Zeolite Beta: The relationship between calcination procedure, aluminum configuration, and Lewis acidity

Zeolite Beta was calcined under a variety of carefully controlled condition s to study the influence of (hydro)thermal treatments on the catalytic acti vity of zeolite Beta in the Lewis acid-catalyzed Meerwein-Ponndorf-Verley r eduction of ketones, The activity of (H)Beta can be increased by several or ders of magnitude by mild steaming. The catalytic activity of the materials following reactivation can be diminished again by adsorption of ammonia fo llowed by an induction period. For these changes, an explanation is offered in term of Lewis acidic framework aluminum atoms which undergo a change of configuration depending on the ligands present, rather than becoming extra framework aluminum. FTIR, Si-29, and Al-27 MAS NMR spectroscopy were applie d to investigate the changes induced by the (hydro)thermal procedures. (C) 1998 Academic Press.