Résumé
Acidity and catalytic properties of zeolite beta depend on the stability of framework aluminium sites. Optimal performances are obtained with crystals of average radius 0.15-0.5 µm 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 tetrahedra distortions and silanol defects, with a significant decrease of the thermal stability.