【作者】 赵敏伟；

【导师】 王亚权； 沈美庆；

【作者基本信息】 天津大学 ， 化学工艺， 2008， 博士

【摘要】 铈锆固溶体储氧材料作为国Ⅲ/国Ⅳ汽车尾气催化剂的重要组成部分,能够拓宽三效催化剂的空燃比窗口,削弱空燃比振荡对三效催化性能的影响。本文以铈锆固溶体、贵金属与氧化铝三者的相互作用为研究体系,动态储放氧为研究手段,研究了铈锆固溶体、贵金属与氧化铝三者协同作用对动态储氧性能和三效催化性能的影响规律,为国Ⅲ/国Ⅳ催化剂的研发提供基础数据。考察了铈锆固溶体组成、比表面积和碱土元素掺杂对动态储氧性能和总储氧性能的影响;成功开发了电子顺磁共振测试原位反应器以及用于铈锆储氧材料性能测试的“原位顺磁共振”技术。结果表明:铈锆固溶体的动态储氧量及储氧速率与铈锆固溶体的比表面积、铈含量成正比,碱土元素掺杂提高了动态储氧性能;总储氧性能与结构中氧空位数量成正比。原位顺磁结果表明体相中氧空位浓度受铈锆组成的影响,与氧迁移性能成正比。通过将贵金属Pd负载至铈锆固溶体,研究Pd烧结与铈锆晶粒烧结对动态储氧性能和总储氧性能的影响。结果表明:小于10%～12%还原度以及低于450～500℃时,贵金属负载提高了铈锆固溶体的动态储氧量和动态储氧速率。与铈锆晶粒烧结相比,贵金属烧结引起的Pd-（Ce, Zr）Ox界面烧结是降低动态储氧性能的主要原因。采用前驱盐溶液混合、沉淀前驱物混合以及粉末机械混合方式,考察了铈锆固溶体与氧化铝相互作用对材料热稳定性和动态储氧性能的影响。结果表明:铈锆固溶体与氧化铝的混合尺度是影响材料性能的主要因素,小尺度混合提高了铈锆晶粒的分散程度,提高了材料的动态储氧性能;铈锆晶粒及Ce3+在氧化铝的表面改性提高了材料的热稳定性。通过优化贵金属分布的负载工艺研究,将贵金属Pd负载到铈锆固溶体-氧化铝二元复合氧化物中,考察三者协同作用对动态储氧性能和三效催化性能的影响。结果表明:受贵金属与载体的结合方式、贵金属Pd的粒径以及价态等因素以及复合氧化物的热稳定性是影响催化剂性能的主要因素。通过优化贵金属分布的负载工艺研究,将贵金属Pd色谱负载到铈锆固溶体和氧化铝单一氧化物体系,考察Pd-（Ce, Zr）Ox和Pd（Al₂O₃）界面对动态储氧性能和三效催化性能的影响。结果表明:Pd-（Ce, Zr）Ox界面促进动态储氧性能和CO催化性能的提高,动态储氧性能与CO的催化转化紧密关联;Pd（Al₂O₃）界面促进了NOx和HC催化性能的提高,NOx和HC催化转化与动态储氧性能关联较小。更多还原

【Abstract】 As the key part of the StateⅢ/Ⅳthree-way-catalyst （TWCs）, ceria-zirconia mixed oxides minimize the effect of air to fuel （A/F） fluctuation to catalytic activities and extend the A/F window. On the basis of ceria-zirconia and dynamic oxygen storage/release measurement, the relationship between ceria-zirconia, precious metal and alumina as well as its effects on dynamic oxygen storage capacity （DOSC） and catalytic activities were also studied, aiming at developing advanced StateⅢ/ⅣTWCs.Combining the XRD, BET, HRTEM, EPR and dynamic oxygen storage/release measurement, effects of intrinsic textural and structural properties, such as surface area, Ce/Zr ratio and alkine earth metal doping etc, on DOSC and dynamic oxygen storage rate （DOSR） were studied. Moreover, in-situ EPR reactor and a set of methods were successfully developed for measuring oxygen vacancy in material. It was shown that DOSC and DOSR are proportional to the surface area and Ce/Zr ratio. Alkine earth metal doping improves the DOSC of ceria-zirconia mixed oxides. Total oxygen storage capacity （TOSC） is proportional to the number of oxygen vacancies in material. The results of in-situ EPR show that oxygen vacancies are essential to Ce/Zr ratio and proportional to oxygen migration.By supporting the Pd on ceria-zirconia, interaction between Pd and ceria-zirconia and its effects on DOSC and TOSC were investigated. When reducibility is lower than 10%～12% and temperature is lower than 450～500℃, Pd supporting promotes the DOSC and DOSR obviously. After hydrothermal aging, both of ceria-zirconia sintering and Pd sintering deteriorate the Pd-（Ce, Zr） Ox interface, as a result of deterioration of DOSC and TOSC. However, compared with sintering of ceria-zirconia, sintering of precious metal has more influence on the OSC deterioration.By mixing the ceria-zirconia and alumina in different mixing scale, DOSC and thermal stability of ceria-zirconia-alumina mixed oxides were investigated. Combining the XRD, BET, XPS, EPR and TEM measurements, mixing scale between ceria-zirconia and alumina is the key factor of improvement of DOSC and thermal stability. Mixing with alumina at small scale improve the distribution and morphology of ceria-zirconia as well as DOSC performance. Whilst mixing with ceria-zirconia at small scale and Ce3+ distribution modifies the surface of alumina and improve the thermal stability.After introducing the Pd into ceria-zirconia-alumina binary oxides, the process of precious metal distribution on binary supports was optimized. The effects among ceria-zirconia, Pd and alumina on DOSC and catalytic activities were investigated. The results show combination of Pd and support, morphology and valence affects the DOSC and catalytic activities. Pd dispersion has less influence on DOSC and catalytic activities. Meanwhile, thermal stability of supports and Pd distribution between ceria-zirconia and alumina play the important role to improve the DOSC and catalytic activities.By charomatagraph distributing the precious metal on single oxide, effects Pd-（Ce, Zr） Ox and Pd （Al₂O₃） on DOSC and catalytic activities were investigated. DOSC and DOSR are more promoted by Pd-（Ce, Zr） Ox than Pd （Al₂O₃）. Pd-（Ce, Zr） Ox interface promotes the DOSC and CO catalytic conversion, CO conversion correlate to the DOSC performance; meanwhile, Pd （Al₂O₃） interface promotes the NO and HC catalytic conversion, NO and HC conversion show less relationship with DOSC performance.更多还原