Influence of Different Subsistence States of CeO_2-ZrO_2 Mixed Oxides in Catalyst Coating on Catalytic Properties

摘要

The metallic substrate-catalysts with different subsistence states of CeO_2-ZrO_2 mixed oxides were prepared and the catalytic properties were investigated. The studies on CeO_2-ZrO_2-V_2O_5-CuO mixed oxides which were prepared by coprecipitation, show that the doping of V~(5+) and Cu~(2+) in CeO_2-ZrO_2 mixed oxides can enhance the catalytic activity and thermal stability of coating materials. Moreover, different additives were doped in slurries of γ-Al_2O_3 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-Al_2O_3 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℃ for 2 h. The light-off curves of CO and HC show that after being treated at 650 ～ 750℃, catalysts present the best activity. XRD patterns show that ceria and zirconia species in the newly proposed active component form a phase of extra CeO_2-ZrO_2 mixed oxides on the surface of catalysts after the thermal treatment at 750℃, which has practical value for improving the preparation process and promoting the catalytic properties. Moreover, XPS results imply the existence of Ce_(1-x)Pd_xO_(2-σ), and Ce_(1-x)Pt_xO_(2_σ), on the surface of these treated samples, which may show influence on the catalytic activities.