第310回触媒化学研究センターコロキウム
共催 日本化学会北海道支部・応用物理学会北海道支部・触媒学会北海道支部・北大加速器科学研究会

Dynamic structure of supported Pt and Pt-Sn
nanoclusters: Real-time, finite-temperature DFT/MDand X-ray Spectroscopy simulations
Professor John. J. Rehr (Department of Physics,
University of Washington, Seattle, Wa 98195 USA)2012年7月9日（月）16：00—17：30（創成科学研究棟4階セミナー室B・C）
http://www.cat.hokudai.ac.jp/access.html
The nature of local atomic and electronic structure at the nanoscale is of both fundamental andtechnological importance. These local and generally dynamical properties are especially important forunderstanding the role of supported metalclusters, which are key ingredients in many catalytic processes.
Understanding these properties thus requires real-time approaches, which are becoming increasingly
important in studies based on x-ray absorption spectra (XAS). In this talk I will discuss a real-time
approach for calculating dynamic structure based on ab initio, finite-temperature density functional
theory/molecular dynamics and the real-space Green's function approach for XAS calculations based on
the FEFF9 code [1]. This approach exploits recent theoretical advances that permit parameter-freecalculations of the key many-body effects in the theory. This method is illustrated for nano-clusters of Pt[2] and Pt-Sn [3] supported on gamma-alumina. The simulations reveal a complex, non-equilibrium
structure on multiple-time scales, including a hindered Brownian motion of the center of mass andfluctuating bonding. In particular their internal structure varies dynamically on a time scale of a few ps.
Charge transfer between atoms in the cluster and between the cluster and the surface are particularlyimportant. These results explain many unusual properties observed for supported Pt nanoclusters
including large temperature dependence, anomalous disorder, and negative thermal expansion. For PtSn, the simulations show that the Sn atoms are especially mobile, but the clusters still have welldefined Pt-Pt and Pt-Sn coordination shells, and between 2 - 5 bonds between Pt or Sn atoms in thecluster and the O atoms at the surface. Simulations of the XANES are observed to be in reasonableagreement with experiment demonstrating the importance of taking into account the large, internalfluctuations in these structures. Implications for bonding and catalytic properties are also briefly
discussed.
*Supported by NSF Grant PHY-0835543 and DOE Grant DE-FG03-97ER45623.
[1] J. J. Rehr, J. J. Kas, M.P. Prange, A.P. Sorini, Y. Takimoto, and F. Vila, Comptes Rendus Physique, 10,548 (2009).
[2] F. Vila, J. J. Rehr, J. Kas, R.G. Nuzzo and A.I Frenkel., Phys. Rev. B 78, 121404(R), (2008).
[3] F. Vila, J. J. Rehr, S. D. Kelly and S. R. Bare, Bull. Am. Phys. Soc. (2011).
問合せ先： 触媒化学研究センター・朝倉清高（askr@cat.hokudai.ac.jp/011-706-9113）
J.J.Rehr 先生は，理論 XAFS 解析手法として，広く使われる FEF を 1980 年代後半から開発され，XAFS 理論を先導されています．この 10 年近く触媒やナノ粒子の XAFS の理論解析に興味を持たれています．せっかくの機会ですので，多くの方の参加を期待しております．

310th Catalysis Research Center (CRC) Colloquium
Hokkaido Branch of The Chemical Society of Japan・Hokkaido Branch of The Japan Society of Applied Physics(JSAP)・
Hokkaido Branch of The Catalysis Society of Japan・Hokkaido University Accelerator Science Research Association