Regensburg 2010 – scientific programme
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O: Fachverband Oberflächenphysik
O 56: Metal substrates: Adsorption of organic / bio molecules VI
O 56.10: Talk
Wednesday, March 24, 2010, 17:15–17:30, H36
Nanojoule Calorimetry of Surface Reactions: Cyclohexene on Pt(111) — •Ole Lytken1,2, Wanda Lew1, Jonathan J.W. Harris1, Ebbe K. Vestergaard1, J. Michael Gottfried2, and Charles T. Campbell1 — 1Department of Chemistry, University of Washington, Seattle, WA, USA — 2Lehrstuhl für Physikalische Chemie II, Universität Erlangen-Nürnberg, Erlangen, Germany
Platinum is an excellent hydrogenation/dehydrogenation catalyst. Many hydrocarbons therefore readily dehydrogenate on platinum instead of desorbing. This severely limits the usefulness of traditional desorption based techniques for measuring heats of adsorption, such as temperature programmed desorption (TPD). Cyclohexene on Pt(111) is a typical such system where reaction prevails over desorption. At 100 K cyclohexene adsorbs intact, but with increasing temperature, it dehydrogenates, forming first a partially dehydrogenated 1-cyclohexenyl species, then benzene and eventually graphite. However, unlike TPD, single-crystal microcalorimetry does not rely upon desorption and can therefore directly measure the heats of adsorption and reaction of the wealth of species formed as hydrocarbons adsorb on platinum. We have used microcalorimetry to successfully measure the heat of adsorption of cyclohexene on Pt(111) at 100 - 300 K and determined the heats of formation as a function of coverage of two adsorbed intermediates in the hydrogenation of benzene to cyclohexane, namely cyclohexene and 1-cyclohexenyl.