Regardless of the simplicity in molecular structure, polyethylene is used in high-performance applications such as medical prostheses and ballistics. Recent advancements in homogeneous catalysis produced UHMWPE in the low-entangled or dis-entangled state that allowed solvent-free-solid-state processing to achieve ultimate mechanical properties ever achieved for a synthetic polymer. Although several homogeneous complexes are known to produce dis-UHMWPE, existing major challenges are uncontrolled nascent polymer morphology, as a consequence reactor fouling/wall sheeting. In such a scenario, a heterogeneous catalyst that can produce dis-UHWMPE to an extent that the characteristics and properties equivalent to that obtained in homogeneous condition, remains an open challenge. The thesis will discuss the know-how for the synthesis of dis-UHMWPE via heterogeneous route to facilitate industrial production by following fundamental understanding of polymerization catalysis, physics, processing, and testing. In this thesis, in-situ formed nano activator/support MgClx/EtnAly(2-ethyl-1-hexoxide)z is employed with a highly active bis[N-(3-tert-butylsalicylidene)pentafluoroanilinato] titanium (IV) dichloride (Cat. 1) for synthesis of dis-UHMWPE. In addition, the relatively easy formation of the MgClx/RnClmAly(OR’) activators/supports allows tailoring by the selection of different aluminum-alkyls and alcohols, giving access to a variety of co-catalysts. This investigation resulted in UHMWPE having Mw from 3 to an unprecedented 43 M g/mol and Ð from 3 to 38 with very high activities up to 2750 kgPE molcat.-1 bar-1 h-1. The adopted route resulted in nano-support that allows tailoring of the entangled state and control over the nascent morphology without reactor fouling, thus providing feasibility of pursuing the polymerization via a continuous process. The nascent polymer shows formation of single crystals of linear UHMWPE and is suggestive of the low-entangled state. The topological differences, with the commercial entangled sample, are identified solid-state NMR, DSC, and rheology. The disentangled crystals allowed desired chain orientation for securing unprecedented tensile modulus (>200 N/tex) and tensile strength (>4.0 N/tex) via solid-state processing. Additionally, the investigation of creep response in the uniaxial tapes has revealed strong influence of molecular weight and entanglement density. These unique characteristics and unprecedented mechanical properties are equivalent to that perceived using a homogeneous catalysis and are the first of their kind achieved for a polymer synthesized using a heterogeneous catalysis.

In the area of sustainable energy, a major focus has been to design robust electrocatalysts that can be used for the electrolysis of water to produce H2 with a sustainable energy source such as solar. Sustainable H2 generation would potentially be a prelude to the adoption of a hydrogen economy, allowing the phasing out of fossil fuels as a primary fuel source. Toward this end, there is a global research effort to develop electrocatalysts that would facilitate the kinetics of the two half-reactions that make up the water-splitting process: the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). A challenge is to develop active electrocatalysts that are largely composed of earth-abundant elements and show catalytic stability during water splitting at low pH, where the scientific community feels that commercial electrolysis will operate most efficiently. Currently, iridium oxide (IrO2) is being looked at for low pH water splitting because of its stability at low pH, but its relative scarcity (e.g., it is a precious metal) may well make it an unacceptable choice in the long run.In this dissertation, we focus on understanding the scientific issues that will allow the development of earth-abundant catalysts that contain a loading of Ir that is low as possible, while maintaining suitable activity and stability. We began by synthesizing a series of Ir-based OER electrocatalysts by incorporating varying amounts of Ir into 2D layered MnO2 (birnessite, nominally δ-MnO2) and 3D MnO2 (pyrolusite, β-MnO2) phases. The Ir-incorporated δ-MnO2 (Ir/δ-MnO2) electrocatalysts with 16-22 wt% Ir were synthesized by a wet chemical method using a ligating agent, such that Ir was present on the surface and partially intercalated into the interlayer of δ-MnO2. Ir-incorporated β-MnO2 (Ir/β-MnO2) was prepared for the first time via a thermally induced phase transition of Ir/δ-MnO2. This phase transition of δ-MnO2 to β-MnO2 was facilitated by the presence of Ir in the structure, as both Ir in IrO2 and Mn in β-MnO2 could adopt the more thermodynamically stable rutile structure. Extended X-ray absorption fine structure (EXAFS) of Ir/β-MnO2 showed that the catalyst consisted of Ir substituted into the crystalline β-MnO2 lattice, additionally, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscopy (SEM) imaging revealed micron-sized particles with non-uniform distribution of Ir in the MnO2. In 0.5 M H2SO4 electrolyte, 22 wt% Ir/β-MnO2 (60 〖μg〗_Ir cm_geo^(-2)) resulted in the most active catalyst with an η@10 (overpotential at 10 mA cm_geo^(-2)) of 337 mV and stability of 6 h. This electrocatalyst outperformed a commercial IrO2 on a per Ir mass basis. EXAFS, HAADF-STEM and X-ray absorption near edge structure (XANES) showed that 22 wt% Ir/β-MnO2 had a strained structure containing ~41% Mn3+, an OER active species, along with a modified Ir bonding due to the presence of Ir-O-Ir and Ir-O-Mn. Density functional theory (DFT) computation has demonstrated that this modified bonding environment in Ir/β-MnO2 has contributed to enhancing the thermodynamic stability of the structure. Furthermore, the literature suggests that the presence of Ir-O-Mn bond can favorably tune the d-orbital energy of Ir, enabling superior performance in the Ir/β-MnO2 compared to IrO2. The thesis research also included the investigation of the activity and stability of Ir/β-MnO2 that was synthesized via a novel strategy. The resulting material maintained a homogeneous distribution of Ir in the MnO2 lattice and exhibited excellent OER activity and stability. A surfactant-assisted (SA) synthesis method was carried out to achieve uniform doping of 22-28 wt.% Ir in 3D MnO2 (ramsdellite, R-MnO2). Upon annealing, Ir/R-MnO2 transformed to Ir/β-MnO2 (SA), composed of nano-sized particles. Electrochemical studies in 0.5 M H2SO4 showed that, Ir/β-MnO2 (SA) with 75.6 〖µg〗_Ir cm_geo^(-2) exhibited an η of 327 mV and exceptional stability (up to 50 h). At similar Ir mass loadings, the Ir/β-MnO2 (SA) outperformed Ir/R-MnO2 (SA) and commercial IrO2. This enhanced activity and stability was attributed to a thermodynamically stable structure composed of uniform distribution of Ir (Ir-O-Mn) in the MnO2 lattice. Overall, the research results presented in this dissertation contributed towards designing a novel class of Ir-MnO2 catalysts, which potentially will point the scientific community in the right direction for designing future noble metal-incorporated earth-abundant metal oxides for electrocatalytic energy conversion reactions. / Chemistry

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The targeted design of new catalyst materials can only be accomplished once a fundamental understanding of the interactions between material surfaces and adsorbed molecules is developed. In situ infrared spectroscopy and mass spectrometry methods were employed to probe interactions at the gas-surface interface of oxide-supported metal nanoparticle materials. High vacuum conditions allowed for systematic investigations to describe detailed reaction mechanisms. Specifically, variable temperature infrared spectroscopy was utilized to uncover the binding energetics of CO to the oxide surface of TiO2-based materials. As binding energetics are related to the electronic structure of the adsorption site, differences in evaluated binding enthalpies are hypothesized to probe electronic metal-support interactions that describe charge transfer between the supported metal nanoparticles and TiO2. Cu/TiO2 aerogels were identified as a candidate for more in-depth studies. Flow reactor methods in combination with the surface-based infrared spectroscopy were utilized to elucidate the CO oxidation reaction mechanism over Cu/TiO2 aerogels. Bridging oxygen atoms on TiO2 regions of the material were identified as the active site for catalysis in a Cu-assisted Mars-van Krevelen lattice extraction mechanism. Methanol oxidation was then studied with similar methods to show the complete conversion to CO2 and H2O at high temperatures through the reduction of titania and formation of a formate intermediate. Higher-order carbonaceous alcohols were probed for adsorption and reactivity on Cu/TiO2 aerogels and were observed to follow a similar reaction pathway. The higher-order alcohols, however, were shown to undergo a partial oxidation pathway in the absence of gaseous O2 that is hypothesized to originate from enhanced binding to Cu sites. The decomposition of the chemical warfare agent simulant dimethyl chlorophosphate was also investigated. A hydrolysis pathway to form the significantly less toxic molecule CH3Cl was observed, highlighting the unique promotional effects and chemistry on Cu/TiO2 aerogels. The results presented exemplify both the influence of electronic metal-support interactions on catalysis and the versatile reactivity of Cu/TiO2 aerogels. / Doctor of Philosophy / Interactions between small gaseous molecules and material surfaces have very important implications for applications regarding the environment, industry, and military/public safety. The mechanisms in which gases interact with a solid surface can determine how the material can be functionally used as catalysts. Scientists and engineers start to build a fundamental understanding of what makes a catalyst successful for different applications by understanding the location and strength of interactions. A catalyst's surface acts to lower activation barriers and provide low-energy pathways for interacting molecules to chemically change, by breaking bonds for molecular decomposition and/or forming new bonds. The vibrations of chemical bonds that break and form on surfaces are probed with infrared spectroscopy at the gas-surface interface to study molecular adsorption and reactivity. In addition, a flow cell reactor is used to characterize reaction progress and identify products in real-time. A class of reactive nanoparticulate materials is utilized as a model system on which to study various chemical reactions for important applications including small molecule oxidation for industrial detoxification and clean energy applications, as well as the decomposition of chemical warfare agents. Reaction mechanisms for the oxidation of carbon monoxide and alcohols were elucidated through the utilization of the methods described above. In addition, the decomposition of a chemical warfare agent simulant is characterized. The discoveries and understanding of important chemical properties presented in this dissertation will aid in the synthesis of effective next-generation catalyst materials.

Biodiesel is currently produced by homogeneous catalysis. More recently however, heterogeneous catalysis is being considered as a cheaper alternative to the homogeneous process. In this research project, heterogeneous catalysts of zirconium oxide were produced by impregnation. Zirconium oxide impregnation with sulfuric acid produced acidic solid catalysts. It was determined that impregnation and calcination at 550^oC (SO₄/ZrO₂-550^oC) produced the best catalyst for palmitic acid esterification with 10 wt % as the optimum concentration in esterification of palmitic acid. SO₄/ZrO₂-550^oC was successfully recycled for eight consecutive runs before permanent deactivation. Its sulfur content was 1.04 wt % using SEM-EDS and 2.05 wt % using XPS for characterization. BET surface area was 90.89 m2/g. The reaction mechanism over Brønsted acid (SO₄/ZrO₂-550^oC) and Lewis acid (Al₂O₃) catalysts obeyed Eley-Rideal kinetics with palmitic acid and methanol adsorbed on the active site respectively. Zirconium oxide was also impregnated with sodium hydroxide to produce basic catalysts. The best catalyst was produced when zirconium oxide was impregnated with 1.5 M NaOH and calcined at 600^oC. Soybean oil was completely converted to biodiesel with 10 wt % catalyst and 1:6 oil to methanol. A mixture of the base catalyst with 30 wt % SO₄/ZrO₂-550^oC effectively converted soybean oil containing 5% oleic acid indicating that this mixture could be used for waste oils. The reaction was first order with respect to triglyceride and second order with respect to methanol. The activation energy was 49.35 kJ/mol and the reaction mechanism obeyed Langmuir-Hinshelwood kinetics. / Master of Science

The purpose of this research was to directly compare the behavior of zeolites containing rhodium with that of homogeneous rhodium species as catalysts for liquid phase hydroformylation of 1-hexene in order to study the effects of zeolite immobilization. NaX zeolite was cation exchanged with several rhodium salts and used as hydroformylation catalysts at 50°C and 125°C in the presence of: triphenylphosphine (PPh₃), dimethylphenylphosphine (PMe₂Ph), and the poison for zeolite surface and solution rhodium: triphenylmethylmercaptan (Ph₃CSH). The results of these experiments were compared with those of several homogeneous catalysts under similar conditions. It was found that previously reported results of intrazeolitic activity with RhNaX at 50°C were probably incorrect, since, the addition of PMe₂Ph, Ph₃CSH, or both, virtually halted all reactivity of RhNax. The catalytic results at 125°C did not conclusively indicate the location of the active rhodium. Thus, intrazeolitic activity at 125°C may or may not have been observed, and needs further investigation. Reaction profiles were obtained for several of the catalyst systems, using an automatic sampling system. From these profiles, it was found that the addition of excess PMe₂Ph halted isomerization of 1-hexene to 2-hexenes for the zeolite-supported rhodium, and hindered, but did not stop isomerization for the homogeneous catalysts. Also, as expected, it was observed that the homogeneous catalysts reacted to completion faster than the heterogeneous catalyst. In addition, the effects of such treatments as preheating in air and precarbonylation of the heterogeneous catalysts were studied. Pretreatments had no effect upon the catalysis. Also, no activity was observed from the heterogeneous catalysts at 125°C unless phosphines were present. Finally, the hydrogenation of 1-hexene was studied. Heterogeneous and homogeneous rhodium catalysts showed hydrogenation activity which was accompanied by isomerization at 60°C and 125°C. / Master of Science

Developing a fundamental understanding of the interactions between catalytic surfaces and adsorbed molecules is imperative to the rational design of new materials for catalytic, sorption and gas separation applications. Experiments that probed the chemistry at the gas-surface interface were employed through the utilization of in situ infrared spectroscopic measurements in high vacuum conditions to allow for detailed and systematic investigations into adsorption and reactive processes. Specifically, the mechanistic details of propene epoxidation on the surface of nanoparticulate Au supported on TiO2 and dimethyl chlorophosphate (DMCP) decomposition on the surface of TiO2 aerogel-supported Cu nanoparticles were investigated. In situ infrared spectroscopy illustrates that TiO2-supported Au nanoparticles exhibit the unprecedented ability to produce the industrially relevant commodity chemical, propene oxide, through the unique adsorption configuration of propene on the surface of Au and a hydroperoxide intermediate (-OOH) in the presence of gaseous hydrogen and oxygen. Whereas, TiO2-supported Cu aerogels oxidize the organophosphate-based simulant, DMCP, into adsorbed CO at ambient environments. Through a variety of spectroscopic methods, each step in these oxidative pathways was investigated, including: adsorption, oxidation and reactivation of the supported-nanoparticle systems to develop full mechanistic pictures. Additionally, the perturbation of vibrational character of the probe molecule, CO, was employed to characterize the intrinsic µ3-hydroxyls and molecular-level defects associated with the metal-organic framework (MOF), UiO-66. The adsorption of CO onto heterogeneous surfaces effectively characterizes surfaces because the C-O bond vibrates differently depending on the nature of the surface site. Therefore, CO adsorption was used within the high vacuum environment to identify atomic-level characteristics that traditional methods of analysis cannot distinguish. / Doctor of Philosophy / The interaction between small gas molecules and solid surfaces is important for environmental, industrial and military applications. In order to chemically change molecules, surfaces act to lower activation barriers and provide a low energy plane to create new chemical bonds. To study the fundamental interactions that occur between gas molecules and surfaces, we employ infrared spectroscopy in order to probe the vibrations of bonds at the gas–surface interface. By tracking the chemical bonds that break and form on the surface of different materials, we can develop surface reaction pathways for a variety of different chemical reactions. We focus our efforts on two different applications: the conversion of propene to propene oxide for industrial applications and the decomposition of chemical warfare agents. Using the techniques described above, we were able to develop reaction pathways for both propene oxidation and chemical warfare agent simulant degradation. Our work is critical to the further development of catalysts that harness the specific structural and chemical properties we identify as important and exploit them for further use.

The commercialization of lithium-ion batteries has played a pivotal role in the development of consumer electronics and electric vehicles. In recent years, much research has focused on the development and modification of the active materials of electrodes to obtain higher energies for a broader range of applications. High voltage spinel materials including LiNi_0.5Mn_1.5O_4-δ (LNMO) have been considered as promising cathode materials to address the increasing demands for improved battery performance due to their high operating potential, high energy density, and stable cycling lifetimes. In an effort to elucidate fundamental structure-property relationships, this thesis explores the tunable properties of single-crystal LNMO. Utilizing facile molten salt synthesis methods, the structural and electronic properties of LNMO can be well controlled. Chapter 2 of this thesis focuses on uncovering the effect of molten salt synthesis parameters including molten salt composition and synthetic temperature on the materials properties. A range of imaging, microscopic, and spectroscopic techniques are used to characterize structural and electronic properties which are investigated in tandem with electrochemical performance. Results indicate the Mn oxidation state is highly dependent on synthesis temperature and can dictate performance, while the molten salt composition strongly influences the particle morphology. In Chapter 3, we explore the concept of utilizing LNMO as a tunable support for heterogeneous metal nanocatalysts, where alteration of the support structure and electronics can have an influence on catalytic properties due to unique support effects. Ultimately, this work illustrates the tunable nature of single-crystal LNMO and can inform the rational design of LNMO materials for energy applications. / M.S. / The development of lithium-ion batteries has been fundamental to the expansion and prevalence of consumer electronics and electric vehicles in the twenty-first century. Despite their ubiquity, there is an ongoing drive by researchers to address the limitations and improve the quality and performance of lithium ion batteries. Much research has focused on altering the composition, structure, or properties of electrodes at the materials level to design higher achieving batteries. A fundamental understanding of how composition and structure effect battery performance is necessary to progress toward better materials. This thesis focuses on investigating the properties of LiNi_0.5Mn_1.5O_4-δ (LNMO). LNMO material is considered a promising cathode material to meet the increasing consumer demands for improved battery performance. Through the synthesis methods, the shape of individual particles and the global electronic properties of LNMO can be tuned. In this work, specific synthesis parameters are systematically tuned and the properties of the resultant LNMO materials are explored. Electrochemical testing also evaluates the performance of the materials and offers insights into how they may fair in real battery systems. In an effort to potentially recycle spent battery materials, LNMO is also utilized as a catalyst support. Alteration of shape and electronic properties of the LNMO support can influence the catalytic properties, or the ability of the material to enhance the rate of a chemical reaction. Overall, this thesis explores how LNMO can be tuned and utilized for different applications. This work provides insights for understanding LNMO properties and direction for the development of future battery materials.