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Ligand‐Stabilized and Atomically Precise Gold Nanocluster Catalysis: A Case Study for Correlating Fundamental Electronic Properties with Catalysis
Authors:Dr. Jing Liu  Dr. Katla Sai Krishna  Dr. Yaroslav B. Losovyj  Dr. Soma Chattopadhyay  Dr. Natalia Lozova  Prof. Jeffrey T. Miller  Prof. James J. Spivey  Dr. Challa S. S. R. Kumar
Affiliation:1. Center for Advanced Microstructures and Devices (CAMD), Louisiana State University, Baton Rouge, LA 70806 (USA);2. Center for Atomic‐Level Catalyst Design, 324, Cain Department of Chemical Engineering, Louisiana State University, 110 Chemical Engineering, South Stadium Road, Baton Rouge, LA 70803 (USA);3. CSRRI‐IIT, MRCAT, Sector 10, Bldg 433B, Argonne National Laboratory, Lemont, IL 60439 (USA), Physics Department, Illinois Institute of Technology, Chicago, IL 60616 (USA);4. CSE Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439‐4837 (USA)
Abstract:We present results from our investigations into correlating the styrene‐oxidation catalysis of atomically precise mixed‐ligand biicosahedral‐structure [Au25(PPh3)10(SC12H25)5Cl2]2+ (Au25bi) and thiol‐stabilized icosahedral core–shell‐structure [Au25(SCH2CH2Ph)18]? (Au25i) clusters with their electronic and atomic structure by using a combination of synchrotron radiation‐based X‐ray absorption fine‐structure spectroscopy (XAFS) and ultraviolet photoemission spectroscopy (UPS). Compared to bulk Au, XAFS revealed low Au–Au coordination, Au? Au bond contraction and higher d‐band vacancies in both the ligand‐stabilized Au clusters. The ligands were found not only to act as colloidal stabilizers, but also as d‐band electron acceptor for Au atoms. Au25bi clusters have a higher first‐shell Au coordination number than Au25i, whereas Au25bi and Au25i clusters have the same number of Au atoms. The UPS revealed a trend of narrower d‐band width, with apparent d‐band spin–orbit splitting and higher binding energy of d‐band center position for Au25bi and Au25i. We propose that the differences in their d‐band unoccupied state population are likely to be responsible for differences in their catalytic activity and selectivity. The findings reported herein help to understand the catalysis of atomically precise ligand‐stabilized metal clusters by correlating their atomic or electronic properties with catalytic activity.
Keywords:cluster compounds  gold  nanostructures  ultraviolet photoemission spectra  X‐ray absorption fine structure
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