IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Thursday Sessions
       Session SS1-ThA

Paper SS1-ThA3
Atomic-scale STM Study of Model Catalysts for Hydrodesulfurization

Thursday, November 1, 2001, 2:40 pm, Room 121

Session: Catalysis on Model Systems
Presenter: J.V. Lauritsen, University of Aarhus, Denmark
Authors: J.V. Lauritsen, University of Aarhus, Denmark
S. Helveg, Haldor Topsoe Research Laboratories, Denmark
B.S Clausen, Haldor Topsoe Research Laboratories, Denmark
H. Topsoe, Haldor Topsoe Research Laboratories, Denmark
F. Besenbacher, University of Aarhus, Denmark
Correspondent: Click to Email
Using scanning tunneling microscopy (STM),@footnote 1@ we have recently attained novel atomic-scale information on model catalysts for hydrodesulfurization (HDS), an area that currently receives world-wide attention due to new environmental legislations regarding the sulfur content in fuel. The HDS activity is related to MoS@sub 2@-like nanoclusters promoted with Co atoms located near the edges. Controversy has, however, prevailed since traditional spectroscopy techniques provide no conclusive information regarding the cluster morphology, catalytically relevant edge structures, active sites or promotional effect of Co. We have successfully synthesized ~30Å wide single-layer MoS@sub 2@ clusters on an inert Au(111) substrate as a model system for HDS catalysts. High resolution STM images display an unprecedented view of the atomic details of the MoS@sub 2@ nanoclusters, which contrary to expectations exhibit a triangular morphology. We have also been able to resolve the structures of the catalytically active edges, and from interplay with DFT theoretical calculations we have determined the detailed atomic-scale structure.@footnote 1,3@ The STM images reveal spectacular electronic features near the edge of the triangles, which with input from theory can be associated with electronic edge states. When the MoS@sub 2@-based catalysts are promoted with Co, the STM images directly show a morphological transition from triangular to hexagonally truncated structures. This is driven by a preference for Co to be located at only one type of MoS@sub 2@ edges.@footnote 2@ We are currently investigating the interaction with thiophene, a typical sulfur containing molecule, and preliminary STM results indicate a strong bonding of the molecules to the cluster edges. @FootnoteText@ @footnote 1@ S. Helveg, J.V. Lauritsen et al., Phys. Rev. Lett. 84, 951 (2000) @footnote 2@ J.V. Lauritsen et al. J. Catal. 197, 1 (2001) @footnote 3@ M. Bollinger, J.K. Norskov, private communication.