| AVS 56th International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS2-TuM |
| Session: | Reactions on Metals and Bimetallics |
| Presenter: | C. Breinlich, University of Bonn, Germany |
| Authors: | M. Moors, University of Bonn, Germany C. Breinlich, University of Bonn, Germany T. Kobiela, Warsaw University of Technology, Poland C. Becker, University of Bonn, Germany K. Wandelt, University of Bonn, Germany |
| Correspondent: | Click to Email |
Investigations of bimetallic systems with regard to their surface composition, morphology and adsorption properties for reactive gases are essential for the development of new catalysts with higher efficiency and durability. An interesting catalytic reaction is the partial hydrogenation of butadiene to 1-butene without complete hydrogenation to butane and the coking of the catalyst due to decomposition of the educt. In this work the hydrogenation of butadiene has been investigated on bimetallic Sn-Pd(111) and Au-Pd(111) surface alloys by means of Ultraviolet Photoelectron Spectroscopy (UPS) and Temperature Programmed Desorption (TPD). The bimetallic surfaces were prepared by depositing Sn or Au onto a clean Pd(111) surface followed by controlled annealing. Annealing an at least 4 ML thick Sn film to 750 K results in an ordered p(2x2) Pd3Sn surface alloy as evidenced by Low Energy Electron Diffraction (LEED). Further annealing to 850 K leads to the formation of the thermodynamically more stable (√3x√3)R30° Pd2Sn surface alloy. After annealing to 1000 K all Sn has diffused into the Pd(111) substrate. No ordered alloy phase has been found for the Au-Pd system. Annealing to temperatures gradually higher then 450 K leads to a continuous decrease of the Au surface concentration until at 1050 K Au has completely disappeared into the bulk. Under UHV conditions the Sn-Pd(111) alloy surfaces exhibit a lower hydrogenation rate of butadiene in comparison to the pure Pd(111) surface. The butene production strongly decreases with increasing Sn amount at the surface. This decreasing reactivity, however, is accompanied by an increasing selectivity and decreasing coking of the surface. Alloying Pd with Au on the other hand results in a significantly improved reactivity towards butene compared to pure Pd(111), while the selectivity is only slightly decreased. Furthermore, the coking of the Au-Pd(111) surface is even lower than observed on pure Pd(111), which makes this system a promising hydrogenation catalyst.