Abstract

Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and Raman spectroscopy were used to examine N₂ and O₂ adsorption on cation-exchanged (K, Na, Sr, Ca, and Li) low silica X (LSX) zeolites. IR and Raman absorption bands were observed for the molecular vibration of adsorbed N₂ and O₂ at room temperature and atmospheric pressure. The intensity (in Kubelka-Munk units) of the IR band increased with N₂ pressure and mirrored the adsorption isotherm for N₂. Both O₂ and N₂ displayed a similar dependence of the molecular vibrational frequency on cation charge density, which suggests that both gases are interacting directly with the cations. The vibrational frequencies for adsorbed N₂ and O₂ were more sensitive to the cation charge density than to framework Al content. Infrared studies of N₂ and O₂ on mixed cation forms of LSX show that N₂ interaction was localized near individual cations within the sorption cavity of the zeolite. Thus, adsorbed N₂ can be used to probe accessibility of specific cations within the zeolite framework. The spectroscopic data are consistent with the theory that the stronger interaction of N₂ over O₂ is caused by the stronger influence of the electric field with the larger quadrupole of N₂.

Infrared Spectra of Water Sorbed on Synthetic Zeolites*

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