AVS 52nd International Symposium
    Surface Science Thursday Sessions
       Session SS3-ThM

Paper SS3-ThM5
Probing Complex Adsorption Structures: A Joint Experimental and Theortical Study of Prenal Adsorbed on Pt(111) and Pt-Sn Surface Alloys

Thursday, November 3, 2005, 9:40 am, Room 203

Session: Reactivity of Bimetallic Surfaces
Presenter: J. Haubrich, University of Bonn, Germany
Authors: J. Haubrich, University of Bonn, Germany
D. Loffreda, Ecole Normale Supérieure de Lyon, France
F. Delbecq, Ecole Normale Supérieure de Lyon, France
P. Sautet, Ecole Normale Supérieure de Lyon, France
A. Krupski, University of Bonn, Germany
C. Becker, University of Bonn, Germany
K. Wandelt, University of Bonn, Germany
Correspondent: Click to Email
Studies on catalysis such as the selective hydrogenation of @alpha@,@beta@–unsaturated aldehydes on transition metal surfaces represent a challenge to both experimentalists and theoreticians. Although numerous studies have been dedicated to systems like acrolein or prenal on Pt(111) in recent years, the details of the molecule-surface bonding still remain under debate. Yet the selectivities of such processes depend crucially on the adsorption complexes. Their characterization is even more complicated when alloy surfaces are considered because alloying is often used to optimize the properties of the catalyst. We here present a joint experimental and theoretical study on molecule-surface bonding of prenal on Pt(111) and two Pt-Sn surface alloys based on the interpretation of HREEL spectra using ab initio density-functional theory (DFT). Additionally TPD and LEED studies of prenal adsorbed at 100K on these surfaces were performed. While on Pt(111) the desorption of prenal is detected at 160K (multilayer) and 199K, also fragmentation reactions are observed giving rise to desorption of H@sub 2@ and CO. On Pt@sub 2@Sn and Pt@sub 3@Sn/Pt(111) this fragmentation process is suppressed. The HREELS experiments were carried out between 100K and 500K on Pt(111) show highly complex spectra of the adsorbed prenal and its fragments, which can be detected above 300K. On both Pt-Sn surface alloys very similar HREEL spectra of prenal are recorded. Combining the HREEL spectra with the results of the vibrational analysis obtained from the DFT calculations, we are able to identify stable adsorption geometries, interpret the normal modes corresponding to the measured loss peaks and to point to likely reaction intermediates.