AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM7
Molecular Mechanisms of Propylene Adsorption and Oxidation on the Stepped Pt(411) Surface

Tuesday, November 5, 2002, 10:20 am, Room C-108

Session: Hydrocarbon Catalysis
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
The influence of surface defects on the chemistry of propylene adsorption and oxidation was investigated using temperature-programmed reaction spectroscopy (TPRS) and in-situ fluorescence yield soft x-ray techniques on the stepped Pt(411) surface. Mass spectrometer based TPRS studies show that propylene adsorbed on Pt(411) at 100 K undergoes disproportionation and decomposition to propylene, propane, hydrogen and surface carbon. Reacting coadsorbed propylene with excess oxygen, complete oxidation occurs with oxydehyrdogenation to water preceding skeletal oxidation to carbon dioxide. Based on the qualitative mechanistic understanding from TPRS, in-situ oxidation experiments were performed in oxygen pressures up to 0.02 Torr. The mechanism is the same in flowing oxygen, and preadsorbed propylene is completely oxidized by 475 K. The 280 K initiation temperature for oxydehydrogenation is independent of oxygen pressure, while the initiation temperature for skeletal oxidation is oxygen pressure dependent beginning at 370 K in 1 x 10@super-5@ Torr oxygen and decreasing to 300 K in 0.02 Torr oxygen. A stable intermediate is observed after oxydehydrogenation is complete. The molecular mechanism for propylene oxidation on Pt(411) with both propylene and oxygen in the gas phase was also studied. With increasing oxygen pressure less propylene is adsorbed and the onset temperature for deep oxidation decreases. Taken together, results indicate that the inhibition of oxygen adsorption is important in limiting this complex oxidation reaction. Results for propylene oxidation on this stepped surface are compared to studies on Pt(111) to delineate the role of surface defects in this interesting surface reaction network.