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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.
Pt is a kind of efficient and stable catalyst, but the shortage and expensive Pt resource limits its extensive commercial application. Alloying can greatly reduce the amount of Pt, and often can significantly improve its catalytic performance, which is widely used in Heterogeneous catalysis and electrocatalysis.Among them, PtCu alloy is a kind of promising catalyst, Cu is rich in resources and low in price, not only reduces the cost, but also improves the activity and the stability of the catalyst due to the alloying effect.As the alloy particle size, However, most industrial metal catalysts are supported on oxides to improve the catalytic performance, the morphology of the alloy nanoparticles, and the morphology of the alloy nanoparticles Surface composition changes with the role of the carrier, that is, the so-called carrier effect, which is reflected in the metal / oxide interface, can promote the dispersion of metal particles, change its morphology or even chemical state, thus changing its catalytic properties, of which the most A representative metal-carrier strong interaction.Therefore, the study of different oxide carrier alloy catalyst dispersion, surface composition, The influence of chemical states, especially different atmospheres, is very important for the key control factors that clearly affect the performance of the catalyst, but due to the complexity of the heterogeneous catalysts and the small number of surface-sensitive test methods, there are not many related reports at present. (HS-LEIS) is a surface layer-sensitive testing technique that can determine the composition and content of the most surface layer.In this paper, a homogeneous single-phase, narrow particle size distribution was successfully prepared by solvothermal co-reduction PtCu_x alloy nanoparticles were prepared and impregnated on the TiO_2 support by impregnation method to ensure the uniformity of nanoparticle composition on the support.Using quasi-in situ X-ray photoelectron spectroscopy (XPS) and high HS-LEIS for PtCu The surface morphology and chemical state of the alloy nano-catalysts were characterized under different conditions and found that the surface composition, distribution, morphology and chemical state of the catalyst were significantly influenced by the support and the treatment conditions, and the surface composition and the surface area of the unsupported catalysts were obtained Phase composition of the phase diagram.The results show that, PtCux / TiO 2 catalyst in the continuous oxidation process, Cu is oxidized and better in the carrier surface During the continuous reduction process, the partially reduced Cu forms a Pt-rich alloy with Pt, resulting in formation of Pt ~ (δ +) at the interface, Particles.Catalyst surface layer is mainly Cu, Pt is very small, and bulk composition is very different, indicating that the carrier plays an important role in the dispersion of Cu.