包裹型纳米贵金属材料制备与应用

发布时间：2018-06-17 10:17

  本文选题：纳米贵金属 + 核壳结构　； 参考：《上海师范大学》2017年硕士论文

【摘要】：纳米贵金属催化剂,特别是金催化剂,由于存在尺度效应,当其颗粒大小小于5 nm时,将表现出很强的催化活性。但是负载型的贵金属催化剂由于纳米粒子其表面原子占有的体积比非常大,表面原子配位不足具有非常高的表面能,从而使得相邻的金纳米粒子容易团聚,而导致催化剂失活。要维持催化剂的催化活性,可以采用在纳米空间上进行物理隔离的方式,将金纳米粒子相互间距离拉远,避免发生迁移团聚。常用合成材料的方法是将纳米贵金属粒子通过包裹的方式分散在另一种材料内部,通过构建核壳结构来保护纳米贵金属粒子不发生团聚。我们选择了三种核壳结构来比较不同核壳结构的特性,并以一氧化碳催化氧化反应作为探针反应评价催化剂反应性能。本论文第一部分采用微乳液的合成方式,一锅法合成了一种二氧化硅包裹的金纳米粒子材料Au@SiO_2,该材料具有均匀的结构,其中金纳米粒子颗粒大小为2.3±0.5 nm,二氧化硅壳层半径为10 nm。该材料用于一氧化碳氧化时,起始反应温度为230℃。400℃下反应65小时,转化率只有小幅下降,由83.4%降至80.5%,材料稳定性优良。第二部分以第一部分材料为硬模板,经水热合成后刻蚀除去模板,得到多孔腔二氧化铈包裹的催化剂Au@HM-CeO_2,该催化剂初始催化活性高,通过调节金纳米粒子的大小,当金纳米粒子大小为4 nm时,催化剂稳定性优异,在250℃反应225小时催化剂活性几乎保持不变。第三部分采用分子筛作为包裹材料,以巯基硅烷键合保护贵金属,得到原位的包裹,同时利用热变性水凝胶作为硬模板,合成纳米分子筛包裹的催化剂Au@nano-LTA及Au-Pt@nano-LTA。由于分子筛的孔径介于二氧化硅与二氧化铈包裹材料之间,既能有效包裹纳米贵金属粒子,同时又保证催化剂与反应物分子的有效接触。其中催化剂Au-Pt@nano-LTA具有本章中最佳的催化活性及稳定性。
[Abstract]:Nanocrystalline noble metal catalysts, especially gold catalysts, show strong catalytic activity when the particle size is less than 5 nm due to the existence of scale effect. However, the supported noble metal catalyst has high surface energy due to its large volume ratio of surface atoms, which leads to the agglomeration of the adjacent gold nanoparticles and the deactivation of the catalyst. In order to maintain the catalytic activity of the catalyst, the gold nanoparticles can be separated from each other by physical isolation in nanospace to avoid migration and agglomeration. The common method of synthesizing materials is to disperse nano-precious metal particles in another material by encapsulation, and to construct core-shell structure to protect nano-precious metal particles from agglomeration. Three core-shell structures were selected to compare the characteristics of different core-shell structures and the catalytic oxidation of carbon monoxide was used as a probe to evaluate the catalytic performance of the catalyst. In the first part of this thesis, a silica coated gold nanoparticle material Aur @ SiO-2 was synthesized by one-pot method using microemulsion. The material has a uniform structure, in which the particle size of gold nanoparticles is 2.3 卤0.5 nm, and the radius of silica shell is 10 nm. When the material was used for CO oxidation, the initial reaction temperature was 230 鈩，

本文编号：2030686