Thermodynamic and Molecular Characterization of Adsorption on Zeolites: A Unified Framework Combining Inverse Gas Chromatography, Hamaker Theory, and Nonlinear Lewis Acid-Base Modeling

A comprehensive thermodynamic and molecular-level investigation of adsorption on MgY and NH4Y zeolites is presented using inverse gas chromatography at infinite dilution (IGC-ID), combined with a Hamaker-based formalism and an extended five-parameter Lewis acid-base model. The study introduces a unified framework that integrates dispersive, polar, and donor-acceptor interactions while explicitly accounting for temperature-dependent intermolecular geometry. The results demonstrate that the London dispersive free energy exhibits a highly linear temperature dependence (R-2 > 0.999), while the corresponding surface energy decreases linearly with temperature (e.g., gamma T-d(s)=-0.297T+189.48 mJ & centerdot;m(-2) for MgY), reflecting the progressive weakening of dispersion forces. Simultaneously, the intermolecular separation distance follows a linear relation r(T)=r(0)+alpha T-eff, with alpha eff values on the order of (2-3) & times; 10(-3) & Aring;& centerdot;K(-1 )for MgY, enabling the determination of intrinsic contact distances r(0) at 0 K, varying between 4.00 & Aring; and 6.60 & Aring;. A major finding is that the molecular surface area of adsorbed probes is not constant but follows a quadratic temperature dependence with excellent accuracy (R-2 > 0.999), establishing adsorption cross-section as a thermodynamic variable. The comparison between MgY and NH4Y reveals two distinct adsorption regimes: MgY exhibits a structured and strongly dispersive interaction field associated with Mg2+ cations, whereas NH4Y displays enhanced polarity, stronger specific interactions, and greater molecular flexibility driven by hydrogen bonding and protonic effects. Thermodynamic analysis of Lewis acid-base interactions shows that classical linear models are insufficient. Statistical evaluation (R-2 approximate to 0.986, minimum AIC/BIC, lowest RMSE) demonstrates that the five-parameter Hamieh model provides the most accurate and physically meaningful description, capturing nonlinear donor-acceptor interactions and amphoteric coupling effects. Overall, this work establishes a novel thermodynamic methodology that quantitatively links macroscopic surface energetics to microscopic interaction parameters, providing new insight into adsorption mechanisms and a robust framework for the rational design of porous materials in catalysis, separation, and energy applications.