【作者】 安源；

【导师】 王亚权；

【作者基本信息】 天津大学 ， 化学工艺， 2007， 博士

【摘要】 本文主要研究铈锆固溶体的碱土金属掺杂改性,以改善材料的储放氧性能。研究了铈基储氧材料的反相微乳法制备工艺的优化,分别研究了四种碱土金属元素掺杂对铈锆固溶体的结构及性能的影响,研究了改性前后储氧材料与贵金属之间的相互作用,并分析了储放氧机理。通过绘制反相微乳体系的拟三元相图、采用TG-DTA、原位XRD等方法优化了铈锆固溶体的制备工艺。并对反相微乳法与溶胶凝胶法制备的样品进行了结构和性能的比较,反相微乳法制备的样品具有更大的比表面积,更高的晶相纯度及氧化还原性能。系统研究了Mg、Ca、Sr、Ba四种掺杂剂及不同掺杂浓度对Ce_0.67Zr_0.33O₂的物相结构和储放氧性能的影响。碱土金属掺杂可提高Ce_0.67Zr_0.33O₂的均相性及结构热稳定性,其中Ca和Sr具有适宜的离子半径,可进入Ce_0.67Zr_0.33O₂晶格形成三元固溶体,基于半径效应和电价平衡效应在面心立方结构的晶体中产生晶格缺陷和氧空位,从而提高体相和表面氧的扩散和迁移性能。Mg的离子半径较小,Ba的离子半径较大,均无法以阳离子取代方式进入Ce_0.67Zr_0.33O₂晶格,对其储放氧性能无明显的改善作用。采用TPR、动态OSC和CO脉冲等实验方法,并对测试前后的样品进行FTIR、Raman及TG-DTA等表征,推断铈基储氧材料的储放氧机理。储放氧过程中主要有表面氧、近表层晶格氧以及体相氧三个氧种参与,OSC过程中的反应遵循L-H机理,此外储放氧过程中发生了CO的歧化反应。以碱土金属改性的Ce_0.67Zr_0.33O₂为载体,负载贵金属Pd（0.5wt.%）后进行高温氧化还原处理,采用H2-TPR、三效催化性能评价对样品进行表征,以考察碱土金属改性对于铈锆固溶体与贵金属Pd之间相互作用的影响。结果表明,碱土金属掺杂对于Pd与CZ的相互作用有很大影响,主要取决于掺杂剂种类和掺杂浓度,这种相互作用的改变进而对于催化剂的三效催化活性也产生了一定的作用,Sr掺杂改性后的储氧材料与贵金属存在较强的相互作用,可显著提高CO、C₃H₈和NO的催化性能。自主研制了储放氧性能（OSC）测试装置,并建立了全面分析铈锆固溶体总储放氧和动态储放氧性能的实验方法,可以达到的最高测试频率为0.1Hz。更多还原

【Abstract】 The aim of this paper is to investigate the doping effect of alkaline earth metals on chemical/structural properties and oxygen storage capacity （OSC） of CeO₂-ZrO₂ solid solution. The preparation procedure of reverse microemulison method was studied to produce ceria-based material. Also, the interaction of modified ceria-based material and Pd was studied. Further, mechanism of CO oxidation over ceria-based solid solution was studied.The quasi-ternary （cyclohexane/water/OP-10/n-hexanol） phase diagram was investigated to determine the W/O type microemulison region. The in situ XRD and TG-DTA technique were used to determine the proper calcine temperature. Some physical-chemical techniques such as XRD, BET, Raman and HRTEM are used to characterize the resultant powders. OSC （total OSC and dynamic OSC） and catalytic performance was also evaluated. The results showed that, compared with the sample with the same composition prepared by sol-gel method, the samples prepared by reversed microemulsion has higher surface area, narrower size distribution, less agglomeration, better purity in phase and better performance.To study the effect of alkaline earth metals （Mg、Ca、Sr、Ba） with the same electronic shell structure and different ionic radius on the structure/performance of Ce0.67Zr0.33O2, alkaline earth metals doped Ce0.67Zr0.33O2 was prepared via reverse microemuslsion method. Further high temperature reduction and mild temperature oxidation treatment （redox aged） was carried out on the samples. Results showed that, alkaline earth doping enhanced the phase purity, the thermal stability, which depends on the ionic radius. Ca and Sr have proper ionic radius and can create more oxygen ion vacancies and lattice defect in the fluorite lattice due to charge compensation and radius effect. So improved OSC was obtained after doping. But the ionic radius of Mg and Ba was either too small or too large for effect modification on the cell, and no positive effect was found on the improvement of OSC.The mechanism of CO oxidation under dynamic condition over ceria-based solid solution was studied using TPR, dynamic OSC and CO pulse measurement. The produced samples after measurement were characterized using FTIR, Raman and TG-DTA analysis. It was suggested that three kinds of oxygen species including surface oxygen, near surface oxygen and bulk oxygen participated the OSC process. The mechanism can be explained using L-H law and CO disproportionation （2CO=CO₂+C） reaction exist. The adsorption/desorption of CO, O2 and CO₂ also occurred with oxygen migration. Alkaline earth doping can promote the oxygen migration by the modification of surface and cell of Ce0.67Zr0.33O2 solid solution. On the other hand, the ability of CO₂ adsorption was improved due to the enhancement of alkalinity from doping.Pd（0.5wt.%）supported on the doped Ce0.67Zr0.33O2 was prepared by the impregnation method. Redox aging treatment was carried out before measurement. H2-TPR and catalytic activity of the samples was evaluated to study the interaction of Pd and OSC materials. Results showed that alkaline earth doping influenced greatly on the interaction depends on the kinds and content of dopant. Pd/CZSr has the best CO, C₃H₈ and NO conversion rate.The oxygen storage capacity （OSC） is a crucial property of CeO₂-ZrO₂ directly linked to the efficiency of TWC operating under fluctuating conditions. In this paper, an apparatus working under transient condition used for dynamic OSC measurement （less than 0.1Hz） was developed in our laboratory. Further, the quantitative and qualitative analysis method was developed to evaluate the OSC systematically.更多还原