AVS 52nd International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM11
Catalytic Hydrodechlorination of Chlorobenzene and Chlorotoluene Isomers on the Pt(111) Surface

Monday, October 31, 2005, 11:40 am, Room 202

Session: Catalytic Chemistry of Hydrocarbons
Presenter: B.M. Haines, University of Michigan
Authors: B.M. Haines, University of Michigan
D.A. Fischer, National Institute of Standards and Technology
J.L. Gland, University of Michigan
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The catalytic hydrodechlorination of chlorobenzene on the Pt(111) surface has been characterized using temperature programmed reaction spectroscopy (TPRS) and fluorescence yield near edge spectroscopy (FYNES) above the carbon K edge. Thermal hydrodechlorination, dehydrogenation and rehydrogenation result in the formation of benzene, HCl, and H@sub 2@ when chlorobenzene is heated on platinum. The effects of methyl substituents on hydrodechlorination were probed using the isomers of chlorotoluene. The chlorobenzene monolayer adsorbs on the Pt(111) surface with the plane of the ring at a 45° angle from the surface as indicated by FYNES. The monolayer partially desorbs at 196 K and the remaining chlorobenzene then undergoes dechlorination via two reaction channels at 270 K and at 420 K as shown by TPRS. Comparison of the integrated peak areas for these two channels yields a 3:2 (270 K: 420 K) ratio. Temperature programmed-FYNES show that a stable cyclohexadiene intermediate is formed above 250 K that is coadsorbed in a 3:2 ratio with molecular chlorobenzene. The remaining molecular chlorobenzene is dechlorinated in the 420 K range to form additional adsorbed cyclohexadiene. For chlorotoluene, substituent effects dominate activation of the C-Cl bond through the ring and dehydrogenation of the methyl group at low temperatures.