| Description |
The research presented in this dissertation probes the effects of the metal oxide support thickness as well as Pdn cluster size on the catalytic efficiency as monitored by the CO oxidation reaction. Before any experiments could be conducted, a reliable Al evaporation source needed to be built and characterized to make a consistent and reliable alumina support for the Pdn clusters. Despite an initial goal of determining how the Pdn cluster size effects the reactivity, it turned out that the effects of the alumina film thickness, substrate dopants in the alumina, and identity of the base refractory metal substrate play a huge role in determining the catalytic reactivity. Before any size-selected experiments could be done, a detailed set of experiments probing the film was necessary to prevent convolution of Pdn cluster size effects with the effects of a varying metal oxide support. In addition to the catalytic activity determined via temperature programed reaction (TPR), both the electronic and geometric structures of the film and Pdn clusters were studied through a combination of photoelectron spectroscopy (PES) and ion scattering spectroscopy, respectively. It will be shown through these methods, that for the conditions used here, the catalytic activity is governed by the ability of the Pdn to bind and activate oxygen into a reactive species. An introduction into the importance of catalysis and, more specifically, size selected model catalysis is described in Chapter 1. The instrument and description of the iv custom made aluminum evaporation source and C type thermocouple are presented in Chapter 2. Chapter 3 focuses on all of the work for both alumina thickness and Pdn cluster size effects supported on alumina films grown on Ta(110). Chapters 4 and 5 discuss the differing effects of the alumina film thickness and Pdn cluster size for alumina films grown on a Re(0001) single crystal, respectively. |
