Net Adsorption of Gas/Vapor Mixtures in Microporous Solids

Document Type


Publication Date


Publication Title

Journal of Physical Chemistry C


Adsorption thermodynamics is based on Gibbs definition, which transforms the nonuniform interfacial region to a uniform three-phase system including a two-dimensional adsorbed phase on a hyper-surface. Gibbs definition is a pure mathematical construct applicable wherever the hyper-surface is located. On the other hand, physical quantification of adsorption and hence its applications require that the hyper-surface be located. Conceptually, the location of hyper-surface differentiates between so-called absolute, excess, and the recently introduced (Gumma and Talu, Langmuir 2010, 26 (22), 17013-17023) net adsorption thermodynamic frameworks. This article details net adsorption thermodynamic framework for mixtures. In addition, a thermodynamic inconsistency is recognized in the calculation of grand potential (or solid chemical potential) with commonly used implementation of excess adsorption in literature. The inconsistency is shown to have a substantial impact on further thermodynamic calculations such as mixture adsorption predictions for even a simple typical example as oxygen-nitrogen-zeolite SA system at 22 C and moderate pressures. Historically, this inconsistency seems to originate from adopting intuitive concepts for planar surfaces to microporous systems without regard to the differences in the physical nature of these two types of interfaces. Net adsorption framework Circumvents. the inconsistency as well as providing an unequivocal description of adsorption in micropores.

Original Citation

Talu O. Net Adsorption of Gas/Vapor Mixtures in Microporous Solids. The Journal of Physical Chemistry C. 2013;117:13059-13071.