We have employed the deposition-precipitation method to prepare Au/CoO/SiO2 catalysts. The structure and activity of Au/CoO/SiO2 catalysts in CO oxidation were found to depend on the Au:CoO ratio. The catalyst preparation process was investigated employing in situ infrared spectroscopy. The gold precursor preferentially deposits and interacts with hydrogen-bonded hydroxyls and then with isolated hydroxyls in Co(OH)(2) on SiO2, eventually forming large and fine Au nanoparticles in the catalysts, respectively. The calcination of SiO2 at 500 degrees C prior to the catalyst preparation can alter the structure of Au nanoparticles in Au/CoO/SiO2 catalysts by changing the distribution of hydrogen-bonded and isolated hydroxyls in Co(OH)(2). Au/CoO/SiO2 catalysts with fine Au nanoparticles are active in low temperature CO oxidation. Our results provide direct evidence that the interaction between the gold precursor and surface hydroxyls on the support during the deposition-precipitation process plays an important role in determining the structure of supported Au nanoparticles. (c) 2010 Elsevier B.V. All rights reserved.