AVS 52nd International Symposium
    Surface Science Monday Sessions
       Session SS-MoP

Paper SS-MoP12
Adsorption and Hydrogenation of 1,3-butadiene on Pd(111) and Pd-Sn/Pd(111) Surface Alloys

Monday, October 31, 2005, 5:00 pm, Room Exhibit Hall C&D

Session: Surface Science Poster Session
Presenter: Chr. Breinlich, University of Bonn, Germany
Authors: Chr. Breinlich, University of Bonn, Germany
J. Haubrich, University of Bonn, Germany
C. Becker, University of Bonn, Germany
K. Wandelt, University of Bonn, Germany
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The selective hydrogenation of dienes into mono-olefines is an important industrial reaction. Industrial processes are usually carried out with supported catalysts containing transition metals such as palladium or platinum. Palladium shows a high activity and selectivity for these reactions. Therefore we have studied the adsorption and hydrogenation of 1,3-butadiene on Pd(111) and Sn-modified Pd(111) surfaces. The Pd-Sn surface alloys were produced by annealing of tin layers of various thicknesses. Depending on the amount of deposited tin this procedure actually resulted in ordered surface alloys of (@sr@3x@sr@3)R30° or p(2x2) superstructure, which were characterized by LEED, AES and UPS. The adsorption and reaction of 1,3-butadiene was investigated by TPD. After 1,3-butadiene adsorption at 55 K the desorption of the multilayer was found near 120 K on all surfaces. Further heating lead to the complete dehydrogenation of the butadiene on the Pd(111) surface. On the surface alloys only a part of the butadiene dehydrogenates while the rest desorbs at 200 - 230 K. By preadsorbing either hydrogen or deuterium the 1,3-butadiene can be partially hydrogenated to butene on the surface alloys. The partial hydrogenation is highly selective since no desorption of butane has been found. The branching ratio of desorption vs. hydrogenation on the surface alloys is clearly a function of the amount of tin, which was deposited and, hence, the surface stoichiometry. HREELS investigations reveal the adsorption modes of 1,3-butadiene and butene on these surfaces.