AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP19
The Decomposition of Ethylene on Rhodium(100): Theory and Experiments

Wednesday, November 5, 2003, 11:00 am, Room Hall A-C

Session: Poster Session
Presenter: A.P. Bavel, Eindhoven University of Technology, The Netherlands
Authors: A.P. Bavel, Eindhoven University of Technology, The Netherlands
D.L.S. Nieskens, Eindhoven University of Technology, The Netherlands
D. Curulla Ferre, Eindhoven University of Technology, The Netherlands
J.W. Niemantsverdriet, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
Hydrocarbon decomposition into C@sub x@H@sub y@ fragments is of great importance for understanding catalytic reactions of these species. We investigate the decomposition pathway of ethylene on the rhodium(100) surface, both on a clean surface and on a hydrogen presaturated surface. We use different experimental techniques: Temperature Programmed Desorption (TPD), Static Secondary Ion Mass Spectrometry (SSIMS), Low Energy Electron Diffraction (LEED) and High Resolution Electron Energy Loss Spectroscopy (HREELS). It is known from literature that ethylene decomposition starts already at low temperatures (<200 K) and continues up to 700 K to give C on the surface. The nature of the intermediate species has been shown to depend on the amount of presaturated hydrogen. Several authors have shown, by using HREELS, the presence of CCH@sub 3@ species in an upright position and CCH species in a "bent" mode.@footnote 1,2,3@ Our LEED experiments indicate a p(2x2) structure for a saturation dosage of ethylene, implying a saturation coverage of 0.25 ML. The TPD spectra show a complicated pattern for the hydrogen desorption. We can distinguish several decomposition limited desorption processes for hydrogen. SIMS measurements show that CCH and CHCH species are present at relatively low temperatures. Some preliminary HREELS experiments in specular and off-specular mode have already been performed. In addition to the experiments we have used periodic DFT calculations to calculate the energy of all possible C@sub x@H@sub y@ species on the Rh(100) surface. We have used a p(2x2) unit cell in the calculations, thus mimicking a saturation coverage of ethylene. The calculations show that CCH@sub 3@ and CCH are the most stable species, in accordance with literature. We have also found, however, that the CHCH species is even more stable. At higher temperatures these species will decompose further into CH and finally carbon. @FootnoteText@@footnote 1@Slavin, A.J., Bent, B.E., Kao, C.T. and Somorjai, G.A., Surface Science 206 (1988) 124-144. @footnote 2@Kose, R., Brown, W.A. and King, D.A., Chemical Physics Letters 311 (1999) 109-116. @footnote 3@Egawa, C., Surface Science 454-456 (2000) 222-226.