27Al&{1H} cross-polarization and ultrahigh-speed 27Al MAS NMR spectroscopy in the characterization of USY zeolites

27Al MAS NMR spectroscopy with 1H cross-polarization is shown to be an efficient technique for distinguishing non-framework from framework A1 in USY zeolites and has revealed the presence of non-framework tetrahedral A1. Field-dependent measurements and simulations show that the non-framework 30 ppm 27Al 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 (νr= 18–20 kHz) is demonstrated to be a prerequisite for obtaining quantitative results for these systems by 27Al MAS NMR. Finally, experimental evidence for the similarity between the non-framework A1 phases in USY zeolites and steamed silica—alumina is presented.