We report an Ag/SBA-15 catalyst with low loading (1.42 wt%) that shows excellently high activity in CO oxidation at room temperature after oxygen pretreatment at 900 degrees C. A 98% conversion of CO is achieved at 20 degrees C (T-98 = 20 degrees C). An evaporation-deposition-diffusion mechanism for Ag/SBA-15 catalyst is proposed. The oxygen adsorbate-induced decrease in the surface-free energy at 900 degrees C induces the evaporated silver atoms to be redeposited on the support, and meanwhile diffuse into the channels of SBA-15, forming more highly dispersed small silver particles inside the channels. The favorable structure of silver catalyst for CO oxidation is believed to arise from the synergistic effect of oxygen atmosphere, high temperature (900 degrees C), and the channel of SBA-15. In addition, the formation of Ag+ on the surface of support after oxygen pretreatment at 900 degrees C is also suggested to be essential for the following reduction and high catalytic activity for CO oxidation. (c) 2012 Elsevier Inc. All rights reserved.