ADSORPTION OF MONOSUBSTITUTED BENZENES ON LOW SURFACE-AREA SILICA STUDIED BY TEMPERATURE-PROGRAMMED DESORPTION AND LASER-INDUCED THERMAL-DESORPTION METHODS

The adsorption of aniline, phenol, and toluene on low surface area sil ica has been studied with temperature-programmed desorption (TPD) and laser desorption methods. These adsorption systems can serve as models for studying the mechanism of laser-induced thermal desorption, where heating rates and desorption rates are orders of magnitude larger tha n in TPD. For this purpose, results obtained at low heating rates need to be extrapolated to the regime of very high laser heating rates. Th is extrapolation relies on a model of the adsorbate-surface interactio n that involves a distribution of binding sites. Calculations based on this model match experimental measurements on the depletion of adsorb ed layers subjected to laser-induced desorption. The interaction energ y of aniline and phenol was found to depend on the hydration of the su rface, demonstrating the role of hydrogen bonding with silanol sites.