AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS1+EM-MoA

Paper SS1+EM-MoA7
Metal Particles on Single Crystal Oxides as Model Catalysts

Monday, October 25, 1999, 4:00 pm, Room 606

Session: Metals on Oxides
Presenter: J.H. Larsen, University of Washington
Authors: J.H. Larsen, University of Washington
J.T. Ranney, University of Washington
A.W. Grant, University of Washington
D.E. Starr, University of Washington
J.E. Musgrove, University of Washington
C.T. Campbell, University of Washington
Correspondent: Click to Email
The growth morphology and reactivity of model oxide-supported metal catalysts are intimately connected. On some well-defined oxides, vapor-deposited metals form two-dimensional islands, typically up to a critical coverage below 1 monolayer (ML). The local electronic environment of the supported metal particles is modified as compared to the surface of the bulk metal, and so changes in reactivity are expected. Above the critical coverage, three-dimensional growth sets in and it becomes possible to measure reactivities as a function of island thickness. Several metal on metal oxide systems were studied. The surface growth mode was investigated using low energy ion scattering (LEIS) and x-ray photoelectron spectroscopy (XPS). In order to probe the nature of the reaction sites on the surface, the decomposition of hydrocarbons was also studied with temperature programmed desorption (TPD). From these experiments, the dependence of the metal reactivity on the lateral dimensions of the two-dimensional metal islands and the thickness of three-dimensional metal clusters was determined. It was found that Pt particles on ZnO(0001)-Zn exhibit reactivity towards methanol decomposition which is characteristic of low-index Pt facets, even below the critical coverage of ~ 0.6 ML where only two-dimensional islands are present. The adsorption energy of some metal on metal oxide systems was furthermore measured as a function of coverage using single crystal adsorption calorimetry. The adsorption energy is a fundamental quantity that gives important insight into the energetic origins of the growth and reactivity of metal particles supported on metal oxides.