ADSORPTION OF ALCOHOLS AND WATER ON ALUMINA .3. DC CONDUCTIVITY AND DIELECTRIC LOSS MEASUREMENTS

dc conductivities of isobutyl alcohol, H2O, and D2O adsorbed on γ- and η-Al2O3 and dielectric absorptions of isobutyl alcohol adsorbed on η-Al2O3 have been measured. The degree of dissociation is strongly enhanced for the adsorbed molecules as compared to the liquid, due to strong coordinative interactions between adsorbent and adsorbed molecule. A degree of dissociation of 10-1 is estimated for H2O adsorbed at 400 K. The resulting surface conductivity is protonic in nature as demonstrated by a large deuterium isotope effect. Dielectric absorption occurs for isobutyl alcohol adsorbed on η-Al2O3 at a frequency of 5 × 104 s-1 at 189 K, which corresponds to a relaxation time of 3.2 × 10-6 s. An activation energy for this relaxation process between 24 and 31 kJ/mol is estimated. A model for the relaxation mechanism is developed on the basis of a previously reported adsorption structure and the results are compared with nuclear magnetic resonance data reported recently. © 1979 American Chemical Society.