Mass Selected Metal and Metal Oxide Clusters as Catalysts
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Date
2016-11-08
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Johns Hopkins University
Abstract
Transition metal and metal oxide nanoparticles/clusters are widely used as catalysts in heterogeneous catalysis. However, the structure sensitivity of the catalysts is still unclear due to the structural complexities of the nano-catalysts. The studies presented in this thesis have used soft-landed mass-selected clusters as model systems for heterogeneous catalysis, which aims to achieve a microscopic level of understanding of the catalytic processes. Therefore, the surface structures of size selected metal oxide, sulfide and oxynitride clusters were studied by scanning tunneling microscope and atomic force microscope. Based on their size, chemical compositions, cluster flux intensity and the substrate temperature, the deposited clusters exhibited various surface morphologies as a result of different cluster-cluster and cluster-surface interactions. In addition, the catalytic properties of mass selected metal oxides were studied by temperature programmed desorption and x-ray photoelectron spectroscopy. It is found that the cluster size, the supporting substrates and the chemical compositions of the clusters played an important role in determining the catalytic activities of the metal oxide clusters.
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Keywords
Clusters, Catalysis