| Description |
The research presented in this dissertation describes fundamental studies of sizeselected palladium and platinum clusters supported on a metal oxide surface. Using carbon monoxide (CO) oxidation as a probe reaction, the catalytic activity as well as the surface properties of the model catalysts were investigated with an emphasis on elucidating the interplay between size-dependent physical and electronic structures. The details and background for model catalyst research are provided in Chapter 1 with a description of the importance of cluster size and how changes in the physical and electronic structure affect catalytic activity. A brief description of the experimental setup is presented at the end of Chapter 1 along with an introduction to a new and important addition to the setup -- a vacuum ultraviolet (VUV) lamp. The lamp was constructed with the goal of performing ultraviolet photoelectron spectroscopy, and the details of the design and operation are given in Chapter 2. Using the newly designed VUV lamp, the valence electronic structure of the Pdn/TiO2(110) model system was investigated in order to determine changes as a function of cluster size, CO exposure, and oxidation. The size-dependent core and valence level shifts were found to track equally in direction and magnitude, with the details given in Chapter 3. The focus then turns to the Ptn/alumina/Re(0001) system to investigate the size-dependent surface properties and catalytic activity. Beginning in Chapter 4, the VUV lamp was used to measure the valence electronic structure of the model catalyst, and it was determined that size-dependent shifts in the Ptn valence band strongly correlate with the size-dependent activity for the CO oxidation reaction. The valence band structure is thought to determine how efficiently the clusters dissociatively adsorb oxygen, which is considered to be the rate limiting step in the reaction. Chapter 5 provides further detailed study of the physical and electronic structure of the model catalyst, and the findings suggest the growth of 3-dimensional clusters (as opposed to single layer, 2-dimensional clusters) to be vitally important in determining the electronic structure of the Ptn clusters, and ultimately their catalytic activities. |
