Surface-activated amorphous Co-Zr alloys containing platinum group elements were used for decomposition of nitrogen monoxide. The alloys were immersed in hydrofluoric acid for activation. The HF-treated amorphous alloys were initially inactive for decomposition of nitrogen monoxide at 773 K, but became active after oxidation by exposure to nitrogen monoxide at 773 K. XRD and XPS analyses revealed that the active catalysts were composed of platinum group elements, Co3O4 and ZrO2. Platinum group elements in both metallic and oxidized states were supported on the oxides. The catalytic activity depended on platinum group elements. The palladium-containing alloy showed the highest activity and even higher activity than that of a palladium-black. The high activity of the palladium-containing catalyst was attributed to the synergistic effect of palladium and oxides of cobalt and zirconium.
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