AVS 46th International Symposium
    Surface Science Division Friday Sessions
       Session SS2-FrM

Paper SS2-FrM9
In-Situ Soft X-ray Studies of Acetylene Oxidation on the Pt(111) Surface

Friday, October 29, 1999, 11:00 am, Room 607

Session: Adsorption on Metals and Silicon
Presenter: D.J. Burnett, University of Michigan
Authors: D.J. Burnett, University of Michigan
A.M. Gabelnick, University of Michigan
D.A. Fischer, National Institute of Standards and Technology
J.L. Gland, University of Michigan
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In-situ studies of acetylene oxidation have been performed using Fluorescence Yield Soft X-ray methods for temperatures up to 600 K and pressures up to 0.01 torr. Absolute carbon coverages have been determined in steady-state and dynamic conditions on the Pt(111) surface over an extended pressure and temperature range using in-situ soft X-ray methods. Transient surface concentration measurements were used during these in-situ studies to provide direct measurement of surface reaction rates. Temperature-programmed oxidation of preadsorbed acetylene monolayers (TP-FYNES) on the Pt(111) surface was conducted in oxygen pressures up to 0.01 torr. Acetylene remains on the surface until skeletal oxidation occurs around 350 K, depending on the oxygen pressure. The onset temperature for skeletal oxidation decreased slightly with increasing oxygen pressures. Transient experiments with both acetylene and oxygen in the gas phase were performed over a wide range of pressures and temperatures. Further, detailed mechanistic studies were performed yielding a substantial amount of high quality kinetic rate data. These kinetic studies, coupled with the TP-FYNES results suggest a mechanism limited by C-H bond activation. In addition to the transient studies above, detailed spectroscopy was accomplished via in-situ, soft X-ray fluorescence yield methods to identify the dominant oxidation intermediates. Both acetylene and ethylene oxidation appear to involve the same surface intermediates since both processes are limited by the same rate-determining step. In both instances, oxidation intermediates have been identified and characterized using in-situ fluorescence yield methods.