MICROCALORIMETRIC MEASUREMENTS OF BASIC MOLECULE ADSORPTION ON SILICA AND SILICA-ALUMINA

The differential heats of adsorption of ammonia, pyridine, trimethylamine, and triethylamine on silica-alumina and silica were determined microcalorimetrically to investigate how the heat of adsorption for a given site depends on the nature of the basic molecule adsorbed. This provides a test of the utility of the Drago-Wayland theory to heterogeneous reactions. Specifically, the acid/base properties of molecules in solution are described in terms of two parameters, the susceptibility of the species to undergo electrostatic interaction and the susceptibility to form covalent bonds. Accordingly, the calorimetric results of this study were correlated successfully in terms of Drago parameters for each catalyst. These parameters describe well the acidic properties of silica-alumina and silica and may allow the prediction of heats of adsorption for a wide range of basic molecules with known Drago parameters. © 1991.