Abstract:
The linear variations in frequency of the stretching O—(Al, Si)—O vibrations (around 1050 and
800 cm-1) with Al content of aluminium-deficient zeolites can also be extended to ultrastable zeolites.
This result confirms the similarities between both types of modified zeolites. Moreover this quanti
tative relationship yields the number of framework Al atoms for ultrastable zeolites.
A detailed study of the band intensities of aluminium-deficient zeolites in the same region was
carried out. Apart from the intensity of the 730 cm-1 band which linearly decreases with decreasing
Al content and is attributed to “ isolated’’AlOj. tetrahedra, the integrated intensities of other bands
around 1150, 1050, 800, 585, 450 and 395 cm-1 are not affected by aluminium removal. This indi
cates that aluminium removal using ethylenediaminetetra-acctic acid does not cause structural
discontinuities in the Y zeolites and it is suggested that Si atoms occupy the sites vacated by Al
atoms.
