Characterization of aluminum and boron containing beta zeolites prepared by solid-state recrystallization of magadiite

A method for the preparation of phase-pure [Al]-BEA and [Al,B]-BEA zeolites based on solid-state recrystallization of synthetic aluminum-containing magadiites is presented. For comparison [B]-BEA was prepared by conventional hydrothermal synthesis. From X-ray diffraction (XRD) measurements conclusions could be drawn in respect to kinetics and mechanism of the recrystallization process. Coordination state and resistance to hydrolysis of framework boron species in as-synthesized and ion-exchanged BEA varieties were investigated by 11B MAS NMR spectroscopy. The acidity of the samples was studied by temperature-programmed ammonia elimination (TPAE) from the NH4-forms and by IR spectroscopy using pyridine as probe molecule. An effect of framework boron on the acid strength of bridged hydroxyls associated with framework aluminum could not be evidenced. Nevertheless, incorporated boron gives rise to weak acid sites which are involved in ion-exchange processes. The number of strong Brønsted sites can be controlled by the aluminum content of the layer silicate.