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

Paper SS1-TuM5
Adsorption of S and Cl on TiO@sub 2@(110) Studied by Ultra-violet Photoelectron Spectroscopy

Tuesday, October 3, 2000, 9:40 am, Room 208

Session: Reactions on Oxides and Environmental Chemistry
Presenter: C.A. Ventrice, Jr., University of New Orleans
Authors: E.L.D. Hebenstreit, Tulane University
W. Hebenstreit, Tulane University
U. Diebold, Tulane University
H. Geisler, Xavier University
D.A. Hite, Louisiana State University
P.T. Sprunger, Louisiana State University
S.N. Thornburg, University of New Orleans
C.A. Ventrice, Jr., University of New Orleans
Correspondent: Click to Email
One of the most severe poisonings of metal and metal oxide catalytic systems is induced by sulfur contamination. In order to obtain a better knowledge of the mechanism for contamination of catalysts at a microscopic level, an ultra-violet photoelectron spectroscopy (UPS) study of the adsorption of elemental S and Cl on reduced TiO@sub 2@(110) surfaces has been performed. A previous study of the adsorption of S on TiO@sub 2@(110) has shown that a variety of overlayer structures can be obtained, depending on the temperature of adsorption.@footnote 1@ Below ~120 °C, S adsorbs preferentially on the exposed Ti rows and forms a weakly ordered overlayer. Above ~120 °C, there is a change in the S adsorption site from on top of the Ti rows to a replacement of the surface O. UPS measurements show that the surface defect state of the reduced TiO@sub 2@ substrate is quenched upon adsorption of S at RT. In addition, there is a shift of 0.4 eV in the valence emission to lower binding energy that results from an "un-bending" of the valence band. Adsorption of S at ~350 °C results in an enhancement of the surface defect state and the appearance of new emission features within the band gap of the TiO@sub 2@. Both the defect state and the emission features within the band gap resonate at the Ti 3p to 3d absorption threshold. A shift in the Ti 3p core emission of ~0.5 eV to lower binding energy and a reduction in the O 2s emission are also observed. These results indicate that there is an increase in the population of Ti 3d states from a loss of surface O. Cl adsorption at RT behaves similarly to S with a quenching of the surface defect state and a 0.4 eV shift of the valence band. Although adsorption of Cl at 200 °C results in an enhancement of the surface defect state, no new emission features are observed within the band gap of the TiO@sub 2@. @FootnoteText@ @footnote 1@ E. L. D. Hebenstreit, W. Hebenstreit, and U. Diebold, Surf. Sci. (in press).