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

TiO₂-supported metal oxides such as CoO_x, CuO_x, NiO_x and FeO_x 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% CoO_x/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 2p_3/2 main peak at 779.8 eV appeared with the 5 wt% CoO_x/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 CoTiO_x 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.