Calorimetric base adsorption and neutralisation studies of supported sulfonic acids

Base adsorption calorimetry (from the gas phase) and acid-base neutralisation titration calorimetry (in the liquid phase) have been used to characterise a series of solid sulfonic acids supported on porous silicas and polystyrene resins. The results illustrate the limitations of using calorimetric techniques for relative acidity measurements and the assumptions that must be made if molar enthalpies of adsorption or molar enthalpies of neutralisation are to be used to compare the strengths of solid acids. They also show how the relative acid strengths of nominally similar acids can be highly dependent on whether measurements are made in the presence or absence of a solvent, and, if the former, on the type of solvent.