATALYTIC ACTIVITY OF ZEOLITE-BETA

Acidity and catalytic properties of zeolite beta depend on the stabili ty of framework aluminium sites. Optimal performances are obtained wit h crystals of average radius 0.15-0.5 mu m and an aluminium content m = Al/(Si + Al) = 0.085. H-beta zeolites with such an aluminium content correspond to as-synthesized zeolites in which tetraethylammonium and aluminium contents are equal. Smaller crystals with higher aluminium contents are formed under synthesis conditions that generate tetrahedr a distortions and silanol defects, with a significant decrease of the thermal stability.