Catalyst development is important to the contemporary world as suitable catalysts can allow chemical processes to proceed with reduced energy consumption and waste production. In order to design catalysts with improved performance, the fundamental studies that correlate catalytic properties with surface structures are essential as they can provide mechanistic insights into the reaction mechanism. Pd−Au bimetallic catalysts have shown exceptional performance for a number of chemical reactions, however, the interplay between the reactive species and surface properties are still unclear at the molecular level. In this dissertation, the catalytic chemistry of Pd−Au surfaces was investigated via model catalyst studies under ultrahigh vacuum conditions. A range of Pd−Au model surfaces were generated by annealing Pd/Au(111) surfaces and characterized/tested by surface science techniques. The findings in this dissertation may prove useful to enhance the fundamental understanding of structure-reactivity relation of Pd−Au catalysts in associated reactions.

This thesis explores the fundamental chemistry of selective oxidation reactions on gold and silver surfaces, developing a predictive framework for oxidative catalysis, which is crucial for rational design of catalytic systems. We begin with an introduction covering the history of precious metal catalyst development, with emphasis on the roles of silver and gold (Chapter 1). Next, we explore selectivity control for oxidative reactions on gold. Specifically, we address the role of coadsorbed oxygen with respect to stability and selectivity control in the reaction of adsorbed acetate (Chapters 2 and 3), the importance of van der Waals forces in controlling the selectivity for cross-coupling reactions (Chapter 4), and the influence of CF3 on alkoxide stability on gold (Chapter 5). Further, we study various oxidative coupling and partial oxidation reactions on silver. In each case we elucidate reaction mechanisms, with attention to control of reaction selectivity. First, we establish oxidative coupling between dimethylamine and formaldehyde to form dimethylformamide (Chapter 6). Then we explore the role of hydroxyl in oxidative reactions silver, establishing its reactivity as a nucleophile in reaction with formaldehyde (Chapter 7). Finally, we directly compare the reactivity of gold and silver, in the acetylation of dimethylamine using acetaldehyde (Chapter 8). Appendices are included which investigate the oxidation of dimethylamine on silver (Appendix A), selectivity control for alcohol and aldehyde coupling on silver (Appendix B), and reactivity of hydroxyl on silver as a Bronsted base (Appendix C). A MATLAB code, which was developed for quantitative analysis of temperature program reaction spectroscopy experiments is also presented (Appendix D), as well as Supporting Material (Appendix E). / Engineering and Applied Sciences

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Implementing effective and environmentally responsible carbon capture technologies is one of the principle challenges of this century. Successful implementation requires a host of engineering advancements, but also a fundamental understanding of the underlying physics, chemistry, and materials science at play in these highly complex systems. A large body of scholarship examines both current technologies as well as future strategies, but to date little exploration of the surface behavior of these systems has been examined. As these carbon capture systems involve uptake of gaseous CO2 to either aqueous or solid substrates, understanding the chemistry and physics governing the boundary between the two reactant phases is critical. Yet probing the unique chemistry and physics of these interfacial systems is very difficult. This dissertation addresses this knowledge gap by examining the surface chemistry of monoethanolamine and CO2. Monoethanolamine is a simple organic amine currently used in small scale CO2 scrubbing, and acts as an industrial benchmark for CO2 capture efficiency. The studies presented throughout this dissertation employ surface selective techniques, including vibrational sum frequency spectroscopy, surface tensiometry, and computation methodologies, in order to determine the behavior governing aqueous amine interfaces. The adsorption behavior and surface orientation of aqueous monoethanolamine is examined first. The results show monoethanolamine is present at the surface, highly ordered, and solvated. Perturbations to this amine surface from gaseous CO2 and SO2, as well as from liquid HCl, are examined in the remainder of the dissertation. Reactions between the amine and acids are shown to cause immediate changes to the interface, but the interface then remains largely unaffected as further reaction evolves. The studies presented herein provide a needed exploration of the interfacial picture of these highly reactive systems, with implications for future carbon capture materials and design.

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Aniline oligomers have become a very interesting topic for research because of their potential application not only in organic electronics but also in smart coatings for corrosion treatment of iron and steel. A majority of the studies in the literature are focussed on the bulk or direct interaction between the organic molecules with metal substrates, without considering the native oxide film. In order to develop smart coatings (has redox activity and self-healing ability) for iron and steel, one must first understand how these oligomers interact with the native iron oxide film. In this thesis, we develop new knowledge from our fundamental understanding of the interactions of redox-active aniline oligomers with the iron oxide surface. Phenyl capped aniline dimer with two oxidation states [fully reduced (DPPD) and fully oxidized (B2Q1)] and phenyl-capped aniline tetramer (PCAT) with three oxidation states [fully reduced (B5), half-oxidized (B4Q1), fully oxidized (B3Q2)] were chosen for investigation. The former is the smallest redox active aniline oligomer but with one fewer oxidation states than polyaniline whereas the latter mimics the redox system as well as corrosion inhibition properties of polyaniline. Moreover, the phenyl-caps help both of these molecules to resist polymerization on the surface. Raman spectroscopy, mid-IR spectroscopy, atomic force microscopy (AFM), temperature programmed desorption (TPD) and electrochemical impedance spectroscopy (EIS) were used to study interactions. We demonstrate that charge transfer and interconversion to different oxidation states take place during interactions between each of these molecules with iron (III) oxides surfaces. During interaction with the surface, all three tetramer molecules and DPPD prefer standing on their edge orientation, whereas B2Q1 molecules tend to orient in lying down direction on the same surface. Having amino groups in the chain helps reduced and half oxidized molecules to strongly hydrogen bond with the surface and make them static on the surface. On the other hand, a lack of amino groups makes oxidized molecules mobile and loosely bound to the surface. Interactions and change of oxidation states impact the corrosion inhibition properties of PCAT. Strong ability of sticking to the surface and not fully oxidizing (B3Q2) during interactions makes B5 molecules superior corrosion inhibitors than B4Q1 and B3Q2 molecules. Transformation into B3Q2 form at the beginning of interaction allows B4Q1 to moderately inhibit corrosion but as it transforms back to its original form with time it becomes the 2nd best corrosion protector of iron oxide surface after B5. The study of all oxidation states and their surface interactions with iron oxide surface will open up pathways towards of designing smart coatings using aniline oligomers and other redox-active molecules. / Thesis / Doctor of Philosophy (PhD) / Aniline oligomers have become a very interesting topic for research because of their potential application not only in organic electronics but also in smart coatings for corrosion treatment of iron and steel. A majority of the studies in the literature are focussed on the bulk or direct interaction between the organic molecules with metal substrates, without considering the native oxide film. In order to develop smart coatings (has redox activity and self-healing ability) for iron and steel, one must first understand how these oligomers interact with the native iron oxide film. In this thesis, we develop new knowledge from our fundamental understanding of the interactions of redox-active aniline oligomers with the iron oxide surface. Phenyl capped aniline dimer with two oxidation states [fully reduced (DPPD) and fully oxidized (B2Q1)] and phenyl-capped aniline tetramer (PCAT) with three oxidation states [fully reduced (B5), half-oxidized (B4Q1), fully oxidized (B3Q2)] were chosen for investigation. The former is the smallest redox active aniline oligomer but with one fewer oxidation states than polyaniline whereas the latter mimics the redox system as well as corrosion inhibition properties of polyaniline. Moreover, the phenyl-caps help both of these molecules to resist polymerization on the surface. Raman spectroscopy, mid-IR spectroscopy, atomic force microscopy (AFM), temperature programmed desorption (TPD) and electrochemical impedance spectroscopy (EIS) were used to study interactions. We demonstrate that charge transfer and interconversion to different oxidation states take place during interactions between each of these molecules with iron (III) oxides surfaces. During interaction with the surface, all three tetramer molecules and DPPD prefer standing on their edge orientation, whereas B2Q1 molecules tend to orient in lying down direction on the same surface. Having amino groups in the chain helps reduced and half oxidized molecules to strongly hydrogen bond with the surface and make them static on the surface. On the other hand, a lack of amino groups makes oxidized molecules mobile and loosely bound to the surface. Interactions and change of oxidation states impact the corrosion inhibition properties of PCAT. Strong ability of sticking to the surface and not fully oxidizing (B3Q2) during interactions makes B5 molecules superior corrosion inhibitors than B4Q1 and B3Q2 molecules. Transformation into B3Q2 form at the beginning of interaction allows B4Q1 to moderately inhibit corrosion but as it transforms back to its original form with time it becomes the 2nd best corrosion protector of iron oxide surface after B5. The study of all oxidation states and their surface interactions with iron oxide surface will open up pathways towards of designing smart coatings using aniline oligomers and other redox-active molecules.

Superconducting thin films are a possible alternative to bulk niobium for superconducting radio frequency cavity applications. Thin film cavities have produced larger Q0 than bulk niobium at low accelerating voltages [1], are less susceptible to external magnetic fields and therefore require less magnetic shielding than bulk niobium cavities [2] and can benefit from substrates which conduct heat more effectively than bulk niobium [3]. The major drawback for current thin film cavity technology is the large Q slope which is observed above accelerating gradients of 6 7 MV/m. The mechanism for the Q slope is not yet fully understood. Theories have been suggested but are not accepted by everyone within the scientific community [2, 4, 5, 6, 7]. It is assumed that a better understanding of the physical properties of superconducting films is required before the origins of the sharp Q slope can be elucidated. This study has been conducted to better understand the physical properties of superconducting thin films deposited by the magnetron sputtering process. In particular, superconducting niobium films have been deposited by high power impulse magnetron sputtering (HiPIMS) and tested by a wide range of analytical techniques as a function of the substrate temperature and applied bias during deposition. Analytical techniques which have been used include x-ray diffraction crystallography, Rutherford backscattering spectroscopy, scanning electron microscopy, residual resistance ratio, DC magnetometry and RF surface resistance measurements. Results showed that the application of an applied bias during deposition resulted in increased energy of bombarding ions and enhanced rates of surface diffusion and defect annihilation within the microstructure of a growing niobium film. However, large numbers of random complex defects formed once the energy of bombarding ions becomes too large. The systematic approach that was described to investigate the changing morphological and DC superconducting properties of deposited films, as a function of the applied bias, allowed the identification of which process conditions produce the fewest random complex defects. The same systematic investigations could be applied to any HiPIMS deposition facility to provide similar results. An important observation during the study is that the initial substrate conditions have a large influence on the properties of a deposited niobium film. Niobium films deposited onto polycrystalline copper substrate that was pre-annealed at 700 ˚C prior to deposition displayed more stable magnetic flux pinning, larger RRR and an enhanced resistance to the onset of flux penetration, than was observed for films deposited with a wide range of process conditions onto as received copper substrate. Superconductors other than niobium have been successfully deposited by HiPIMS and tested. Niobium titanium nitride thin films displayed a superconducting transition temperature up to 16.7 K, with a normal state resistivity as small as 45±7 μΩcm. The findings suggest that similar niobium titanium nitride thin films could produce smaller RF surface resistance than bulk niobium cavities at 4.2 K.

This thesis includes two parts. The first part reviews the history and fundamentals of surface science and tribology. The second part presents the major research outcomes and contributions. This research explores the aspects of friction, wear, and surface modification for tribological augmentation of surfaces. An effort has been made to study these aspects through gaining insights by fundamental studies leading to specific practical applications in railroads. The basic idea was to surface engineer metals for enhanced surface properties. A micro- and nano- scale experimental approach has been used to achieve these objectives. Novel principles of nano technology are incorporated into the experiments. Friction has the potential to generate sufficient energy to cause surface reactions through high flash temperatures at the interface of two materials moving in relative motion. This allows surface modifications which can be tailored to be tribologically beneficial through a controlled process. The present work developed a novel methodology to generate a functional tribofilm that has combined properties of high hardness and high wear resistance. A novel methodology was implemented to distinguish sliding/rolling contact modes during experiments. Using this method, a super hard high-performance functional tribofilm with “regenerative” properties was formed. The main instrument used in this research for laboratory experiments is a tribometer, using which friction, wear and phase transformation characteristics of railroad tribo-pairs have been experimentally studied. A variety of material characterization techniques have been used to study these characteristics at both micro and nano scale. Various characterization tools used include profilometer, scanning electron microscope, transmission electron microscope, atomic force microscope, X-ray diffractometer, nanoindenter, and X-ray photon spectroscope. The regenerative tribofilms promise exciting applications in areas like gas turbines, automotive industry, compressors, and heavy industrial equipment. The outcome of this technology will be an economical and more productive utilization of resources, and a higher end performance.

Pt-group metals were some of the first metals to be studied as catalysts for industrial use. The goal of these studies was to ascertain a fundamental understanding of CO oxidation and acetylene cyclotrimerization reactions on Ptgroup metals. A further goal was to determine the optimal conditions for each reaction. CO oxidation on Rh(111),Pt(100), and Pd(100) was scrutinized on various oxide surfaces from chemisorbed to bulk metal oxides. Low pressure reactions on Rh(111) reveal the highest activity was a CO uninhibited surface with <1ML of chemisorbed oxygen. Pt(100) high pressure oxidation revealed that only <1ML oxygen is formed during high pressures reactions. High pressure CO oxidation reactions on Pd(100) show oxygen penetration after CO has been consumed; however, during the highest activity XPS found only chemisorbed species. The cyclotrimerization of acetylene to benzene is another reaction found in industry typically carried out on Pd. The active site is considered to be a 7 atom configuration with 6 atoms surrounding a central atom. By adding relatively catalytically inert Au atoms to the active Pd(111) surface the acetylene coupling activity is enhanced. Cyclization activity is a function of the surface composition and the surface structure. A single Pd atom surrounded by six Au atoms is found to have the highest activity at 300K for acetylene cyclotrimerization.