| 题名 | 纳米结构二氧化铈基材料制备与催化性能的研究 |
| 作者 | 王震 |
| 学位类别 | 博士 |
| 答辩日期 | 2012-06-01 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 陈运法 |
| 关键词 | 二氧化铈 形貌调控 氧空位 协同效应 催化应用 |
| 其他题名 | Preparation and Catalytic Performance of CeO2-based Nanostructured oxides |
| 学位专业 | 化学工程 |
| 中文摘要 | 纳米材料的诸多特性与其形貌密切相关，因此无机纳米氧化物的形貌调控研究已引起人们的普遍关注，但对形貌与性能的内在关系以及应用研究还有待深入。CeO2作为一种典型的稀土氧化物，因其内部存在Ce4+/Ce3+之间的转换，使其具备了储氧特性，在催化等领域有着广泛的应用。本文以制备不同形貌和微观结构的CeO2为基础，选择CO和苯催化氧化反应作为典型体系，考察了CeO2纳微形貌、纳微结构以及元素掺杂复合对其催化性能的影响，研究了它们之间相互作用机制和关联关系，以期为制备性能优异的催化剂提供实验基础。主要研究内容与结果包括： 1、CeO2纳微结构的调控研究 (1) 多晶态CeO2球形颗粒的制备：以Ce(NO3)3·6H2O为铈源，聚乙烯吡咯烷酮(PVP)为表面活性剂，探索发明了一种制备CeO2球形颗粒的新方法，即二步水热晶种诱导法：先将铈源与表面活性剂的混合溶液在160℃下进行水热反应，反应结束后经过离心分离得到上层清液，再在相同的水热条件下，将上层清液作为反应前驱液，向其中加入铈源，经过反应最终得到CeO2球形颗粒。结果表明，该方法实现了颗粒生长过程中结晶化与熟化的分离，所制备的CeO2颗粒球形度高，分散均匀，并容易实现宏量制备，不仅为调控CeO2的形貌提供了一种新的方法，也为制备CeO2标准颗粒奠定了基础。 (2) 单晶态CeO2纤维、立方体的制备：以Ce(NO3)3·6H2O为铈源，NaOH为沉淀剂，在无表面活性剂的辅助下，通过水热反应，分别在120℃和160℃下制备得到了CeO2纳米纤维和立方体。通过对它们生长过程的分析，得知随着温度的提高、时间的增长，CeO2纳米纤维可以逐渐生长成为立方体，表明前者是后者形成过程中的中间产物。此外，通过理论计算和谱学分析得知，两种形貌的CeO2具有不同浓度的氧空位(纤维中氧空位的浓度高于立方体)，这也为研究纳微结构的差异对其催化能力的影响提供了理论基础。 2、CeO2纳微结构对CO催化反应的影响研究 以CO的催化氧化反应为模型，选取单晶态CeO2纳米纤维和立方体作为研究对象，详细分析了CeO2的不同晶面尤其是不同氧空位浓度对CO催化反应的影响以及作用机制。结果发现，氧空位浓度高的CeO2纤维催化活性优于氧空位浓度低的立方体，说明氧空位与催化性能密切相关。为了进一步增加氧空位的浓度，同时提高热稳定性，选取两种低价态的稀土元素(Sm3+和Gd3+)对CeO2进行掺杂，结果证实Sm3+掺杂后的CeO2催化活性明显提高，但是Gd3+掺杂后的CeO2催化活性反而降低，表明除了氧空位外掺杂剂的选择也应结合考虑。 3、CeO2纳微结构对苯催化性能的影响选取过渡金属Co和Mn分别与CeO2进行掺杂复合，得到了Ce-Co和Ce-Mn两组复合氧化物。以苯的催化氧化反应为模型，详细研究了两组复合氧化物对苯催化效果的影响及作用机理。研究结果发现，Ce-Co和Ce-Mn两组复合氧化物活性最优的物料比分别为Ce:Co为1:9和Ce:Mn为3:7，此时两组复合氧化物中氧空穴浓度均低于纯相CeO2，但两相组分可以达到更好的互溶，协同效应更明显，表明除了氧空位外两相组分间的相互作用同样重要。在此基础上负载了贵金属的活性组分(Pd物种)，催化效果相较于载体有了明显地提高，为在VOCs的去除中制备性能更加优异的催化剂提供了理论指导和实验基础。 |
| 英文摘要 | The morphology control of nano-inoganic oxide has attracted a lot of attention because the morphology always affects the properties of materials. However, the relationship between morphology and property and application need to be further researched. CeO2, a typical functional rare earth material, possesses unique oxygen storage/release capacity due to the transformation between Ce4+ and Ce3+. It has been applied in many fields, especially catalysis application. This work aims to show CeO2-based nano-inorganic oxides, particularly explore the effects of morphology, microstructure and doping/mixing on the catalytic behaviours through CO oxidation and benzene oxidation. Interactions and associated relationship are studied in order to guide synthesis of catalysts with better performance. The main progresses are as follows: 1. Microstructure control of CeO2 (1) Synthesis of CeO2 spheres with polycrystalline structures: Ce(NO3)3·6H2O and Poly(vinylpyrrolidone) (PVP) were used as cerium source and surfactant,respectively. A novel method (two-step hydrothermal process) was explored to prepare the CeO2 spheres: firstly, cerium source and surfactant in the solution were processed in a hydrothermal reaction at 160 ℃. After the hydrothermal treatment, the supernatant was attained through centrifugation; then, the cerium source was added into the upper solution as the reaction precursor solution to experience a second hydrothermal reaction under the same conditions; finally, the CeO2 spheres were obtained. The results indicate that crystallization and ripening were separated into two independent stages through the novel method. The CeO2 spheres synthesized through two-step hydrothermal process exhibited better spherical degree and dispersity. CeO2 spheres in macro-scale were also easy to be produced through this method, which not only offered a new technology for the morphology control of CeO2, but also established the foundation for the preparation of CeO2 standard particles. (2) Synthesis of CeO2 nanofiber and nanocube with single-crystalline nature: cerium source (Ce(NO3)3·6H2O) and precipitant (NaOH) were applied as reactants. CeO2 nanofiber and nanocube were synthesized through hydrothermal process without surfactant at 120 ℃ and 160 ℃, respectively. Through researching on their growth process, it can be acquired that CeO2 nanofiber can be transformed into nanocube with the increase of temperature and time. Through theoretical calculation and spectroscopic analysis，CeO2 nanofiber possessed more oxygen vacancies than that of CeO2 nanocube, which helped us to acquire the relationships between microstructure and catalytic ability. 2. Effect of microstructure of CeO2 on the CO catalytic oxidaton CeO2 nanofiber and nanocube with single-crystalline nature were chosen to be the research objects to analyze the effects of crystal planes and oxygen vacancy on the CO catalytic reaction. The results showed that the ability of CeO2 nanofiber with more oxygen vacancy was higher than that of CeO2 nanocube, indicating the close relation between oxygen vacancy and catalytic ability. In order to increase the concentration of oxygen vacancy and enhance the thermal stability, Sm3+ and Gd3+ were doped with CeO2. The catalytic results identified that the property of Sm-doped CeO2 was enhanced. However, Gd-doped CeO2 exhibited the negative effect on CO oxidation. Therefore, the options of dopants should be considered besides oxygen vacancy. 3. Effect of microstructure of CeO2 on the benzene catalytic oxidation Ce-Co and Ce-Mn composite oxides were synthesized through transition metal (Co and Mn) doping and mixing with CeO2, respectively. Their catalytic properties and mechanisms were researched in detail through benzene oxidation. When the ratios of Ce/Co and Ce/Mn were 1:9 and 3:7 respectively, the catalytic activities of Ce-Co and Ce-Mn composite oxides over benzene reached the best. However, the concentrations of oxygen vacancy were both lower than that of pure CeO2. Two components in Ce-Co and Ce-Mn composite oxides (Ce/Co=1:9 and Ce/Mn=3:7) can accomplish intermiscibility and exhibit better synergistic effect. Therefore, the interaction between two components for composite oxide was also important to catalytic ability besides oxygen vacancy. Nobel metal active phase (Pd species) was loaded at the surface of Ce-Co and Ce-Mn composite oxides, respectively. The results demonstrated that the activities of supported Pd species catalysts were enhanced greatly. This work offers us theoretical guidance and experimental basis for preparing more fantastic catalyst in the removal of other VOCs gases. |
| 语种 | 中文 |
| 公开日期 | 2013-09-25 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1803]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 王震. 纳米结构二氧化铈基材料制备与催化性能的研究[D]. 中国科学院研究生院. 2012. |
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