Ferric hydroxide supported Au catalysts prepared with co-precipitation method at room temperature without any heat treatment hereafter exhibited high catalytic activity and selectivity for CO oxidation in air and CO selective oxidation in the presence of H-2. With calcination temperature rising, both activity and selectivity decreased. X-ray Photoelectron Spectra (XPS) indicated that Au existed as Au-0 and Au+ in the catalyst without heat treatment and even after being calcined at 200 degrees C, while after being calcined at 400 degrees C, Au existed as Au-0 completely. X-ray Diffraction (XRD) and High Resolution Transmission Electron Microscopic (HRTEM) investigations indicated that both the supports and Au species were highly dispersed as nano or sub-nano particles even after being calcined at 200 degrees C, but after being calcined at 400 degrees C the supports transformed to crystal Fe2O3 with typical diameter of 30 nm and Au species aggregated to nano-particles with typical diameter of 2-4 run. HRTEM investigations also suggested that the supports calcined at 200 degrees C were composed of amorphous ferric hydroxide and crystal ferric oxide. Results of computer simulation (CS) showed that O-2 was adsorbed on Au crystal cell and then were activated, which should be the key factor for the subsequent reaction. It also suggested that 02 species were more easily adsorbed on Au+ than on Au-0, indicating that higher positive charge of the Au species possessed the higher activity for CO oxidation. (c) 2008 Elsevier B.V. All rights reserved.