DRIFTS AND RAMAN INVESTIGATION OF N-2 AND O-2 ADSORPTION ON ZEOLITES AT AMBIENT-TEMPERATURE

Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) a nd Raman spectroscopy were used to examine N-2 and O-2 adsorption on c ation-exchanged (K, Na, Sr, Ca, and Li) low silica X (LSX) zeolites. I R 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 frequ ency on cation charge density, which suggests that both gases are inte racting directly with the cations. The vibrational frequencies for ads orbed N-2 and O-2 were more sensitive to the cation charge density tha n to framework Al content. Infrared studies of N-2 and O-2 on mixed ca tion forms of LSX show that N-2 interaction was localized near individ ual 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 theo ry that the stronger interaction of N-2 over O-2 is caused by the stro nger influence of the electric field with the larger quadrupole of N-2 .