Correlation of Sorption Behavior of Nitrogen, Oxygen, and Argon with Cation Locations in Zeolite X

Specific retention volume, sorption selectivity, and heat of sorption for nitrogen, oxygen, and argon have been measured in zeolite X having alkali or alkaline-earth metals as extra-framework cations using gas chromatography. These sorption properties show a strong dependence on the nature as well as the extent of extra-framework cation, reflecting that the cations are the principle sites for interactions with the sorbate molecule. Zeolites studied show sorption selectivity toward nitrogen from its mixture with oxygen or argon. The electrostatic interactions between sorbate molecules and the cations are largely responsible for the observed nitrogen selectivity for the zeolite from its mixture with oxygen or argon. The nonlinear dependence of the sorption properties with cation charge density indicates that the interactions of the sorbate molecule depend not only on the cation type but also on the sites it occupies in a zeolite structure. The correlation observed between sorption properties and the cation site occupancy shows that nitrogen can be used as a probe for determining cationic sites in a zeolite structure.