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Author Cremer, P. S. ♦ Su, X. ♦ Shen, Y. R. ♦ Somorjai, G. A.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword CHEMISTRY ♦ MATERIALS SCIENCE ♦ ETHYLENE ♦ HYDROGENATION ♦ ENERGY SPECTRA ♦ REACTION INTERMEDIATES ♦ ABUNDANCE ♦ PLATINUM ♦ VIBRATIONAL STATES ♦ CHEMICAL REACTION KINETICS ♦ PRESSURE DEPENDENCE
Abstract Infrared-visible sum frequency generation (SFG) has been used to monitor the surface vibrational spectrum in situ during ethylene hydrogenation on Pt(111). Measurements were made near 1 atm of total pressure of ethylene and hydrogen and at 395 K. Kinetic information was obtained simultaneously with the surface vibrational spectroscopy by monitoring the reaction rate with gas chromatography. The macroscopic turnover rate and surface adsorbate concentration could then be correlated. During the reaction ethylidyne, di-{sigma}-bonded ethylene, ethyl, and {pi}-bonded ethylene were observed on the surface in various amounts depending on conditions. Ethylidyne, a spectator species during hydrogenation, competed directly for sites with di-{sigma}-bonded ethylene and its surface concentration could be shown to be completely uncorrelated with the rate of hydrogenation. In contrast, {pi}-bonded ethylene did not compete for sites with the ethylidyne overlayer and was observed on the surface regardless of the surface concentration of ethylidyne. Evidence points to the {pi}-bonded species as being the primary intermediate in ethylene hydrogenation on Pt(111). The surface concentration of this species is about 0.04 ML (ML = monolayer) during reaction. Thus, the turnover rate per reaction intermediate is 25 times faster than the turnover rate if measured per surface platinum atom. 30 refs., 11 figs.
ISSN 00027863
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-03-27
Publisher Place United States
Journal Journal of the American Chemical Society
Volume Number 118
Issue Number 12


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