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Heterogeneous Transition Metal Oxide Nanostructures: Synthesis and Applications in Catalysis
Transition metal oxides are a fascinating group of compounds that exhibit diverse physical and chemical properties. Since the past few decades, these oxides have attracted a large amount of attention from the scientific community and consequently find applications in myriad areas that include electronics, energy storage, and biomedicine. Catalysis is one such field that heavily relies on heterogeneous transition metal oxides. Although, advancements in synthetic techniques along with the advances of sophisticated characterization tools have led to the production of high-performance catalysts, the true catalytic ability of these materials is not fully understood. This dissertation describes the synthesis, detailed structural characterization, and catalytic applications of two transition metal oxides: magnetite (iron oxide or Fe3O4) and ceria (cerium oxide or CeO2-x (0 < x ≤ 2)). An in-depth understanding of the structure-activity relationship was attained to elucidate the reaction mechanism in these two catalytic systems. Magnetite-based catalysts coated with active functional groups are commonly used for the conversion of biomass to valuable platform chemicals. However, the role of the magnetite core in these conversions is not thoroughly investigated. This dissertation explores the catalytic activity of uncoated magnetite nanoparticles for the dehydration of cellobiose to 5-hydroxymethylfurfural (5-HMF) in an aqueous medium under hydrothermal conditions. These nanoparticles were synthesized by the co-precipitation technique and were found effective at converting aldohexoses as well as ketohexoses to 5-HMF. Furthermore, magnetite nanoparticles outperformed common iron salts (such as FeCl2 and FeCl3) in producing 5-HMF under similar experimental conditions. Inherent redox chemistry between Ce3+ and Ce4+ in combination with high oxygen affinity makes ceria an important industrial catalyst. A rapid, room temperature ozone-mediated strategy was developed for producing fluorite-structured ceria nanoparticles in this dissertation. The presence of higher amount of oxygen vacancies in these nanoparticles makes them viable catalysts for the oxidation of CO to CO2. Additionally, fabrication of ceria nanoparticles with various concentrations of gadolinium (III) ions (Gd3+) by the ozone-mediated method was reported. Catalytic performance of these doped nanoparticles for the disproportionation of hydrogen peroxide to hydroxyl radicals was also described. A direct correlation between the concentration of Gd3+ and the catalytic activity of Gd-doped ceria nanoparticles towards the production of hydroxyl radicals was revealed.
Analytical chemistry|Inorganic chemistry|Nanoscience
Bhalkikar, Anuja, "Heterogeneous Transition Metal Oxide Nanostructures: Synthesis and Applications in Catalysis" (2019). ETD collection for University of Nebraska - Lincoln. AAI13861463.