Theses and Dissertations at Montana State University (MSU)

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A critical assessment of technologies for the study of organic matter in glaciers and ice sheets
(Montana State University - Bozeman, College of Agriculture, 2019) Willis, Madelyne Claire; Chairperson, Graduate Committee: Christine Foreman
Polar and temperate glaciers harbor active microbial communities and a substantial storage of organic carbon. These frozen ecosystems are especially sensitive to the effects of climate change and are expected to release roughly 15 teragrams of carbon by 2050. This creates a sense of urgency for further experimentation to increase our understanding of glacier ecosystem function and the impact glacier habitats have on local and global biogeochemical cycles. Due to the complex nature of organic matter, there is no single method which is suitable for every study. Technological advancements have improved methods for determining the quantity and quality of organic matter and emerging new technologies are providing faster and less-costly ways to overcome the challenges of working in these harsh environments. Consequently, a synthesis of peer-reviewed literature was conducted to summarize the current state of microbial ecology of glaciers and ice sheets, and to explore the techniques and new tools which are being developed to aid in the study of these rapidly disappearing ecosystems. The culmination of this work is an introduction and guide for analysts interested in examining the source, transformation history, and fate of organic matter in glacial systems. It was found that there is not one single technique superior to another, rather the appropriate technique is dependent on the questions being addressed and the resources available.
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.
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.
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.
A structural analysis of zeolite-templated carbons
(Montana State University - Bozeman, College of Letters & Science, 2022) Taylor, Erin Elizabeth; Chairperson, Graduate Committee: Nicholas P. Stadie
Zeolite-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.
A multi-scale assessment of the coupling between the nitrogen cycle and the terrestrial carbon sink under global change
(Montana State University - Bozeman, College of Agriculture, 2022) Gay, Justin David; Chairperson, Graduate Committee: Jack Brookshire; This is a manuscript style paper that includes co-authored chapters.
It is now unequivocal that the main driver of greenhouse gas (GHG) accumulation in Earth's atmosphere over the industrial era has been due to anthropogenic global change. Despite the recent and rapid rise in GHGs, global terrestrial ecosystems have slowed the rate of carbon dioxide accumulation in the atmosphere, and thus the rate of climate change, through the uptake and storage of carbon (C) in plant biomass and soil organic matter. However, the global cycles of C and nitrogen (N) are tightly coupled through primary production and the turnover of soil organic matter, highlighting a stoichiometric relationship that is critical to understanding the future stability and strength of the terrestrial C sink. Thus, our ability to understand the response of the terrestrial C sink to global change hinges on critical -- but often overlooked -- feedback with N cycling. In this dissertation, I examine how different aspects of global change and land management practices are impacting the terrestrial C sink by evaluating interactions with the N cycle in both managed and natural ecosystems. I use observational and experimental methods to quantitatively assess C and N dynamics at plot, landscape, and global scales. I focus this work on crop- and range-lands of the Upper Missouri River Basin in the United States, and in equatorial mountain forests across the globe to address three overarching research questions: 1. What are the controls over the soil-atmosphere gas exchange of greenhouse gases, and how do they change in response to management and vegetation cover? 2. How do changes in plant community composition influence ecosystem C and N dynamics? 3. How is global change altering the stability and rate of C and N accumulation and storage?
Forming parameters and quantification of continous and stretch broken carbon fibers
(Montana State University - Bozeman, College of Engineering, 2021) Janicki, Joseph Charles; Chairperson, Graduate Committee: Dilpreet S. Bajwa; This thesis contains two articles of which Joseph Charles Janicki is not the main author.
Continuous carbon fibers are premium reinforcing material for aerospace composites. Carbon fiber reinforced polymers are five times stronger than steel and twice as stiff, making it an ideal candidate for structural aircraft components where weight is an important factor. The challenge with continuous carbon fibers is their difficulty to form deep drawn parts requiring intricate manufacturing techniques that increase manufacturing time, cost, and material waste. An alternative to continuous carbon fibers is stretch broken carbon fiber (SBCF). SBCF is a form of aligned discontinuous fiber, it has been proposed as an alternative to overcome this formability challenge. SBCF provides flexibility to form complex shapes while maintaining comparable strength and stiffness. A variety of testing methods have been developed to study both the ability of SBCF to form over traditional continuous carbon fiber and how different iterations of SBCF perform against each other. These include testing carbon fiber tows in tension on a universal test stand as well as designing and creating a forming tool that tests resin impregnated tows under different geometry conditions and temperatures. Tensile properties of both a continuous tow and a SBCF tow were evaluated at different gauge lengths and temperatures. It shows that SBCF tow maximum load increases as the gauge length decreases as well as elevated temperature has a clear effect on the tensile properties when fiber continuity is considered. Cross-sectional areas of continuous and SBCF tows were calculated using both areal weight and scanning electron microscopy showing that in general continuous fiber tows have a larger cross-section than SBCF. Using a forming fixture to test samples, results were statistically analyzed in order to display the significance of geometry and temperature on the maximum forming load of different fibers. The suite of testing and results indicate that in general SBCF maintains superior formability to that of continuous fibers. Overall lower maximum force is required for SBCF to form into deep drawn shapes. This supports their ability to be used more readily in complex aircraft structure while minimizing the disadvantages posed by traditional carbon composites.
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.
Evaluation of nitorgen and carbon supplementation strategies for optimizing biomass generation during cultivation of Chlorella sorokiniana, strain SLA-04
(Montana State University - Bozeman, College of Engineering, 2021) Jackson, Matthew Clifford; Chairperson, Graduate Committee: Catherine Kirkland
Algal cultivation requires significant nitrogen and carbon inputs, which are expensive and can offset benefits associated with biofuel production. This research investigates growth of an alkali-tolerant Chlorella sorokiniana, strain SLA-04, using different nitrogen and carbon regimes to improve physiological knowledge of this novel organism, and improve biomass production and resource demand. Nitrate, ammonium, and urea were used efficiently by SLA-04, however pH changes during utilization of nitrate and ammonium impacted inorganic carbon availability (species and concentration). Generation of OH- during use of nitrate increased pH, increasing mass transfer of CO 2 into solution and increasing the ratio of HCO 3-/CO 2. Ammonium utilization resulted in proton generation, lowering pH and inhibiting growth. When bicarbonate, rather than CO 2, was provided, productivity improved for the urea and mixed nitrogen conditions. This likely resulted from upregulation of genes related to nitrogen and carbon assimilation in the presence of bicarbonate, however Na + cotransport with urea and nitrate is required in some organisms. It is possible that Na + was insufficient when CO 2 was provided, but not in conditions with bicarbonate since it was added as NaHCO 3-. The impact of Na +, as well as other ions, on nitrogen and carbon utilization is not well understood, but it may alter gene regulation. Bicarbonate and CO 2 both promoted increased growth relative to cultures without inorganic carbon supplementation. The highest productivities were observed when carbon supplementation, either as continued CO 2 augmentation to the air sparge or as a 50mM bicarbonate amendment, was provided during nitrogen deplete growth. Glucose availability improved productivity for conditions without CO 2 supplementation. The use of urea or a combination of nitrogen sources with bicarbonate, instead of CO 2, was promising due to (a) the low cost of urea, relative to the other nitrogen sources; (b) the potential for using wastewater containing a mix of nitrogen sources; and (c) the low cost and easy transport of bicarbonate. Future research should evaluate changes in SLA-04 gene expression resulting from the supply of different nutrients, including nitrogen and carbon sources, as well as other ions essential for growth.
Bacterial and archaeal community diversity in relation to organic carbon consumption and sulfate gradients in the Powder River Basin
(Montana State University - Bozeman, College of Letters & Science, 2019) Schweitzer, Hannah Doris; Chairperson, Graduate Committee: Matthew Fields and Sara Branco (co-chair); Elliott Barnhart, Al Cunningham and Matthew Fields were co-authors of the article, 'Comparison of attached and planktonic microbial assemblages across geochemically distinct coal seam habitats' submitted to the journal 'International journal of coal geology' which is contained within this dissertation.; Daniel Ritter, Jennifer McIntosh, Elliott Barnhart, Al B. Cunningham, David Vinson, William Orem and Matthew Fields were co-authors of the article, 'Changes in microbial communities and associated water and geochemistry across a sulfate gradient in coal beds: Powder River Basin, USA' submitted to the journal 'Geochimica et cosmochimica acta' which is contained within this dissertation.; Heidi J. Smith was an author and Elliott P. Barnhart, William Orem, Robin Gerlach and Matthew W. Fields were co-authors of the article, 'Linking organic matter degradation and microbial assemblage composition to subsurface methane production in the Powder River Basin' submitted to the journal 'Applied and environmental microbiology' which is contained within this dissertation.; Heidi J. Smith, Elliott P. Barnhart, Boris Wawrik, Amy Callaghan, Luke McKay, Robin Gerlach and Matthew W. Fields were co-authors of the article, 'Metagenomic analysis of recalcitrant rich coal seams from coal seams with varying sulfate concentrations' submitted to the journal 'Applied and environmental microbiology' which is contained within this dissertation.
The rate limiting step in biogenic coal bed methane production has been attributed to the predominantly recalcitrant composition of coal, making it difficult for bacteria to anaerobically break down into methanogenic substrates. The significance of different carbon (C) cycling pathways involved in the turnover of recalcitrant, terrestrial C under various redox conditions is still a topic of debate, and in fact, unknown C cycling metabolic pathways are still being discovered in sub-oxic and anoxic environments. Redox transitions exist along gradients of increasingly recalcitrant C in many environments, and subsurface environments represent a large reservoir of C. The Powder River Basin in southeastern Montana is a model environment for studying in situ redox gradients for terrestrial subsurface C and were selected to investigate i) the temporal and spatial variation in the microbial assemblage from four different coal seams with varying depth profiles, ii) the physicochemical controls that impact the turnover of recalcitrant coal to methane, and iii) the functional potential for hydrocarbon degradation under different sulfate concentrations. Similar to the methane-sulfate critical zone in marine habitats, the presented work highlights the crucial role sulfate has on microbial assemblages, methane production, and C consumption in shallow coal seams. Given the accepted differences between groundwater and surface-associated communities of subsurface porous media, diffusive microbial samplers packed with native coal material were used to enhance the establishment of microbial communities that better re-capitulated in situ communities. The microbial community inhabiting low sulfate coal seams consisted of sequences indicative of syntrophic bacteria such as Syntrophomonas and Hydrogenophaga which have previously demonstrated degradation of polycyclic aromatic hydrocarbons (PAH) and coupled growth with hydrogenotrophic methanogens. The assemblages inhabiting high sulfate coal seams were comprised of methylotrophic methanogens and sulfate reducing bacteria. Methylotrophic methanogens are observed in methane producing coal seams that have intermediate levels of sulfate, suggesting an important transition role in early stage methanogenesis. Low sulfate microcosms experienced an increase in humic-like material and consumed more C compared to high sulfate conditions that demonstrated changes in more labile C, including amino acid-like molecules. Moreover, we used a highly curated anaerobic and aerobic hydrocarbon degradation (AnHyDeg and AromaDeg) and redox (nitrogen, sulfur, methane cycle) gene database and pipeline to analyze metagenomic samples that were obtained from three different coal beds that had increasing sulfate levels. While the functional potential for methanogenesis (mcrA) was detected in all metagenomes, the diversity and relative quantity of these genes was greater in the coal beds that contained methane. Of interest was a significantly greater percentage of aerobic hydrocarbon degradation genes (dioxygenases) from one of the methane-containing coal bed samples. These metabolic markers were identified in co-assembled metagenomes. These results provide an enhanced understanding of recalcitrant carbon turnover in the terrestrial subsurface under different redox conditions and the presumptive metabolic capacities involved in subsurface C turnover in relationship to biogenic CH4.

Theses and Dissertations at Montana State University (MSU)

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