Cobalt oxide is a typical transition metal oxide that exhibits high catalytic activity for the total oxidation of volatile organic compounds. In this study, a reduction process in a glycerol solution was adopted to generate mesoporous CoO (meso-CoO) or CoOx (meso-CoOx) from mesoporous Co3O4 (meso-Co3O4). The obtained samples were rich in Co2+ species and exhibited high catalytic activity for o-xylene oxidation. The meso-CoOx sample with the largest surface Co2+ amount performed the best: The o-xylene conversion at 240 degrees C was 83%, and the reaction rate over meso-CoOx was nine times higher than that over meso-Co3O4. It is found that the samples with more surface Co2+ species possessed better oxygen activation ability, and the Co2+ species were the active sites that favored the formation of highly active O-2(-) and O-2(2-) (especially O-2(-)) species. (C) 2017 Elsevier Inc. All rights reserved.