title: In Situ Detection of Active Edge Sites in Single-Layer MoS2 Catalysts.
abstract: MoS2 nanoparticles are proven catalysts for processes such as hydrodesulfurization and hydrogen evolution, but unravelling their atomic-scale structure under catalytic working conditions has remained significantly challenging. Ambient pressure X-ray Photoelectron Spectroscopy (AP-XPS) allows us to follow in situ the formation of the catalytically relevant MoS2 edge sites in their active state. The XPS fingerprint is described by independent contributions to the Mo 3d core level spectrum whose relative intensity is sensitive to the thermodynamic conditions. Density Functional Theory (DFT) is used to model the triangular MoS2 particles on Au(111) and identify the particular sulphidation state of the edge sites. A consistent picture emerges in which the core level shifts for the edge Mo atoms evolve counterintuitively toward higher binding energies when the active edges are reduced. The shift is explained by a surprising alteration in the metallic character of the edge sites, which is a distinct spectroscopic signature of the MoS2 edges under working conditions.
authors.affiliation: Interdisciplinary Nanoscience Center (iNANO), Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
authors.forename: Albert
authors.initials: A
authors.lastname: Bruix
authors.affiliation: Interdisciplinary Nanoscience Center (iNANO), Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
authors.forename: Henrik Gøbel
authors.initials: HG
authors.lastname: Füchtbauer
authors.affiliation: Interdisciplinary Nanoscience Center (iNANO), Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
authors.forename: Anders K
authors.initials: AK
authors.lastname: Tuxen
authors.affiliation: Interdisciplinary Nanoscience Center (iNANO), Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Walton
authors.affiliation: Interdisciplinary Nanoscience Center (iNANO), Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
authors.forename: Mie
authors.initials: M
authors.lastname: Andersen
authors.affiliation: Interdisciplinary Nanoscience Center (iNANO), Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
authors.forename: Søren
authors.initials: S
authors.lastname: Porsgaard
authors.affiliation: Interdisciplinary Nanoscience Center (iNANO), Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
authors.forename: Flemming
authors.initials: F
authors.lastname: Besenbacher
authors.affiliation: Interdisciplinary Nanoscience Center (iNANO), Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
authors.forename: Bjørk
authors.initials: B
authors.lastname: Hammer
authors.affiliation: Interdisciplinary Nanoscience Center (iNANO), Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
authors.forename: Jeppe V
authors.initials: JV
authors.lastname: Lauritsen
keywords: DFT; X-ray photoelectron spectroscopy; catalysis; density functional theory; hydrotreating; molybdenumdisulfide (MoS2); nanoparticles; scanning tunnelling microscopy; water splitting