【作者】 文雪梅；

【导师】 沈美庆；

【作者基本信息】 天津大学 ， 化学工艺， 2007， 硕士

【摘要】 以Pt、Rh、Pd等贵金属为活性组分的三效催化剂是目前控制汽车尾气污染最有效的手段。但随着燃油质量的改善,单Pd三效催化剂以其低廉的价格和高效的氧化活性得到普遍关注。同时,铈锆固溶体（CZ）在三效催化剂中的应用提高了催化剂的储放氧性能（OSC）,有效地拓宽了三效催化剂的空燃比工作窗口,提高了传统氧化铝（A）载体的热稳定性。但在催化剂制备中,贵金属Pd与载体（CZ和A）之间的结合方式,以及结合方式对催化剂储放氧性能和催化活性的影响规律和机理还未有清楚认识。因此,系统而深入地研究贵金属与载体之间的相互作用以及其对催化性能的影响,对于汽车尾气净化催化剂的制备具有理论指导作用。本文以共沉淀法制备CZ和A,以CZ,A为载体采用等体积浸渍法制备负载量为1wt.%和0.5wt.%单Pd负载催化剂,并对新鲜样品进行水热老化处理。采用动态储放氧测试和模拟尾气催化剂评价等手段,考察贵金属与载体界面,贵金属负载量对催化剂储放氧性能和催化活性的影响。利用XRD,BET,H₂-TPR等表征手段对催化剂的晶相结构,比表面积,氧化还原性能等方面进行研究。储放氧性能测试表明Pd负载在CZ上极大地促进了样品的OSC性能和CO₂的生成速率,这是由于Pd-CZ界面有助于氧从CZ迁移到Pd上的反溢流过程,而Pd负载在A上则没有氧的反溢流作用。H2-TPR结果表明Pd-CZ界面的H2还原性能要好与Pd-A界面。对于催化活性来说,Pd-载体界面与催化活性有很好的对应关系,Pd-CZ界面有利于CO转化,良好的OSC性能有助于CO的催化转化,而Pd-A界面有利于HC,NO的转化。当Pd负载量从1wt.%减少到0.5wt.%时,催化剂的三效起燃温度T₅₀相差较小,说明Pd负载催化剂在保持一定催化活性的同时可以进一步减少贵金属Pd的负载量。更多还原

【Abstract】 In recent years, typical three-way catalyst （TWC） formulations contain noble metal （such as platinum, palladium and rhodium） as the active components, but more attention has been paid to Pd as a single active metal component in TWC due to its low cost and low light-off temperature, particularly for HC conversion; other components of these systems have included alumina, which is employed as a high surface area support and ceria-zirconia solid solution, principally added as oxygen storage promoters. The research of the interaction between Pd and different support in application, resulting in changing in catalytic activity and oxygen storage capacity （OSC） performance is of important influence.In this paper, ceria-zirconia solid solution and alumina are prepared by co-precipitation method. Pd supported on CZ and Al₂O₃ are prepared by incipient wetness impregnation, which Pd loading is 1wt.% and 0.5wt.%. Both fresh and aged samples are tested on home-made dynamic OSC measure instrument and TWC measure equipment for their dynamic OSC and TWC performance. Structure analysis is also done by Brunnauer-Emmett-Teller （BET）, X-ray diffraction （XRD） and Temperature-programmed reduction （TPR）. Meanwhile, the effect of different Pd loading on catalytic activity is also investigated.OSC is greatly enhanced on Pd/CZ, Pd/CZ+Al₂O₃, Pd/CZ+Pd/Al₂O₃ sample showing as an obvious reduction peak by H2-TPR. In addition, DOSC shows greatly promotion when Pd supported on ceria-zirconia material. It can be concluded that interface between Pd-CZ is more favorable for OSC promotion due to oxygen back-spillover from ceria to the Pd metal. Contrastly, Pd/Al₂O₃ is inferior to Pd/CZ, ascribing to the absent of oxygen back-spillover process. As for catalytic activity we are concerned, direct relationship between interfaces of Pd-support and catalytic activity is found. By supported Pd on ceria-zirconia, high OSC contributes to the behavior CO oxidation, however, less effect on the HC and NO conversion. When Pd loading decreased from 1wt.% to 0.5wt.% , light-off temperature increased slightly.更多还原