化学
催化作用
水煤气变换反应
氧气
离子键合
金属
化学物理
粒子(生态学)
X射线吸收光谱法
纳米颗粒
吸收光谱法
纳米技术
离子
地质学
物理
有机化学
材料科学
海洋学
量子力学
生物化学
作者
Tomás Ramírez Reina,M. González-Castaño,Vı́ctor López-Flores,L. Marcela Martínez T,Andrea Zitolo,Svetlana Ivanova,Wenquian Xu,Miguel Ángel Centeno,José A. Rodríguez,J.A. Odriozola
摘要
The active forms of Au and Pt in CeO2-based catalysts for the water-gas shift (WGS) reaction are an issue that remains unclear, although it has been widely studied. On one hand, ionic species might be responsible for weakening the Ce-O bonds, thus increasing the oxygen mobility and WGS activity. On the other hand, the close contact of Au or Pt atoms with CeO2 oxygen vacancies at the metal-CeO2 interface might provide the active sites for an efficient reaction. In this work, using in situ X-ray absorption spectroscopy, we demonstrate that both Au and Pt remain unoxidized during the reaction. Remarkable differences involving the dynamics established by both species under WGS atmospheres were recognized. For the prereduced Pt catalyst, the increase of the conversion coincided with a restructuration of the Pt atoms into cuboctahedrical metallic particles without significant variations on the overall particle size. Contrary to the relatively static behavior of Pt0, Au0 nanoparticles exhibited a sequence of particle splitting and agglomeration while maintaining a zero oxidation state despite not being located in a metallic environment during the process. High WGS activity was obtained when Au atoms were surrounded by oxygen. The fact that Au preserves its unoxidized state indicates that the chemical interaction between Au and oxygen must be necessarily electrostatic and that such an electrostatic interaction is fundamental for a top performance in the WGS process.
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