【作者】 温静；

【导师】 沈美庆；

【作者基本信息】 天津大学 ， 化学工艺， 2008， 硕士

【摘要】 为了满足日益严格的汽车排放标准,对三效催化剂(TWCs)的性能提出了愈加苛刻的要求。在TWCs的改进过程中,寻找最佳的催化剂制备工艺,及进行催化剂组分间相互作用对催化剂性能影响的研究已成为目前研究热点之一。本论文以三效催化剂Pd/Ce0.7Zr0.3O2/Al2O3为研究对象,将获得优越性能催化剂作为研究目标,比较了不同的催化剂制备工艺路线,优化制备条件后获得了最佳路线,进一步研究了TWCs中Pd、Ce0.7Zr0.3O2及Al2O3间相互作用对催化剂性能的影响作用。经研究确立,使用前驱溶液混合方法制备Ce0.7Zr0.3O2-Al2O3复合载体,等体积浸渍Pd溶液,可制备得到热稳定性优良、储氧性能及三效催化转化性能突出的Pd/Ce0.7Zr0.3O2/Al2O3催化剂。使用不同钯负载方式制备Pd/Ce0.7Zr0.3O2可控制组分间相互作用程度。比较五种不同方式获得样品,等体积浸渍法制备催化剂Pd分布于表面具有较多表面活性位,表现出最优的储放氧以及三效催化性能。研究表明,使用前驱溶液混合方法制备的复合载体,Ce0.7Zr0.3O2与Al2O3间存在强相互作用。此强相互作用有利于形成规则大孔的均匀材料并可提高载体热稳定性,抑制高温老化过程中Al2O3相变以及Ce0.7Zr0.3O2分相。同时也能提高材料的Ce3+与氧空位浓度,提高氧迁移速率,增强材料储放氧性能。采用原位红外漫反射、H2吸附等表征手段研究不同载体负载Pd样品,结果显示:Pd-Al2O3相互作用使Pd具有更适合NO与C3H8转化的粒径与形貌,促进C3H8的吸附、N-O键的断裂和N-N键的重组。Pd-Ce0.7Zr0.3O2间相互作用使Pd更倾向于以氧化价态存在,并具有较高分散度以及较小粒径,形成大量的活性位,有利于CO氧化反应发生。更多还原

【Abstract】 In order to satisfy the increasing strict regulations on emission of vehicle exhausts, development of advanced automobile three-way-catalyst (TWCs) have been widely investigated. For the purpose of promoting the activities, optimizing preparation technology of TWCs is considered as the sticking point to advance efficient solutions. In this work, to obtain catalyst with excellent thermal stability and high catalytic properties, different preparation technologies were studied. The results show the best preparation method is: CeO2–ZrO2–Al2O3 supports are obtained by precursor mixing co-precipitation, and Pd is supported on the supports by the incipient wetness method.Pd/Ce0.7Zr0.3O2 samples prepared by various Pd support methods have different interaction between components on different level. The sample obtained by co-precipitation which possesses intimate interaction between Pd and Ce0.7Zr0.3O2 has high thermal stability but few Pd active sites; the sample obtained by incipient wetness has most Pd active sites, outstanding oxygen storage/release capability and catalytic activity.Obtained by precursor mixing co-precipitation, strong interaction between Ce0.7Zr0.3O2 and Al2O3 exists in mixed ceria-zirconia-alumina oxides. With most incorporation of Al3+ into the lattices of Ce0.7Zr0.3O2 indicates the essential of the interaction between Ce0.7Zr0.3O2 and Al2O3. This sample has the smallest crystallites and highest surface area confirmed through BET and XRD measurements. Meanwhile, EPR detected increasing Ce3+ and OSC is obviously enhanced by intimate interaction between ceria-zirconia and alumina. The results show that the intimate interaction between ceria-zirconia and alumina could modify the structural properties,improve thermal stability and enhance OSC.Moreover, to induce the interactive effect between Pd and different supports, a series Pd-loaded sample was designed to obtain different interaction forms. The results show that the interaction between Pd and Al2O3 benefits the conversion of HC and NO under stoichiometric air/fuel condition. Pd tends to exist on Al2O3 with large particles and metallic state, which improves the adsorption of HC, N-O bond rupture and N-N bond recombination. Meanwhile, Pd loaded on Ce0.7Zr0.3O2 with small Pd particle size and high Pd dispersion is in favor of CO elimination.更多还原