Influence of different subsistence states of CeO₂-ZrO₂ mixed oxides in catalyst coating on catalytic properties

The metallic substrate-catalysts with different subsistence states of CeO₂-ZrO₂ mixed oxides were prepared and the catalytic properties were investigated. The studies on CeO₂-ZrO₂-V₂O₅-CuO mixed oxides which were prepared by co-precipitation, show that the doping of V⁵⁺ and Cu²⁺ in CeO₂-ZrO₂ mixed oxides can enhance the catalytic activity and thermal stability of coating materials. Moreover, different additives were doped in slurries of γ-Al₂O₃ to investigate the influence of additives on oxidation activity of catalysts. The mixture of ceria-zirconia, alkali metals and other rare earths acting as additives exhibits promotion effect on oxidation activity by optimizing the distribution of oxygen on the surface and in the bulk of ceria species. This mentioned mixture was mixed with γ-Al₂O₃ and a newly proposed active component to prepare a new catalyst. Afterward, the influence of thermal treatment on the new catalyst were investigated by calcinations at 500, 650, 750, 800, 850 and 900°C for 2 h. The light-off curves of CO and HC show that after being treated at 650-750°C, catalysts present the best activity. XRD patterns show that ceria and zirconia species in the newly proposed active component form a phase of extra CeO₂-ZrO₂ mixed oxides on the surface of catalysts after the thermal treatment at 750°C, which has practical value for improving the preparation process and promoting the catalytic properties. Moreover, XPS results imply the existence of Ce_1-xPd_xO_2-σ and Ce_1-xPt_xO_2-σ on the surface of these treated samples, which may show influence on the catalytic activities.