AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM3
Dissociative Adsorption of Cyclohexene on Pt(111) at 300 K studied by Single-Crystal Microcalorimetry and Sticking Probability Measurements

Tuesday, November 4, 2003, 9:00 am, Room 327

Session: Catalysis II: Hydrocarbons at Metal Surfaces
Presenter: H. Ihm, University of Washington
Authors: H. Ihm, University of Washington
H.M. Ajo, University of Washington
D.E. Moilanen, University of Washington
C.T. Campbell, University of Washington
Correspondent: Click to Email
The dehydrogenation reaction of cyclohexene to benzene on platinum surfaces is of fundamental interest due to the importance of the surface chemistry occurring in hydrocarbon conversion. There have been many studies to understand its reaction, mechanism, energetics, and kinetics using experimental and theoretical methods. They agree that cyclohexene on Pt(111) converts to cyclohexenyl between 200-250 K and further converts to benzene between 300-350 K.@footnote 1,2@ There have been studies to estimate reaction (activation) energies from cyclohexene to cyclohexenyl or benzene, but these were in a limited coverage regime and either by indirect experimental measurements or by theoretical calculation.@footnote 1,3@ Here, we report direct calorimetric measurements of the heats of reactive adsorption of cyclohexene on Pt(111) at 300 K as a function of coverage. These calorimetry measurements were performed by using a pyroelectric detector and a pulsed cyclohexene molecular beam impinging onto a 1 µm thick Pt(111) sample. We also measured the sticking probability as a function of coverage. The sticking probability is initially high (0.86) and stays constant up to 0.7 ML then decreases linearly to 0 at 1 ML. The flux of the cyclohexene molecular beam was measured with a liquid-nitrogen cooled quartz crystal microbalance. Work supported by NSF. @FootnoteText@@footnote 1@ F.C. Henn, A.L. Diaz, M.E. Bussell, M.B. Hugenschmidt, M.E. Domagala, and C.T. Campbell, J. Phys. Chem. 1992, 96, 5965-5974. @footnote 2@ W.L. Manner, G. S. Girolami, and R.G. Nuzzo, J. Phys. Chem. B 1998, 102, 10295-10306.@footnote 3@ B.E. Koel, D.A. Blank, and E.A. Carter, J. Molecular Catal. A: Chemical 131 (1998) 39-53.