Infrared Spectra of Nitrogen Adsorbed on Ion-Exchanged ZSM-5 Zeolite

Abstract Amounts of nitrogen adsorbed by ion-exchanged ZSM-5 zeolites (H+, Li+, Na+, K+, Rb+, and Cs+) and silicalite have been measured under various conditions; pressure=6.7×102–6.7×104 Pa, temperature=196–273 K. IR spectra of adsorbed nitrogen have also been measured at 226 K under various nitrogen pressures (1.3×102–4.0×104 Pa). The adsorption capacity, the specific surface area, and the heat of adsorption have been evaluated from the adsorption data. These quantities coupled with the IR peak shifts observed have revealed that the nitrogen molecule adsorbed on a small and strong cationic site (Li+, Na+) has an orientation in which the longer molecular axis lies in parallel with the direction of the electric field of the cation site. It has also been revealed that the nitrogen molecule adsorbed on a large (K+, Rb+, Cs+) or weak (H+) cationic site takes on no special orientation. The electric field evaluated by analyzing the IR intensity is consistent with the adsorption model obtained.