THERMAL-STABILITY OF (B)ZSM-5 MOLECULAR-SIEVE

The thermal stability of [B]ZSM-5 (boronsilicalite) has been examined by IR, XRD, B-11 MAS NMR and XPS techniques. [B]ZSM-5 and amorphous borosilicate were converted to alpha-cristobalite at high temperatures (= 750-degrees-C). However, Na-free amorphous borosilicate was not converted to alpha-cristobalite at 750-degrees-C. Therefore, the presence of Na+ ions in [B]ZSM-5 would determine whether this transition occurred or not. When the phase transition to alpha-cristobalite occurred, most of B atoms tetrahedrally coordinated were released from the ZSM-5 structure and migrated to the exterior surface as a boron compound having trigonal BO3 units and oxidation states of 3.