Low-temperature continuous wet oxidation of trichloroethylene over CoOx/TiO2 catalysts

TiO2-supported metal oxides such as CoOx, CuOx, NiOx and FeOx have been used for catalytic wet oxidation of trichloroethylene (TCE) in a continuous flow type fixed-bed reactor system, and the most promising catalyst for this wet catalysis has been characterized using XPS and XRD techniques. All the supported catalysts gave relatively low conversions for the wet oxidation at 36 °C, except for 5 wt% CoOx/TiO2 which exhibited a steady-state conversion of 45% via a transient activity behavior up to 1 h on stream. XPS measurements yielded that a Co 2p3/2 main peak at 779.8 eV appeared with the 5 wt% CoOx/TiO2 catalyst after the continuous wet TCE oxidation at 36 °C for ca. 6 h (spent catalyst) and this binding energy value was equal to that of Co3O4 among reference Co compounds used here, while the catalyst calcined at 570 °C (fresh catalyst) possessed a main peak at 781.3 eV, very similar to that for CoTiOx species such as CoTiO3 and Co2TiO4. Only characteristic reflections for Co3O4 were indicated upon XRD measurements even with the fresh catalyst sample. The simplest model, based on these XPS and XRD results, for nanosized Co3O4 particles existing with the fresh catalyst could reasonably explain the transient activity behavior observed upon the wet TCE oxidation.