Non-Linear Enthalpy-Entropy Correlation for Nitrogen Adsorption in Zeolites.

The thermodynamics of dinitrogen adsorption in faujasite-type zeolites, Na-Y, Ca-Y and Sr-Y, were investigated by means of variable-temperature infrared spectroscopy, a technique that affords determination of the standard adsorption enthalpy (Δ H ⁰) and entropy (Δ S ⁰) from an analysis of the IR spectra recorded over a range of temperatures. The results obtained, taken together with previously reported values for N₂ adsorption on protonic zeolites, revealed a non-linear correlation between Δ H ⁰ and Δ S ⁰. Implications of such a correlation for gas separation and purification by adsorption in porous solids are highlighted.