Song Chulho, Tayal Akhil, Seo Okkyun, Kim Jaemyung, Chen Yanna, Hiroi Satoshi, Kumara L S R, Kusada Kohei, Kobayashi Hirokazu, Kitagawa Hiroshi, Sakata Osami
Synchrotron X-ray Station at SPring-8, Research Network and Facility Services Division, National Institute for Materials Science (NIMS) 1-1-1 Kouto, Sayo Hyogo 679-5148 Japan
Synchrotron X-ray Group, Research Center for Advanced Measurement and Characterization, NIMS 1-1-1 Kouto, Sayo Hyogo 679-5148 Japan.
Nanoscale Adv. 2018 Dec 19;1(2):546-553. doi: 10.1039/c8na00305j. eCollection 2019 Feb 12.
Pd Ru nanoparticles (NPs) were observed to display enhanced CO oxidation activity with the maximum performance obtained at the composition = 0.5. To unveil the origin of this superior CO oxidation activity, we investigated the local structure, valence state, and electronic properties of Pd Ru NPs using synchrotron-based X-ray techniques. Site specific information obtained from X-ray absorption fine structure (XAFS) spectroscopy revealed that the local disorder around Pd and Ru atoms and their valence state can be systematically tuned by varying the Pd composition. Furthermore, the XAFS results indicated a strong correlation among the structural and valence state and the observed CO oxidation catalytic properties of Pd Ru NPs. Hard X-ray photoelectron spectroscopy (HAXPES) analysis suggested that the capability of CO oxidation requires an optimum balance between the adsorption and desorption energy for CO adsorption and eventually conversion to CO. A comparison between the experimental valence band (VB) HAXPES spectra of Pd Ru NPs and the linear combination of VB HAXPES spectra of Pd and Ru NPs revealed that the charge transfer from Pd to Ru occurs in the Pd Ru alloy at intermediate compositions, causing electron enrichment of the Ru surface. In addition, the maximum red-shift in the edge-position relative to that of bulk Pd/Ru and high structural disorder were observed for the PdRu alloy at the intermediate composition. This coupled behavior of structure and electronic properties followed the experimental trend of CO oxidation activity in this system.
观察到钯钌纳米颗粒（NPs）表现出增强的一氧化碳氧化活性，在钯含量为0.5时获得了最佳性能。为了揭示这种卓越的一氧化碳氧化活性的起源，我们使用基于同步加速器的X射线技术研究了钯钌纳米颗粒的局部结构、价态和电子性质。从X射线吸收精细结构（XAFS）光谱获得的位点特异性信息表明，通过改变钯的组成，可以系统地调节钯和钌原子周围的局部无序及其价态。此外，XAFS结果表明结构和价态与观察到的钯钌纳米颗粒的一氧化碳氧化催化性能之间存在很强的相关性。硬X射线光电子能谱（HAXPES）分析表明，一氧化碳氧化的能力需要一氧化碳吸附和最终转化为二氧化碳的吸附和解吸能量之间的最佳平衡。钯钌纳米颗粒的实验价带（VB）HAXPES光谱与钯和钌纳米颗粒的VB HAXPES光谱的线性组合之间的比较表明，在中间组成的钯钌合金中发生了从钯到钌的电荷转移，导致钌表面电子富集。此外，在中间组成的钯钌合金中观察到相对于块状钯/钌的边缘位置的最大红移和高结构无序。结构和电子性质的这种耦合行为遵循了该系统中一氧化碳氧化活性的实验趋势。
