AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM6
Thermal Production of Phosgene from Carbon Tetrachloride Reactions on Natural Single Crystal @alpha@-Fe@sub 2@O@sub 3@ Surfaces in Ultrahigh Vacuum

Tuesday, October 3, 2000, 10:00 am, Room 208

Session: Reactions on Oxides and Environmental Chemistry
Presenter: K. Adib, Columbia University
Authors: K. Adib, Columbia University
N. Camillone III, Columbia University
J.P. Fitts, Columbia University
D. Mocuta, Columbia University
K.T. Rim, Columbia University
G.W. Flynn, Columbia University
R.M. Osgood, Jr., Columbia University
S.A. Joyce, Pacific Northwest National Laboratory
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Oxides of iron have important applications as catalysts and reactive sites for various classes of chemical reactions. They have a significant environmental role in the speciation of toxic metal cations and the dehalogenation of halocarbons. This environmental role is important due to the abundance of iron oxides in the Earth's crust and due to their higher reactivity compared to other metal oxides. We use ultrahigh vacuum for a detailed study of the chemistry of a well-characterized surface of @alpha@-Fe@sub 2@O@sub 3@ (hematite). Natural single crystal samples of hematite were cut and polished in the (0001) orientation. They were processed in-situ to produce a surface selvedge of Fe@sub 3@O@sub 4@ 2x2 reconstruction, as verified by LEED, and dosed at ~100K with CCl@sub 4@. The surface reactions were studied by temperature-programmed desorption (TPD). The multiplicity of desorption waves observed indicates a complex chemistry involving molecular adsorption and dissociative adsorption on at least two distinct kinds of surface site. The TPD results indicate the formation of COCl@sub 2@ (phosgene) as well as C@sub 2@Cl@sub 4@ and high temperature desorption of iron chlorides. We observe significant differences in the TPD spectrum following the first dosing of the surface as compared to those measured following subsequent dosings indicating a marked change in the surface upon initial exposure. This change is commensurate with the titration of surface defects during the initial reaction stages. Preliminary measurements of the UV photochemistry of the adsorbed CCl@sub 4@ on this surface will be presented.