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Zirconia-alumina mixed oxides (Zr + Ce)O 2 À Al 2 O 3 with various mol. ratios (5, 10, 20, 50, and 75 % alumina) were prepared using the sol-gel method. The catalysts were characterised via XRD, SEM, DTA/TG, BET, and FT-IR spectroscopy. The acidities of the catalysts were measured through the absorption of anthraquinone and pyridine probe molecules using EPR and IR spectroscopy, respectively. Catalytic activity and selectivity were investigated for ethanol conversion to acetaldehyde, ethylene, and diethyl ether, which were used as model reactions to identify surface-active sites. The relationship between the surface structure and the dehydration/dehydrogenation activity was evaluated. Diethyl ether formation is promoted by the presence of the ZrO 2 tetragonal phase at a low ZrO 2 /Al 2 O 3 ratio in the sample composition, at which the Lewis acid site has an aluminum-oxygen environment. The reaction mechanism was also discussed. In the low-temperature reaction region, dehydrogenation competes with dehydration; ethylene and acetaldehyde share a common reactive intermediate.