(303d) A Rigorous Thermodynamic Framework for Isosteric Heat of Adsorption

Isosteric heat of adsorption is an important thermodynamic quantity from both experimental and theoretical point of view. It is essential not only for understanding thermal effects and heat management related to gas adsorption, but also for developing and validating adsorption models and materials force fields. Despite a long history of theoretical studies and extensive literature, controversies often arise on the analysis of isosteric heat due to empirical assumptions to describe gas adsorption, and due to the inconsistency between calorimetrically measured isosteric heat and the indirectly correlated isosteric heat from adsorption isotherms. In this talk, we present a rigorous thermodynamic framework to analyze isosteric heat effects without any unjustified assumptions on the pore geometry of the porous adsorbents or operating conditions. The new thermodynamic framework avoids problematic division of the thermodynamic system into a bulk gas phase and an adsorbed phase or empirical estimation of the pore volume. It enables a rigorous prediction of the isosteric heat of adsorption from adsorption isotherms in a thermodynamically consistent manner. We demonstrate applications of the new theoretical framework with simulation results and experimental data for gas adsorption in model adsorbents and in realistic nanoporous materials, respectively, and compare the results with conventional thermodynamic models. We will show that theoretically predicted isosteric heats of adsorption for nanoporous materials including MOF and zeolites are in good agreement with experimental calorimetry data.