Origin of the optimum in catalytic activity of zeolite beta

Abstract

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.