Structure and catalysis of cobalt oxide overlayers prepared on zirconia by low-temperature-plasma oxidation

Abstract

The structure of cobalt oxide overlayers on the surface of ZrO₂ powder, i.e., CoO_x/ZrO₂, prepared by low-temperature-plasma oxidation has been investigated using EXAFS, XPS, XRD and IR spectroscopy. XRD and EXAFS revealed that CoO_x on ZrO₂ is present as fine particles having the structure of Co₃O₄(spinel). It was found that CoO_x/ZrO₂ prepared by plasma oxidation was more active for oxidations of CO and propane that Pt/Al₂O₃, La_0.8Sr_0.2CoO₃, and CoO_x/ZrO₂ prepared by impregnation. The dispersion of CoO_x estimated by XPS and CO adsorption was higher for CoO_x/ZrO₂ prepared by plasma oxidation than that prepared by the impregnation. The high dispersion is responsible for the higher activity of CoO_x/ZrO₂ prepared by plasma oxidation.