An intense and narrow infrared band was observed around 885 cm(-1) in the s
pectrum of activated dealuminated beta zeolites. This band does not corresp
ond to the vibration of a hydroxy group, as was shown by in situ deuterium
exchange and heavy-water steaming of the sample in the infrared cell. It is
rather linked to the vibration of a site corresponding to specific defects
in the structure. Pyridine adsorption evidenced the strong Lewis character
of this site. At the same time, a diner link with a nu(OH) band at 3782 cm
(-1) was found. CO2 adsorption partially transformed these OH groups into h
ydrogen-carbonate species, thus showing their basic properties. Assignment
is proposed to a tricoordinated aluminum atom partially connected to the fr
amework, with a hydroxy group on the aluminum atom. The electronic vacancy
on the Al atom, together with the basic hydroxy group, constitutes an acid-
base pair on an acidic zeolite. The 885 cm(-1) band is a direct infrared fi
ngerprint of a Lewis site.