ZEOLITE ADSORPTION SITE LOCATION AND SHAPE SHOWN BY SIMULATED ISODENSITY SURFACES

The graphics software package Ribbons' is used to display isodensity s urfaces of Xe atoms adsorbed in the alpha cage of zeolite NaA. The loc ation, size, and shape of the adsorption sites are highly dependent on the loading and the crystal cation content. When the zeolite has a hi gh number of cations, ellipsoidal sites arrange in a cuboctahedron. Wh en the zeolite has fewer cations, cone-shaped sites arrange in an octa hedron at low loading, but at high loading the sites become ellipsoida l and new sites form at cuboctahedral positions. The effect of the nat ure of the adsorption site on the development of a universal adsorptio n model is discussed.