Solid basic metal oxides have been extensively studied for biodiesel production via transesterification, researches are now focused on attaining high catalytic activity and durability towards one-step alkali transesterification, as well as high stability towards high free fatty acids (FFAs) and water content in oils for simultaneous esterification and transesterification, to enable their commercialization in industry. This work encompasses the design and characterization of three mixed metal oxide systems, with a detailed evaluation of their potential application in catalyzing transesterification of camelina oil to yield biodiesel. Na0.1Ca0.9TiO3 nanorods were synthesized via a simple alkaline hydrothermal pathway with ethanol as a co-solvent. Owing to their high basic strength of 11<H_<15, 92.7% biodiesel conversion was reached at mild reaction conditions. However, the catalyst showed poor recycle performance, probably attributed to the leaching of active species during transesterification, as revealed by X-ray photoelectron spectroscopy (XPS). A new class of mesoporous Zn/MgO catalyst was synthesized by a simple alkaline hydrothermal method. Zn/MgO calcinated at 600 ℃ exhibited 88.7% biodiesel conversion at 120 ℃ with 3% w/w catalyst, 24:1 methanol to oil molar ratio for 8 h. The catalyst could be reused for five runs without significant loss of activity (≥84.0% biodiesel conversion). The excellent catalyst performance is possibly attributed to its high surface area and large mesopores. The higher surface basic sites density as compared to mesoporous MgO, as indicated by higher total basicity determined from benzoic titration and an increased lattice O2- percentage as revealed from XPS, attributing to its superior catalytic activity. A series of nano-sized MgO-ZnO catalysts with precise stoichiometry were successfully prepared by a simple EDTA complexing approach. Mg0.5Zn0.5 calcinated at 600 ℃ gave a maximum biodiesel conversion of 89.3% at 120 ℃ with 3% w/w catalyst, 24:1 methanol to oil molar ratio for 8 h. Its superior catalytic performance to MgO is mainly associated with the high basic sites density as determined from benzoic titration and XPS. The biodiesel conversion retained over 83.0% for five runs. The enhanced catalyst activity and stability might be contributed by the incorporation of Zn2+ for Mg2+ in MgO lattice and a high homogeneous distribution of MgO particles on ZnO, with the formation of Mg-O-Zn bond as evidenced by Fourier transform infrared spectroscope (FTIR) and XPS. The catalyst also demonstrated high tolerance to FFAs (10% w/w) and water (2% w/w) content, which make it desirable for direct conversion of oils with high FFAs level to biodiesel in a single-step process. Lastly, a Zn/La2O3 catalyst was synthesized by a simple hydrothermal pathway. It exhibits a higher basic strength than La2O3, as evidenced by the slightly lower O1s binding energy determined by XPS, leading to a higher catalytic activity. The enhanced catalytic activity and stability is likely contributed by the incorporation of Zn2+ for La3+ in the lattice. Using 1% w/w Zn/La2O3 as catalyst, the highest biodiesel conversion of 92.7% was obtained at 120 ℃ for 16 h with 36:1 methanol to oil molar ratio. The effective catalyst displayed a biodiesel conversion greater than 84.0% for four runs. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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Complexes of the type MX(η²-NO₃)(CO)₂(PPh₃)₂, (M = Mo, X = Cl, Br; M = W, X = Br) were prepared from the reactions of MX₂(CO)₂(PPh₃)₂ with ammonium nitrate in acetone. The complexes were characterized by elemental analyses, ¹⁵N labelling, infrared and NMR spectroscopy. The nitrate ligand is bidentate and the complexes are seven-coordinate. Novel nitrite complexes of molybdenum and tungsten of the type M(NO₂)₂(PPh₃)₂ were prepared. The compounds were characterized by elemental analyses, ¹⁵N labelling, infrared and multinuclear NMR spectroscopy. Both NO₂ ligands are chelating and the two NO₂, PPh₃ and CO ligands are equivalent. Molybdenum dinitrosyl complexes were synthesized by the reduction of nitrate ions. The crystal structure of cis-dinitrosyl-cis-dichloro-trans-bis-(triphenylphosphine)molybdenum(II) was determined by x-ray diffraction. Both the nitrosyl groups are linear. Mo(NO)₂Cl₂(OPPh₃)₂ and Mo(NO)₂Cl(NO₃)(OPPh₃)₂ were synthesized by the reaction of MoCl(η²-NO₃)(CO)₂(PPh₃)₂ with NO in acetone/toluene mixture. The nitrosyl ligands are linear and the phosphineoxide ligands are cis to each other. The dinitrite complex Rh(NO)(NO₂)₂(PPh₃)₂ of the series Rh(NO)X₂(PPh₃)₂ (X - monodentate anions) was prepared as a direct derivative of Rh(NO)Cl₂(PPh₃)₂ by its reaction with sodium nitrite. The complex is square pyramidal with an apical nitrosyl ligand. The two NO₂ groups are present as the nitro and the nitrito group. Rh(NO)(NO₂)₂(PPh₃) reacted with oxygen and formed Rh(NO₃)₃(PPh₃)₂. The reaction of Rh(NO)(NO₂)₂(PPh₃)₂ with CO in acetonitrile produced Rh(CO)(NO₂)(PPh₃)₂. The complex Rh(CO)(NO₂)(PPh₃)₂ is square planar with the phosphine ligands in the trans positions.

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Ni-based superalloys are used for high-temperature components of gas turbines in both industrial and aerospace applications due to their ability to maintain dimensional stability under conditions of high stress and strain. The oxidation resistance of these alloys often dictates their service lifetime. This study focuses on the isothermal oxidation behaviour of three nickel-based superalloys; namely, polycrystalline cast IN738LC, single-crystal N5 and a ternary Ni-Fe-Cr (TAS) powder metallurgy alloy. The isothermal oxidation tests were conducted at 900°C in the static air up to 1000h and the specific aspects studied were the oxidation behaviour of these chromia-forming and alumina-forming alloys that are used extensively in industry. In particular, the behaviour of oxide scale growth and subsurface changes were analysed in detail using various techniques such as SEM, EDS and AFM. From the isothermal oxidation kinetics, the oxidation rate constant, kp was calculated for each alloy and found to be; kp = 2.79 x 10-6 mg2.cm-4.s-1 for IN738LC, kp = 1.42 x 10-7 mg2.cm-4.s-1 for N5 and kp = 1.64 x 10-7 mg2.cm-4.s-1 for TAS. Based on a microstructural analysis, IN738LC exhibited a continuous dense outer scale of Cr2O3 and discontinuous inner scale of Al2O3, whereas N5 and TAS showed a dense outer scale of Al2O3 alone. The results suggested that the N5 and PM-TAS alloys are more oxidation resistant than the IN738LC under these conditions. / October 2016

Oxides of manganese have received considerable attention lately, mainly because of the colossal magnetoresistance they exhibit. After a careful interpretation of the large body of available experimental results, the paramount importance of intrinsic inhomogeneities to the understanding of these materials, can no longer be ignored. A scenario, based on the competition between different ordered phases which are mixed by the intrinsic disorder, is proposed. Several quantities that follow from this scenario can be evaluated and are found to correspond to experiments. / Dissertation / PhD

"Catalysts are involved at some stage in the manufacture process of virtually all commercially produced chemical product. Among the materials used as catalysts, metal oxides are one of the most used due to their versatility and wide range of physical properties. Identifying the principles of surface to adsorbate charge transfer is key to a better understanding of metal oxide materials as both catalysts and gas sensors. Using density functional theory (DFT), we modeled the adsorption of small molecules over stoichiometric and reduced metal oxide surfaces of group IV metals and quantify the effect of electron transfer upon adsorption. We found that charge transfer only occurs during the adsorption process of an adsorbate more electronegative than the surface. We also found a correlation between the work function of the metal oxide, and the ionic adsorption of the oxygen molecule. Mixed phase rutile/anatase catalysts show increased reactivity compared with the pure phases alone. However, the mechanism causing this effect is not fully understood. Using DFT and the +U correction we calculated the bands offsets between the phases taking into account the effect of the interface. We found rutile to have both higher conduction and valence band offsets than anatase, leading to an accumulation of electrons in the anatase phase accompanied by hole accumulation in the rutile phase. We also probed the electronic structure of our heterostructure and found a gap state caused by electrons localized in undercoordinated Ti atoms which were present within the interfacial region. Interfaces between bulk materials and between exposed surfaces both showed electron trapping at undercoordinated sites. Finally, we studied the effect of the size of gold nanoparticles in the catalytic properties of gold decorated titania surfaces. We found that the adsorption energy of several intermediates reactives in the CO oxidation and water gas shift reaction does not change with the size of the nanoparticles. In conclusion, the factor that affects the reactivity of the system is the density of undercoodinated gold atoms on the interface perimeter."

The short title of this dissertation is Size Matters. And it really does. Before diving into the original findings of this dissertation, this abstract starts by contextualizing their significance. To that end, recall that some of the earliest concepts learned by sophomore organic chemistry students include explaining physical properties based on carbon chain length, for example, and polymer length has enormous influence on macroscopic material properties. In the 1980s it was found that the electronic properties of small inorganic semiconductor crystallites can be rigorously tied to the physical size of the crystallites, and this understanding has led directly to the successful integration of so-called quantum dots into readily available technologies today, including flat screen televisions, as well as emerging technologies, such as quantum dot solar cells. Oxides, for their part, are important components of many technologies, from paints and cosmetics to microelectronics and catalytic converters. The crystallite size dependency of fundamental mechanical properties of oxides is the topic of this dissertation. First, this dissertation reports that consistent preparation methods were used to produce batches of specific crystallite sizes for a diverse family of five cubic oxides: CeO2 (ceria), MgO (magnesia), Cu2O (cuprite), Fe3O4 (magnetite), and Co3O4. The size-based lattice changes for small crystallites was carefully measured with X-ray diffraction. Expanded lattice parameters were found in small crystallites of all five oxides (notably for the first time in Fe3O4). This behavior is rationalized with an atomic model reliant on differing coordination levels of atoms at the surface, and fundamental calculations of physical properties including surface stress and expansion energy are derived from the measured lattice expansion for these oxides. Then, the size dependency of the pressure response in ceria nanoparticles was measured using diamond anvil cells and synchrotron radiation. In a study unmatched in its comprehensiveness, it was found that the bulk modulus of ceria peaked at an intermediate crystallite size of 33 nm. This is rationalized with a core-shell model with a size dependent shell compressibility whose influence naturally grows as crystallite size shrinks. Complimentary thermal expansion measurements were carried out to probe the structural response of crystallites to heat. Overall, the thermal expansion of ceria decreased with crystallite size. Through careful heating cycles, it was possible to separate out quantitatively the two primary factors contributing to negative surface stress in ceria: ambient surface adsorbents and surface non-stoichiometry. These may be the first instances of such a calculation that provides this insight into the surface stress of oxide nanoparticles. Next, pressure and temperature studies parallel to those in ceria were carried out on magnesia as well. Magnesia is an important oxide to compare to ceria because it does not share ceria's tendency to form oxygen vacancy defects with cation charge variances. Nonetheless, magneisa was shown to possess a peak (albeit a less dramatic peak) in bulk modulus at an intermediate crystallite size, about 14 nm. Magnesia, like ceria, also had decreased thermal expansion at smaller crystallite sizes. Finally, experiments on molecular oxygen exchange properties of a series of oxides were carried out using a thermocycling reactor system designed and built in-house, with the aim of developing materials to convert carbon dioxide to carbon monoxide. Experiments were carried out under 1200C, much lower than the 1500C typically required for ceria oxygen exchange. It is thought that crystallite morphology could play an important role in dictating the effectiveness of this catalytic process. The increased understanding of fundamental physical properties of oxide nanoparticles, as explored here, may lead to their more rational integration into such emerging technologies.