AVS 47th International Symposium
    Surface Science Thursday Sessions
       Session SS2+VT-ThM

Paper SS2+VT-ThM7
Reactions of cis-, trans-, and 1,1-dichloroethene on Pd(111) Studied by TDS, LITD, and STM

Thursday, October 5, 2000, 10:20 am, Room 209

Session: Adsorption and Desorption Phenomena II
Presenter: D.P. Land, University of California, Davis
Authors: D.E. Hunka, University of California, Davis
D.M. Jaramillo, University of California, Davis
D.C. Herman, University of North Carolina, Chapel Hill
K.D. Lormand, University of California, Davis
D. Futaba, University of California, Davis
S. Chiang, University of California, Davis
D.P. Land, University of California, Davis
Correspondent: Click to Email
Chloroethylenes are the among the most abundant groundwater and soil contaminants. Catalytic degradation on transition metal surfaces offers a promising method for the alleviation of this ubiquitous problem. Large differences in the reaction rates of the various compounds have been observed. However, little is known about the reaction mechanisms or the origin of these rate differences. In aqueous solutions, for example, cis-dichloroethylene (cis-DCE) reacts an order of magnitude more slowly on Fe than do trans- or 1,1-DCE. The reactivities do not follow any monotonic trends in dipole, solubility, or bond strength. Addition of Pd to Fe catalysts has been shown to increase the rate of reaction for some of these species by orders of magnitude. We have undertaken to study the reactivity of the three isomers of DCE on Pd(111). As in aqueous solution, the cis isomer reacts very differently from the other two isomers. Decomposition on Pd(111) occurs below room temperature and H@sub 2@ is evolved with C and Cl remaining on the surface to very high temperatures. In contrast, both trans- and 1,1-DCE rearrange to yield chlorinated intermediates that decompose in two steps above room temperature liberating HCl. Some subtle differences exist in the reaction mechanisms, but both are drastically different from the cis isomer. Laser-induced thermal desorption and conventional thermal desorption with FT mass spectrometry, infrared spectroscopy, scannin tunneling microscopy and other surface techniques are used to elucidate the surface reaction mechanisms and energetics.