MEASUREMENT OF CATALYST ACIDITY .1. TITRATION MEASUREMENTS

The n-butylamine titration method has been widely used for the measurement of acid strength distributions on solid catalysts. An implicit assumption with this technique is that both the n-butylamine titrant and the indicators are in adsorption equilibrium with acid sites on the surfaces. This assumption has been tested and found invalid. Serious doubt is therefore cast on the utility of such methods for the assessment of surface acidity. It is shown that instead of determining an acid site distribution, the total acidity of the sample is usually obtained. Having ascertained the problems involved, an alternative method has been devised for characterizing the site energy distribution. A series of bases of varying pKa dissolved in one of several solvents was employed. The strong irreversible chemisorption of these yielded distributions quite different from those obtained by the n-butylamine technique. © 1979.