IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Thursday Sessions
       Session SS1-ThA

Paper SS1-ThA8
Catalytic Oxidation of Propylene on Stepped Pt(411): In-situ Mechanistic Studies Over an Extended Pressure Range

Thursday, November 1, 2001, 4:20 pm, Room 121

Session: Catalysis on Model Systems
Presenter: H.D. Lewis, University of Michigan
Authors: H.D. Lewis, University of Michigan
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
Correspondent: Click to Email
Surface defects play an important role in reactivity by, for example, lowering activation barriers for dissociation and increasing the bonding energy of adsorbed species. In this work the catalytic oxidation of preadsorbed propylene has been studied in oxygen pressures up to 0.01 Torr on the stepped Pt(411) surface. Using a combination of kinetic and spectroscopic in-situ fluorescence yield soft x-ray techniques we have characterized the oxidation of propylene. In pressures of oxygen, propylene is completely oxidized by 475 K with oxydehydrogenation preceding skeletal oxidation. The 280 K initiation temperature for oxydehydrogenation is independent of oxygen pressure. The temperature where skeletal oxidation begins decreases from 315 K in 0.0005 Torr oxygen to 300 K in 0.02 Torr oxygen. In the temperature range between oxydehydrogenation and skeletal oxidation a reaction intermediate has been spectroscopically characterized. In-situ catalytic oxidation studies with both propylene and oxygen in the gas phase were also studied. With increasing oxygen pressure the concentration of carbon containing surface species decreases showing competitive adsorption. In this catalytic environment, the onset temperature for deep oxidation decreases with increasing oxygen pressures. Taken together, these results suggest that the inhibition of oxygen adsorption is important in limiting this complex reaction system. This new molecular understanding provides a basis for elucidating the mechanism of this complex surface reaction network.