AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM2
Chemistry of One-dimensional Metallic Edge States in MoS@sub 2@ Nanoclusters

Tuesday, November 5, 2002, 8:40 am, Room C-108

Session: Hydrocarbon Catalysis
Presenter: J.V. Lauritsen, University of Aarhus, Denmark
Authors: J.V. Lauritsen, University of Aarhus, Denmark
B.S. Clausen, Haldor Topsoe A/S, Denmark
H. Topsoe, Haldor Topsoe A/S, Denmark
F. Besenbacher, University of Aarhus, Denmark
Correspondent: Click to Email
We report on interesting chemistry of MoS@sub 2@ nanoclusters, which we show to be able to hydrogenate and break up thiophene (C@sub 4@H@sub 4@S) molecules at unusual sites on the cluster edges. We associate this behavior with one-dimensional metallic electron states located at the perimeter of the otherwise insulating nanoclusters. Since MoS@sub 2@ nanoclusters constitute the basis of hydrotreating catalysts used to remove sulfur from oil products through the hydrodesulfurization (HDS) process, the kind of chemistry identified in this work has significant implications. Our approach exploits recent progress in the synthesis of a relevant catalyst model system, i.e. we can synthesize MoS@sub 2@ nanoclusters image them on the atomic-scale with STM.@footnote 1@ With STM prominent electronic features are observed near the edges of triangular MoS@sub 2@ clusters, which are associated with 1D metallic edge states.@footnote 2@ By adsorbing hydrogen and thiophene, we pin-point, in the STM studies, active sites on these metallic edge states and reveal signatures of thiophene reaction intermediates adsorbed onto the metallic edge state. At the cluster edges, we find that S-H groups form, which are involved in a hydrogenation reaction and subsequent C-S cleavage of thiophene. In an interplay with density functional theory we elucidate the reaction pathway and classify the adsorbed species as ring-opened thiolates. We have thus identified a new route for activating a relatively inert, sulfur containing molecule like thiophene. Unexpectedly, this process does not take place through direct interaction with the Mo atoms. Instead, metallic states on the fully sulfided edges have the ability to donate and accept electrons and thus act as catalytic sites just like ordinary metal surfaces. @FootnoteText@ @footnote 1@ S. Helveg, J. V. Lauritsen et al. Phys. Rev. Lett. 84, 951 (2000).@footnote 2@ M. Bollinger, J. V. Lauritsen et al., Phys. Rev. Lett. 87, 196803 (2001).