PhD, University of Cincinnati, 2024, Arts and Sciences: Chemistry

Electrosynthesis is a popular and green alternative to traditional organic methods for synthesizing small organic molecules. Due to its ability to generate highly reactive species under mild conditions by anodic oxidation or cathodic reduction, electrosynthesis is particularly interesting for otherwise challenging transformations. The contents of this dissertation are primarily focused on the evaluation of molecular electrocatalysts and their role in small molecule activation such as carbon dioxide (CO2) reduction and dehalogenation reactions. The electrochemical reduction of CO2 to produce value-added chemicals is of great significance in mitigating environmental and energy concerns. In this work, an iron porphyrin catalyst, FePEG8T, with multiple triazole units tethered to a porphyrin ligand via flexible oxymethylene linkers, is reported for efficient electrocatalytic reduction of CO2 to afford carbon monoxide (CO). The electrocatalyst exhibits excellent catalytic activity with a current density of –17.5 mA/cm2 and CO Faradaic efficiency of 95% at –2.5 V vs. Fc/Fc+ in acetonitrile using water as the proton source. The maximum turnover frequency (TOFmax) was calculated to be 5.5 x 104 s-1 using foot-of-the-wave analysis (FOWA), which is thirty times higher than the result from our previous zinc complex with the same triazole-porphyrin ligand. Long-term electrolysis of 40 hours was also performed and demonstrated high catalyst stability. Further, Tafel plot was generated for the catalyst FePEG8T for comparison with previously reported iron porphyrin catalysts. This work demonstrates an efficient CO2 reduction catalyst containing an iron metal center and a flexible triazole in the second coordination sphere toward CO formation with high stability, activity, and selectivity. Reductive hydrodechlorination is an effective approach to enhance the degradation rate of chlorinated herbicides such as alachlor, which are frequently detected in ground and surface (open full item for complete abstract)

Committee: Jianbing Jiang Ph.D. (Committee Chair); Noe Alvarez Ph.D. (Committee Member); Hairong Guan Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy (PhD), Ohio University, 2023, Chemistry and Biochemistry (Arts and Sciences)

The purpose of this study was to examine the redox behavior of the fac-[Re(bpy)] Lewis base catalysts in CO2 reduction processes using the Lewis acid co-catalyst [Zn(cyclam)]2+. Experimental and computational data indicate that [Zn(cyclam)]2+ facilitates Cl ion dissociation, thus shifting the ReI(bpy) first reduction to a less negative potential, allowing the catalyst to be activated with a lower energy requirement. Further, the addition of [Zn(cyclam)]2+ usually reduced the amount of energy needed for CO2 reduction, except for catalysts with electron-withdrawing groups (EWGs). In another study, with the help of a new ligand and Europium ions, we have designed and synthesized a lantern-shaped coordination cage. It is capable of selectively trapping charged molecules and exhibits changes in its photophysical properties when compared to individual molecules. We measured the strength of the interaction and the binding constant of guest molecules. The luminescence properties of the cage were affected by the presence of the guest molecules.

Committee: Michael Jensen Dr. (Committee Member); Eric Masson Dr. (Advisor); Katherine Fornash Dr. (Committee Member); Jixin Chen Dr. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2023, Chemical Engineering

Solid oxide electrocatalytic cell (SOEC) is a promising technology for facilitating reactions involving the removal or addition of oxide ions. By designing the appropriate electrode catalysts, reactions such as CO2 electrolysis, H2O electrolysis, oxidative dehydrogenation (ODH) of light alkanes (C2H6, C3H8), and oxidative coupling of methane can be efficiently carried out in an SOEC. Perovskite materials based on Fe, such as La(Sr)FeO3, possess a range of beneficial properties for use in electrocatalysis. They are compatible with electrolyte materials, have high electrical conductivity, and are stable in both oxidizing and reducing atmospheres. Additionally, the formation of exsolved B-site metal nanoparticles on the surface of the perovskite material can significantly improve its electrochemical activity when exposed to a reducing atmosphere. In chapter 1, La0.7Sr0.2Ni0.2Fe0.8O3 (LSNF), having thermochemical stability, superior ionic and electronic conductivity, and structural flexibility, was investigated as a cathode in SOECs. Exsolution of nanoparticles by reduction of LSNF at elevated temperatures can modulate the characteristics of adsorption, electron transfer, and oxidation states of catalytically active atoms, consequently improving the electrocatalytic activity. The exsolution of NiFe and La2NiO4 nanoparticles to the surface of LSNF under reducing atmosphere (5% H2/N2) was verified at various temperatures (500–800 °C) by IFFT from ETEM, TPR and in situ XRD. The exsolved nanoparticles obtained uniform size distribution (4.2–9.2 nm) and dispersion (1.31 to 0.61 × 104 particle per μm2) depending on the reduction temperature (700–800 °C) and time (0–10 h). The reoxidation of the reduced LSNF (Red-LSNF) was verified by the XRD patterns, indicative of its redox ability, which allows for redistribution of the nanoparticles between the surface and the bulk. TPD-DRIFTS analysis demonstrated that Red-LSNF had superior H2O and CO2 adsorption behavior as compared to (open full item for complete abstract)

Committee: Umit Ozkan (Advisor); Anne Co (Committee Member); Jeffrey Chalmers (Committee Member); Jose Castro (Committee Member) Subjects: Chemical Engineering

MS, University of Cincinnati, 2022, Engineering and Applied Science: Chemical Engineering

The electrochemical CO2 reduction reaction (CO2RR) with renewable energy is an approach to reduce CO2 emissions. Multi-carbon products (C2+), including ethylene and ethanol, are known as the desired products from CO2RR due to their high market prices and high energy contents. CO is a key intermediate to form multi-carbon products because C-C coupling requires adsorbed CO on a copper catalyst. Enhancement of CO binding strength and CO concentration leads to enhanced C2+ formation. Pulse electrolysis is one of the electrolytic methods to accomplish the selective and productive formation of multi-carbon products, and the different selection of potentials provides different aspects of the local environment. The first approach of pulse electrolysis is the cycle of oxidation and reduction with anodic and cathodic potentials. The cycle can form and reconstruct grain boundaries that have stronger CO binding continuously. Then, the higher density of grain boundaries leads to enhanced C2+ faradaic efficiency (FE) and current density. Commercial copper nanoparticles and CuO nanowires were analyzed, and the results of CuO nanowires show the enhancement of C2+ formation due to the high density of grain boundaries at anodic potentials from 0.5 to 1.1 V versus reversible hydrogen electrode (RHE). The difference in performance due to the change of catalysts reveals that the formation of grain boundaries using pulse electrolysis is critically sensitive to the catalyst morphology. On the other hand, the enhanced methane formation is observed at anodic potentials of 1.3V versus RHE or above for both copper-derived catalysts due to significant consumption of OH- during anodic potentials. The second approach of pulse electrolysis involves a cycle of reductions at different cathodic potentials. One of the cathodic potentials is selected for CO formation to utilize CO during the electrolysis, and another cathodic potential takes over C2+ formation. Pulse electrolysis with different cathod (open full item for complete abstract)

Committee: Jingjie Wu Ph.D. (Committee Member); Maobing Tu Ph.D. (Committee Member); Aashish Priye Ph.D. (Committee Member) Subjects: Chemical Engineering

PhD, University of Cincinnati, 2022, Engineering and Applied Science: Materials Science

Floating Catalyst Chemical Vapor Deposition (FCCVD) has many unique advantages in synthesizing Carbon Nanotubes (CNTs). These advantages include the ease of continuously producing CNTs with minimal human intervention, customizable reactor design, and easy production scaling. However, FCCVD has also encountered many problems, which are usually associated with low efficiency, sensitivity to the reaction environment, as well as potential safety issues that could endanger reactor operators. This dissertation demonstrates the progress that has been made to stabilize the reactor operation, as well as adding safety features to ensure the safe operation of the reactor. This modified reactor with the enhanced safety features was then used to synthesize CNT with good electrical and mechanical properties. CNTs from the FCCVD reactor were used in four different applications in this dissertation, which are supercapacitor, heater, EMI shielding, and Zn-CO2 battery. The devices' fabrication processes are detailed in three separate chapters of this dissertation, which also include their respective characterization and performance analysis. In the first application of this dissertation, an electrochemical-based method was used to activate the CNT sheet materials to increase the surface area. Electrochemical activation delaminates the CNT sheet thereby increasing the effective surface area of the CNT strands. The increased surface area allows increasing the active materials concentration that can be integrated into the CNT sheet. A Randle-Sevcik plot was used to assess and calculate the activated surface area. Polyaniline (PANI) used as an electrochemically active material was then deposited on the activated CNTs by using a process called oxidation polymerization to create a CNT-PANI composite material for supercapacitor energy storage applications. A fully fabricated supercapacitor device with CNT-PANI electrodes was then created with excellent volumetric energy dens (open full item for complete abstract)

Committee: Mark Schulz Ph.D. (Committee Member); Vijay Vasudevan Ph.D. (Committee Member); Matthew Steiner Ph.D. (Committee Member); Vesselin Shanov Ph.D. (Committee Member) Subjects: Materials Science

PhD, University of Cincinnati, 2022, Engineering and Applied Science: Chemical Engineering

The concentration of carbon dioxide (CO2) in the atmosphere reaches a record high level of 412 parts per million. This high CO2 concentration has caused a series of undesirable climate effects, like erratic weather. There is a pressing need to develop a sustainable strategy to achieve negative CO2 emissions. Electrochemical CO2 reduction at ambient conditions employing renewable energy is recognized as a viable technology for the distributed generation of chemicals such as methane (CH4) and ethylene (C2H4) using CO2 recovered from industrial exhaust streams. This dissertation optimizes the CO2 reduction performance from the aspects of intrinsic catalyst design and extrinsic micro-environment regulation. Chapter 2 rationally designs metal-free graphene quantum dots (GQDs) catalysts for CO2 to CH4 conversion by regulating functional groups. The CH4 Faradaic efficiency reaches 70% at 200 mA cm-2 partial current density. Electron-donating functional groups facilitate the yield of CH4 while electron-withdrawing groups suppress CO2 reduction. Chapters 3, 4, and 5 study the role of the micro-environment in promoting the active and durable CO2 to C2H4 conversion. Chapters 3 and 4 design tandem gas diffusion electrodes (GDE), which integrate a CO-selective catalyst for complementary CO supply and a C2H4-selective catalyst for further CO reduction, to implement the cascade CO2?CO?C2H4 conversion. The C2H4 productivity was determined to be positively correlated with CO concentration (reaction order > 0). Therefore, the tandem GDEs were designed following the principle of plug flow reactor (PFR) in which CO intermediate conversion maximizes compared to the counterpart of continuous stirred tank reactor (CSTR). Chapter 3 investigates the PFR-analogous layered tandem GDEs with a CO-selective catalyst layer (CL) on the top and a C2H4-selective CL underneath. The CO concentration tops at the electrode/electrolyte interface and is consumed gradually along the electrode (open full item for complete abstract)

Committee: Jingjie Wu Ph.D. (Committee Member); Joo-Youp Lee Ph.D. (Committee Member); Maobing Tu Ph.D. (Committee Member); Yujie Sun Ph.D. (Committee Member); Peter Panagiotis Smirniotis Ph.D. (Committee Member) Subjects: Chemical Engineering

PhD, University of Cincinnati, 2022, Arts and Sciences: Chemistry

The contents of this dissertation are primarily focused on the evaluation of molecular electrocatalysts and their intrinsic properties during electroreduction reactions such as carbon dioxide (CO2) reduction, hydrodehalogenation, and hydrogen evolution. The control of the second coordination sphere in a coordination complex plays an important role in improving catalytic efficiency. Herein, we report a zinc porphyrin complex ZnPor8T with multiple flexible triazole units comprising the second coordination sphere, as an electrocatalyst for the highly selective electrochemical reduction of carbon dioxide (CO2) to carbon monoxide (CO). This electrocatalyst converted CO2 to CO with a Faradaic efficiency of 99% and a current density of –6.2 mA/cm2 at –2.4 V vs Fc/Fc+ in N,N-dimethylformamide using water as the proton source. Structure-function relationship studies were carried out on ZnPor8T analogs containing different numbers of triazole units and distinct triazole geometries; these unveiled that the triazole units function cooperatively to stabilize the CO2-catalyst adduct in order to facilitate intramolecular proton transfer. This demonstrates that incorporating triazole units that function in a cooperative manner is a versatile strategy to enhance the activity of electrocatalytic CO2 conversion. The effects of primary and second coordination spheres on molecular electrocatalysis have been extensively studied, yet investigations of third functional spheres are rarely reported. Here we report an electrocatalyst (ZnPEG8T) with a hydrophilic channel as a third functional sphere that facilitates relay proton shuttling to the primary and second coordination spheres for enhanced catalytic CO2 reduction. Using foot-of-the-wave analysis, the ZnPEG8T catalyst displayed CO2-to-CO activity (TOFmax) thirty times greater than that of the benchmark catalyst without a third functional sphere. A kinetic isotopic effect (KIE) study, in conjunction with volta (open full item for complete abstract)

Committee: Jianbing Jiang Ph.D. (Committee Member); Ryan White Ph.D. (Committee Member); Hairong Guan Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, University of Akron, 2021, Chemical Engineering

The elevated environmental challenges caused by human activities have yielded a growing demand for more sustainable and environmental-friendly chemical synthesis processes. Hydrogenation reaction, an indispensable part of chemical industry which accounts for 10~20 % of total chemicals produced, can be a possible answer to that demand. Hence, the main topic in this dissertation is sustainable and energy-efficient chemical synthesis via hydrogenation processes. The research branches out 3 sub-topics: CO2 hydrogenation, CO electroreduction and plastic hydrogenolysis. For CO2 hydrogenation, In2O3-based catalyst composites were developed as selective catalysts for methanol/dimethyl ether synthesis, meanwhile their reaction mechanisms were uncovered via in situ IR. CO electroreduction using molybdenum phosphide catalyst leads to direct, selective formaldehyde synthesis under ambient condition for the first time. A spontaneous, full-cell CO reduction was demonstrated under zero energy input. A new non-thermal plasma-assisted plastic hydrogenolysis method was developed, leading to fast depolymerization and high yield of light hydrocarbons (C1-C3) for polyethylene and polystyrene. Capability of processing plastic wastes was also evidenced. There findings offer promising methods and strategies for achieving energy-efficient, cost-effective and sustainable chemical synthesis via hydrogenation of carbon-based feedstocks.

Committee: Zhenmeng Peng (Committee Chair); Jie Zheng (Committee Member); Qixin Zhou (Committee Member); Steven Chuang (Committee Member); Guo-Xiang Wang (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, The Ohio State University, 2020, Chemistry

The world has a potential global energy crisis that is expected to erupt before 2050. To combat these issues, there needs to be a development of alternative, solar-based energy technologies for the reduction of CO2 and hydrogen evolution. The key to this problem lies in understanding the energy conversion and storage technologies through the reduction of CO2 or hydrogen evolution. These processes only becomes practical if reaction efficiency is improved and production costs are minimized. To increase the efficiency of these reactions, catalysts are often used to control efficiency and selectivity to various products for these reactions. These catalysts are often used in a process of photoelectrocatalysis, where selectivity to various products can be controlled using potential bias as well as UV-visible light to overcome thermodynamic and kinetic barriers. Metal oxides are cost-effective catalysts for these reactions; however, they suffer from issues with activity and stability in CO2 reduction conditions. The addition of a second metal to a metal oxide has been used to tune structural and electronic properties in the material toward more efficient photoelectrolysis. Delafossite metal oxides containing two metals tend to be promising photocathodes for these reactions because of their greater stability, low-cost, and small band-gaps needed to drive hydrogen evolution and CO2 reduction. However, the activity needed for practical application of these materials is still lacking. Additionally, bulk and surface defects can complicate studies on the photoactivity of these materials. Therefore, understanding the role of these lattice defects and their impact on catalysis is critical to improving design of photoelectrodes. CuFeO2 is a delafossite material that primarily exhibits three main defect types: O atom interstitials, Cu vacancies, and the formation of heterojunctions with CuO. However, recent research is unclear which defect, if any, is responsible for the (open full item for complete abstract)

Committee: L. Robert Baker (Advisor); Abraham Badu-Tawiah (Committee Member); Prabir Dutta (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2020, Chemistry

Electrochemical reduction of CO2 (CO2RR) is a promising route to convert CO2 to value-added chemicals such as carbon monoxide, formic acid, methanol, and others. Efficient conversion of CO2 using renewable sources of electricity can potentially mitigate the rising CO2 concentration in the atmosphere in addition to alleviating our dependence on fossil fuels to generate chemicals. Most of the CO2RR studies to date focus on designing novel catalysts to improve the reaction activity and selectivity for real-world applications. However, being able to quickly and accurately evaluate the performance of newly-designed catalysts and to rapidly screen catalyst candidates remain an essential part of the catalyst discovery process. Traditional product analysis routine includes sample pre-concentration (e.g. using long electrolysis time), sample preparation, instrument detection (e.g. GC or NMR) and/or instrument availability. This time-consuming routine heavily impedes the efficient evaluation and screening of newly-designed CO2RR catalysts. It also limits our ability to investigate the catalyst degradation mechanism within a short time frame like minutes. In this work, a rotating ring-disc electrode (RRDE)-based method was proposed and demonstrated to be able to shorten the total product analysis time from several hours (even days) to less than 1 minute. Small CO2RR product molecules such as H2, CO, HCOOH and their mixtures were proved to be quantified successfully on an RRDE assembly based on their electrochemical fingerprints. During CO2RR, OH- is always generated concurrently with reduction products. The accumulation of OH- near the catalyst surface during CO2RR remains a critical issue since the local pH can easily be over 3 pH units higher than the bulk during electrolysis and thus directly affects the CO2RR activity and selectivity. To systematically investigate the role of local pH on CO2RR selectivity and consequently the reaction pathway, in this work, an RR (open full item for complete abstract)

Committee: Anne Co (Advisor) Subjects: Analytical Chemistry; Chemistry

Master of Science in Chemistry, Youngstown State University, 2019, Department of Chemistry

1,3–bis(2,4,6–trimethylphenyl)imidazolium carboxylate, an adduct between CO2 and the N–heterocyclic carbene (NHC), 1,3–bis(2,4,6–trimethylphenyl)–1,3–dihydro–2H–imidazol–2–ylidene, was synthesized to study the reactivity of CO2 after binding to the carbene intermediate. Nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, X–ray powder diffraction (XRD), gas chromatography (GC) and thermal gravimetric analysis (TGA) were employed to characterize the final imidazolium carboxylate. GC was specifically used to study the dissociation of the CO2 adduct. The structure of the synthesized zwitterion was confirmed via 1H and 13C NMR, where adduct formation generated a new peak in the 13C NMR spectrum. IR spectroscopic data showed a significant characteristic peak for C=O stretch at around 1670 cm–1. TGA spectra showed that the zwitterion‟s weight loss of 13% at 155 °C which is the percent weight of CO2 . The GC study of CO2 , which was released after treating the imidazolium carboxylate with 5% H2O in CH3CN, enabled the possibility of the reversibility of CO2– NHC adduct formation. The stability and air sensitivity of the imidazolium carboxylate were tested in polar, nonpolar, acidic, basic, and mixed solvents via simple effervescence tests and GC. The hydrolytic stability of the imidazolium carboxylate was examined. The bis-mesityl carboxylate showed reasonable stability in water, in contrast to carboxylates with smaller alkyl substituents, but admixture with organic solvent would cause it to break down into the corresponding imidazolium bicarbonate. After exposure to H2 (g) and heat, there was evidence for the reductive conversion of the carboxylate into imidazolium formate. This suggests the application of the mesityl imidazolyl carbene as an organic catalyst for CO2 reduction.

Committee: Linkous Clovis PhD (Advisor); Jackson John PhD (Committee Member); Serra Michael PhD (Committee Member) Subjects: Analytical Chemistry; Chemistry; Climate Change

Master of Science in Chemistry, Youngstown State University, 2019, Department of Chemistry

N-Heterocyclic carbenes have been recognized for their ability to capture CO2 at standard temperature and pressure. This makes them a molecule that could be used for renewable energy synthetic methods. Synthesis and characterization of an IMesCO2 derivative based on bis-mesityl imidazolium chloride was performed, followed by one of four commonly used reduction methods. Methanol is a possible product from a successful reduction through hydrogenation. Efficient production of this species could establish CO2 as a viable renewable energy source. A high pressure hydrogen gas experiment as well as three possible hydride reduction pathways were investigated. Hydrogen gas was used to beak the C2-carbon dioxide bond. This technique explores the results of introducing the IMesCO2 to a neutral hydrogen, which resulted in the formation of formic acid. Hydride reductions were done with lithium aluminum hydride, lithium borohydride and sodium borohydride. They were introduced to the IMesCO2 to donate a hydride to the C2-carbon dioxide bond. The different hydrides varied in selectivity toward IMesCO2 reduction. IMesCO2, possessing a carbonyl group, was subjected to all the hydrides in appropriate solvents. Therefore, the reaction showed the formation of formate for several scenarios. The key to these reductions was the solvent: tetrahydrofuran in conjunction with lithium aluminum hydride; tetrahydrofuran, acetonitrile, and dimethyl sulfoxide used with lithium borohydride; and tetrahydrofuran, acetonitrile, and dimethyl sulfoxide with sodium borohydride. However, there seemed to be a need for a balance between reducing strength of the hydride and selectivity for the carbonyl. To further expand on the idea of using appropriate solvents, sodium tetraphenyl borate was included as an additive to promote reduction via increased solubility, but reactivity with the sodium borohydride did not generally increase. Furthermore, several reaction spectra show evidence of the imidazol (open full item for complete abstract)

Committee: Clovis Linkous PhD (Advisor); Brian Leskiw PhD (Committee Member); Douglas Genna PhD (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2017, Arts and Sciences: Chemistry

The development of new catalysts for the reduction of carbon dioxide is of utmost importance to both limit the harmful greenhouse gas as well as to provide usable C1 feedstock chemicals. One method to reduce this CO2 is through the use of a metal hydride complex. Of these metal complexes, nickel POCOP pincer hydride complexes have been highly successful at catalyzing the reduction of carbonyl functionalities. Although these catalysts are effective at catalyzing this reduction, there are few processes to make these hydrides. Additionally, not much is known about which factors will improve catalytic reduction or what other reactions they can catalyze. Nickel chloride complexes bearing POCOP pincer ligands were easily synthesized using a microwave reactor. Through this methodology nickel POCOP pincer chloride complexes can be made in as little as 5 minutes in very high purities and yields. Nickel complexes with iPr, cPe, Cy, Ph, and tBu substituents on the phosphorous atoms can all be synthesized using this method. Additionally, palladium chloride complexes bearing isopropyl substituted POCOP ligands can be made. This method was also found to greatly limit the solvent needed to make these complexes. Alternative routes to synthesize nickel hydride complexes is an important problem due to the harsh methods used to synthesize them. To explore an additional method for hydride synthesis, nickel fluoride complexes bearing POCOP pincer ligands were synthesized. These complexes can be easily converted to hydride complexes using silanes or boranes. The factors that influence a metal hydrides ability to reduce CO2 were investigated. To determine which factors had an impact on the reduction of CO2 to formate complex, a series of nickel hydride and formate complexes were synthesized. The complexes were tested to determine the relative thermodynamic favorability for the reduction of CO2 to formate. Complexes bearing more electron donating ligands were found to be (open full item for complete abstract)

Committee: Hairong Guan Ph.D. (Committee Chair); William Connick Ph.D. (Committee Member); Allan Pinhas Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2017, Chemistry

The class of dirhodium(II,II) complexes [Rh2(µ-BL)2(NN)2][BF4] (µ-BL = DTolF = p-ditolylformamidinate, acam = acetamidate, OAc = acetate; NN = dpq = dipyrido[3,2-f:20,30-h]quinoxaline, dppz = dipyrido[3,2-a:2',3'c]phenazine, dppn = benzo[i]dipyrido[3,2-a:2',3'-h]quinoxaline, phen = 1,10-phenanthroline) were investigated as catalysts for the generation of fuels and useful chemicals from abundant, inexpensive sources. When coupled to a light absorber that can transfer electrons to the Rh2(II,II) complexes, it was hypothesized that they would be able to reduced H+ to H2 and CO2 to molecules useful as fuels or in industry. As such, the ability of these complexes to electrocatalytically reduce each substrate was investigated. When reduced electrochemically, the [Rh2(DTolF)2(NN)2][BF4] (1) complexes were shown to serve as a highly efficient and robust catalysts for the reduction of H+ to H2. Turnover frequencies (TOF) of 2.8 × 104, 2.6 × 104, and 5.9 × 104 s-1 were determined for 1.2, (NN = dppz) 1.3 (NN = dppn), and 1.4 (NN = phen), respectively, with overpotential values of 0.50 (1.2), 0.56 (1.3), and 0.64 V (1.4). Bulk electrolysis followed by headspace injection into a gas chromatograph confirmed the only product to be H2. The proposed catalytic mechanism proceeds through electrochemical generation of a Rh2II,I species that may be protonated to form a Rh2II,III-hydride; the latter undergoes subsequent reduction and protonation to release H2 gas. Complexes 1.1 and 1.4 were shown to also electrocatalytically reduce CO2 in 3 M H2O to produce HCOOH and carbonate. However, ~70% of the electrons in these systems generate H2, such that 1 is not selective for CO2 in the presence of H+. [Rh2(OAc)2(phen)2][BF4] (2) and [Rh2(acam)2(phen)2][BF4] (3) generate greater current enhancement than 1.1 and 1.4 in the presence of CO2 and exhibit significantly different selectivity when compared to 1, with nearly 100% HCOOH production achieved for 3 without degradation. The ca (open full item for complete abstract)

Committee: Claudia Turro (Advisor); Anne Co (Committee Member); James Cowan (Committee Member); David Bromwich (Committee Member) Subjects: Analytical Chemistry; Chemistry; Inorganic Chemistry

Master of Science (MS), Bowling Green State University, 2017, Chemistry

Recent scientific efforts aim to blend light harvesting with the fuel forming catalysis, as a novel method to store the energy captured from the Sun. Our approach is to construct an efficient photoelectrochemical cell using earth-abundant materials. The proposed system contains bioinspired metal-free hydride donors suitable for fuel forming reductions and a p-type semiconductor that serve as a light harvester and source of electrons. In this thesis, we investigate fundamental steps that determine the efficiency of the photoelectrochemical cell: photoreduction of NAD+ dyes by p-GaP semiconductor and the hydricity of NADH analogs. First, thermodynamics for photo-induced electron transfer from p-GaP to NAD+ dyes are evaluated using steady-state UV/Vis absorption and cyclic voltammetry experiments. Photoelectrochemical measurement conducted on p-GaP electrodes immersed in aqueous electrolytes and dye show sensitization for only two dyes. Pump-probe measurements reveal that the “inefficient” dyes have short-lived excited states, inhibiting the successful charge transfer into p-GaP surface. This work provides an insight on timescales of hole-injection rates during dye-sensitization processes. Furthermore, we evaluate the hydricity for model NADH analogs using experimental methods and calculations. The obtained hydricity values display a strong dependence on structural and electronic properties of the model compounds. When compared with metal-based analogs, NADH analogs show similar hydride donor ability. However, the high reduction potentials for metal-free hydride donors hinder their applicability in the catalysis. This work offers a reasonable explanation on why NADH analogs have not been utilized in fuel forming catalysis and provides the answers how to overcome these limitations.

Committee: Ksenija D. Glusac Prof. Dr. (Advisor); R. Marshall Wilson Prof. Dr. (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2017, Arts and Sciences: Chemistry

This dissertation research focuses on the development of tridentate ligand supported nickel complexes for both catalytic and stoichiometric bond activation reactions. One of the main objectives of this research is to understand how the flexibility of ligands impacts the reactivity of transition-metal complexes. To this end, three different ligands with varying degree of flexibility have been studied. Chelating ligands have been used to enhance the stability of transition-metal complexes because compared to monodentate ligands these ligands are less likely to dissociate from the metal. Guided by this hypothesis, a chelating secondary phosphine oxide (SPO) ligand has been synthesized and shown to act as either a bidentate or a pseudo tridentate ligand depending on the electronic demand and geometry at the nickel center. Nickel(0) species supported by this SPO is a more effective catalyst than Ni(0)–Ph2P(O)H for cross-coupling of aryl iodides with aryl thiols. Both electron-donating and electron-withdrawing groups including OMe, CF3, CN, pyridyl or ester groups are tolerated in this catalytic system. However, low isolated yields are observed with sterically crowded aryl iodides and aryl thiols. Nickel complexes bearing a tridentate pyridine bis-amide ligand have also been studied for carbon-sulfur cross-coupling reaction of aryl iodide with aryl thiol. One of the nickel chloride complexes in which (o-Me)2C6H3 group is the substituent on the amide nitrogens has been used as the catalyst. Harsh reaction conditions including high catalyst loadings, high temperatures and long reaction times are required to obtain nearly quantitative yields. Two cationic nickel hydride complexes containing a PNHPiPr ligand have been synthesized. For the cationic hydride with Br- as the counter anion, NaBH4 is the main hydride source whereas alcohol and residual water are the proton sources for NH hydrogen. These cationic hydrides have been studied for the reduction of CO2. The rate of CO2 i (open full item for complete abstract)

Committee: Hairong Guan Ph.D. (Committee Chair); William Connick Ph.D. (Committee Member); Allan Pinhas Ph.D. (Committee Member) Subjects: Chemistry; Inorganic Chemistry; Organic Chemistry

Master of Science, The Ohio State University, 2016, Chemistry

Rhenium polypyridyl complexes have long been used as CO2 reduction catalysts both electrochemically and photochemically. The Ruthenium-Rhenium bimetallic complexes [(biq)2Ru(µ-dpp)Re(CO)3Cl](PF6)2, [(biq)2Ru(µ-dpq)Re(CO)3Cl](PF6)2 and [(biq)2Ru(µ-dpb)Re(CO)3Cl](PF6)2 (biq= 2,2'- biquinoline, dpp=2,3-bis(2-pyridyl)pyrazine, dpq= 2,3-bis(2-pyridyl)quinoxaline, dpb = 2,3-bis(2-pyridyl)benzoquinoxaline) were synthesized and studied as potential electrocatalytic and photocatalytic CO2 reduction agents. The catalytic efficiency of the Ru-Re bimetallic complexes is compared to that of each Ru and Re monometallic compound. A total of 9 compounds were investigated. In cyclic voltammograms of the Re monometallic and Ru-Re bimetallic complexes, current increase was observed under a CO2 atmosphere when compared to measurements conducted under N2. The only CO2 reduction product detected was CO following bulk electrolysis on the complexes using with gas chromatography and 1H and 13C NMR spectroscopy. Photochemically, Re monometallic compounds were shown to reduce CO2 with the assistance of Ru(bpy)32+ as a photosensitizer. However, Ru-Re bimetallic compounds failed to produce any CO. The possible reasons for the difference in reactivity are discussed.

Committee: Claudia Turro (Advisor); Hannah Shafaat (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2012, Arts and Sciences: Chemistry

This dissertation is focused on the synthesis of well-defined nickel hydride complexes bearing a bis(phosphinite) pincer ligand (commonly known as a POCOP ligand) and utilities of these metal complexes in varieties of useful organic transformations. Aldehydes insert cleanly and selectively into the Ni-H bonds of (POCOP)NiH complexes to form nickel alkoxide complexes. These nickel alkoxide compounds further react with phenylsilane to regenerate (POCOP)NiH and produce silyl ethers. Based on these observations, an efficient and chemoselective hydrosilylation process has been developed utilizing nickel hydrides as catalysts. The process is highly compatible with varieties of functional groups in aldehydes. A nickel hydride complex with smaller substituents on the POCOP ligand proves to be more effective hydrosilylation catalyst. In case of ketones, partial hydrosilylation occurs. (POCOP)NiH complexes also react with CO2 to produce nickel formate complexes. When stoichiometric amounts of boranes are used, nickel hydrides are cleanly reformed. The use of catalytic amounts of nickel hydrides and excess of boranes reduces CO2 to the corresponding methanol derivatives. The initial reduction products can be further hydrolyzed to yield methanol. The overall transformation is comprised of three catalytic cycles. A catalyst with more bulky substituents on the phosphorus atoms of pincer ligand is a more effective catalyst than those containing smaller substituents. This phenomenon has been rationalized by invoking more favorable dihydridoborate adduct formation between less bulky nickel hydrides and boranes. One of such dihydridoborate adduct has been successfully isolated and its influence on the catalytic CO2 reduction has been demonstrated. (POCOP)NiH complexes have been found be active catalysts for the decomposition of formic acid to release dihydrogen. When the kinetics the reaction is monitored by in-situ IR spectroscopy, a unique sigmoidal pattern is observed. Seve (open full item for complete abstract)

Committee: Hairong Guan PhD (Committee Chair); William Connick PhD (Committee Member); Allan Pinhas PhD (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2011, Statistics

This dissertation is comprised of an introductory chapter and three stand-alone chapters, tied together by a unifying theme: the statistical analysis of very large spatial and spatio-temporal datasets. These datasets now arise in many fields, but our focus here is on environmental remote-sensing data. Due to sparseness of daily datasets, there is a need to fill spatial gaps and to borrow strength from adjacent days. Nonetheless, many satellite instruments are capable of conducting on the order of 100,000 retrievals per day, which makes it computationally challenging to apply traditional spatial and spatio-temporal statistical methods, even in supercomputing environments. In addition, the datasets are often observed on the entire globe. For such large domains, spatial stationarity assumptions are typically unrealistic. We address these challenges using dimension-reduction techniques based on a flexible spatial random effects (SRE) model, where dimension reduction is achieved by projecting the process onto a basis-function space of low dimension. The spatio-temporal random effects (STRE) model extends the SRE model to the spatio-temporal case by modeling the temporal evolution, on the reduced space, using a dynamical autoregressive model in time. Another focus of this work is the modeling of fine-scale variation. Such variability is typically not part of the reduced space spanned by the basis functions, and one needs to account for a component of variability at a fine scale. We address this issue throughout the dissertation with increasingly complex and realistic models for a component of fine-scale variation. After a general introductory chapter, the subsequent two chapters focus on estimation of the reduced-dimensional parameters in the STRE model from both an empirical-Bayes and a fully Bayesian perspective, respectively. In Chapter 2, we develop maximum likelihood estimation via an expectation-maximization (EM) algorithm, which offers stable computation (open full item for complete abstract)

Committee: Noel Cressie PhD (Advisor); Peter Craigmile PhD (Committee Member); Tao Shi PhD (Committee Member) Subjects: Statistics

Master of Sciences, Case Western Reserve University, 2012, Chemical Engineering

The study of CO2 reduction to produce C‐C bond and hydrogenated carbon bonds as the final product has been discussed for the past decade (methane,ethane, etc). The C‐C bond and hydrogenated carbon can be used as a high value energy source and for chemical feedstocks. The long‐term goal of this research is to be able to take abundant CO2 and electrochemically reduce it to a useful energy source or chemical feedstock using renewable electric energy sources . A comprehensive review of electrochemical CO2 reduction has been performed, and there are numerous literature references for many different metal electrocatalyst, and in general it is concluded that copper is most active surface for CO2 reduction. In the mechanism of CO2 reduction, the step involving CO(ads)as an intermediate is key, then this intermediate reacts to form C‐C bonds as a final product. Therefore we wanted to explore this reaction further on controlled copper layers on metal substrates as an approach to modify the copper surface energetics towards reactant adsorption and stabilization of reaction of intermediates on the surface. Underpotential deposition of copper adlayers is a highly promising technique for modification of a substrate surface such as Pt and Au (among others) of either bulk disk electrodes or supported nanoparticle electrocatalyst, and it has been explored for synthesizing shell‐core electrocatalyst to promote the oxygen reduction reaction (ORR). However,underpotential deposition of copper has not been studied for CO2 reduction. Since the preparation of these upd layers involves deposition in one electrolyte (acid) and electrochemical reduction of CO2 in another electrolyte (neutral), it was unclear that these electrocatalyst could be prepared and maintained stable while transferring electrolytes for electrocatalyst studies (copper easily oxidizes in air). This research set out to demonstrate that a Cuupd film on a Pt or Au substrate (macro size disk electrodes or carbon supported (open full item for complete abstract)

Committee: Robert Savinell (Advisor); Chung-Chiun Liu (Committee Member); Jesse Wainright (Committee Member) Subjects: Chemical Engineering