Multiple equilibrium analysis description of adsorption on Na-mordenite and H-mordenite

Adsorption isotherms are reported for Wa-mordenite and H-mordenite at sever al temperatures with a series of gas adsorptives above their critical tempe rature. The data sets are analyzed with the multiple equilibrium analysis ( MEA) method [Drago, R. S.; et al. J. Am. Chem. Sec. 1998, 120, 538-547. Dra go, R. S.; et al. J. Phys. Chem. B 1997, 101, 7548-7555], which produces eq uilibrium constants (Ki), capacities (ni), and thermodynamic parameters (en thalpies, Delta H-i, and entropies, Delta S-i) of adsorption for each proce ss. The limited pore size distribution present in the zeolite mordenite pre sents an interesting comparison to the amorphous carbons studied previously by MEA [Drago,:R. S.; et al. J. Phys. Chem. B 1997, 101, 7548-7555]. The r esults of the MEA description of the adsorption data gathered for the inter action of an adsorbate (particularly, N-2, CO, and Xe) with Na-mordenite an d H-mordenite are compared to other literature reports (including infrared spectroscopic studies and Monte Carlo simulations), and good agreement is f ound. In general, for adsorbates that can access the small channel (small a dsorbates), three processes are required to describe adsorption. Two proces ses are required to describe adsorption for the larger adsorbates into the large (main) channel. The smaller total micropore volumes of Na- and H-mord enite for these adsorptives result in decreased capacity compared to that o f the amorphous carbons. The process capacities from MEA (mol g(-1)) are co nverted to pore volumes using the calculated molar volume of the adsorbate, and the accessible surface area for a given process is converted with the excluded molecular area of the adsorbate. The results show that MEA provide s a more detailed and accurate assessment of the interaction of admolecules with microporous solids, which addresses a matter of fundamental importanc e to researchers and practitioners-the interactions between gas-phase molec ules and a surface of a condensed phase. This analysis leads to an increase d understanding of this behavior in gas adsorption and catalysis.