Conversion of ethanol was investigated over four commercial aluminas prepared by different industrial procedures and one commercial silica-alumina. Characterization was performed by TEM, XRD, S-BET and porosity measurements, and IR spectroscopy of the surface OH groups and of adsorbed CO and pyridine. Different features are attributed to different phases (gamma-, delta-, theta-Al2O3) and different impurities (Na+, Cl-) Total conversion of ethanol with >99% selectivity to ethylene is achieved at 623 K over the purer Al2O3 catalyst (Na < 0.002 wt%). The most active sites are believed to be Lewis acidic Al3+ sites in a tetrahedral environment located on edges and corners of the nanocrystals. Ethanol adsorbs dissociatively on Lewis acid-base pair sites but may also displace water and/or hydroxyl groups from Lewis acidic Al3+ sites forming the active intermediate ethoxy species. Surface ethoxy groups are supposed to be intermediate species for both diethyl ether and ethylene production. Silica-alumina also works as a Lewis acid catalyst. The slightly lower activity on surface area basis of silica-alumina than aluminas attributed to the lower density of Lewis acid sites and the absence of significant basicity. (C) 2013 Elsevier Inc. All rights reserved.