铈基核壳纳米材料的制备及其催化性能的研究

发布时间：2018-06-29 08:07

本文选题：CeO_2 + Au/CeO_2　；参考：《山东大学》2017年硕士论文

【摘要】：空气污染已成为了中国乃至全球的世界性难题,这主要是由过多依赖化石燃料的工业化发展以及汽车保有量迅猛增加造成的。因此,脱除CO迫在眉睫,而CO催化氧化作为简便节能的CO脱除方法成为了研究焦点。在CO催化剂中,氧化铈(CeO_2)因为拥有丰富的氧空位缺陷,高储氧能力和Ce3+/Ce4+电子对的氧化还原特性,能够提高CO催化氧化反应速率,而得到广泛的关注。铈基纳米材料的催化活性的影响因素有很多,如形貌、氧空位、界面结构、暴露的晶面和纳米复合材料间的协同作用等。本文的研究内容是以壳聚糖为软模板,利用简单的溶剂热法可控制备了 CeO_2核壳纳米球,并用沉淀沉积法在其表面负载贵金属金进行化学改性来提高样品的CO催化性能。本课题的主要研究内容及结果如下:1.氧化铈核壳纳米球的制备及其催化性能的研究我们以壳聚糖为软模板通过溶剂热的方法制备了大小均匀,分散性良好的CeO_2核壳纳米球。为了进一步研究核壳纳米球的形成机理和壳聚糖在反应中的作用,我们进行了一系列的对比实验。结果表明,CeO_2核壳纳米球的形成经历了 CeO_2纳米晶的形成、不定向自组装以及部分纳米晶的溶解过程。通过与没有壳聚糖参与制备的CeO_2类立方块对比发现,在整个形成过程中,作为软模板和还原剂,壳聚糖起到了重要作用,改变了 CeO_2的形貌和暴露晶面。更重要的是,壳聚糖的存在显著增加了 CeO_2中的氧空位数量,从而提高了催化效能。2.载金氧化铈核壳纳米球的制备及其催化性能的研究为了提高CeO_2的催化性能,我们对制备的CeO_2核壳纳米球进行化学改性——负载贵金属金纳米颗粒。本节通过沉淀沉积法把不同量的金负载到CeO_2核壳纳米球和类立方块上,制备出一系列不同载金量的样品。我们通过SEM-EDS mapping、XPS、H2-TPR、CO催化氧化等测试对所得产物进行表征。EDS mapping的测试结果表明,金在CeO_2上呈均匀分布状态。载金后的氧化钸的氧空位数量明显增加,还原性能得到显著改善,进而使催化性能得到显著的提高。另外,载体是具有介孔结构的氧化铈,能够在一定程度上固定住金颗粒,所以得到的载金氧化铈(Au/CeO_2)具有良好的催化稳定性。XPS的测试结果表明,核壳纳米球上负载的金纳米颗粒是以Au0和Au3+的混合价态存在的,而在催化CO之后,金颗粒只有Au0这一个价态。而类立方块的负载的金纳米颗粒价态在催化前后保持不变,呈零价态。而催化性能的差异证明了 Au0和Au3+的混合价态的存在对CO催化性能的提高有促进作用。
[Abstract]:Air pollution has become a worldwide problem in China and even the whole world, which is mainly caused by the excessive dependence on fossil fuels and the rapid increase of automobile ownership. Therefore, CO removal is imminent, and CO catalytic oxidation as a simple and energy saving CO removal method has become the focus of research. In CO catalysts, cerium oxide (CeO2) has attracted much attention because of its abundant oxygen vacancy defects, high oxygen storage capacity and the redox characteristics of ce _ 3 / ce _ 4 electron pairs. There are many factors affecting the catalytic activity of cerium based nanomaterials, such as morphology, oxygen vacancies, interfacial structure, the synergism between exposed crystal planes and nanocomposites, etc. In this paper, using chitosan as a soft template, CEO _ 2 core-shell nanospheres were prepared by a simple solvothermal method, and the surface of CEO _ 2 core-shell nanospheres was chemically modified by precipitation deposition method to improve the CO catalytic performance of the samples. The main contents and results of this subject are as follows: 1. Preparation of ce _ 2O _ 3 core-shell nanospheres and their catalytic properties; CEO _ 2 core-shell nanospheres with uniform size and good dispersion were prepared by solvothermal method using chitosan as soft template. In order to further study the formation mechanism of core-shell nanospheres and the role of chitosan in the reaction, a series of comparative experiments were carried out. The results show that the formation of ce _ 2O _ 2 core-shell nanospheres has experienced the formation of CEO _ 2 nanocrystals, non-directional self-assembly and the dissolution of some nanocrystals. By comparing with CeOstack 2 square prepared without chitosan, it was found that chitosan played an important role as a soft template and reductant in the whole formation process, which changed the morphology and exposed crystal plane of CeOSP _ 2. More importantly, the presence of chitosan significantly increased the number of oxygen vacancies in CEO _ 2, thus enhancing the catalytic efficiency of .2. Preparation of ce _ 2O _ 3 Core-shell nanoparticles and their Catalytic Properties; in order to improve the catalytic performance of CEO _ 2, we chemically modified ce _ 2O _ 2 core-shell nanospheres loaded with noble metal gold nanoparticles. In this section, a series of samples with different amounts of gold were prepared by depositing different amounts of gold onto CEO _ s _ 2 core-shell nanospheres and standing squares. The obtained products were characterized by SEM-EDS mappingn XPSH2-TPRCO catalytic oxidation. The results of EDS mapping show that gold is uniformly distributed on CeO-2. After gold loading, the amount of oxygen vacancies in plutonium oxide is obviously increased, the reduction performance is improved significantly, and the catalytic performance is greatly improved. In addition, the carrier is cerium oxide with mesoporous structure, which can immobilize gold particles to a certain extent, so the au / CEO _ 2 has good catalytic stability. XPS results show that, The gold nanoparticles loaded on core-shell nanospheres exist in the mixed valence state of Au0 and Au3, but after CO catalysis, the gold particles have only one valence state of Au0. However, the valence state of gold nanoparticles supported on cubic like blocks remained unchanged before and after the catalyst, showing a zero valence state. The difference of catalytic performance shows that the existence of mixed valence state of Au0 and Au3 can promote the improvement of CO catalytic performance.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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