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Site-selective sulfurization of bromide-capped palladium nanocubes by polysulfide and the underlying mechanism

机译：多硫化物对溴化物覆盖的钯纳米立方体的定点硫化及其潜在机理

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This article describes site-selective sulfurization of Pd nanocubes capped by a monolayer of chemisorbed Br- ions. High-resolution transmission electron microscopy and high-angle annular dark-field scanning TEM observations showed that PdS was not formed until a certain quantity of polysulfide ions had been introduced (300 μl, or 18.8 ppm in the final reaction solution). Spot energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy analyses confirmed that the surface-chemisorbed Br~- ions were completely substituted by ions before the initiation of the sulfurization reaction. In the presence of sufficient ions (>300 μl or >18.8 ppm), PdS phase was selectively developed from the highly active corners, which then moved to the edges and finally towards the center until the entire nanocube was converted into PdS. The resultant PdS was found to be amorphous by electron microscopy and powder x-ray diffraction measurements. The amorphous structure of PdS facilitated the penetration and diffusion of species and thus acceleration of the reaction kinetics. As a result, the sulfurization of 13 nm Pd nanocubes was completed within a few minutes after the addition of adequate Na2Sx, leading to a much more severe poisoning effect, compared with other noble metals such as Ag, by sulfur.
机译：本文介绍了由化学吸附的Br-离子单层覆盖的Pd纳米立方的选择性硫化。高分辨率透射电子显微镜和大角度环形暗场扫描TEM观察表明，直到引入一定量的多硫化物离子（最终反应溶液中为300μl或18.8 ppm），才形成PdS。斑点能量色散X射线光谱法和X射线光电子能谱分析证实，在硫化反应开始之前，表面化学吸附的Br〜-离子已被离子完全取代。在存在足够的离子（> 300μl或> 18.8 ppm）的情况下，PdS相从高活性角选择性地发展，然后移至边缘，最后移向中心，直到整个纳米立方体被转化为PdS。通过电子显微镜和粉末X射线衍射测量发现所得的PdS为非晶态。 PdS的无定形结构促进了物质的渗透和扩散，从而促进了反应动力学。结果，在加入适量的Na2Sx之后的几分钟内，完成了13 nm Pd纳米立方的硫化，与其他贵金属（如Ag）相比，硫导致的毒害作用更为严重。

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