CO preferential oxidation (PROX) reactions were performed over the supported Co3O4-CeO2 catalysts on modified activated carbon (AC) for eliminating the trace CO from H-2-rich gases. The effects of support modification by H2O2 oxidation treatment, catalyst calcination temperature, Ce/Co atomic ratio (n(Ce/Co)). Co3O4-CeO2 loading and reaction parameters on catalytic properties of the Co3O4-CeO2/AC catalysts were investigated. Various characterization techniques like scanning electron microscopy (SEM). X-ray diffraction (XRD) and H-2 temperature-programmed reduction (H-2-TPR) were employed to reveal the relationship between catalysts nature and catalytic performance. Results illustrate that the supported Co3O4-CeO2 catalyst on modified AC exhibits excellent catalytic properties, which highly depends on dispersity and reducibility of Co3O4 affected by the time of support treatment (t(p)). calcination temperature, n(Ce/Co) and loading. The supported 35 wt% Co3O4-CeO2 catalyst (1:8 of n(Ce/Co)) on the modified AC with H2O2 oxidation treatment for 6 h demonstrates the best catalytic properties and the almost complete CO transformation takes place in a wide temperature range of 125-190 degrees C. Moreover, it is also found that the developed catalyst exhibits an outstanding catalytic stability, and 100% CO conversion can be maintained as the time on stream evolutes up to 1800 min even in the presence of CO2 and H2O in the feed. The optimized Co3O4-CeO2/AC may be a robust and promising catalyst for eliminating trace CO from H-2-rich gases. (C) 2012 Elsevier B.V. All rights reserved.