Electrical conductivity of gamma-Al2O3 at atmospheric pressure under dehydrating/hydrating conditions

Changes of electrical conductance and capacity of gamma -Al2O3 were studied in situ during dehydration/rehydration in gas flow. The measurements were performed at atmospheric pressure by following a standard protocol of exper iments, and were coupled with simultaneous monitoring of the composition of the inlet/effluent gas. The electrical properties are dominated by the pro tonic conduction. It was shown that at low temperature this occurs by vehic le mechanism, being facilitated by the presence of water molecule adsorbed on gamma -Al2O3 surface; the decrease of electrical conductance on heating is obviously connected with dehydration. At higher temperature (t > 200 deg reesC) conduction is dominated by proton hopping between OH groups (Grotthu ss mechanism). It is suggested that in current operating conditions in cata lysis, gamma -Al2O3 is only partially dehydrated/dehydroxylated, the bulk a cting as a source of water/OH groups for the surface; this process controls the acidity of alumina and alumina-supported catalysts. (C) 2001 Elsevier Science B.V. All rights reserved.