AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS2-ThM

Paper SS2-ThM9
Lateral Interactions in the Kinetics of Surface Reactions

Thursday, November 6, 2003, 11:00 am, Room 327

Session: Catalysis III: High vs. Low Pressures
Presenter: D.L.S. Nieskens, Eindhoven University of Technology, The Netherlands
Authors: D.L.S. Nieskens, Eindhoven University of Technology, The Netherlands
D. Curulla Ferre, Eindhoven University of Technology, The Netherlands
A.P. van Bavel, Eindhoven University of Technology, The Netherlands
J.W. Niemantsverdriet, Eindhoven University of Technology, The Netherlands
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The rate of a chemical reaction on a surface depends strongly on the presence of neighboring adsorbate species. As lateral interactions between adsorbates are predominantly repulsive, their effect becomes notable at highly covered surfaces. Lateral interactions can change the kinetic parameters (the activation energy and the pre-exponential factor) of a reaction. A change in these kinetic parameters can cause a reaction to occur at a different temperature or pressure. Lateral interactions can even enable a certain reaction pathway which otherwise would be inaccessible. Our goal is first to quantitate these lateral interactions, and second to make good use of them in enabling new reaction pathways. For this we do experiments on single crystal surfaces. We use a combination of techniques: Temperature Programmed Desorption (TPD), Static Secondary Ion Mass Spectrometry (SSIMS), Low Energy Electron Diffraction (LEED) and High Resolution Electron Energy Loss Spectroscopy (HREELS). Using this combination of techniques we obtain a complete picture of the concentration of species, both in the gas phase as well as on the surface. Furthermore we can detect any ordering that occurs on the surface. In addition to the experimental work we also performed Density Functional Theory (DFT) calculations on the same kind of systems. Our strategy for determining lateral interactions is to find ordered structures of an adsorbate A on the surface, then co-adsorb a species B and determine the effect of A on the desorption of this species B. By using an ordered structure of adsorbate A, we are able to "count" the number of "A-neighbors" of the desorbing species B and thus assign the total interaction energy to a known number of neighbors. This enables us to quantify the lateral interaction energy between adsorbate A and B. The energies acquired by the experiments are quite consistent with the ones determined by the computational approach.