AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoA

Paper SS2-MoA7
Propylene Oxidation on the Pt (111) Surface over an Extended Range of Coverages

Monday, November 2, 1998, 4:00 pm, Room 309

Session: Surface Chemistry on Model Catalysts
Presenter: A.M. Gabelnick, University of Michigan
Authors: A.M. Gabelnick, University of Michigan
J.T. Sipowska, University of Michigan
J.L. Gland, University of Michigan
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The reactions of propylene and oxygen coadsorbed on the Pt (111) surface have been characterized over an extended range of coverages using TPRS. Unexpected modification of the oxidation process is observed for high coadsorbed coverages. Initiation of propylene oxidation results in water formation at 200K which appears to involve abstraction of the acid methyl hydrogens. This low temperature reaction becomes increasingly important for high coadsorbed coverages suggesting that direct interaction between propylene and coadsorbed atomic oxygen may play an important role for high coadsorbed coverages. For the highest coadsorbed coverages and excess propylene we were surprised to observe acetone and acetic acid partial oxidation products. Large coverages of coadsorbed propylene also cause the formation of a new low temperature molecular oxygen peak at 140 K. For both coadsorbed molecular and atomic oxygen, the primary products observed are water, carbon dioxide, and carbon monoxide. Following initial water formation near 200 K, the dominant water peak appears at 300 K over the entire range of coverages. Further increase in temperature results in carbon dioxide formation at 350K. Oxidation of propylidyne has a larger activation energy and occurs in one step at 370K. At higher temperatures further propylidyne oxidation and decomposition resembles that of propylene. Large coadsorbed coverages result in low temperature reaction and modified reaction selectivities.