Abstract
Abstract FTIR has been used to investigate structural and acidic modification carried out upon calcination of La-, Nd-, Sm-, Gd- and Dy-exchanged NaY zeolite. The introduction of RE cations brought about no significant changes in the structural region of the zeolites. However, in the hydroxyl region, a band ranging from 3530 to 3498 cm −1 may be observed. This band was attributed to OH groups interacting with RE cations and the position thereof is shifted to higher wavenumbers as the ionic radius of the cations increases. After pyridine adsorption, Bronsted acid sites at 1540 cm −1 and 1630 cm −1 are detected. The intensity of the 1540 cm −1 band is a function of the type of RE cation introduced. The higher the ionic radius of the RE (rare earth) cation, the higher the intensity of this band, indicating that the calcination of zeolites containing lighter RE generates more acidic materials. Similar results were also observed when another probe molecule, 2,6-lutidine, was used.
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