AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoM

Paper SS2-MoM3
Thermal Conversion of C@sub 3@ Fragments on Pt(111): Evidence for the Formation of Allylic Intermediates

Monday, October 25, 1999, 9:00 am, Room 607

Session: Catalysis on Metals
Presenter: F. Zaera, University of California, Riverside
Authors: D. Chrysostomou, University of California, Riverside
C.R. French, University of California, Riverside
J.M. Guevremont, University of California, Riverside
F. Zaera, University of California, Riverside
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Platinacyclobutane was selectively formed on Pt(111) via the thermal activation of adsorbed 1,3-diiodopropane, and the mechanism for its conversion to propene was investigated using temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). Thermal desorption of propene from 1,3-diiodopropane occurs at 370 K. The conversion is suggested to involve the formation of a surface bound allylic intermediate. Allyl iodide was used to investigate the further reactivity of that intermediate, and additional experiments were carried out with propyl iodide and propylene as well. Selective deuteration of 1,3-diiodopropane was explored as a mean to determine the C'H bonds active in the metallacycle to propene conversion, but the usefulness of this approach was limited by extensive scrambling in platinacyclobutane prior to the formation of propene. Propene itself was identified to exist on the surface in three different configurations depending on the coverage: di-sigma bonded, pi bonded, and weakly physisorbed. The results from this work provide new insights into the mechanism of hydrocarbon reforming reactions.