Observation of Nonframework Al Species in Zeolite β by Solid-State NMR Spectroscopy

Dealumination of zeolite β by hydrothermal or calcination treatments has been investigated in detail using 1 H magic angle spinning (MAS), 1 H{ 27 Al} spin echo double-resonance, and 27 Al MAS NMR. The NMR experiments provide direct evidence for the existence of nonframework Al species in zeolite β, which give rise to a 1 H resonance at ca. 2.7 ppm and two 27 Al signals at ca. 30 and 0 ppm (corresponding to 5- and 6-coordiante Al, respectively). The nonframework 6- and 5-coordinate Al species do not revert to framework 4-coordinate Al (54 ppm) in the dehydration process of zeolite β. For the 27 Al signal at 30 ppm, hydration may probably lead to a dispersion in its chemical shift or quadrupole interaction, which broadens its line width in the hydrated sample.