Distribution of Aluminum in the Periodical Building Units of Faujasites

Four NH 4 −Y faujasites (FAU) with different Si/Al ratios were characterized by 27 Al and 29 Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The quantitative contributions of the Al sites, defect-free Si( n Al), and silanol groups to the different double-six-ring (D6R) periodical building units (PerBUs) of the zeolite framework were calculated from the various Si/Al ratios and relative 27 Al and 29 Si NMR signal intensities. Four different PerBU systems were assumed in the FAU structure, but only the distribution of PerBUs containing three, two, or one Al atom pairs in body-diagonal positions of D6Rs followed the composition of the framework with appropriate precision in the studied composition range (Si/Al = 2.6−19.5). Contrary to BEA, FER, and MOR zeolites, the PerBUs of FAU do not contain Al atoms in unpaired “lone” positions.