【作者】 王薇；

【导师】 王健礼；

【作者基本信息】 四川大学 ， 物理化学， 2021， 硕士

【摘要】 CeO₂-ZrO₂-Al₂O₃（CZA）催化材料结合了CeO₂-ZrO₂（CZ）的储/释氧性能和Al₂O₃的高比表面积,广泛应用于三效催化剂中。然而,CZ和Al₂O₃之间较强的相互作用会破坏CZ固溶体的均一性,造成CZA材料还原性能的劣化,这限制了其在三效催化剂（TWC）中的应用。随着汽车尾气排放法规的日益严格,对TWC的催化性能和热稳定性均提出了更高的要求,因此需要进一步提高CZA材料的高温热稳定性能和氧化还原性能。本文以CZA催化材料为研究对象,旨在通过改变制备条件及方法调控CZ与Al₂O₃之间的相互作用,进而实现对材料织构性能、结构性能、热稳定性能以及氧化还原性能的改性,以期望得到性能更优的CZA催化材料。具体内容如下:（1）通过调控Al₂O₃前驱体NH₄Al（OH）₂CO₃（AACH）的水热温度,系统探究了AACH的晶粒尺寸与CZA催化材料的织构性能、热稳定性能以及氧化还原性能之间的匹配关系。XRD、N₂-吸/脱附、H₂-TPR和XPS等结果表明,随着AACH的水热温度从50℃升高到150℃（50℃,80℃,100℃,120℃和150℃）,其晶粒尺寸逐渐增加,分别为6.3、7.6、8.8、10.0和12.7 nm。其中,当AACH的水热温度为100℃,即,AACH的晶粒尺寸为8.8 nm时,CZ与Al₂O₃之间的相互作用强度适中。同时,Ce、Zr和Al分布相对均匀,这有利于发挥CZ和Al₂O₃之间的“扩散障碍”效应,所得CZA材料表现出良好的织构热稳定性和氧化还原性能,1000℃老化4 h后,比表面积为72.5 m²/g,孔容高达0.71 mL/g,还原温度仅为489℃。（2）通过调控铝前驱体,研究不同铝前驱体（硝酸铝、拟薄水铝石以及氧化铝）对CZA催化材料氧化还原性能和热稳定性的影响规律。XRD、N₂-吸/脱附、H₂-TPR和XPS等结果表明,铝前驱体会影响CZ与Al₂O₃之间的相互作用,导致CZA材料的织构性能和氧化还原性能存在差异。以硝酸铝为铝前驱体有利于Ce³⁺、Ce⁴⁺、Zr⁴⁺和Al³⁺等多种离子的同时均匀沉淀,这有利于发挥各组分纳米晶之间的“扩散障碍”效应。同时,Al³⁺沉淀物在焙烧过程中分解释放的气体（CO₂、H₂O和NH₃等）会起到“扩孔”和“造孔”作用,因而得到的CZA具有高比表面和高热稳定性,老化后其表面积高达86.3 m²/g。以拟薄水铝石和氧化铝为铝前驱体有助于削弱CZ与Al₂O₃之间的强相互作用,促进均匀CZ固溶体、富Ce表面以及缺陷结构的形成,由此提高CZA材料的氧化还原性能。尤其是以拟薄水铝石为铝前驱体时,老化材料的还原温度可以低至495℃,但使用拟薄水铝石无法实现多种离子的同时沉淀,因此CZ和Al₂O₃分布不均匀,得到的CZA材料呈现出较差的织构热稳定性,老化后比表面积仅为60.0 m²/g。（3）对比研究三种不同制备方法（沉淀法、胶溶-沉淀法和胶溶法）对CZA材料性能的影响规律。结果表明,以拟薄水铝石为铝前驱体,通过沉淀法制备的CZA材料会造成材料各组分的不均匀分布,尤其是Al₂O₃的团聚,最终导致“扩散障碍”效应减弱。所以,得到的CZA1在老化后出现严重的烧结,其CZ的晶粒尺寸最大（16.3nm）。相反,胶溶法有助于分散各组分,抑制CZ颗粒的烧结长大,得到的CZA3在老化后CZ的晶粒尺寸仅为7.0 nm。同时,胶溶法还可以显著调变CZA材料的表面性质,促进具有丰富缺陷位点和富-Ce表面的形成,这有利于增强材CZA材料和贵金属的相互作用。因此,以CZA3为载体制备的单Pd三效催化剂具有更好的催化活性。此外,胶溶-沉淀法可以结合两种方法的优点,制备的CZA2具有更好的织构性能和还原性能。1000℃老化4h后,材料的比表面积高达72.5 m²/g,还原峰温度低至576℃。更多还原

【Abstract】 The CeO₂-ZrO₂-Al₂O₃（CZA）catalytic material combines the oxygen storage/release performance of CeO₂-ZrO₂（CZ）and the high specific surface area of Al₂O₃,showing a great superioroty in three-way catalysts.However,the stronger interaction between CZ and Al₂O₃ weakens the homogeneity of CZ solid solution,resulting in the deterioration of the reduction performance,and hence limits its application in three-way catalyst（TWC）.With the increasingly stringent automobile emission regulations,higher requirements are put forward for the catalytic performance and thermal stability of TWC.Therefore,it is quite necessary to further improve the high-temperature thermal stability and redox performance of CZA composite oxide.In this paper,the CZA catalytic material is taken as the study object.And the purpose is to adjust the interaction between CZ and Al₂O₃ by changing the systhesis condition and method.As a result,the more excellent CZA support material and corresponding single Pd three-way catalyst are obtained by modify the texture,structural,thermal stability and redox properties of the material.The details are as follows:（1）The matching relationship between the grain size of Al₂O₃ precipitate NH₄Al（OH）₂CO₃（AACH）and the texture,thermal stability and redox properties of CZA catalytic materials was systematically explored by regulating the hydrothermal temperature of AACH.The results of XRD,N₂ adsorption-desorption,H₂-TPR and XPS indicate that the grain size of AACH increases gradually from 50℃ to 150℃（50℃,80℃,100℃,120℃ and 150℃）,which are 6.3,7.6,8.8,10.0 and 12.7nm,respectively.Among that,when the hydrothermal temperature of AACH is 100℃,namely,the grain size of AACH is 8.8 nm,the interaction intensity between CZ and Al₂O₃ is moderate.At this time,the distribution of Ce,Zr and Al is more uniform,which facilitates the"diffusion barrier effect"between CZ and Al₂O₃.Therefore,the obtained CZA material（CZA100）displays preeminent texture thermal stability and reduction performance.Even after aging at 1000℃ for 4 h,its specific surface area and pore volume reach are up to 72.5 m²/g and 0.71 mL/g,respectively.Meanwhile,the reduction temperature is as low as 489℃.（2）The effects of different aluminum precursors（Al（NO₃）₃·9H₂O,pseudo-boehmite and Al2O3）on the redox performance and thermal stability of CZA catalytic materials were studied.And the results of XRD,N₂ adsorption-desorption,H₂-TPR and XPS suggest that aluminum precursors will affect the interaction between CZ and Al₂O₃,resulting in the difference in texture properties and redox properties of CZA materials.Taking Al（NO₃）₃·9H₂O as aluminum precursor can realize the the simultaneous and uniform precipitation of Ce³⁺,Ce⁴⁺,Zr⁴⁺and Al³⁺,which is conducive to play the role of"diffusion barrier effect".Besides,the decomposition and release of Al³⁺precipitate during the calcination process is beneficial to"pore expansion"and"pore forming".As a result,the prepared CZA material shows the high specific surface and high thermal stability,whose surface area is up to 86.3 m²/g after aging.When pseudo-boehmite and Al₂O₃ are used,the strong interaction between CZ and Al₂O₃ is weakened,which is more favourable to the formation of homogeneous CZ solid solution,Ce-rich surface and defect structures,and hence improve the redox properties of CZA materials.Especially in pseudo-boehmite,its reduction temperature is just 495℃.Nevertheless,the simultaneous precipitation of multiple ions cannot be achieved by using pseudo-boehmite.Therefore,the distribution of CZ and Al₂O₃ is uneven.The obtained CZA material shows poor texture and thermal stability,and the specific surface area is only 60.0 m²/g after aging.（3）The effects of three different synthesis methods（precipitation method,peptization-precipitation method and peptization method）on the properties of CZA material are investigated.The result demonstrates that the CZA material prepared by precipitation method with pseudo boehmite as aluminum precursor will cause the uneven distribution of components,especially the agglomeration of Al₂O₃,and finally weaken the"diffusion barrier"effect.Therefore,the obtained CZA1 appears serious sintering after aging,and the grain size of CZ is the largest（16.3 nm）.On the contrary,the peptization method is helpful to disperse the components and inhibit the sintering growth of CZ particles.The grain size of CZA3 after aging is only 7.0 nm.At the same time,the peptization can also significantly modify the surface properties of the material and form a Ce-rich surface with plenty of defect sites.It favors the interaction between the support and noble metals,therefore,the single Pd three-way catalyst with peptization as the support shows better activity.In addition,the peptization-precipitation can combine the advantages of others,and the prepared CZA2 displays better texture and reduction properties.After aging at 1000℃for 4 h,its specific surface area is up to 72.5 m²/g,and the reduction peak temperature is as low as 576℃.更多还原