The effect of treatment conditions during preparation and activation of gamma-Bi2MoO6 catalysts was investigated. Catalytic evaluation shows that CO conversion is much higher for catalysts obtained under vapor controlled evaporation conditions (CE) than for standard evaporation catalysts (SE). Characterization results show that preparation under SE conditions induces segregation of Bi2O3 On the surface of Bi2MoO6 catalysts decreasing their catalytic activity. Catalysts treatment under hydrogen reactivates the catalytic properties of SE samples.