Determination of the acid/base properties of MgY and NH4Y molecular sieves by inverse gas chromatography

The surface characterization of MgY and NH4Y zeolites was performed using inverse gas chromatography (IGC). The adsorption thermodynamic parameters (the standard enthalpy (ΔH°), standard entropy change (ΔS°), and free energy change of adsorption (ΔG  °), the dispersive component of the surface free energies (γSd), and the acid–base character of the surface of MgY and NH4Y zeolites were estimated using the retention time of different non-polar and polar probes at infinite dilution region. The specific free energy of adsorption (ΔGsp), the specific enthalpy of adsorption (ΔHsp), and the specific entropy of adsorption (ΔSsp) of polar probes on MgY and NH4Y zeolites were determined. The values of the ΔHsp were correlated with both the donor and acceptor numbers of the probes to quantify the acidic KA and the basic KD parameters of the zeolite surfaces. The values obtained for the KA and KD parameters indicated a basic character for the surface of MgY and NH4Y zeolites.