Does the Cal-Ad Method Distinguish Differences in the Acid Sites of H-MFI?

Recent claims that calorimetric measurements of solid acidity can be performed more effectively in the presence of a solvent, the “cal-ad” method, were examined using vapor-phase measurements for the coadsorption of pyridine and n-hexane in H-MFI. The results indicate that equilibrium is not achieved for pyridine titration measurements in a solvent at room temperature. Therefore, the ability of the cal-ad method to distinguish Brønsted-acid sites of widely different strengths in H-MFI is unproven.