FT-IR studies of the interaction between zeolitic hydroxyl groups and small molecules .3. Adsorption of oxygen, argon, nitrogen, and xenon on H-ZSM-5 at low temperatures'

Adsorption of O-2, Ar, N-2, and Xe on H-ZSM-5 at low temperatures has been studied by transmission Fourier transform. infrared spectroscopy. These molecules form 1:1 hydrogen-bonded complexes with the acidic OH groups in H-ZSM-5, which is characterized by the downward shift and the broadening of the v(OH) band due to the acidic OH groups. The accompanying behavior of the adsorbed species has been examined simultaneously for the case of the O-2 and N-2 adsorption; their absorption bands have been observed at 1550 cm(-1) for the dioxygen species adsorbed on Bronsted acid sites (BAS) and at 2334 and 2352 cm(-1) for the dinitrogen species on BAS and Lewis acid sites (LAS), respectively. The broadening of the v(OH) band caused by Xe is much larger than those by the other gases, which is tentatively associated with the large polarizability of Xe. The degrees of the shift of the acidic-OH band caused by the adsorption of these molecules were systematically in the order of H-ZSM-5 > H-MOR > H-Y. Using these data, the correlation between the shift and the acidity of the zeolites has been discussed.