AL-27(H-1) CROSS-POLARIZATION AND ULTRAHIGH-SPEED AL-27 MAS NMR-SPECTROSCOPY IN THE CHARACTERIZATION OF USY ZEOLITES

Al-27 MAS NMR spectroscopy with H-1 cross-polarization is shown to be an efficient technique for distinguishing non-framework from framework Al in USY zeolites and has revealed the presence of non-framework tetrahedral Al. Field-dependent measurements and simulations show that the non-framework 30 ppm Al-27 resonance observed for USY zeolites must be considered an individual signal and not part of a second-order quadrupole lineshape as recently suggested. Ultrahigh-speed spinning (nu-r = 18-20 kHz) is demonstrated to be a prerequisite for obtaining quantitative results for these systems by Al-27 MAS NMR. Finally, experimental evidence for the similarity between the non-framework Al phases in USY zeolites and steamed silica-alumina is presented.