A series of CoOx-doped silica xerogels with various Co2+ loadings (Co/Si = 0, 1, 2, 4, 6, and 10 mol %) has been prepared. All xerogels exhibit large (800-1050 m(2)/g) surface areas. Narrow pore size distributions with pore size maxima around 3 nm are characteristic for Co/Si = 1, 2, 4, 6, 10 samples. As-prepared CoOx/SiO2 xerogels show high catalytic activity in the air oxidation of gaseous acetaldehyde at room temperature. Carbon dioxide and trace amounts of methane are the only products detected in the gas phase. Acetic acid, a less volatile product, resides on the surface of the xerogels but can slowly desorb. The formation of CO2 begins after an induction period. The beginning of CO2 production coincides with the conversion of CO2+ incorporated in the SiO2 framework into Co3+. Thermogravimetry/gas chromatography/ mass spectrometry analysis, UV-vis and FTIR spectroscopies, as well as kinetic measurements are employed for CoOx/SiO2 catalyst characterization. A possible mechanism of the reaction is discussed.