Selective oxidation of alcohols to carbonyl compounds with molecular oxygen was carried out over ruthenium supported on a CaO-ZrO2 solid solution prepared by the co-precipitation method. In the oxidation of benzyl alcohol, the Ru/CaO-ZrO2 catalyst gave benzaldehyde in a yield higher than 98% at 90 degrees C, and the turnover frequency reached 224 h(-1). The Ru/CaO-ZrO2 catalyst also exhibited high catalytic activities and selectivities to carbonyl compounds in the oxidation of aromatic ring-substituted benzylic, allylic, and aliphatic alcohols. Moreover, this catalyst exhibited high activities in the oxidation of alcohols at a low temperature (40 degrees C). The catalytic activity and oxidation state of ruthenium depended on the Ca/Zr molar ratio of the support, and the highest catalytic activity was obtained with Ca/Zr = 0.125. DRIFT and XPS analyses revealed that Run+-OH (n=3, 4) on the surface of CaO-ZrO2 were likely the active species in the oxidation of alcohols. (C) 2010 Elsevier B.V. All rights reserved.