Role of small and big gold particles in CO oxidation and methanol selective oxidation to formaldehyde has been studied by the methods of diffuse reflectance electron spectroscopy, XRD, XPS, HRTEM and catalytic testing. By comparison of catalytic and spectroscopic data it was concluded that states Au delta+ with certain effective charge (delta < 1) are active sites in low-temperature CO oxidation as well as in alcohol partial oxidation. These states can be formed under the action of different factors, such as metal-support interaction, redox treatments, and modifying additives. Modifiers stabilizing the ionic states of gold (Ce and Zr oxides) increase the selectivity of the catalyst in alcohol partial oxidation, whereas electron-releasing additions (La and Cs oxides) impair the catalyst properties. (C) 2012 Elsevier Ltd. All rights reserved.