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Zinc air batteries have great promise as a new age energy storage device due to their environmental benignity, high energy density in terms of both mass and volume, and low cost Zinc air batteries get their high energy density by using oxygen from the air as the active material. This means that all the mass and volume that are normally required for active material in a battery are replaced by a thin gas diffusion electrode which allows for oxygen from the air to diffuse into the cell. Although this seems ideal, there are many technical challenges associated with the cell being open to the atmosphere. Some of these issues include electrolyte and electrode drying out, poor reaction kinetics involving sluggish reaction, the need for bifunctional catalysts to charge and discharge, and durability of the gas diffusion electrode itself. The bifuntional catalysts used in these systems are often platinum or other precious metals since these are commonly known to have the highest performance, however the inherent cost of these materials limits the feasibility of zinc air systems. Thus, there is a need to limit or remove the necessity for platinum carbon catalysts. There are many types of non precious metal catalysts which can be used in place of platinum, however their performance is often not as high, and the durability of these catalysts is also weak. Similar limitations on feasibility are invoked by the poor durability of the gas diffusion electrodes. Carbon corrosion occurs at the harsh caustic conditions present at the gas diffusion electrodes, and this corrosion causes catalyst dissolution. Moreover, many issues with zinc electrode fabrication limit durability and usable anode surface area within these systems. There is a need for a stable, porous, high surface area anode with good structural integrity. These issues are addressed in this work by three studies which each focuses on solving some of the issues pertaining to a crucial component of zinc air batteries, those being the gas diffusion electrode, the zinc electrode, and the bifunctional catalyst necessary for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). The first study addresses the need for improvements to the zinc anode electrode. A new process is proposed for the production of porous zinc electrodes in which the porosity can be easily controlled. This process involves the mixing of atomized zinc powder with a filler compound such as ammonium chloride. The mixture is then pressed into a pellet and heat treated to a temperature which simultaneously sublimes/decomposes the filler compound, and anneals the zinc structure to improve structural integrity. The resultant porous anode showed significantly charge and discharge potentials over the solid plate anode, while allowing for increased control of porosity over other porous electrodes due to the ability to adjust pore size based on the filler compound particle size. The discharge potentials observed from these porous anodes were 20% greater than zinc plate anodes at 100mA, but up to 200% greater at elevated currents of 200mA. Similarly the charging potentials were 53.8% lower at 100mA, and 55.5% lower at 200mA., suggesting greatly improved performance by the porous anode. The second study addresses the need for more durable gas diffusion electrodes. In this study, the bifunctional catalyst was bound directly to a stainless steel current collector via polymer binding in an attempt to remove the possibility of carbon corrosion and catalyst dissolution. The new gas diffusion electrode was successful in eliminating carbon corrosion, wherein, the durability of cells which incorporate this type of electrode was significantly increased. The durability of cell was increased to a point where little to no degradation occurred over 1000 cycles of full cell testing, showing great promise for future use and commercial viability. The final study addresses the need for durable and high performance non precious metal catalysts. The effects of catalyst morphology were studied wherein various morphologies of spinel type cobalt oxide were synthesized and compared. Cobalt oxide nanosheets were successfully synthesized and compared to nanoparticles of comparable size. The cobalt oxide nanosheets showed better charge and discharge potentials as well as durability of the nanoparticles. Impedance analyses showed reduced charge transfer and cell component resistances associated with the nanosheet morphology. Cobalt oxide nanosheets were further compared against platinum carbon. Cobalt oxide nanosheets showed significantly better durability as well as lower charging potentials and higher discharge potentials over 75 cycles. After 75 cycles the platinum carbon had lost 55.7% of its discharge potential wherein cobalt oxide nanosheets lost none of its discharge potential. Three issues pertaining to three major cell components a zinc air were addressed with promising solutions proposed for each. This work provides a basis for advanced zinc electrode fabrication in which further improvements can be incorporated to address other issues pertaining to zinc electrode use. This work set up a basis for electrode design which focuses on non carbon supported catalysts, eliminating the issue of carbon corrosion and associated catalyst dissolution. Finally, the results from the morphology study elucidate the benefits of controlled morphology for bifunctional catalysts, showing how morphology can be adjusted to improve performance by improving cell and charge transfer resistances.

This thesis studied the catalytic upgrading of pyrolysis oil derived from both ethanol organosolv (EOL) lignin and whole biomass. There are four major components of this thesis. In the first part, several lignin model compounds and the commonly used noble metal catalysts were evaluated. During the reaction, coke formation deactivated several catalysts. The reaction pathway of the coke formation was proposed. Ruthenium/activated carbon can hydrogenate the aromatic ring and remove the methoxyl group as well due to its unique catalytic behavior. The reaction mechanism was deduced based on the products distribution of the model compounds. The second part of this study focuses on the catalytic HDO reaction with real EOL pyrolysis oil. The results indicate the reaction mechanism with EOL pyrolysis oil is similar to the results of the model compound study. Due to the deactivation of the Ru/C catalyst by tar produced during the upgrading, two-step hydrodeoxygenation at different temperature was adopted in this study. The second part mainly discussed the first-step HDO reaction. The upgraded pyrolysis oil was analyzed using GC-MS, ¹H, ¹³C, and HSQC ²D NMR. The chemical structure change after the first-step upgrading and the cleavage of the inter-linkages were included. The third part focuses on the product analysis after the second-step HDO. All the products were completely hydrogenated. The molecular weight of the upgraded oil is in the monomer range and the GC-MS study provided detailed compound structures. However, some of them still contain oxygen atoms. To produce completely deoxygenated products, alkali treated ZSM-5 was used as a supporting material and it was effective in catalyzing the dehydration reaction and producing deoxygenated compounds. In the fourth part, light oil derived from whole biomass also underwent treatment under the same HDO reaction conditions as those used in upgrading EOL pyrolysis oil. In this reaction, the biomass were separated into three components: stem, residue and bark. The compound structures of the three different types of light oil were analyzed by GC, ¹H and ¹H-¹³C HSQC-NMR. Then the light oil was processed under the same condition as the heavy oil upgrading. The reaction mechanisms with cellulose and hemicellulose were also studied. These results will be of value in developing of complete hydrogenation of whole biomass pyrolysis oils.

The use of heterogeneous catalysts containing Au nanoparticles supported on TiO2 has been explored for oxidative aqueous phase transformations of sustainable phenolic and benzoic acid derivatives that can be obtained from lignin. Au/TiO2 catalysts were chosen because of their high activity for ambient pressure oxidations of gas phase species, and because their synthesis is facile and reproducible through a modified deposition-precipitation method. The aerobic oxidation of syringic, vanillic, and ferulic acid as well as of guaiacol, eugenol and anisole was investigated at temperatures up to 70°C under (i) atmospheric air sparging in an open reactor and (ii) at 10 atm air pressure in a closed reactor system. The catalysts were characterised by Transmission Electron Microscopy (TEM), Inductively Coupled Plasma (ICP) Optical Emission Spectroscopy and the reproducibility of their catalytic activity independently monitored by determining their activity for carbon monoxide oxidation in a gas flow reactor. The oxidation of syringic acid, vanillic acid, ferulic acid over Au/TiO2 resulted in the formation of 2,6-dimethoxy benzoquinone, guaiacol, and vanillin, respectively, indicating high selectivity for decarboxylation followed by selective oxidation at the position releasing the leaving group. Guaiacol was found to form tetraguaiacol, while eugenol produced quinone methide. Generally, higher air pressure strongly accelerated the transformations, indicating that availability of oxidants formed from O2 is the rate limiting step in the observed transformations. No transformations took place when O2 was excluded from the systems. Overall, guaiacol was found to react fastest, followed by syringic acid, ferulic acid, then vanillic acid. Anisole was found to be unreactive, even at elevated air pressure. The overall reaction pattern emerging from these studies is that the aerobic oxidation in the presence of Au/TiO2 mimics known biotransformations, for example peroxidase-catalysed oxidations involving H2O2.To assess how the functional groups on the aromatic ring influence reactivity the oxidation of p-hydroxybenzoic acid and of 2,6-dimethoxybenzoic acid was also assessed. It was found that decarboxylation of p-hydroxybenzoic acid proceeds, albeit rather slowly, forming phenol, with no further oxidation to hydroquinone or benzoquinone. Taken together these results indicate that the methoxy moieties influence reactivity through both their inductive and resonance effects: leaving of the carboxylic acid group appears to be enhanced through the inductive effect, while further oxidation at the phenolic site seems to be activated through the resonance effect in ortho-position. In line with this hypothesis, it was recently found that dimethoxybenzoic acid converts fast.

M.Sc. (Chemistry) / Catalyst deactivation is a process that plays an important role in many catalytic processes. The forming of coke is in this respect the most common cause for deactivation. The research that has been done here has tried to give some insight into the mechanism of cokeforming with the help of Fourier Transform Infrared Spectroscopy (F)'IR). For this purpose a cobalt catalyst on an alumina carrier was used. The influence of the reaction time, the carbon monoxide to hydrogen ratio and the temperature on the rate and amount of coke formed was determined. A cell was developed that could be heated up to 500°C and could simultaneously be used in FTIR-spectroscopy in situ research. This enabled the determination of spectra at certain time intervals. In this way the development of the characteristic bands could be followed. Two other methods were used to support the transmission spectra : Diffuse Reflectance Spectroscopy and the burning of the coke from the catalyst. The latter was done to determine the amount of coke that had formed on the catalyst surface during the run. The amount of coke decreased with an increase of the hydrogen to carbonmonoxide ratio in the feed. Temperature also had a marked influence on coke formation: It decreased at higher temperatures. As expected the amount of coke increased with reaction time. In general the coke contained only a small hydrogen content. In conclusion it may be mentioned that the results obtained can contribute to the characterization of coke formed on Fischer-Tropsch catalysts.

Ruthenium-alkylidene catalysts are widely used in organic synthesis to generate new C=C bonds in a process known as olefin metathesis. Much research has been dedicated to examining the organometallic species responsible for this transformation, and understanding the benefits and limitations of current state-of-the-art catalysts allows for the design of new and more efficient alternatives. Over the past decade, a topic of much debate has been the so-called “boomerang” (or release-return) mechanism, and whether it operates in the Hoveyda catalysts. The ability of the styrenyl ether ligand, once released from the catalyst during initiation, to be recaptured by the vulnerable active species, has major implications in catalyst recyclability. Chapter 3 describes the use of a 13C-labeled styrenyl ether ligand, in conjunction with an unlabeled second-generation Hoveyda catalyst, to confirm the operation of this mechanism during catalysis. This study demonstrated that the labeled styrenyl ether ligand competes with the substrate for the four-coordinate active species: the labeled moiety rapidly incorporates into the Hoveyda catalyst during both ring-closing- and cross-metathesis examples. Chapter 4 focuses on addressing the selectivity challenges associated with olefin metathesis, particularly during RCM macrocyclization reactions where E/Z mixtures are typically obtained. Designing catalysts that can dictate and control the stereochemistry of a product mixture minimizes waste, and ultimately reduces cost by eliminating the need for separation techniques. A great deal of research has focused on constructing catalysts with ligands that can exert the appropriate steric pressure on a metallocyclobutane intermediate, in order to generate the desired Z-product. Chapter 4 of this thesis examined the ability of a Hoveyda- and Grubbs-type catalyst containing monothiolate ligands, to promote Z-selective RCM macrocyclization. Catalyst lifetimes were also examined, in addition to the impact of altering reaction conditions, specifically concentration, on product distribution. These experiments afford information that will aid in the design of improved catalysts for Z-selective RCM macrocyclization.

Bibliography : pages 244-253. / The objective of this study was to determine the effect that the type of catalyst and reaction would have on the rate of deactivation, properties of coke and transport properties of the catalyst. HY and HM were chosen because of their different pore structures and acid site distributions. Hexane cracking at 1 atmosphere and high pressure propene oligomerisation provided two different reaction types. The transport properties of the catalysts were compared by measuring adsorption and diffusion using the GC technique with ancillary information obtained from ammonia TPD, mercury porosimetry and BET surface area measurements. It was confirmed that a knowledge of the crystallite size distribution was necessary to predict the adsorption and diffusion of light hydrocarbons in HY and HM. The adsorption constants and heats of sorption were found to,be much greater in HM than in HY, in agreement with the presence of a greater number of strong acid sites detected in HM by ammonia TPD. The diffusivities of the Tight hydrocarbons were too large to measure in HY. In HM only methane diffusion was too fast to measure. Diffusivities decreased and adsorption constant increased with increasing molecular size. HY had greater activity and slower deactivation than HM towards hexane cracking. The reaction as well as coking took place in the micro-pores. The graphitic coke content of HY was much greater than in HM. The introduction of the macro-pore adsorption term was necessary to predict diffusion in coked samples, emphasizing the severity of the diffusional resistance. While hydrocarbon diffusivities decreased after cracking, adsorption constants were found to increase in the presence of graphitic coke in J-IY. In HM the deactivation took place primarily by pore blockage, with strong acid sites being preferentially removed. Both diffusivities and adsorption constants decreased in the presence of coke in HM. In HY and HM deactivated by oligomerisation, macro-pore adsorption had to be taken into account, again emphasizing the severe diffusional resistance. Reaction as well as graphitic coke occurred predominantly in the micro-pores in HY. High boiling point hydrocarbons were able to migrate into the mesopores where they closed the mouths of the micro-pores in HY. Strongly adsorbed high boiling point hydrocarbons which deactivated the catalyst presented far less diffusional resistance in HY than the equivalent mass of graphitic coke. These high boiling point hydrocarbons also markedly lowered the adsorption constants. Graphitic coke was responsible for the modification of the catalyst selectivity. Temperature runaway in HY caused severe coking and hence deactivation. The inactivity of HM below 200°C was caused by strong adsorption and high diffusional resistance of reactant and product. Pore blockage was the dominant deactivation mechanism in HM, while in HY it was partial pore blockage by graphitic coke and pore mouth closure by high boiling point hydrocarbons. It was possible to restore the activity of HY for oligomerisation by flushing the high boiling point hydrocarbons in flowing nitrogen.

There is a high demand for the development of processes for the conversion of ubiquitous molecules into industrially useful commodities. Transition metal catalysts are often utilized for the activation and functionalization of small organic molecules due to their diverse nature and proven utility with a myriad of chemical transformations. The functionalization of methane (CH4) and dinitrogen (N2) to methanol (CH3OH) and ammonia (NH3) respectively is of particular interest; however, both methane and dinitrogen are essentially inert due to the inherit strength of their bonds. In this dissertation a series of computational studies is performed to better understand the fundamental chemistry behind the functionalization of methane and the activation of dinitrogen in a homogeneous environment. A catalytic cycle is proposed for the oxy-functionalization of methane to methanol. The cycle consists of two key steps: (1) C-H activation across a metal-alkoxide bond (M-OR), and (2) regeneration of the M-OR species through an oxy-insertion step utilizing external oxidants. The C-H activation step has been extensively studied; however, the latter step is not as well understood with limited examples. For this work, we focus on the oxy-insertion step starting with a class of compounds known to do C-H activation (i.e., Pt(II) systems). Computational studies have been carried out in an attempt to guide experimental collaborators to promising new systems. Thus, the majority of this dissertation is an attempt to extend transition metal mediated C-O bond forming reactions to complexes known to perform C-H activation chemistry. The last chapter involves a computational study of the homogeneous cleavage of N2 utilizing iron-?-diketiminate fragments. This reaction has been studied experimentally, however, the reactive intermediates were not isolated and the mechanism of this reaction was unknown. Density functional theory (DFT) calculations are carried out to elucidate the mechanism of the reductive cleavage of N2 via the sequential addition of iron- ?-diketiminate fragments to N2 to form a bis-nitride (N3-) intermediate. The role of potassium promoters on the dinitrogen and bis-nitride species is also investigated.

To combat the escalating environmental challenges and alleviate the current energy crisis, CO2 conversion to fuels and chemical feedstocks provides a reliable approach to mitigate the devastating impact of greenhouse emissions on climate change. CO2 conversion/reduction could be carried out by several methods; however, the electrochemical CO2 reduction (CO2R) approach has coupled several advantages. For instance, CO2R occurs in near-ambient reaction conditions and could be driven through the employment of renewable energy resources (wind or solar) to generate electricity. However, this reaction has a large energy barrier which requires a catalyst to facilitate its pathway. In this context, various catalyst designs were developed and investigated during the last decades, such as heterogenous (metal and metal oxide) and homogenous (organic molecules) catalysts. A new class of materials – atomically dispersed metal nitrogen–doped carbon support (M–N–C)– has emerged recently and showed remarkable enhancement for CO2R compared to the state-of-the-art. In particular, Ni–N–C catalysts have demonstrated an improved selectivity toward CO production compared to precious metal catalysts. Researchers have postulated this superior performance to the high atomic utilization (theoretically 100%) of the metal sites under reaction conditions and the enhanced electronic properties. In addition, intermetallic carbides have been included as a promising class of catalysts for CO2R due to their unique physical and chemical characteristics. These catalysts could be synthesized using different precursors; among them, MOFs are currently one of the most promising platforms that generate several catalyst designs. It was demonstrated that MOF’s unique characteristics, such as high surface area and porosity, would be transitioned to the derived catalysts. In this thesis, two MOF architectures (ZIF-8 and MOF-74) were initially selected to be employed as precursors for deriving atomically dispersed Ni–N–C catalysts. Both MOF-derived catalysts were evaluated for CO2R using a customized electrochemical cell (E-cell) with a 3–electrode configuration. The derived Ni–N–C catalysts using ZIF-8 and MOF-74 have achieved enhanced CO selectivity with Faradaic efficiencies (FE) > 90% at less negative applied potentials, –0.68 and –0.76 V vs RHE, respectively. Further, various synthetic conditions were explored in these studies, such as the role of the Ni content and the pyrolysis temperature on the resulted catalyst structure, and the electrocatalytic performance during CO2 electrolysis. Subsequently, one of the MOF topologies – ZIF-8 – was further utilized to develop other designs of electrocatalysts by introducing different synthetic conditions. This has resulted in generating various moieties that are able to produce CO during CO2R. For example, one derived catalyst design consists of homogenously distributed atomically dispersed dual Ni–Zn–NX/C sites. Whereas the other design demonstrated a heterogenous structure of Ni3ZnC-based particles anchored on atomically dispersed dual Ni–Zn–NX/C sites. Both electrocatalyst designs were integrated into a gas diffusion electrode (GDE) and evaluated for CO2R using an MEA-based electrolyzer. Our findings revealed that the co-existence of Ni3ZnC particles and dual Ni–Zn–NX/C active sites in a heterogenous structure has boosted the electrocatalytic activity towards CO production, achieving near unity CO FE at 448 mA/cm2 at an overall cell voltage of 3.1 V. Aside from the electrocatalytic performance, the nature of active sites in the developed catalyst designs has been studied using in-situ and ex-situ X-ray absorption spectroscopy. Other analytical techniques such as transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), powder X-ray diffraction (PXRD), and X-ray photoelectron spectroscopy (XPS) have also been used to identify the catalysts’ composition and morphology. / Thesis / Doctor of Philosophy (PhD) / This PhD thesis aims to develop and implement a sustainable technology that tackles increased CO2 emissions in the atmosphere and mitigates the greenhouse effect on climate change. The approach of this thesis focuses on developing efficient catalyst designs for CO2 electroreduction (CO2R) to CO as a beneficial chemical feedstock, and then pursues the practical implementation of these catalysts in an industrially relative reactor design in the form of a membrane electrode assembly (MEA)-type electrolyzer. This study selected atomically dispersed metal-doped nitrogen-carbon (M–N–C) and intermetallic carbide electrocatalysts as promising materials for CO2R. Among different precursors, metal-organic frameworks (MOFs) have been employed to synthesize the desired electrocatalysts due to their unique geometric structure and high surface area. On a fundamental level, our findings demonstrated that all MOF-derived catalysts have exhibited high selectivity towards CO during CO2 R. However, the conversion rates were governed by the nature of the active sites and the implemented electrochemical systems.

The development of peptides as catalysts for preparing optically active molecules is an ongoing investigation. Efforts at expanding the use of peptides are explored in two ways: investigating novel reactions in which peptides can act as asymmetric catalysts and through expanding the substrate scope of peptides in performing kinetic resolutions. Attempts at furthering the reaction scope of acylsulfonamide-containing peptides to act as BrØnsted acids through promoting the attack of 7-methyl oct-6-ene-1-tosylaziridine (9) by an internal π-nucleophile are discussed herein. Also reported is the use of pentameric peptides containing a π(-methyl)histidine residue in the kinetic resolution of the primary alcohol 4-hydroxymethyl cyclopent-2-enone (76) and the secondary aliphatic alcohol 2- pentanol. Moderate selectivities were observed in the kinetic resolution of 4-hydroxymethyl cyclopent-2-enone (76) and promising results were obtained in the initial screening of catalysts for the resolution of 2-pentanol. / Thesis (MS) — Boston College, 2008. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.