高效贵金属纳米新材料的制备及其催化氧化CO和HCHO性能研究

发布时间：2018-08-16 09:40

【摘要】：贵金属催化剂由于在化工、环保、能源等领域表现出优异的性能而受到广泛的关注与研究。然而资源稀缺、价格昂贵以及较差的热稳定性,严重影响了贵金属催化剂的实际应用价值。因此,如何制备稳定而高分散度的贵金属催化剂以降低贵金属用量是当前的研究热点。本文以提高贵金属利用率为目标展开研究,取得了如下结果:第一部分采用不同方法合成了不同Pd@SiO_2核壳结构纳米材料,并与传统浸渍法制备的Pd/SiO_2催化剂对照。用反相微乳液法一步合成了只有1.1 nm超小Pd纳米粒子的Pd@SiO_2-RM核壳结构纳米材料。HRTEM结果显示超小Pd纳米粒子镶嵌在30 nm左右的SiO_2微球里面形成多核型核壳结构纳米材料。因此,可以有效限制超小Pd核在高温下的烧结聚集。与其他方法合成的Pd@SiO_2和Pd/SiO_2催化剂相比,Pd@SiO_2-RM具有更大的活性金属表面积,从而表现出最好的CO氧化性能以及优异抗热稳定性。研究结果表明Pd的颗粒大小和活性金属表面积是影响催化剂活性的决定因素,并且反应速率与Pd颗粒大小以及活性金属表面积之间具有很好的线性关系。第二部分以高比表面积(572 m2/g)的枝状介孔SiO_2(KCC-1)为载体制备了Pt-Ni双金属催化剂。XRD,TEM,HAADF EDX-Mapping结果显示,由于枝状介孔SiO_2(KCC-1)限域作用,3 nm左右的Pt-Ni双金属纳米粒子在载体上高度分散,有效地促进了催化剂对CO的氧化活性。此外,相对于单金属组分Pt/KCC-1和Ni/KCC-1催化剂,适当比例的PtxNi10-x/KCC-1双金属催化剂由于Pt,Ni之间的协同催化效应,可以进一步提高催化剂的反应活性。并且1%Pt_7Ni_3/KCC-1催化剂展现了最高效的CO氧化活性,在100℃将CO完全反应。很显然,Ni的加入不仅减少了Pt的用量,同时还增强了催化剂的活性。第三部分研究了稀土La_2O_3改性的TiO_2载体负载Pt制备的催化剂对甲醛室温氧化性能的影响。HRTEM,HAADF-STEM以及CO-TPD结果表明,La_2O_3的加入使Pt纳米粒子从原来的2.2 nm减小到1.7 nm,有效的促进了Pt的分散,从而催化剂的活性大大加强。此外,XPS结果显示,La_2O_3的加入使催化剂表面吸附氧物种增多,促使金属与载体之间相互作用加强,这也进一步使催化剂的活性得到改善。最后,对3%La-TiO_2粉体进行挂浆处理并负载极少量的Pt制备了整体催化剂,并模拟实际工况对催化剂进行了活性评价。该催化剂表现出高效的室内甲醛净化效果及长时间反应稳定性。
[Abstract]:Noble metal catalysts have attracted extensive attention and research because of their excellent performance in chemical industry, environmental protection, energy and other fields. However, the scarcity of resources, high price and poor thermal stability seriously affect the practical application value of noble metal catalysts. Therefore, how to prepare stable and highly dispersed noble metal catalysts to reduce the cost The amount of precious metals is a hot topic in the current research. This paper aims at improving the utilization ratio of precious metals. The following results are obtained: the first part is to synthesize different Pd@SiO_2 core shell nanostructured materials by different methods, and compare them with the Pd/SiO_2 catalyst prepared by traditional impregnation method. Only 1.1 NM is synthesized by one-step synthesis by inverse microemulsion method. HRTEM results show that the Pd nanoparticles embedded in the SiO_2 microspheres around 30 nm form multi-core-shell structure nanomaterials. Therefore, the agglomeration of the Pd nanoparticles at high temperatures can be effectively limited. Compared with Pd@SiO_2 and Pd/SiO_2 catalysts synthesized by other methods, the Pd@SiO_2 and Pd/SiO_2 nanoparticles synthesized by HRTEM show that the Pd nanoparticles can form multi-core-shell structure nanomaterials. Pd@SiO_2-RM exhibits the best CO oxidation performance and excellent thermal stability due to its larger active metal surface area. The results show that the particle size and active metal surface area of Pd are the determinants of catalyst activity, and the reaction rate has a good linear relationship with the size of Pd particles and the active metal surface area. In the second part, Pt-Ni bimetallic catalysts were prepared with high specific surface area (572 m2/g) dendritic mesoporous SiO_2 (KCC-1) as support. XRD, TEM, HAADF EDX-Mapping results showed that the Pt-Ni bimetallic nanoparticles around 3 nm were highly dispersed on the support due to the limited effect of dendritic mesoporous SiO_2 (KCC-1). In addition, compared with Pt/KCC-1 and Ni/KCC-1 catalysts, a proper proportion of Pt x Ni 1 0-x/KCC-1 bimetallic catalysts can further enhance the catalytic activity of the catalysts because of the synergistic catalytic effect between Pt and Ni. Moreover, 1% Pt_7Ni_3/KCC-1 catalyst exhibits the most efficient CO oxidation activity, and CO is completely reacted at 100 C. Apparently, the addition of Ni not only reduces the amount of Pt, but also enhances the activity of the catalyst. In the third part, the effect of Pt supported on the catalysts modified by La_2O_3 on the oxidation of formaldehyde at room temperature was studied. HRTEM, HAADF-STEM and CO-TPD results showed that the addition of La_2O_3 reduced the Pt nanoparticles from the original 2.2 nm. In addition, XPS results showed that the addition of La_2O_3 increased the number of oxygen species adsorbed on the surface of the catalyst and enhanced the interaction between the metal and the support, which further improved the activity of the catalyst. Finally, 3% La-TiO_2 powder was suspended for slurry treatment. The monolithic catalyst was prepared by loading a very small amount of PT, and its activity was evaluated by simulating the actual working conditions. The catalyst showed high efficiency in indoor formaldehyde purification and long-term reaction stability.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36

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