摘要
挥发性有机物（V olatile Organic Compounds，VOCs）是臭氧以及光化学烟雾的重要前驱体，严重影响空气环境质量以及人民身体健康。催化燃烧法具有高去除效率、无二次污染等优势，被认为是治理VOCs最有效的技术之一，研发高效的催化剂是提升该技术核心竞争力的关键。贵金属催化剂，尤其是铂基催化剂，对于VOCs的催化燃烧具有较高的催化活性。稀土氧化物二氧化铈（CeO2）具有较高的储存与释放氧能力，作为贵金属催化剂载体时，其表面存在的氧空位能锚定贵金属颗粒，提升催化剂稳定性；另一方面，CeO2可以参与氧化还原过程，为反应提供新的活性位点。基于此，本文以Pt/CeO2催化氧化甲苯为研究体系，制备了具有不同结构的催化材料，研究了催化剂结构与催化活性之间的构-效关系，并对Pt/CeO2催化氧化甲苯反应机制进行了探讨。主要内容与结论如下：
支付宝扫福（1）通过水热合成法制备了具有不同形貌的CeO2纳米材料（纳米棒、纳米颗粒、纳米立方块），并通过吸附法负载了单分散、尺寸均一的Pt纳米颗粒。Pt/CeO2-r催化剂由于具有最好的还原性能以及最高的表面氧空位浓度，展现最优的甲苯催化性能。分别以Pt分散度以及CeO2表面氧空位浓度为基准计算了各催化剂的转换频率值（Turn over frequency，TOF），结果表明CeO2表面氧空位是控制反应速率的活性位点。通过原位拉曼（In-situ Raman）技术，分析了不同气氛、不同温度条件下催化剂氧空位浓度变化情况，发现CeO2表面氧空位在反应中扮演着吸附、活化气相氧及加速体系氧循环的重要角色。
（2）通过乙二醇还原法制备了系列具有不同Pt颗粒尺寸的Pt/CeO2催化剂，其中，Pt/CeO2-1.8催化剂展现最优的甲苯催化性能。X射线衍射光电子能谱（XPS）、氢-程序升温还原（H2-TPR）和Raman等表征结果表明，该催化剂活性最好的原因是其同时具有高Pt分散度以及CeO2表面氧空位浓度。分别计算了以Pt分散度、氧空位浓度以及两者之积为基准的TOF值，发现CeO2表面氧空位和暴露的Pt原子均是Pt/CeO2催化氧化甲苯反应的活性位点，同时控制反应进行。此外，水热稳定性测试表明，Pt/CeO2-1.8催化剂具有优异的稳定性以及抗甲苯浓度冲击能力；5 vol%水汽的引入会降低催化剂降解甲苯活性，但温度高于155 o C时，水汽影响较小。
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（3）采用水热法合成了Ce0.8Ln0.2O2（Ln: La，Pr，Nd，Sm和Gd）纳米棒材料，以其为载体通过浸渍法负载相同含量的Pt，制备了Pt/CeLnO2催化剂。XPS、H2-TPR、Raman等表征结果表明，Pt/CeGdO2催化剂含有最高浓度的Ce3+和Pt0、具有最好的还原性能以及表面氧吸附能力，展现出最优的甲苯催化氧化性能。而Pr由于离子半径较大且存在+4价，其掺杂对催化剂活性表现负效应。因此，对于Pt/CeO2催化氧化甲苯体系而言，引入异价且离子半径较小的元素，有利于提升其催化活性。
（4）通过浸渍法制备了Pt/CeO2和Pt/Al2O3催化材料，其中，Pt/CeO2样品具有更好的甲苯催化氧化
活性。通过H2-TPR、甲苯-程序升温脱附（TPD）、CO-透射红外（FTIR）以及气相色谱质谱联用（GC-MS）等表征技术，对比研究Pt/CeO2和Pt/Al2O3催化剂表面Pt电子环境、甲苯吸附/脱附以及甲苯反应过程的中间产物/副产物发现，负载在CeO2表面的Pt原子具有更高的电子密度，使甲苯分子更容易进一步反应；CeO2载体可以提供活性氧物种，直接参与催化氧化甲苯的反应，提高甲苯催化氧化效率。此外，甲苯在两催化剂上的主要反应历程基本相同为：甲苯→苯甲醛→苯甲酸→长链酸类、醛类物质→小分子酸、醛类物质→二氧化碳和水。
排比的修辞手法>拜年日记关键词：Pt/CeO2；甲苯催化氧化；形貌和尺寸效应；镧系元素掺杂；反应机制
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Abstract
V olatile organic compounds (VOCs) are known as the important precursors of ozone and photochemical smog, having detrimental effects on air quality and human health. Catalytic oxidation is generally regarded as one of the most effective routes for eliminating VOCs emissions with lots of distinguished advantages, such as high destructive efficiency and no generation of organic by-products. The key issue of such a technology is the development of high performance catalytic materials. The supported noble metals (NMs), especially Pt-bad materials, are considered as the
most commonly promising catalysts for VOCs catalytic combustion. As an important rare-earth metal oxide, ceria (CeO2) exhibits a nice ability of oxygen releasing and storage. In addition, as an ex ample of ‘‘active support” for noble metals, CeO2 could not only bind NMs particles strongly through surface oxygen vacancies but also involve in redox process and create new active sites for reaction. Therefore, this paper lected catalytic oxidation of toluene over Pt/CeO2 catalysts as the rearch system. A ries of catalysts with various structures were prepared, and their relationships between structure and catalytic performance were studied. Moreover, the reaction mechanism of toluene catalytic oxidation over Pt/CeO2 had been investigated. The main rearch contents and results are as follows:
1. CeO2 material with rod, particle, and cube shape were prepared by hydrothermal method and then employed to immobilize Pt nanoparticles with tunable size by adsorption method. The Pt/CeO2-r sample exhibited the best catalytic activity due to the best reducibility and highest surface oxygen vacancies concentration. Two types of TOFs bad on Pt dispersion and surface oxygen vacancies concentration were calculated, and the results suggested that the oxygen vacancies on ceria surface controlled the reaction rate. In addition, the variation of surface oxygen vacancies concentration were investigated by in-situ UV Raman, demonstrating that the surface oxygen vacancies played a r
ole in replenishing active oxygen species from gaous pha and accelerating oxygen cycle for the toluene oxidation.
2. A ries of size-controllable Pt nanoparticles had been fabricated through a glycol reduction method and then supported on CeO2nanorod by adsorption. The XPS, H2-TPR, Raman and OSC characterization results showed that Pt/CeO2-1.8 sample exhibited the best
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catalytic performance due to the balance of both Pt dispersion and oxygen vacancy concentration of ceria. Three types of TOFs values bad on Pt dispersion, oxygen vacancy concentration and both of them were calculated respectively, and the result demonstrated that the reaction rate was controlled by both of the expod Pt atom and oxygen vacancies. In addition, the Pt/CeO2-1.8 catalyst exhibited excellent stability and resistance to toluene concentration and could be completely negligible for 5 vol% water vapor at 155 o C.
3. A ries of Ce0.8Ln0.2O2nanorods (Ln: La, Pr, Nd, Sm and Gd) were prepared by hydrothermal method and then employed to Pt nanoparticles via wet impregnation method. XRD, XPS, H2-TPR and Raman results showed that Pt/CeGdO2 catalyst possd the highest content of Ce3+ and Pt0,
and had the best reduction performance and surface oxygen adsorption capacity, exhibiting the best performance for toluene catalytic oxidation. While for Pr, becau of larger ion radius and +4 state, its doping had a negative effect on the activity. Therefore, in the ca of toluene catalytic oxidation over Pt/CeO2 catalysts, it was beneficial to promote the catalytic activity by doping aliovalent element with a small ion radius.
4. Pt/CeO2and Pt/Al2O3catalysts were successfully prepared via wet impregnation method. A comparative study of the two catalysts on Pt electronic environment, toluene adsorption-desorption and intermediate products/by-products had been carried out by H2-TPR, Toluene-TPD, CO-FTIR and GC-MS. And the results showed that the Pt nanoparticle over Pt/CeO2 catalyst prented higher electron concentration, resulting in better performance for toluene activation, and CeO2 support could supply more reactive oxygen species and increa the catalytic activity for toluene oxidation. In addition, the main reaction process of toluene on two catalysts was basically the same: toluene →benzoic aldehyde →benzoic acid →long-chain acids and aldehyde →small molecules of acid and aldehydes →carbon dioxide and water.
Key words：Pt/CeO2; Toluene catalytic oxidation; Shape and size effect; Lanthanide doping; Reaction mechanism
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目录
不管别人怎么说
摘要......................................................................................................................................... I Abstract .................................................................................................................................... III 目录..................................................................................................................................... V 第一章绪论 (1)
学生营养改善计划
1.1 挥发性有机物（VOCs）概况 (2)
1.1.1 VOCs的定义及分类 (2)
1.1.2 VOCs的来源及危害 (2)
1.1.3 VOCs的控制技术 (3)
1.2 VOCs催化剂的研究 (5)
1.2.1 过渡金属氧化物催化剂 (5)
1.2.2 贵金属催化剂 (11)
1.3 VOCs催化氧化反应机理的研究 (17)
1.4 选题依据、研究思路和研究内容 (21)
1.4.1 选题依据 (21)
山清水秀造句1.4.2研究目标与研究内容 (21)
第二章载体形貌对Pt/CeO2催化甲苯性能的影响 (23)
2.1 引言 (23)
2.2 实验部分 (23)
2.2.1 化学试剂与气体 (23)
2.2.2 主要实验仪器 (24)
2.2.3催化剂制备 (25)
2.2.4催化剂表征 (26)销售人才
2.2.5催化剂活性评价 (29)
2.3 结果与讨论 (31)纷至沓来造句
2.3.1 催化剂物理性质 (31)
2.3.2 Pt尺寸及载体形貌 (33)
2.3.3 表面组成及化学价态 (35)
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