Synthesis of New Oxide Solid Solutions of High Redox Activities and Their Application to Automotive Exhaust Catalysts

降低氧化还原温度和增加高热稳定性是汽车尾气催化剂氧化物固溶体迫切需要解决的问题。本研究通过添加透氧组分银来促进CeO2-ZrO2-Bi2O3固溶体的低温还原。其机理可归结为银在CeO2-ZrO2-Bi2O3晶格中的部分溶解和银在固溶体上的表面沉积的协同作用。此外，我们还制备并表征了La稳定的γ-Al_2O_3(CZB/Al_2O_3)固溶体，该固溶体有望成为先进催化转化器的关键材料。CZB/Al_2O_3催化剂表现出的低温氧化还原活性，在低于100℃的低温下仍然有效，即使在1000℃焙烧后也是有效的，这是传统催化剂在没有贵金属的帮助下所无法达到的。通过在γ-Al_2O_3表面沉积CeO_2-ZrO_2-Bi_2O_3固溶体，固溶体的颗粒尺寸大大减小到纳米级，其动态储氧量是没有γ-Al_2O_3载体的CeO_2-ZrO_2-Bi2O_3催化剂(600℃)的7.5倍。以甲烷氧化为模型反应的研究表明，这类催化剂的低温氧化还原活性与其催化活性有关。

Because of recent environmental regulations, reduction of the redox temperature and addition of high thermal stability are urgent subjects for oxide solid solutions employed in the automotive exhaust catalysts.In this study, low temperature reduction behavior of CeO_2-ZrO_2-Bi_2O_3 solid solutions was promoted by the addition of silver, which is an oxygen permeable component. The mechanism of the behavior was attributed to the synergetic effects of the partial solution of silver into the CeO_2-ZrO_2-Bi_2O_3 lattice and the surface deposition of silver on the solid solution. The reactivity of oxygen in the bulk of the catalyst greatly improves the soot combustion activities at low temperatures.Furthermore, we prepared and characterized a CeO_2-ZrO_2-Bi_2O_3 solid solution supported on La-stabilised γ-Al_2O_3 (CZB/Al_2O_3), which has the potential to be a key material in advanced catalytic converters. The low temperature redox activities demonstrated by the CZB/Al_2O_3 catalyst, which is effective at low temperatures below 100 ℃ even after calcination at 1000 ℃, have never been attained in conventional catalysts without help of precious metals. By the deposition of the CeO_2-ZrO_2-Bi_2O_3 solid solution on the surface of γ-Al_2O_3, particle size of the solid solution considerably decreased to a nanoscale, and the dynamic oxygen storage capacity became 7.5 times of the bulk CeO_2-ZrO_2-Bi_2O_3 catalyst without the γ-Al_2O_3 support (at 600 ℃). Studies using CH_4 oxidation, as a model reaction, showed that the redox activities of such catalysts at low temperatures correlates with their catalytic activities.