Atomic Ordering and Sn Segregation in Pt–Sn Nanoalloys Supported on CeO2 Thin Films

• Published in: Topics in catalysis 2017-05, Vol.60 (6-7), p.522-532
• Main Authors: Neitzel, Armin, Kovács, Gábor, Lykhach, Yaroslava, Kozlov, Sergey M., Tsud, Nataliya, Skála, Tomáš, Vorokhta, Mykhailo, Matolín, Vladimír, Neyman, Konstantin M., Libuda, Jörg
• Format: Article
• Language: English
• Subjects: Adsorption; Annealing; Atomic properties; Atomic structure; Bonding; Catalysis; Characterization and Evaluation of Materials; Charge transfer; Chemical bonds; Chemistry; Chemistry and Materials Science; Correlation; Density functional theory; Industrial Chemistry/Chemical Engineering; Mathematical models; Molecular structure; Nanoalloys; Nanoparticles; Original Paper; Pharmacy; Photoelectron spectroscopy; Physical Chemistry; Platinum base alloys; Spectroscopic analysis; Stability; Stoichiometry; Surface chemistry; Surface structure; Synchrotron radiation; Thermodynamic equilibrium; Thin films
• ISSN: 1022-5528; 1572-9028
• DOI: 10.1007/s11244-016-0709-5

The stability and atomic ordering in Pt–Sn nanoalloys supported on CeO 2 thin films have been studied by means of synchrotron radiation photoelectron spectroscopy and density functional calculations. Using CO molecules as a probe, we explored the development of the surface structure of supported Pt–Sn nanoalloys with respect to a reference Pt/CeO 2 model system. We found a significant decrease in the density of CO adsorption sites on supported Pt–Sn nanoalloys caused by Sn segregation to the surface upon annealing. Additionally, we found that atomic ordering in Pt–Sn nanoalloys is driven by the balance between the surface segregation energy of Sn atoms and the energy of heteroatomic bond formation. Our calculations demonstrate a clear tendency for Sn segregation to the nanoalloy surface. For Pt 105 Sn 35 and Pt 1097 Sn 386 nanoparticles, we calculated a surface stoichiometry of Pt 2 Sn which is only slightly dependent on temperature in thermodynamic equilibrium. The analysis of Bader charges in Pt–Sn nanoalloys revealed a strong correlation between the charge and the coordination number of Sn atoms with respect to Pt neighbors. In particular, the magnitude of the charge transfer from Sn to Pt increases as a function of the Sn coordination number.