OBSERVATION OF NONFRAMEWORK AL SPECIES IN ZEOLITE-BETA BY SOLID-STATENMR-SPECTROSCOPY

Dealumination of zeolite beta by hydrothermal or calcination treatment s has been investigated in detail using H-1 magic angle spinning (MAS) , H-1((27)A1) spin echo double-resonance, and Al-27 MAS NMR. The NMR e xperiments provide direct evidence for the existence of nonframework A l species in zeolite beta, which give rise to a H-1 resonance at ca. 2 .7 ppm and two Al-27 signals at ca. 30 and 0 ppm (corresponding to 5- and 6-coordiante Al, respectively). The nonframework 6- and 5-coordina te Al species do not revert to framework 4-coordinate Al (54 ppm) in t he dehydration process of zeolite beta. For the Al-27 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.