M. Caldararu et al., Electrical conductivity of gamma-Al2O3 at atmospheric pressure under dehydrating/hydrating conditions, APPL SURF S, 181(3-4), 2001, pp. 255-264
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
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