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.

Effect of edge plasmons on the optical properties of MoS2 monolayer flakes

“…This feature seems to be in agreement with earlier calculations [12,13,26] and possibly with the scanningtunneling-microscope images of MoS 2 triangles exhibiting a period of two along the Mo edges [12,15,27]. The resulting structure and the corresponding S 2 −S 2 distances are shown in Fig.…”

“…It is understood that the edges of the MoS 2 nanoclusters are catalytically active [11][12][13] and that this is due to the existence of metallic states present at certain edge configurations [14][15][16][17][18]. It has recently been shown that these states can lead to the formation of plasmons, i.e., quantized oscillations of electron gas plasma, along the edges of infinite MoS 2 nanoribbons [19].…”

Molecular Nanowire Bonding to Epitaxial Single‐Layer MoS2 by an On‐Surface Ullmann Coupling Reaction

“…Overall, the absence of reactivity of the pristine s‐ MoS 2 is attributed to the fully sulfided nature of both basal plane sites and the edges, which leaves no affinity for direct chemical bonding to the thiophenic S group of DBDBT nor for activation of the debromination step to allow for bonding to C. The Mo‐edge, exposed both in the pristine triangular NP‐MoS 2 and SL‐MoS 2 , are terminated by a full (100%) sulfur coverage as determined from previous atom‐resolved STM and theory studies (see Figure 1e). The terminal edge sulfurs in s ‐MoS 2 form stable S 2 dimers by combination of the S from the upper and lower layer,37,38 respectively, which may further explain the absent reactivity here. The S edges are present in the hexagonal SL‐MoS 2 structures, and are likewise terminated by a full (100%) sulfur coverage as shown in Figure 1e 38–40…”

Inverse Oxide/Metal Catalysts in Fundamental Studies and Practical Applications: A Perspective of Recent Developments

“…Figure 17 shows STM images for RuS 2 and MoS 2 on a Au(111) substrate. 75,76 The ionic character of these compounds is smaller than in an oxide and they do have catalytic properties on their own. 76 …”