Ethylene oxide is an important raw material in manufacturing processes of ethylene glycol, acrylonitrile and nonionic surfactants, etc. In general, commercial scaled ethylene oxide is synthesized over Ag catalysts. In this work, a series of alpha-Al2O3 supported Ag catalysts were prepared by several methods, i.e., precipitation, modified precipitation, water-alcohol, and micro emulsion methods. Particle sizes of the supported Ag were analyzed by TEM and XRD, and the TPD/TPR profiles were compared to investigate the state of adsorbed oxygen in view of the elucidation of the active oxygen species. The Ag particles of about 30 nm showed enhanced stability and higher activity than the particles less than 15 nm. The activities for the ethylene oxide of the catalysts prepared by water-alcohol method were higher than those of the catalysts prepared by micro emulsion method. It seems due to the larger particle sizes as well as the easier desorption of molecular oxygen from the catalysts. An unique TPD/TPR peak of the molecular oxygen was observed at about 400degreesC in the catalysts prepared by water-alcohol method. However, the desorption peaks of the molecular and the atomic oxygens were observed at about 400 and 650degreesC, respectively, in the micro emulsion prepared catalysts. (C) 2003 Elsevier B.V. All rights reserved.