Abstract We have prepared and characterized atomically well-defined model systems for ceria-supported Pt–Co core–shell catalysts. Pt@Co and Co@Pt core–shell nanostructures were grown on well-ordered CeO2(111) films on Cu(111) by physical vapour deposition of Pt and Co metals in ultrahigh vacuum and investigated by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy. The deposition of Co onto CeO2(111) yields Co–CeO2(111) solid solution at low Co coverage (0.5 ML), followed by the growth of metallic Co nanoparticles at higher Co coverages. Both Pt@Co and Co@Pt model structures are stable against sintering in the temperature range between 300 and 500 K. After annealing at 500 K, the Pt@Co nanostructure contains nearly pure Co-shell while the Pt-shell in the Co@Pt is partially covered by metallic Co. Above 550 K, the re-ordering in the near surface regions yields a subsurface Pt–Co alloy and Pt-rich shells in both Pt@Co and Co@Pt nanostructures. In the case of Co@Pt nanoparticles, the chemical ordering in the near surface region depends on the initial thickness of the deposited Pt-shell. Annealing of the Co@Pt nanostructures in the presence of O2 triggers the decomposition of Pt–Co alloy along with the oxidation of Co, regardless of the thickness of the initial Pt-shell. Progressive oxidation of Co coupled with adsorbate-induced Co segregation leads to the formation of thick CoO layers on the surfaces of the supported Co@Pt nanostructures. This process is accompanied by the disintegration of the CeO2(111) film and encapsulation of oxidized Co@Pt nanostructures by CeO2 upon annealing in O2 above 550 K. Notably, during oxidation and reduction cycles with O2 and H2 at different temperatures, the changes in the structure and chemical composition of supported Co@Pt nanostructures were driven mainly by oxidation while reduction treatments had little effect regardless of the initial thickness of the Pt-shell.

中文翻译：

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基于氧化铈的模型催化剂的纳米级结构：有序 CeO2(111) 薄膜上的 Pt-Co 纳米结构

摘要 我们已经为氧化铈负载的 Pt-Co 核壳催化剂制备并表征了原子上明确定义的模型系统。Pt@Co 和 Co@Pt 核壳纳米结构在 Cu(111) 上有序的 CeO2(111) 薄膜上通过 Pt 和 Co 金属在超高真空中的物理气相沉积生长，并通过同步辐射光电子能谱和谐振进行研究光发射光谱。Co在CeO2(111)上的沉积在低Co覆盖率(0.5ML)下产生Co-CeO2(111)固溶体，随后在较高Co覆盖率下生长金属Co纳米颗粒。Pt@Co 和 Co@Pt 模型结构在 300 到 500 K 的温度范围内对烧结都是稳定的。在 500 K 退火后，Pt@Co 纳米结构包含几乎纯的 Co-shell，而 Co@中的 Pt-shell Pt 部分被金属 Co 覆盖。高于 550 K，近表面区域的重新排序在 Pt@Co 和 Co@Pt 纳米结构中产生亚表面 Pt-Co 合金和富含 Pt 的壳。在 Co@Pt 纳米粒子的情况下，近表面区域的化学排序取决于沉积的 Pt 壳的初始厚度。无论初始 Pt 壳的厚度如何，在 O2 存在下对 Co@Pt 纳米结构的退火都会触发 Pt-Co 合金的分解以及 Co 的氧化。Co 的逐步氧化与吸附物诱导的 Co 偏析相结合，导致在负载的 Co@Pt 纳米结构的表面形成厚的 CoO 层。这个过程伴随着 CeO2(111) 膜的分解和氧化的 Co@Pt 纳米结构在 550 K 以上的 O2 中退火后被 CeO2 包封。值得注意的是，