Adsorption behavior of some gas molecules in Ω-zeolite pores

Abstract

The adsorptive behavior of CH 4 and CO in the pores of Ω-zeolite was investigated by FT-IR spectroscopy and adsorption measurements. Adsorption isotherms of Xe were also studied for comparison under the same conditions. Ω-zeolite has two kind of pores namely, one consisted of an 8-membered oxygen ring and the other of a 12-membered ring. CO was preferentially adsorbed in the smaller pores, but Xe was not at temperatures between 203 and 271 K. CH 4 was scarcely adsorbed in smaller pores at temperatures below 214 K, but most of the adsorbed CH 4 was distributed in the pores above 250 K. The admolecules in the smaller pores suffer strong van der Waals interaction, and the translational and the rotational freedom of adsorbed methane are significantly restricted at lower temperatures, although no evidence of a strong electric field was detected. On the contrary, the admolecules in the larger pores experience a strong electric field (about 6.3 × 10 9 V m −1), but the translational and rotational freedom is kept rather even at lower temperatures. The cations on larger pore surfaces effectively interact with admolecules, and their amount is estimated to be about one site per unit cell. On the contrary, it was suggested that ca. five molecules per unit cell of CO was adsorbed in the smaller pores, and they weakly interacted with the cations in gmelinite cage.