The Atomic Structural Dynamics of 纬-Al2O3 Supported Ir鈭扨t Nanocluster Catalysts Prepared from a Bimetallic Molecular Precursor: A Study Using Aberration-Corrected Electron Micros

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• 作者：Matthew W. Small ; Sergio I. Sanchez ; Laurent D. Menard ; Joo H. Kang ; Anatoly I. Frenkel ; Ralph G. Nuzzo
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：March 16, 2011
• 年：2011
• 卷：133
• 期：10
• 页码：3582-3591
• 全文大小：1033K
• 年卷期：v.133,no.10(March 16, 2011)
• ISSN：1520-5126

文摘

This study describes a prototypical, bimetallic heterogeneous catalyst: compositionally well-defined Ir鈭扨t nanoclusters with sizes in the range of 1鈭? nm supported on 纬-Al₂O₃. Deposition of the molecular bimetallic cluster [Ir₃Pt₃(渭-CO)₃(CO)₃(畏-C₅Me₅)₃] on 纬-Al₂O₃, and its subsequent reduction with hydrogen, provides highly dispersed supported bimetallic Ir鈭扨t nanoparticles. Using spherical aberration-corrected scanning transmission electron microscopy (C_s-STEM) and theoretical modeling of synchrotron-based X-ray absorption spectroscopy (XAS) measurements, our studies provide unambiguous structural assignments for this model catalytic system. The atomic resolution C_s-STEM images reveal strong and specific lattice-directed strains in the clusters that follow local bonding configurations of the 纬-Al₂O₃ support. Combined nanobeam diffraction (NBD) and high-resolution transmission electron microscopy (HRTEM) data suggest the polycrystalline 纬-Al₂O₃ support material predominantly exposes (001) and (011) surface planes (ones commensurate with the zone axis orientations frequently exhibited by the bimetallic clusters). The data reveal that the supported bimetallic clusters exhibit complex patterns of structural dynamics, ones evidencing perturbations of an underlying oblate/hemispherical cuboctahedral cluster鈭抍ore geometry with cores that are enriched in Ir (a result consistent with models based on surface energetics, which favor an ambient cluster termination by Pt) due to the dynamical responses of the M鈭扢 bonding to the specifics of the adsorbate and metal鈭抯upport interactions. Taken together, the data demonstrate that strong temperature-dependent charge-transfer effects occur that are likely mediated variably by the cluster鈭抯upport, cluster鈭抋dsorbate, and intermetallic bonding interactions.