AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM4
The Reaction of 1-chloro-2-methyl-2-propanol (Cl@super t@BuOH)on Oxygen-covered Ag(110): C-Cl Bond Cleavage in Epoxide Formation

Tuesday, November 4, 2003, 9:20 am, Room 327

Session: Catalysis II: Hydrocarbons at Metal Surfaces
Presenter: H. Piao, Brookhaven National Laboratory
Authors: H. Piao, Brookhaven National Laboratory
K. Adib, Brookhaven National Laboratory
M. Enever, University of Delaware
Z. Chang, Brookhaven National Laboratory
D.R. Mullins, Oak Ridge National Laboratory
J. Hrbek, Brookhaven National Laboratory
M.A. Barteau, University of Delaware
Correspondent: Click to Email
Synchrotron-based Temperature Programmed X-ray Photoelectron Spectroscopy in combination of Temperature Programmed Desorption has been used to explore the C-Cl scission in the reaction of Cl@super t@BuOH on oxygen-covered Ag(110) surface to produce isobutylene oxide (IBO). Although the C-Cl bond cleavage is involved in the rate-determining step for the evolution of IBO, the mechanism was not fully understood. This motivated the surface reaction mechanism study to determine whether the surface chlorohydrin reaction follows an S@sub N@1 reaction or a concerted S@sub N@2 path. Using experimental data we also developed a kinetic model for surface reaction chemistry. The combination of experimental and theoretical results indicates that Cl@super t@BuO decomposition does not occur by an S@sub N@2 process that releases IBO directly into the gas phase. Instead, C-Cl scission deposits organic intermediates or products on the surface, and that the appearance of these products in the gas phase lags the appearance of atomic chlorine on the surface. Therefore, we can conclude that the production of IBO is the result of a process involving two kinetically significant steps: C-Cl scission that deposits Cl atoms and IBO molecules on the Ag(110) surface followed by desorption of molecularly adsorbed IBO. Low barrier and pre-exponential for the second step on the high coverage surface indicate that the rate of C-Cl scission may be influenced by other factors, e.g., the availability of surface adsorption sites for Cl adatoms.