Theses and Dissertations from UMD
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Item ELECTRIFIED HIGH-TEMPERATURE MANUFACTURING AND APPLICATIONS IN ENVIRONMENTAL SCIENCE(2023) Li, Shuke; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High temperature processes hold great potential for material and chemical manufacturing.On the one hand, high temperature can help overcome energy barriers and thus effectively convert precursors to desired products. On the other hand, high temperature can also boost the reaction rate and improve synthesis efficiency. Recent development of electrified high temperature technologies by our group further revealed the important role played by non-equilibrium conditions on nanomaterial and chemical syntheses. For example, Joule-heating of carbon-based materials through a programmable electrical signal can offer spatial and temporal temperature profiles, which can be used to manipulate the chemical reaction pathways. For another example, tunable heating duration and quenching rates can be used to achieve a range of compositions and structures of nanoparticles. In this dissertation, two specific applications of the electrified high temperature technology will be explored, including: (1) Thermal shock synthesis of multielemental nanoparticles as selective and stable catalysts; and (2) Efficient biomass upgrading via pulsed electrical heating. Supported nanoparticle (NP) catalysts are widely used for various reactions. However, it remains challenging to synthesize high quality NPs with accurate morphologically and structure control. In this part of the research, NP catalysts with morphology or structural design were prepared by high temperature thermal shock methods. Ultra-small and high-loading carbon supported Pt3Ni NPs: Strong electrostatic effect was introduced between metal salts and carbon particles that can largely improve anchoring and dispersion of the precursors, thereby achieving high NP loading (40 wt%) as well as small NP size and good distribution (1.66 ± 0.56 nm). This method is not only limited to bimetallic NPs synthesis or NPs on carbon black but can be extended to a range of NP compositions on various substrate materials, thus providing a general strategy for developing ultrafine and high-loading NPs as electrocatalysts for various reactions. Sustainable aviation fuels (SAFs) are essential to meet future air travel demand while reducing the carbon footprint. Among many potential feedstocks to produce SAFs, lignin stands out as it is an abundant and renewable aromatic biopolymer that is usually treated as a waste material from the paper industry. However, converting lignin to SAFs by conventional thermochemical processes has been challenging due to poor control on the reaction pathway which leads to undesired product distribution. In this study, a programmed electrified heating method was designed and used to break down large lignin molecule to small aromatic molecules with targeted product distribution. A controlled heating step offers sufficient energy input to break down lignin molecules to smaller fragments without excessive secondary reactions toward undesired species such as coke. The lignin thermal decomposition products were evaluated as potential precursor for SAFs generation. This process can be further extended to process other biomass materials such as algae and sawdust to value-added chemicals.Item UNDERSTANDING THE SURFACE CHEMISTRY OF GAS PHASE ORGANOPHOSPHORUS CHEMICAL WARFARE AGENTS WITH SORBENT MATERIALS(2019) Holdren, Scott; Zachariah, Michael R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Chemical warfare agents (CWAs) pose a serious threat to civilians and warfighters due to their high toxicity and usage in recent attacks. Although existing filtration media (ASZM-TEDA) used in gas mask devices absorbs and decomposes a wide spectrum of CWAs, the filtration performance of this material can be compromised in the battlefield due to poorly understood mechanisms. The high toxicity of CWAs remains a barrier for most research institutions to study these compounds experimentally which hinders the search for improved filtration materials. To overcome this issue, studies are performed using relatively benign simulant compounds that have similar adsorption and decomposition properties as toxic CWAs. In this work, a report of experimental findings will be presented regarding how dimethyl methylphosphonate (DMMP), an organophosphorus CWA simulant, will adsorb and decompose on components that makeup ASZM-TEDA. The work presented in this dissertation deconstructs the components that makeup ASZM-TEDA in order to identify the role of specific metal oxides and the carbon support. This approach was facilitated using different analytical techniques including TGA, FTIR spectroscopy, and DFT modeling to gain a molecular understanding of how DMMP interacts with porous carbon (Chapter 3) and metal oxide nanoparticles/surfaces (Chapters 4 and 5). Lastly, a new method is described (Chapter 6) that overcomes many of the difficulties encountered in conventional measurements that monitor gas phase DMMP adsorption/desorption processes on sorbent materials. This method can be used to obtain reliable quantitative measurements and parameters (e.g. adsorption capacities, ∆Hads, and kads) of low vapor pressure adsorbate/sorbent systems making it particularly useful for CWAs/CWA simulants and new filtration materials (e.g. DMMP and porous carbon).Item METHANE VALORIZATION OVER NOVEL CATALYST SYSTEMS VIA DIRECT PATHWAYS(2019) Oh, Su Cheun; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Methane, when converted to higher hydrocarbons, promises a great future as the substituent for liquid petroleum in petrochemical and fine chemical industries. Methane conversion via direct pathways such as oxidative coupling of methane (OCM) to ethylene and direct non-oxidative methane conversion (DNMC) to C2 (acetylene, ethylene and ethane) and aromatics have attracted much attention given their unique capability in circumventing the intermediate energy-intensive steps found in indirect processes. In the OCM process, the more reactive nature of C2 products leads to the sequential oxidation of C2 to COx (CO or CO2). Selective catalysts that favor C2 formation are desired. The DNMC is challenged by low equilibrium conversion, high endothermicity, and high coke selectivity. Catalysts or reaction systems that concurrently solve these challenges are required. This dissertation aims to develop novel catalyst systems to conquer limitations in OCM and DNMC to realize efficient and effective C2 production. For OCM reaction, hydroxyapatite (HAP), a bioceramic material with the capability of cation and/or anion substitutions, was innovatively employed as a catalyst. The effects of cation and/or anion substitutions in HAP on OCM reaction were studied. The rigorous description of the reaction kinetics of OCM in HAP-based catalysts was conducted. Finally, the selective control of exposed crystalline plane of HAP was realized to further understand the catalytic behaviors of HAP-based catalysts in OCM reactions. It is shown that cation and/or anion substitution can change the physicochemical properties of the HAP catalysts, and as consequences, the OCM catalytic performances. The c-surface (i.e., (002) crystalline plane) of HAP-based catalysts exhibited significant enhancement in areal rate in OCM reaction. The single iron sites confined in the lattice of silica matrix (Fe/SiO2) is an emerging type of methane activation catalyst in DNMC. We innovated a millisecond catalytic wall reactor made of Fe/SiO2 catalyst to enabling stable and high methane conversion, C2+ selectivity, low coke yield, and long-term durability. These effects originate from initiation of DNMC by surface catalysis on reactor wall, and maintenance of the reaction by gas-phase chemistry in reactor compartment. Autothermal operation of the catalytic wall reactor is potentially feasible by coupling and periodical swapping of endothermic DNMC and exothermic oxidative coke removal on opposite side of the reactor. High carbon and thermal efficiencies and low cost in reactor materials are realized for the techno-economic process viability of the DNMC technology. In addition, we created a process of tailoring product selectivity towards to C2 hydrocarbons by employing a mixture of Fe/SiO2 catalyst and mixed ionic-electronic conductive perovskite (SrCe0.8Zr0.2O3−δ) oxide in the presence of hydrogen co-feed in methane stream. The unprecedentedly high C2 yield was realized in DNMC reaction to maximize its potential as a feedstock for ethylene production in chemical industries.Item NEW LIGAND SCAFFOLDS FOR COMBINING ARENE C-H ACTIVATION AND AEROBIC OXIDATION AT PLATINUM(2018) Watts, David; Vedernikov, Andrei N; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Extensive research over the past half-century has proven the utility of late transition metal complexes in the activation and functionalization of alkanes and arenes. Homogeneous platinum compounds have been particularly promising as they readily form air and water stable complexes that can react with some of the strongest C-H bonds (e.g., CH3-H, Ph-H) under relatively benign conditions. Yet, the development of methods for the application of O2 or air as the terminal oxidant in the oxidative functionalization of inert C-H bonds remains an elusive but important goal. The focus of this work is to enable the direct involvement of O2 with PtII-mediated C-H activation processes through computation directed intelligent ligand design, with the end goal of selective aerobic C-H functionalization. Prior experience with the hemi-labile tripodal ligand di-(2-pyridyl)methanesulfonate (dpms) lead us to develop a new class of sulfonated k3-CNN pincer pre-ligand, 6-phenyl-di-(2-pyridyl)methanesulfonate (ph-dpms). The ph-dpms derived PtII-aqua complex, (C6H4-dpms)PtII(H2O), was shown to be an especially active hydrogen/deuterium exchange catalyst with arene substrates. While facile, the arene C-H activation chemistry was also selective for aryl C(sp2)-H bonds over benzyl C(sp3)-H, despite severe steric protection of the former in some cases. Ph-dpms also supports the aerobic oxidation chemistry for which the earlier generation ligand, dpms, was engineered. An anionic [PtII(Ph)]- complex derived from ph-dpms undergoes relatively fast oxidation in trifluoroethanol (TFE) solvent resulting in oxidative C-C coupling between the phenyl substituent and ligand. Changing the solvent to MeOH allows for isolation of the PtIV-Ph intermediate. Furthermore, the ability to support both C-H and O2 activation was combined in the one-pot aerobic C-H oxidation of both electron rich and electron poor arenes to give (C6H4-dpms)PtIV(Aryl)(OH) complexes from (C6H4-dpms)PtII(H2O); a feat never accomplished before by a PtII complex without the use of co-catalysts or reagents to mediate the O2 chemistry. The limits of the new ligand scaffold were then explored through the reactivity of PtII chloro and aqua complexes derived from more rigid analogs of ph-dpms. The rigidity of the ligand was found to be intimately tied to both C-H and O2 activation chemistry as well as some detrimental bimolecular decomposition pathways.Item ELECTRONIC MODIFICATION WITHIN THE WELL-ESTABLISHED CPAM FRAMEWORK AS A MEANS TOWARD INCREASED REACTIVITY(2017) Thompson, Richard; Sita, Lawrence R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Early transition metals (group IV-VI) supported by the pentamethylcyclopentadienyl-amidinate mixed ligand set (CPAM) have been found to enable a number of important chemical transformations including (living) coordinative polymerization of alpha-olefins, fixation of dinitrogen and group transfer chemistry involving oxo, imido and sulfido ligands to unsaturated organic substrates, including carbon dioxide. A great deal of the allure and success associated with these complexes is their modularity, particularly as it concerns the amidinate component which is tunable at both the N-bound substituents as well as the distal position. Accordingly, a great deal of work has established that by reducing the sterics in all three positions engendered higher reactivity. There exists, however, a practical “steric wall” such that the size of substituents can only be contracted so much. Tuning of the electronic character of these well-established systems could prove to be a novel and potent method for affecting reactivity of these complexes within an already well understood steric environment.Item THE UPGRADING OF METHANE TO AROMATICS OVER TRANSITION METAL LOADED HIERARCHICAL ZEOLITES(2017) WU, YIQING; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the boom of shale gas production, the conversion of methane to higher hydrocarbons (MTH) promises a great future as the substituent for hydrocarbon production from crude oil based processes. Among various MTH processes, direct methane aromatization (DMA) is promising since it can achieve one-step methane valorization to aromatics. The molybdenum/zeolite (Mo/MFI or Mo/MWW) has been the most active catalyst for the DMA reaction, which, however, is impeded from industrial practice due to the rapid deactivation by coke deposition. To address this challenge, in this work, transition metal loaded hierarchical 2 dimensional (2D) lamellar MFI and MWW zeolites have been studied as catalysts for the DMA reaction. The effects of micro- and mesoporosity, external and internal Brønsted acid sites, as well as particle size of 2D lamellar zeolites on the DMA reaction have been investigated. Firstly, the spatial distribution of Brønsted acid sites in 2D lamellar MFI and MWW zeolites has been quantified by a combination of organic base titration and methanol dehydration reaction. The unit-cell thick 2D zeolites after Mo loading showed mitigation on deactivation, increase in activity, and comparable aromatics selectivity to the Mo loaded 3D zeolite analogues. A detailed analysis of the DMA reaction over Mo/hierarchical MFI zeolites with variable micro- and mesoporosity (equivalent to variation in particle sizes) showed a balance between dual porosity was essential to modulate the distribution of active sites (Mo and Brønsted acid sites) in the catalysts as well as the consequent reaction and transport events to optimize performance in the DMA reaction. External Brønsted acid sites have been proposed to be the cause of coke deposition on Mo/zeolite catalysts. Deactivation of the external acid sites have been practiced to improve the catalyst performances in the DMA reaction in this work. Atomic layer deposition (ALD) of silica species was conducted on the external surface of 2D lamellar MFI and MWW zeolites to deactivate the external acid sites in Mo/2D lamellar zeolites for the DMA reaction. Another strategy to deactivate external acid sites in Mo/zeolite catalysts was the overgrowth of 2D lamellar silicalite-1 on the microporous zeolites. The as-prepared catalysts showed higher methane conversion and aromatics formation as well as higher selectivity to naphthalene and coke in comparison with Mo loaded microporous analogues.Item ENGINEERING HIERARCHICAL MESO-/MICROPOROUS LAMELLAR ZEOLITES WITH VARIABLE TEXTURAL AND CATALYTIC PROPERTIES(2016) EMDADI, LALEH; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Meso-/microporous zeolites combine the charactersitics of well-defined micropores of zeolite with efficient mass transfer consequences of mesopores to increase the efficiency of the catalysts in reactions involving bulky molecules. Different methods such as demetallation and templating have been explored for the synthesis of meso-/microporous zeolites. However, they all have limitations in production of meso-/microporous zeolites with tunable textural and catalytic properties using few synthesis steps. To address this challenge, a simple one-step dual template synthesis approach has been developed in this work to engineer lamellar meso-/microporous zeolites structures with tunable textural and catalytic properties. First, one-step dual template synthesis of meso-/microporous mordenite framework inverted (MFI) zeolite structures was investigated. Tetrapropyl ammonium hydroxide (TPAOH) and diquaternary ammonium surfactant ([C22H45-N+(CH3)2-C6H12-N+(CH3)2-C6H13]Br2, C22-6-6) were used as templates to produce micropores and mesopores, respectively. The variation in concentration ratios of dual templates and hydrothermal synthesis conditions resulted in production of multi-lamellar MFI and the hybrid lamellar-bulk MFI (HLBM) zeolite structures. The relationship between the morphology, porosity, acidity, and catalytic properties of these catalysts was systematically studied. Then, the validity of the proposed synthesis approach for production of other types of zeolites composites was examined by creating a meso-/microporous bulk polymorph A (BEA)-lamellar MFI (BBLM) composite. The resulted composite samples showed higher catalytic stability compared to their single component zeolites. The studies demonstrated the high potential of the one-step dual template synthesis procedure for engineering the textural and catalytic properties of the synthesized zeolites.Item Small Molecule Activation and Atom and Group Transfer Reactions Mediated by Mid Valent Group 6 'CPAM' Complexes(2015) Farrell, Wesley Scott; Sita, Lawrence R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of organometallic compounds to activate small molecules (e.g. CO2, N2, N2O, O2, etc.) has long been of significant scientific interest. Described here is the synthesis and characterization of mid valent group 6 compounds supported by the pentamethylcyclopentadienyl, amidinate (CpAm) ligand framework, along with their ability to not only activate small molecules that are inexpensive, abundant, and/or hazardous, but use them to generate many value added products under mild conditions. Sulfur atom transfer (SAT) was employed to catalytically prepare carbonyl sulfide and isothiocyanates from elemental sulfur. In the case of carbonyl sulfide, this process was able to be performed in the presence of primary amines, allowing for the isolation of symmetric ureas, and in the case of isothiocyanates, the reaction was successful in the presence of benzhydrazide to allow for the isolation of aroylthiosemicarbazides in good yields. Molecular oxygen was found to afford high valent dioxo species which were inactive towards oxygen atom transfer (OAT). However, OAT was achieved for the catalytic deoxygenation of sulfoxides. Dinitrogen fixation has previously been discovered by our group to afford -ER3 (E = C, Si, Ge) derivatized isocyanates through [2+1] cycloaddition of CO. Reported here is an extension of this work to include N2 fixation with concomitant reduction of the greenhouse gas CO2 to prepare the same isocyanates via [2+2] cycloaddition of CO2. Furthermore, the completion of several efficient N2 fixation synthetic cycles through two distinct pathways is discussed. Additionally, given the tremendous impact of high valent group 6 alkylidene compounds to catalyze olefin metathesis reactions, the synthesis of mid valent CpAm group 6 alkylidenes was a challenging, yet attractive target. Attempts to isolate such compounds are presented, along with descriptions of the products obtained and their reactivity towards small molecules.Item Earth Abundant Bimetallic Nanoparticles for Heterogeneous Catalysis(2014) Senn Jr, Jonathan Fitzgerald; Eichhorn, Bryan; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polymer exchange membrane fuel cells have the potential to replace current fossil fuel-based technologies in terms of emissions and efficiency, but CO contamination of H2 fuel, which is derived from steam methane reforming, leads to system inefficiency or failure. Solutions currently under development are bimetallic nanoparticles comprised of earth-abundant metals in different architectures to reduce the concentration of CO by PROX during fuel cell operation. Chapter One introduces the Pt-Sn and Co-Ni bimetallic nanoparticle systems, and the intermetallic and core-shell architectures of interest for catalytic evaluation. Application, theory, and studies associated with the efficacy of these nanoparticles are briefly reviewed. Chapter Two describes the concepts of the synthetic and characterization methods used in this work. Chapter Three presents the synthetic, characterization, and catalytic findings of this research. Pt, PtSn, PtSn2, and Pt3Sn nanoparticles have been synthesized and supported on γ-Al2O3. Pt3Sn was shown to be an effective PROX catalyst in various gas feed conditions, such as the gas mixture incorporating 0.1% CO, which displayed a light-off temperatures of ~95°C. Co and Ni monometallic and CoNi bimetallic nanoparticles have been synthesized and characterized, ultimately leading to the development of target Co@Ni core-shell nanoparticles. Proposed studies of catalytic properties of these nanoparticles in preferential oxidation of CO (PROX) reactions will further elucidate the effects of different crystallographic phases, nanoparticle-support interactions, and architecture on catalysis, and provide fundamental understanding of catalysis with nanoparticles composed of earth abundant metals in different architectures.Item Applications of 2,3-Diketoesters in Organic Synthesis and Stereoselective Transformations(2014) Truong, Phong Minh; Doyle, Michael P; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dimethyldioxyrane oxidation of δ-hydroxy-α-diazo-β-ketoesters that are prepared by zinc triflate catalyzed Mukaiyama-aldol condensation of methyl diazoacetoacetates with aldehydes, occurred in quantitative yield to form dihydrofuranols that undergo acid catalyzed dehydration under mild conditions to generate 3-methoxyfuran-2-carboxylates in good yield. Oxidation of ζ-keto-α-diazo-β-ketoesters that are formed by zinc triflate catalyzed Mukaiyama-Michael condensation of methyl diazoacetoacetate enones procduced their 2,3,7-diketoester derivative in quantitative yield. The intramolecular acid catalyzed aldol cyclization of 2,3,7-triketoesters provides highly functionalized cyclopentanones with good diastereoselectivity in high overall yields via kinetically controlled and stereodivergent catalytic processes. Lewis acid catalysis gives high selectivity for the 1,3-anti tetrasubstituted cyclopentanones, whereas Brønsted acid catalysis produces the corresponding 1,3-syn diastereomer. The first enantioselective transformation of 2,3-diketoesters was demonstrated in carbonyl-ene reactions catalyzed by [Cu((S,S)-tert-Bu-box)](SbF6)2 generating chiral α-functionalized-α-hydroxy-β-ketoesters in up to 94% yield and 97% ee. The suggested mode of activation is bi-dentate coordination between copper and the oxygen atoms of the two keto-carbonyl groups. The 2,3-diketoesters are conveniently accessed from the corresponding α-diazo-β-ketoester, and catalyst loading as low as 1.0 mol % is achieved.