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Design and synthesis of new ceria-based materials for low-temperature methane oxidation Vickers, Susan Michaela


The main goal of this research is the development of new mesoporous materials for low-temperature methane oxidation that could be used in catalytic convertors of natural gas powered vehicles. Natural gas is a more environmentally friendly fuel than gasoline or diesel and is seen as a stepping-stone to renewable energy sources. The synthesis and characterization of novel ceria-based materials is reported. Modification of synthetic routes reported in the literature produced several new doped and undoped ceria samples, which were tested for catalytic activity for low-temperature methane oxidation. These tests showed that the presence of a second, redox active metal oxide results in materials with higher catalytic activity than those with only ceria. In addition, several new routes to ceria-based materials with various morphologies, including nanorods and hollow, mesoporous nanospheres, were developed. The nanospheres were successfully doped with lanthanum, giving rise to the first non-hydrothermal route to hollow, mesoporous nanospheres of both doped and undoped ceria. Further examination of materials containing two redox active metal oxides generated mesoporous cobalt oxide with doped and undoped ceria in the pores. Cobalt oxide was templated with KIT-6 silica to produce a material with highly ordered mesopores. The ceria/cobalt oxide materials have remarkably high activity for low-temperature methane oxidation given that they contain no noble metals. However, surprisingly, the mesoporous cobalt oxide on its own exhibited the highest catalytic activity with 50% complete methane conversion to carbon dioxide and water below 400 ˚C. Cerium-based precursors were also used as a starting material to synthesize Pd/ceria materials via a new method termed surface-assisted reduction. Surface-assisted reduction produces ceria with PdO highly dispersed on the surface. These materials showed exceptionally high activity for methane oxidation, with the best materials exhibiting 50% methane conversion below 300 ˚C. Exploration of the scope of surface-assisted reduction successfully produced ceria materials with gold or silver deposited on their surface.

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