Adsorption of argon and nitrogen in X-faujasites: relationships for understanding the interactions with monovalent and divalent cations

The adsorption of a polar (nitrogen) and a non polar (argon) gas has been investigated in a variety of monovalent (Li+, Na+, K+) and divalent (Ca2+, Sr2+, Ba2+) ion exchanged X-faujasites by direct microcalorimetry measurements performed at ambient temperature. Isotherms and differential enthalpies of adsorption in the low pressure domain as well as the Henry's constants are reported for each investigated system. The effect of the extra-framework cations on adsorbate/adsorbent interactions are discussed on the basis of the values of differential enthalpies of adsorption at zero coverage. This quantity increases in the sequences LiX > NaX > KX and CaX > SrX > BaX for both argon and nitrogen. These experimental trends can be interpreted from predominant polarisation effects induced by the cations for argon adsorption whereas a combination of both electrostatic and polarisation contributions is required for nitrogen adsorption.