INFLUENCE OF FRAMEWORK AND NONFRAMEWORK ALUMINUM ON THE ACIDITY OF HIGH-SILICA, PROTON-EXCHANGED FAU-FRAMEWORK ZEOLITES

Measured selectivities and activities in isobutane conversion investigations on high-silica FAU materials prepared by different methods of dealumination indicate that the strong acidity exhibited by hydrothermally dealuminated (ultrastable) materials, while directly related to framework aluminum content, depends on a balance between aluminum in the framework and dislodged or nonframework aluminum that is entrained in the lattice during steam treatment. Isobutane conversions over ultrastable FAU materials containing low fractions of dislodged aluminum exhibit markedly enhanced activities, indicating that conventionally prepared ultrastable materials may contain a higher fraction of dislodged aluminum than is optimum.