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

The structure of cobalt oxide overlayers on the surface of ZrO2 powder, i.e., CoOx/ZrO2, prepared by low-temperature-plasma oxidation has been investigated using EXAFS, XPS, XRD and IR spectroscopy. XRD and EXAFS revealed that CoOx on ZrO2 is present as fine particles having the structure of Co3O4 (spinel). It was found that CoOx/ZrO2 prepared by plasma oxidation was more active for oxidations of CO and propane than Pt/Al2O3, La0.8Sr0.2CoO3, and CoOx/ZrO2 prepared by impregnation. The dispersion of CoOx estimated by XPS and CO adsorption was higher for CoOx/ZrO2 prepared by plasma oxidation than that prepared by the impregnation. The high dispersion is responsible for the higher activity of CoOx/ZrO2 prepared by plasma oxidation.