AVS 54th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP9
Low Temperature Microcalorimetry to Measure the Heat of Adsorption of Cyclohexene, Cis and Trans 2-Butene on Pt(111)

Tuesday, October 16, 2007, 6:00 pm, Room 4C

Session: Surface Science Poster Session
Presenter: W. Lew, University of Washington
Authors: O. Lytken, University of Washington
W. Lew, University of Washington
J.W. Harris, University of Washington
E.K. Vestergaard, University of Washington
C.T. Campbell, University of Washington
Correspondent: Click to Email

The hydrogenation and dehydrogenation of cyclic hydrocarbons and short chain alkenes on platinum catalysts are important petrochemical reactions. We have used low temperature microcalorimetry measurements to determine their enthalpy of adsorption and sticking probability on Pt(111) at 100 K. Cyclohexene adsorbs intact at surface temperatures below 180 K, but decomposes at higher temperatures via several intermediates, including benzene and hydrogen starting at ~300 K. Trans-butene adsorbs intact below 200 K and cis butane adsorbs intact below 230 K. The difference between the heat of adsorption energy of the two isomers is compared with results from Zaera et al.[1] Since cyclohexene and butene both adsorb irreversibly on platinum, the traditional method to measure adsorption enthalpies, Temperature Programmed Desorption (TPD), cannot be used. Low temperature microcalorimetry makes it possible to measure the heats of formation of important reaction intermediates that are frequently unstable at room temperature. One of the major challenges of conducting low temperature calorimetric studies for small heats of adsorption is getting the microcalorimeter to detect small temperature changes on the order of 10 milliKelvins with minimal noise. This study explores modifications to the microcalorimetry apparatus to detect small adsorption energies.

1. Ilkeun Lee, I., Zaera, F. J. Amer. Chem. Soc. 2005, 127, 12174.