The concentration of oxygen atoms on defect sites in a highly siliceous HZSM-5 type zeolite was estimated by the I80-exchange reaction between CI8O2 and the zeolite. The concentration of oxygen atoms on defect sites could be controlled by means of changes of the gel composition and of the use of various silica sources in the hydrothermal synthesis. The relationship between the concentration of oxygen atoms on defect sites in a highly siliceous HZSM-5 and the concentration of aluminum introduced into the framework of the HZSM-5 by an alumination was examined. The concentration of the framework aluminum was the same as one-fourth that of the oxygen atoms on defect sites. These results suggest that the defect sites into which aluminum atoms are introduced tetrahedrally can be identified with hydroxyl nests that consist of four silanol groups. The existence of hydroxyl nests could be confirmed by IR spectroscopy. From the I80-exchange reaction and IR measurements, we conclude that the sharp band at 3740 cm-' can be attributed to both isolated SiOH groups on the external surface and intracrystalline isolated S O H groups and that the broad band at 3505 cm-' can be attributed to the SiOH groups in hydroxyl nests.

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Aluminosilicates, gallosilicates, and indosilicates with the ZSM-5 type structure were prepared by the “Atom-Planting method”. The introduction of metal cations into the framework of highly siliceous ZSM-5 zeolites was confirmed by IR and unit cell volume measurements. The acidic properties of these metallosilicates were examined by pyridine-IR and NH3-temperature programmed desorption spectroscopies. The increasing order of the acid strengths of the metallosilicates is indosilicate<gallosilicate<aluminosilicate.

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