准原位XPS和HS-LEIS研究载体对PtCu合金纳米催化剂表面组成的影响（英文）

发布时间：2018-04-23 17:31

本文选题：铂铜合金 + 双金属催化剂　；参考：《催化学报》2017年07期

【摘要】：Pt是一类高效、稳定的催化剂,但Pt资源短缺且价格昂贵,限制了其广泛商业化应用.合金化可以使Pt的用量大为减少,且往往能显著提高其催化性能,因而广泛应用于多相催化和电催化.其中PtCu合金是一类很有前景的催化剂,Cu资源丰富、价格低廉,不仅降低了成本,而且由于合金效应提高了催化剂的活性和稳定性.由于合金的粒径、形状、组成及结构是影响其催化性能的重要因素,目前研究大多关注这些特征的可控合成.然而,大多工业金属催化剂都是负载于氧化物上以提高催化性能,合金纳米粒子的形貌以及表面组成因与载体作用而发生改变,也就是所谓的载体效应.这体现在金属/氧化物界面处,能够促进金属粒子分散、改变其形貌甚至化学态、进而改变其催化性能,其中最具代表性的金属-载体强相互作用.因此,研究不同氧化物载体上合金催化剂的分散度、表面组成、化学态,特别是不同气氛的影响,对明确影响催化剂性能的关键控制因素非常重要.但是由于多相催化剂的复杂性,且表面灵敏的测试手段很少,目前相关报道还不多.近年发展起来的高灵敏度低能离子散射谱(HS-LEIS)是表面层灵敏的测试技术,可以测定最表面层的组成和含量.本文采用溶剂热共还原法成功制备了均一单相、粒径分布较窄的PtCu_x合金纳米颗粒,并运用浸渍法将其负载在TiO_2载体上,以保证载体上纳米粒子组成的均一性.应用准原位X-射线光电子能谱(XPS)和高HS-LEIS对负载的PtCu合金纳米催化剂在不同条件处理后的表面组成和化学状态进行表征,发现催化剂的表面组成、分布、形貌和化学状态显著受到载体和处理条件的影响,同时得到负载和未负载的催化剂表面组成与体相组成关系的相图.结果表明,PtCux/TiO_2催化剂在连续氧化过程中,Cu被氧化并较好在载体表面铺展,Pt-Cu合金状态被破坏,Pt可能主要形成单一金属的纳米粒子,并在界面处形成Pt~(δ+).在连续还原过程中,部分被还原的Cu,与Pt形成富Pt合金粒子.催化剂表面层主要是Cu,Pt很少,与体相组成有很大差别,说明载体对Cu的分散起到重要作用.
[Abstract]:Pt is a kind of efficient and stable catalyst, but the shortage of Pt resources and the high price limit its wide commercial application. The amount of Pt can be greatly reduced by alloying, and the catalytic performance of Pt can be greatly improved, so it is widely used in heterogeneous catalysis and electrocatalysis. Among them, PtCu alloy is a promising catalyst with rich resources and low price, which not only reduces the cost, but also improves the activity and stability of the catalyst because of the alloy effect. As the particle size, shape, composition and structure of alloys are important factors affecting their catalytic performance, many studies have focused on the controllable synthesis of these characteristics. However, most industrial metal catalysts are supported on oxides to improve their catalytic performance. The morphology and surface composition of alloy nanoparticles are changed by interaction with the support, which is the so-called carrier effect. This is reflected in the metal / oxide interface, which can promote the dispersion of metal particles, change the morphology and even the chemical state of metal particles, and then change their catalytic performance, among which the most representative metal-carrier strongly interacts. Therefore, it is very important to study the influence of the dispersity, surface composition, chemical state, especially the different atmosphere of the alloy catalysts on different oxide supports to determine the key control factors that affect the performance of the catalysts. However, due to the complexity of heterogeneous catalysts and the lack of surface sensitive testing methods, there are few reports. The high sensitivity and low energy ion scattering spectroscopy developed in recent years is a sensitive measurement technique for the surface layer, which can be used to determine the composition and content of the most surface layer. The surface composition and chemical state of the supported PtCu alloy nanocatalysts were characterized by in situ X-ray photoelectron spectroscopy (XPS) and high HS-LEIS. The surface composition and distribution of the catalysts were found. The morphology and chemical state of the catalyst were significantly affected by the carrier and the treatment conditions, and the phase diagrams of the relationship between the surface composition and bulk phase composition of the supported and unloaded catalysts were obtained. In the continuous reduction process, partial reduction of Cu and Pt forms Pt rich alloy particles. The surface layer of the catalyst is mainly Cu-Pt, which is very different from the bulk phase composition, which indicates that the support plays an important role in the dispersion of Cu.
【作者单位】：厦门大学化学化工学院固体表面物理化学国家重点实验室醇醚酯化工清洁生产国家工程实验室;
【基金】：supported by the National Basic Research Program of China(973 Program,2013CB933102) the National Natural Science Foundation of China(21273178,21573180,91545204) Xiamen-Zhuoyue Biomass Energy Co.Ltd~~
【分类号】：O643.36

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