In the l80-exchanged reaction, the 02 atoms in the internal SiOH groups or in the nonintact Si-O-Si groups in the nest type defect sites attained the equilibrium state at ca. 15 h. Moreover, the bands at 3505 cm"1 2were observed less in the IR spectra for the HZSM-5 having fewer defect sites. From these results, it is suggested that the broad band at 3505 cm"1 can be identified with the SiOH groups of the hydroxyl nests.If aluminum atoms are inserted into hydroxyl nests in the HZSM-5 by alumination with A1C13, the band at 3505 cm"1 will disappear. The IR spectrum for aluminated HZSM-5 prepared from the parent HZSM-5 (sample 9 in Table I) is depicted in Figure 8E. The aluminated HZSM-5 exhibited a new band at 3610 cm"1 attributed to the framework Si(OH)Al groups,23 while the band at 3505 cm"' disappeared. These results indicate that (23) Jacobs, P.

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