Theses and Dissertations at Montana State University (MSU)
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Item Synthetic and mechanistic strategies to achieve unconventional site-selectivity in cross-couplings of dihalo-heteroarenes(Montana State University - Bozeman, College of Letters & Science, 2024) Norman, Jacob Patrick; Chairperson, Graduate Committee: Sharon Neufeldt; This is a manuscript style paper that includes co-authored chapters.Pd-catalyzed cross-couplings rank among the most powerful methods for constructing substituted biaryls, polyaryls, and heteroarenes. Frequently, di- or polyhalogenated (hetero)arenes are employed as starting materials in cross-couplings to access products with increased structural complexity via multiple cross-coupling or substitution steps. N-heteroarenes bearing multiple reactive handles--such as halides, are of particular interest as starting materials since their cross- coupled products can be medicinally relevant. Non-symmetrical dihalogenated N-heteroarenes typically exhibit a site-selectivity bias for C-X bonds which are adjacent to at least one heteroatom in Pd-catalyzed cross-couplings. However, some Pd catalysts--particularly those with hindered ligands, promote atypical selectivity at distal C-X bonds of 2,X-dichloropyridines and related heterocycles during the selectivity-determining oxidative addition step. This dissertation explores the mechanistic origins of these ligand trends and emphasizes the critical importance of Pd's ligation state--either mono (PdL) or bis (PdL 2), in controlling the site of oxidative addition. Ligation state is also relevant when selecting for the products of mono- vs difunctionalization in cross-couplings of dihalogenated substrates, since bisligated 14 e - Pd dissociates quickly from the monofunctionalized intermediate after an initial cross-coupling cycle, whereas monoligated 12 e - Pd is slow to dissociate and may "ring-walk" to the remaining reactive site(s). Additionally, this dissertation explores alternative methods to access minor regioisomers in cross-couplings of dichloro-azines. One approach involves ligand-free conditions where atypical site-selectivity at dichloropyridines and dichloropyrimidines arises from a change in Pd's speciation from mono- to multinuclearity. Another approach employs a thiolation/Liebeskind-Srogl arylation sequence to achieve site-selectivity which is orthogonal to that of Suzuki-Miyaura couplings.Item Synthesis and characterization of boron-doped graphitic carbon for energy storage applications(Montana State University - Bozeman, College of Letters & Science, 2023) McGlamery, Devin Gray; Chairperson, Graduate Committee: Nicholas P. Stadie; This is a manuscript style paper that includes co-authored chapters.Carbonaceous materials offer great utility as a medium for electrochemical energy storage of ions or for the storage of chemical fuels. The low molecular weight of the second-row element carbon affords access to materials that express remarkably high gravimetric energy densities, and the robust nature of carbon-carbon bonds allow for good cyclability and longevity of carbon-based materials for use in energy storage applications. With the growing popularity and recent advancement of electric vehicles, current battery technologies are pushed to their limits in terms of capacities as well as in minimizing charging times. This has motivated great efforts to discover new lightweight materials that outperform what has traditionally been used in these applications. Alternative energy carriers, such as hydrogen, are also critical for the development of our energy landscape yet are plagued with their own technical challenges; mainly low volumetric energy densities and safety concerns associated with high pressure gas storage systems. Chapter 2 reviews hydrogen storage in today's society as well as provides a review of past synthetic methods to generate high boron content graphite (BC 3'); being a promising metastable material for the storage of alkali metal ions as well as for solid state hydrogen storage at near ambient conditions. Chapter 3 focuses on the discovery of a new lithium storage mechanism within a novel carbon-based material possessing a high hydrogen content that is tolerant of extremely fast charging, yet still expresses high reversible capacities. Chapter 4 presents a systematic investigation for the detection of chemical environments within BC 3' through an examination of unique spectroscopic properties that originate from the materials phonon structure. Chapter 5 explores the generation of boron and carbon binary phases by the co-pyrolysis of molecular precursors and establishes a density functional theory based approach to align the cracking temperatures of molecular feedstocks; affording access to bulk metastable materials that contain a homogeneous distribution of chemical environments. This work is concluded with an assessment of the materials investigated herein from the perspective of energy storage, as well as provides directions for future work.Item Operando optical and quantitative electrochemical studies of solid oxide fuel cell anode degradation and regeneration(Montana State University - Bozeman, College of Letters & Science, 2022) Pomeroy, Elias Deen; Chairperson, Graduate Committee: Robert Walker; This is a manuscript style paper that includes co-authored chapters.Solid Oxide Fuel Cells (SOFCs) are high temperature (600-1000 °C) devices that can generate electricity with extremely high efficiencies from a wide variety of fuels, including H 2, CH 4, Biogas, and crushed coal. Unfortunately, the SOFC anodes are highly sensitive to gas phase contaminants, including sulfur and carbon containing fuels. Sulfur is ubiquitous in all carbon containing fuels, with concentrations as low as a few parts per million to as high as 1% by mass. At all concentrations sulfur substantially decreases SOFC performance. Conventional models propose that sulfur decreases fuel cell performance by blocking anode active sites, preventing electrochemical reactions, and reducing surface area for heterogeneous catalysis. Carbon containing fuels can rapidly degrade SOFCs due to graphitic carbon formation. Graphite blocks active sites on the anode, causes damage within the anode microstructure, and removes electrocatalytic material via metal dusting. Studies presented in this work used operando optical techniques and quantitative electrochemistry to study degradation and remediation of SOFC anodes. First, since typical electrochemical techniques infer microstructural changes rather than directly measuring surface area, a traditional electrochemical technique, chronocoulometry (CC), was adapted to SOFCs for the first time to measure the electrochemically active area of the anode. This technique showed that active area is temperature dependent, and that sulfur participates in electrochemical reactions, decreasing performance with sluggish oxidation kinetics, rather than simply blocking active sites. Carbon monoxide, on the other hand, decreased the number of active sites, rather than participating in electrochemical reactions, either by blocking active sites or forming carbon. Then, a comparative study was undertaken of different methodologies of carbon remediation, comparing electrochemical oxidation, molecular oxygen, and steam as methods to remove graphite accumulated on SOFC anodes. This study found that with all methods, CO 2 played a key role in removing carbon, that both electrochemical oxidation and steam removed carbon more globally than oxygen, and that imaging the entire cell is critical for understanding the complex, spatially and temporally heterogeneous chemistry occurring across SOFC anodes. Finally, sulfur was employed to passivate SOFC anodes operating on dry methane, significantly reducing carbon formation with only slight decreases in electrochemical performance.Item A structural analysis of zeolite-templated carbons(Montana State University - Bozeman, College of Letters & Science, 2022) Taylor, Erin Elizabeth; Chairperson, Graduate Committee: Nicholas P. StadieZeolite-templated carbons (ZTCs) are a distinct class of porous framework materials comprised of a three-dimensional pore network contained between atomically thin, polycyclic hydrocarbon walls. This class of materials arose from the goal to develop carbon- based frameworks with ordered, homogeneous microporosity (see Chapter 1), as opposed to activated carbons where the pore network is random. It has more recently been suggested that zeolite-templating may be a viable synthetic route to carbon schwarzites, an elusive class of theoretical materials, which follow triply periodic minimal surfaces and are predicted to have many fundamentally interesting properties. Herein we show that while experimentally synthesized ZTCs (see Chapters 2 and 3) are too amorphous to be considered schwarzites, understanding the current structural features of ZTCs may be the key to finally isolating a schwarzite via zeolite-templating. The experimentally relevant open- blade model developed in our work predicts paramagnetism of ZTC materials (see Chapter 5); superconducting quantum interference device measurements on archetypical ZTC materials confirms this prediction, highlighting the unique nature of spin polarization in porous carbon materials. While the current ZTC structure resembles an open-blade, generating a closed- tube schwarzite-like ZTC variant may be accessible by tuning the catalytic activity of the zeolite template pore walls. In Chapter 6, alkali metal exchange is explored as a route to strengthen cation-? interactions between the growing ZTC framework and zeolite template in an attempt to achieve a more schwarzite-like ZTC. LiY-templated ZTCs show beginning signs of conversion to a closed-tube structure. Lastly, recent benchmark computational studies suggest that nitrogen-doping of open-blade porous carbon surfaces has a significant, beneficial effect on the binding energy toward methane: a strengthening by up to 3 kJ mol -1 over pure carbon. The work presented in Chapter 7 identifies optimal conditions to achieve nitrogen-doped ZTCs with N-contents ranging from 0-9 at%. Therein, we show that indeed high-pressure (100 bar) methane adsorption characterization of nitrogen-doped ZTCs exhibit an increased methane binding energy of 1.3 kJ mol -1, validating the theoretical predictions.Item Catalysis with early and late transition metals: C-H activation at tantalocene hydrides and oxidative addition at palladium solvato complexes(Montana State University - Bozeman, College of Letters & Science, 2021) Rehbein, Steven Mark; Chairperson, Graduate Committee: Sharon Neufeldt; Matthew J. Kania and Sharon R. Neufeldt were co-authors of the article, 'Experimental and computational evaluation of tantalocene hydrides for C-H activation of arenes' in the journal 'Organometallics' which is contained within this dissertation.; Steven M. Rehbein and Sharon R. Neufeldt were co-authors of the article, 'Solvent coordination to palladium can invert the selectivity of oxidative addition' in the journal 'Organometallics' which is contained within this dissertation.Herein we present our work on transition metal catalysis using metals from two sides of the periodic table: C-H activation catalyzed by early transition metals and cross-couplings catalyzed by late transition metals. In the first part, a synergistic experimental and computational approach was employed to investigate the possibility of extending the reactivity of bent tantalocene hydrides beyond aromatic C-H activation to enable activation of aliphatic substrates. In situ monitoring of the characteristic 1 H NMR metal hydride signals in the reaction of Cp 2TaH 3 and related complexes with deuterated aromatic substrates allowed for the evaluation of reaction kinetics of catalyst decomposition, H/D exchange, and off-cycle reactions. The insight gained from in situ reaction monitoring with aromatic substrates, combined with computational analyses, allowed for the extension of this chemistry to intra- and intermolecular aliphatic C-H activation. This work represents the first example of aliphatic C-H activation by homogeneous tantalum hydrides. In the second part, we provide compelling evidence that solvent coordination to palladium during oxidative addition of chloroaryl triflates can result in an inversion of chemoselectivity of this step. Previous investigations attributed a solvent-dependent switch in chemoselectivity to the propensity of polar solvents to stabilize anionic transition states of the type [Pd(P t Bu 3)(X)]- (X = anionic ligand). However, our detailed investigations show that solvent polarity alone is not a sufficient predictor of selectivity. Instead, solvent coordinating ability is selectivity-determining, with polar coordinating and polar noncoordinating solvents giving differing selectivity, even in the absence of anionic ligands 'X'. A solvent-coordinated bisligated transition state of the type Pd(P t Bu 3)(solvent) is implicated by density functional theory calculations. This work provides a new mechanistic framework for selectivity control during oxidative addition.Item The reactive form of a C-S bond-cleaving CO 2-fixing flavoenzyme(Montana State University - Bozeman, College of Letters & Science, 2019) Mattice, Jenna Rose; Chairperson, Graduate Committee: Jennifer DuBois; Thesis includes a paper of which Jenna R. Mattice is not the main author.Atmospheric carbon dioxide (CO 2) is used as a carbon source for building biomass in plants and most engineered synthetic microbes. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the most abundant enzyme on earth, is used by these organisms to catalyze the first step in CO 2 fixation. 1,2 Microbial processes that also fix carbon dioxide or bicarbonate have more recently been discovered. My research focuses on a reaction catalyzed by 2-KPCC (NADPH:2-ketopropyl-coenzyme M oxidorectuase/ carboxylase), a bacterial enzyme that is part of the flavin and cysteine-disulfide containing oxidoreductase family (DSORs) which are best known for reducing metallic or disulfide substrates. 2-KPCC is unique because it breaks a comparatively strong C-S bond, leading to the generation of a reactive enolacetone intermediate which can directly attack and fix CO 2. 2-KPCC contains a phenylalanine in the place where most other DSOR members have a catalytically essential histidine. This research focuses on studying the unique reactive form of 2-KPCC in presence of an active site phenylalanine.Item Gas-surface interactions with sp 2 carbon in extreme environments(Montana State University - Bozeman, College of Letters & Science, 2018) Murray, Vanessa Jean; Chairperson, Graduate Committee: Timothy Minton; Brooks C. Marshall, Philip J. Woodburn and Timothy K. Minton were co-authors of the article, 'Inelastic and reactive scattering dynamics of hyperthermal O and O 2 on hot vitreous carbon surfaces' in the journal 'Journal of physical chemistry C' which is contained within this thesis.; Eric J. Smoll Jr. and Timothy K Minton were co-authors of the article, 'Dynamics of graphite oxidation at high temperature' in the journal 'Journal of physical chemistry C' which is contained within this thesis.; Marcin D. Pilinski, Eric J. Smoll, Jr., Min Qian, Timothy K. Minton, Stojan M. Madzunkov and Murray R. Darrach were co-authors of the article, 'Gas-surface scattering dynamics applied to concentration of gases for mass spectrometry in tenuous atmospheres' in the journal 'Journal of physical chemistry C' which is contained within this thesis.; Neil A. Mehta is an author and Chenbiao Xu, Deborah A. Levin and Timothy K. Minton were co-authors of the article, 'Scattering dynamics of N 2 from highly oriented pyrolytic graphite' in the journal 'Journal of physical chemistry C' which is contained within this thesis.; Chenbiao Xu, Savio Poovatthingal and Timothy K. Minton were co-authors of the article, 'Scattering dynamics of nitromethane and methyl formate on HOPG' submitted to the journal 'Journal of physical chemistry C' which is contained within this thesis.Molecular beam scattering experiments can determine the relative importance of reactive and non-reactive processes that occur when a surface is bombarded with high energy atoms and molecules. The mechanisms by which these processes proceed are inferred by analyzing the angle-resolved flux and energy distributions of the scattered products. The studies presented in this thesis have been conducted with a crossed molecular beams machine reconfigured for surface scattering. Two molecular beam sources were used. One uses a laser detonation process to produce high translational energy O atoms in the ground electronic state, and the other uses a supersonic expansion to produce continuous beams of N 2, nitromethane, or methyl formate. In the first two studies presented in this thesis, the oxidation of dynamics vitreous carbon and highly oriented pyrolytic graphite (HOPG) held at surface temperatures in the range of 800 - 2300 K by O atoms with a translational energy of ~ 500 kJ mol -1 are presented. These two studies revealed that the reactivity is suppressed at high temperature because O atoms desorb from the surface before they react to form CO and CO 2. Even though the translational energy of the O atoms was high, the surface reactions proceeded primarily through reactions that occurred in thermal equilibrium with the surface. The third study focuses on the scattering dynamics of O, O 2, and Ar with the surfaces of a gold thin-film, SiO 2, and HOPG. The results of the experiments were used to evaluate the efficacy of a proposed gas concentrator. The strong forward scattering on the HOPG surface made it the most suitable surface for the gas concentrator. The fourth study examines the non-reactive scattering dynamics of N 2 with HOPG. At high surface temperature, the residence time of N 2 is too short for the molecule to fully accommodate to the surface. Thus, even if the molecule suffers multiple collisions with the surface, it will scatter into the vacuum before it can come into thermal equilibrium with the surface. The results have been used in conjunction with theoretical calculations by a collaborator to investigate the relationship between the potential energy surface and the scattering dynamics. In order determine the usefulness of an HOPG concentrator with complex molecules, the scattering dynamics of methyl formate and nitromethane on HOPG were studied. These molecules do not shatter upon impact with the surface and they both scatter strongly in the forward direction through direct and indirect mechanisms, suggesting that the proposed HOPG concentrator should perform as desired. In all studies described in this thesis, the fundamental gas-surface scattering dynamics were elucidated from molecular beam experiments, and these fundamental results have direct links to modeling the performance of hypersonic vehicles and designing a gas concentrator for mass spectrometry in tenuous atmospheres.Item Chlorine induced degradation of SOFCS operating on carbon containing fuels(Montana State University - Bozeman, College of Letters & Science, 2017) Reeping, Kyle Wyatt; Chairperson, Graduate Committee: Robert Walker; Robert A. Walker was a co-author of the article, 'In operando vibrational raman studies of chlorine contamination in solid oxide fuel cells' in the journal 'The journal of the Electrochemical Society' which is contained within this thesis.; John D. Kirtley, Jessie M. Bohn, Daniel A. Steinhurst, Jeffrey C. Owrutsky and Robert A. Walker were co-authors of the article, 'Chlorine-induced degradation in solid oxide fuel cells identified by optical methods' in the journal 'The journal of physical chemistry C' which is contained within this thesis.; Jessie, M. Bohn and Robert A. Walker were co-authors of the article, 'Chlorine-induced degradation in SOFCS operating with biogas' in the journal 'Sustainable energy and fuels' which is contained within this thesis.; Jessie, M. Bohn and Robert A. Walker were co-authors of the article, 'The palliative effect of H 2 on SOFCS operating on contaminated carbon containing fuels' submitted to the journal 'The journal of power sources' which is contained within this thesis.Chlorine present in green and synthetic fuels such as biogas and syngas can accelerate degradation of solid oxide fuel cell (SOFC) nickel-based anodes. Chlorine contamination has been studied in SOFCs where H 2 was the primary fuel but little attention has focused on deleterious, cooperative effects that result from Cl-contamination in predominantly carbon-containing fuels. Experiments described in this work examine degradation mechanisms in SOFCs with Ni-YSZ cermet anodes operating with a biogas surrogate and exposed to 110 ppm Cl (delivered either as CH 3Cl or HCl). Operando Raman spectroscopy is used to directly observe the the anode's catalytic activity as evidenced by observable carbon accumulation, and electrochemical impedance and voltammetry measurements report on overall cell performance. Studies performed at 650 °C and 700 °C show that Cl suppresses carbon accumulation and causes slow but steady cell degradation. Prolonged exposure to Cl results in and irreversible device failure. These results differ markedly from recent reports of Cl contamination in SOFCs operating independently with H 2 and CH 4.Item Spatial distribution of carbon accumulation on solid oxide fuel cells operating under methane(Montana State University - Bozeman, College of Letters & Science, 2015) Neuburger, Daniel Miller; Chairperson, Graduate Committee: Robert WalkerWith the looming threat of climate change, new technologies that can reduce the use of fossil fuels are desirable. One such technology is the solid oxide fuel cell (SOFC). SOFCs convert chemical energy directly into electrical energy, so they can be much more efficient than traditional sources of electrical power generation. SOFCs utilize an oxide-ion conducting electrolyte to generate electricity by reducing molecular oxygen at the cathode and oxidizing fuel at the anode. High temperatures (<650 °C) are required to catalyze oxide conduction through the electrolyte. High temperatures enable SOFCs to use a variety of fuels, but these same conditions also accelerate unfavorable reactions that can cause anode degradation. Research described in this dissertation examined the effects of carbon accumulation in SOFC anodes on overall device performance, and the spatial variation in anode degradation. Fuel was introduced to the fuel cell using a single fuel inlet. This method of fuel introduction created spatial variance in factors such as fuel concentration, and this variance was expected to affect carbon accumulation on the anode. Carbon accumulation is a major contributor to anode degradation through a variety of mechanisms including mass transport obstruction, anode delamination from the electrolyte, and metal dusting, a process describing anode disintegration induced by carbon growth disrupting the anode's electronically conducting network. The amount of carbon accumulation on the surface of the anode was analyzed in operando using Raman spectroscopy. Spectroscopic results showed that more carbon accumulated on the anode further from the fuel inlet than closer to it. In situ electrochemical measurements coupled with post mortem visual and FEM analysis suggested that severe anode degradation occurred early in an experiment, affecting spectroscopic results. We infer that the highest amount of carbon accumulation occurs close to the fuel inlet causing fast and severe anode degradation, decreasing the amount of carbon that can accumulate in further trials when the majority of the spectroscopic data was collected. These results suggest that spectroscopic results should be analyzed with experimental factors such as anode location and trial sequence specifically in mind.Item Conifer cover increase in the Greater Yellowstone Ecosystem : rates, extent, and consequences for carbon(Montana State University - Bozeman, College of Letters & Science, 2004) Powell, Scott Lael; Chairperson, Graduate Committee: Andrew J. HansenIncreases in the extent and density of woody vegetation have been observed in many locations worldwide. Conifer cover increase in the Greater Yellowstone Ecosystem (GYE) has been documented by historical photos, but the rate and extent remain unquantified. Elevated atmospheric CO2 levels have focused research attention on carbon budgeting. Carbon sinks associated with conifer cover increase are believed to account for a fraction of the βmissing carbon sink,γ although estimates of the fraction are highly uncertain. I examined changes in conifer cover and aboveground carbon across biophysical gradients in the GYE using a combination of aerial photos, satellite imagery, field data, allometric equations, and statistical techniques. I quantified the percent conifer cover for samples in 1971 and 1999 to determine the frequency and rate of conifer cover increase. I used satellite image change detection to map the extent of conifer cover increase and aerial photo interpretation to quantify the rates of conifer cover increase. I then estimated aboveground carbon stocks for 1985 and 1999 and quantified the source/sink dynamics associated with conifer cover increase and other trajectories of forest change. I determined that the area of conifer forest increased by 7% during the period 1971-1999, at highly variable rates depending upon elevation, aspect, vegetation type, and proximity to conifer forest. Much of the variation in the rates of change was associated with gradients of soil moisture. Conifer cover increased across 685,075 ha between 1985-1999 and was responsible for the aboveground sequestration of 369 Gg C yr-1, offsetting 34% of the carbon source associated with widespread fire and logging during that time period. Climate variability, fire suppression, grazing dynamics, and elevated atmospheric CO2 levels are the hypothesized determinants of conifer cover increase. Although it is likely that no single factor is singularly responsible, fire frequency has been sufficiently reduced throughout the GYE, and the majority of carbon uptake occurred in forest types adapted to frequent fire. The temporal duration of a carbon sink associated with conifer cover increase therefore remains in question.