The effects of support structure and reducibility, oxidation and reduction treatment and ruthenium loading amount were studied in SiO2 nanospheres and CeO2 nanorods supported ruthenium catalysts on CO oxidation. 0.4, 1.0 and 5.0 wt% Ru were impregnated on SiO2 nanospheres and CeO2 nanorods using precipitation method and then the samples were oxidized in air. Half of the oxidized samples were also further reduced under hydrogen atmosphere to compare the effect of reduction treatment on the catalytic activity. Detailed XRD, Raman, TEM, H-2-TPR, and CO oxidation analyses were carried out to understand the effects of RuOx-support interaction, oxidation and reduction treatment and ruthenium loading amount on the catalytic performance. Compared to SiO2 nanospheres supported ruthenium catalysts, both the oxidized and reduced RuOx/CeO2 catalysts exhibited superior catalytic performance in terms of CO conversion and low-temperature hydrogen consumption. After the reduction treatment in H-2, the RuOx/CeO2 catalysts is further activated for low-temperature CO conversion. Especially, the 5.0 wt% Ru/CeO2-reduction sample can achieve similar to 9% CO conversion at near room temperature. The enhanced low-temperature activity of CeO2 nanorods supported ruthenium catalysts was correlated strongly to the surface defects on CeO2 nanorods, dispersion of RuOx, and interfacial structures between CeO2 and RuOx. (C) 2018 Elsevier Inc. All rights reserved.