title: Ligand-stabilized and atomically precise gold nanocluster catalysis: a case study for correlating fundamental electronic properties with catalysis.
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+) (Au25-bi) and thiol-stabilized icosahedral core-shell-structure [Au25(SCH2CH2Ph)18](-) (Au25-i) 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. Au25-bi clusters have a higher first-shell Au coordination number than Au25-i, whereas Au25-bi and Au25-i 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 Au25-bi and Au25-i. 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.
authors.affiliation: Center for Advanced Microstructures and Devices (CAMD), Louisiana State University, Baton Rouge, LA 70806, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.forename: Katla Sai
authors.initials: KS
authors.lastname: Krishna
authors.forename: Yaroslav B
authors.initials: YB
authors.lastname: Losovyj
authors.forename: Soma
authors.initials: S
authors.lastname: Chattopadhyay
authors.forename: Natalia
authors.initials: N
authors.lastname: Lozova
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Miller
authors.forename: James J
authors.initials: JJ
authors.lastname: Spivey
authors.forename: Challa S S R
authors.initials: CS
authors.lastname: Kumar
keywords: X-ray absorption fine structure; cluster compounds; gold; nanostructures; ultraviolet photoemission spectra