IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Thursday Sessions
       Session SS1-ThA

Paper SS1-ThA4
A Temperature Programmed Desorption Study of Propene Adsorption on Gold Islands Dispersed on TiO@sub 2@(110)

Thursday, November 1, 2001, 3:00 pm, Room 121

Session: Catalysis on Model Systems
Presenter: H.M. Ajo, University of Washington
Authors: H.M. Ajo, University of Washington
V.A. Bondzie, University of California at Riverside
C.T. Campbell, University of Washington
Correspondent: Click to Email
The adsorption of propene on TiO@sub 2@(110) and on gold islands dispersed on TiO@sub 2@(110) [Au/TiO@sub 2@(110)], both at 120 K, has been studied using temperature programmed desorption (TPD), x-ray photoelectron spectroscopy(XPS) and low energy ion scattering spectroscopy (LEIS). Propene adsorbs on both TiO@sub 2@(110) and Au/TiO@sub 2@(110), with desorption peak temperatures of ~190 and ~240 K, respectively, for tiny doses of propene. When only 17% of the TiO@sub 2@(110) surface is covered by gold islands [17% Au/TiO@sub 2@(110)], moderate propene doses populate both the 240 and 190 K TPD peaks, in that order. Since both the dose of propene needed to saturate the 240 K peak and its peak area increase with the gold island coverage, the desorption peak at 240 K is attributed to propene adsorbed at the edges of gold islands. This feature is also seen at about this same temperature even when the gold islands are only one atom thick. Temperature-dependent LEIS results suggest that this propene binds to both a gold island edge and a titanium site. Tiny doses of propene to the 17% Au/TiO@sub 2@(110) surface give the 240 K TPD peak but no 190 K feature. This shows that all of the propene desorbs from these island edge sites. Since some propene molecules must initially physisorb on TiO@sub 2@(110) sites, but no propene molecules desorb from these sites during TPD, the propene must be mobile enough on the TiO@sub 2@(110) surface, either at the dosing temperature or during TPD, to migrate to the gold island edge before desorption (i. e., below 190 K).