The physicochemical and catalytic properties of some gamma-Al2O3 samples have been investigated by XRD. S-BET, porosity measurements, TEM, chemical analysis (ICP-MS) and IR spectroscopy of the surface OH groups and of adsorbed CO and pyridine. Catalytic activities in the ethanol dehydration reaction were also studied in gas phase in a tubular flow reactor from 423 K to 723 K at atmospheric pressure with 1.44 h(-1) WHSV in nitrogen as well as by ethanol temperature programmed reaction (Ethanol-TPR) in a TGIDTA/MS thermal analyzer. Even small amounts of alkali (300 ppm) modify significantly the spectra in the OH stretching region and kill part of the alumina strongest Lewis acid sites with a clear decrease of catalytic activity, while 1% Na completely modifies the surface behaviour. Differences are also observed for clean samples showing slightly different morphology (lamellar versus bulky). The data showed that the catalytic activity of gamma-Al2O3 is determined by a small number of sites, which are likely located on edges, corners and defects of the crystals more than on plain surfaces. (C) 2014 Elsevier B.V. All rights reserved.