DRIFTS and Raman investigation of N-2 and O-2 adsorption on zeolites at ambient temperature

Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and Raman spectroscopy were used to examine N-2 and O-2 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 N-2 and O-2 at room temperature and atmospheric pressure. The intensity (in Kubelka-Munk units) of the IR band increased with N-2 pressure and mirrored the adsorption isotherm for N-2. Both O-2 and N-2 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 N-2 and O-2 were more sensitive to the cation charge density than to framework Al content. Infrared studies of N-2 and O-2 on mixed cation forms of LSX show that N-2 interaction was localized near individual cations within the sorption cavity of the zeolite. Thus, adsorbed N-2 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 N-2 over O-2 is caused by the stronger influence of the electric field with the larger quadrupole of N-2.