Nanometric CeO2-supported cobalt oxide materials with variable Co/Ce atomic ratios were prepared by the method of ultrasonic-assisted incipient-wetness impregnation. The catalytic behaviors of a series of CoOx/nmCeO(2) catalysts have been studied for soot combustion, XRD, XPS, Raman, UV-vis DRS and FNR spectroscopy characterization results indicated that CoO or cobalt-cerium solid solutions were formed in the samples with the low Co loading amount, while Co3O4 was formed in the samples with high Co loading amount. CoOx/nmCeO(2) catalysts can further promote soot combustion in contrast to nanometric CeO2. This improvement is related to the increase in the redox properties of the catalysts brought about by loading cobalt oxide on nanometric CeO2. The TPR experiment results under hydrogen atmosphere indicated that the presence of Co decreases the reduction temperature of catalyst from 555 degrees C (nanometric CeO2) to 286 degrees C (Co-20/nmCeO(2)). On the other hand, attributing to nanoparticle effect and NO2 formation, Co-m/nmCeO(2) oxide catalysts prepared in this study have very high activity for soot combustion. The best catalytic activity was obtained over Co-20/nmCeO(2) catalyst that T-10, T-50, T-90 were 286 degrees C, 368 degrees C. 418 degrees C, respectively, and S-CO2(m) was 98.8%. Compared with the blank case (i.e., without catalyst) for soot combustion, T-50 decreased by more than 200 degrees C and S-CO2(m) increased by 40% point. And CO2 this catalytic activity for the combustion of soot particle is as good as supported Pt catalysts, which is the best catalyst system so far reported for soot combustion under loose contact conditions. This temperature of soot combustion can ensure immediate activation of the catalyst on the filter under the conditions of diesel engine emissions. (c) 2008 Elsevier B.V. All rights reserved.