A thermodynamic analysis of the Cal–Ad method with respect to gas–solid calorimetry

A recent article claims that the Cal–Ad method cannot discriminate multiple acid sites in the analysis of the interaction of pyridine (dilute pyridine in n -hexane) with HZSM-5. The Cal–Ad technique measures the enthalpy of a base-displacement reaction, while gas–solid calorimetry is a measure of an adduct formation between pyridine and the solid. A Born–Haber cycle with the appropriate values can demonstrate that the enthalpies derived from gas–solid calorimetry are an average of the two enthalpies of the interaction of pyridine with the two acid sites observed with the Cal–Ad method.