.An earlier sample of 5% CoOx/TiO2 used for the wet oxidation of TCE at 310 K for ca. 6 h has been characterized with a fresh catalyst via XRD and XPS measurements. The binding energy for Co 2p3/2 of the fresh sample appeared at 781.3 eV, which was very similar to the chemical states of CoTiOx such as Co2TiO4 and CoTiO3, whereas the spent catalyst indicated a 780.3-eV main peak for Co 2p3/2 with a satellite structure at a higher energy region. This binding energy was almost equal to that of Co3O4 among reference Co compounds used. The phase structure of Co3O4 was revealed upon XRD measurements for all the catalyst samples. Based on these XPS and XRD results, a surface chemical structure of CoOx species existing with the fresh catalyst can be proposed to be predominantly Co3O4 encapsulated completely by very thin filmlike CoTiOx consisting of Co2TiO4 and/or CoTiO3, with a tiny amount of Co3O4 particles covered partially by such cobalt titanates which may be responsible to the initial catalytic activity. Those CoTiOx overlayers on Co3O4 particles may be readily removed into the wet media within 1 h at 310 K based on our earlier study, thereby giving rapid increase in the catalytic activity for that period.