Browsing by Subject "Catalysis"
Now showing 1 - 20 of 46
Results Per Page
Sort Options
Item Activity of methanol electro-oxidation at PtRu materials at temperatures in the range of 23°C to 70°C(Texas Tech University, 2004-05) Xu, ShanhongThe electrochemical oxidation of 0.5 M methanol in 0.1 M HCIO4 on catalyst materials comprised of platinum and ruthenium (PtRu) was investigated. Cyclic voltammetry and constant potential amperometry were used to characterize the catalyst materials and study the methanol reaction kinetics. Measurements were performed at temperature in the range of 23°C to 70°C. The following catalyst materials were employed: PtRu black containing 50 at. % Ru supplied by Johnson Matthey of Ward Hill. MA (JM PtRu black); sonochemically prepared nanoparticles of PtRu containing either 50 at. % Ru (SC PtRu(50)) or 25 at. % Ru (SC PtRu(25)); and Pt black (supplied by Johnson Matthey) modified by spontaneous deposition of Ru via either two (JM Pt-Ru(2)) or four deposition cycles (JM Pt-Ru(4)). The rate of methanol oxidation was assessed through constant potential amperometry measurements. Current was recorded 20 min after stepping to the reaction potential. Mechanistic information was derived from Tafel plots (plot of the logarithm of the current versus the reaction potential).Item An infrared investigation of certain hydroxy aromatic ketones(Texas Tech University, 1960-05) Brasch, Jimmie WatsonNot availableItem Carbon-Heteroatom Reductive Elimination and Catalysis Utilizing (POCOP)Rh and (POCOP)Co Complexes(2014-07-29) Timpa, Samuel DTransition metal catalyzed cross-coupling reactions of aryl halides have revolutionized the synthesis of organic molecules. These reactions, which are commonly catalyzed by group 10 metals, have found applications including natural product synthesis, pharmaceuticals, and agrochemicals. Pd catalyzed cross-coupling reactions have undergone the greatest development due to their wide applicability, high efficiency, and selectivity. The success of Pd is attributed to its ability to readily traverse between Pd(0) and Pd(II) oxidation states, which is essential to the mechanistic steps oxidative addition and reductive elimination. The utility of transition metals outside of group 10 has largely been limited to Cu, but more recently several examples of Rh catalyzed cross-coupling reactions have been described. These examples propose a Rh(I)/Rh(III) cycle analogous to the Pd(0)/Pd(II) catalytic cycle involving aryl halide oxidative addition, transmetallation, and product forming reductive elimination; however, there has been little experimental evidence to support these claims. Examples of aryl halide oxidative addition to Rh(I) have been reported, but examples of reductive elimination from Rh(III) are less prevalent. Pincer ligands, tridentate ligands that typically coordinate in a meridional fashion, provide an excellent scaffold for the examination of both oxidative addition and reductive elimination at Rh due to their ability to access to three-coordinate Rh(I) and stable five-coordinate Rh(III) complexes. The ability of the (PNP)Rh center to undergo each of the stoichiometric reactions of catalytic C-C coupling reactions, including aryl halide oxidative addition and C-C reductive elimination, has been established. This dissertation describes the ability of the (POCOP)Rh system to catalytically form C-C as well as C-N and C-S bonds. Several proposed catalytic intermediates have been isolated and their reactivity examined to gain insight into the mechanism of these catalytic transformations. C-N and C-S reductive elimination from Rh(III) have been closely examined, with results providing insight to their respective steric and electronic properties. In addition, the potential for (POCOP)Rh systems to undergo C-F reductive elimination were also examined both theoretically and experimentally. Finally, early investigations into the synthesis of (POCOP)Co complexes will be described, with an emphasis on demonstrating the aptitude for this system to experience concerted reductive elimination. Numerous (POCOP)Co complexes were isolated and characterized, including Co(II) and stable Co(III) compounds.Item Catalytic chemistry of Pd−Au bimetallic surfaces(2015-08) Yu, Wen-Yueh; Mullins, C. B.; Henkelman, Graeme; Hwang, Gyeong S.; Korgel, Brian A.; Sitz, Greg O.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.Item Catalytic nitrate reduction in drinking water using a trickle bed reactor(2016-05) Bertoch, Madison; Werth, Charles J.; Lawler, DesmondPalladium-based bimetallic catalysts hold promise as an alternative water treatment technology for nitrate (NO3-), but practical application requires development of a flow-through reactor that efficiently delivers hydrogen (H2) from the gas phase into water, where it serves as the electron donor for NO3- reduction. In this work, a trickle bed reactor (TBR) was fabricated and evaluated to address this challenge. A series of batch experiments with Pd-In/γ-Al2O3 catalysts were conducted in excess H2 to identify a highly active catalyst for the TBR. A 0.1wt%Pd-0.01wt%In on 1 mm γ-Al2O3 catalyst was selected due to its high activity and support size that promotes a uniform liquid distribution in a packed bed. The TBR was packed with the same catalyst, and various liquid and gas flow rates were tested to evaluate apparent catalyst activity. Influent and effluent NO3- concentrations were used to calculate apparent zero-order rate constants, and they generally increased with H2 flow rate. Above 900 mL/min, a change in flow regime from pulse to bubble flow was observed, and the calculated zero-order rate constants decreased. An optimal catalyst activity in the TBR of 19.5 mg NO3-/min∙g Pd was obtained at a liquid flow rate of 900 mL/min and H2 flow rate of 320 sccm, which is ~22% of the activity obtained in the batch reactor by the same catalyst, indicating H2 mass transfer limitations. A reactive transport model was developed and used to quantify H2 mass transfer rate coefficients from the liquid to gas phase. Mass transfer coefficients initially decrease and then stabilize as the H2 flow rate increases. At elevated H2 flow rates, the highest mass transfer coefficients were obtained at the 900 mL/min liquid flow rate, in agreement with activity trends. Evaluation of a larger range of liquid and gas flow rates is warranted to determine if H2 mass transfer in the TBR can be further enhanced.Item Controlling selectivity in novel transition metal catalyzed carbon-carbon bond forming hydrogenations(2012-05) Zbieg, Jason Robert; Krische, Michael J.; Anslyn, Eric V.; Siegel, Dionicio R.; Brodbelt, Jennifer S.; Liu, Hung-WenThe focus of my graduate research in the Krische group has been the development of catalytic carbon-carbon bond forming reactions with an emphasis on controlling diastereo- and enatio-selectivity in transfer hydrogenative couplings. The broad goal of our research program has been the development and implementation of efficient green methods for carbonyl addition employing [pi]-unsaturates as surrogates to preformed organometallic reagents, thus enabling byproduct free variants of traditional carbanion chemistry. This dissertation shows the new reactions that I have developed toward this goal. These reactions includes new metal catalyzed approaches for carbonyl crotylation, aminoallylation, and vinylogous reformatsky aldol reactions.Item Development and application of metal catalyzed transfer hydrogenative C-C bond forming reactions(2016-05) Waldeck, Andrew Robert; Krische, Michael J.; Martin, Stephen F; Dong, Guangbin; Brodbelt, Jennifer S; Kerwin, Sean MWhile polyketides display a diverse range of biological properties and are used extensively in human medicine, a lack of methods for the concise preparation of these complex structures still poses a significant challenge in the field of synthetic organic chemistry. To address this issue, metal catalyzed methods for transfer hydrogenative C-C bond formation have been developed. These methods construct products of carbonyl addition through direct C-H bond functionalization, which provides a more atom economic and efficient approach to carbonyl addition products and circumvents the need for stoichiometric use of chiral auxiliaries, premetallated C-nucleophiles, and discrete alcohol-to-carbonyl redox reactions. Efforts have been focused on the development of ruthenium-catalyzed coupling reactions of secondary alcohols to basic chemical feedstocks as well as the application of iridum-catalyzed couplings of primary alcohols with π-unsaturates in the context of the total syntheses of (−)-cyanolide A and (+)-cryptocaryol A. These total syntheses represent the most concise route reported to date for each natural product and illustrate the synthetic utility of transfer hydrogenative C-C bond forming methodology.Item Development of novel porous coordination polymers with interest in catalysis, structure directing agents, and magnetism(2016-12) Waggoner, Nolan Wayne; Humphrey, Simon M.; Anslyn, Eric V; Rose, Michael J; Milliron, Deila J; Wood, Paul TPorous coordination polymers (PCPs) have emerged as a novel and versatile class of crystalline materials since the late 1990’s due to their high porosity and tunable reactivity. Applications for these materials have spread to areas including gas storage and separations, sensing, magnetism, and more recently, catalysis. However, designing a PCP-based material for a specific application remains a struggle within this field due to their unpredictable self-assembly. In order to overcome this hurdle, linker design has become paramount to the process. The Humphrey Group has developed a new class of PCPs called Phosphine Coordination Materials (PCMs). These materials incorporate one or more phosphorous sites within the linker to act as a point of functionalization. The lone pair of each P(III) site can act as a tunable handle, which allows for access to increased chemical versatility. With this larger goal in mind, the research discussed herein has been focused on the development of novel materials on three fronts: catalytically active linkers, employment of structure directing agents, and examination of PCMs in magnetism. Several catalytically active organic linkers were developed for the purpose of taking known homogenous reactivity and applying that knowledge to a heterogeneous framework. The linker systems described herein include trans-RuCl2(1,2-C6H4-((P-C6H4-p-CO2H)2)2, the ferrocene backbone system Fe(C5H4)2-(P-(C6H4-p-CO2H)2)2, and the extended building block 1,2-C6H4-(P-(¬p-C6H4-p-C6H4-CO2H)2)2. The second study examined a [Me-P-(C6H4-p-CO2H)3]+ Cl- linker to create a series of frameworks through variation of only the alkali hydroxide added during synthesis. This resulted in five frameworks, four of which were non-isostructural. Designated PCMs 6-9, the frameworks demonstrated unusual pore topology as well as the highest cryogenic oxygen uptake to date for a saturated metal site material. Next, two isostructural materials termed Ln-PCM-21 were synthesized and their experimental bulk magnetic properties were studied. Afterwards, three theoretical models were considered in relation to this experimental data and their relatability was reported. The final study explored the magnetic behavior of a set of 1-dimensional coordination polymers that conversely employed thiolate groups; referred to as Thiolate Coordination Materials (TCMs). One material, Fe-TCM-1, was extensively studied and two isostructural materials were attempted (CoII, MnII), with interest in single-chain magnetic behavior.Item Development of ruthenium catalyzed hydrogenative carbonyl addition reactions(2014-05) McInturff, Emma Leigh; Krische, Michael J.Metal-catalyzed, hydrogenative methods for carbon-carbon bond formation are attractive alternatives to traditional carbonyl addition reactions. Through in situ generation of aldehyde and organometallic species, these redox-triggered reactions circumvent the need for preactivation of reactive partners, thereby providing a more atom economic, efficient approach to carbonyl addition products. Efforts have been focused on the development of ruthenium-catalyzed coupling reactions of primary and secondary alcohols to basic feedstock chemicals and easily accessible and stable unsaturated compounds. To perform highly stereoselective reactions, investigation into the factors that control stereoselectivity in ruthenium catalyzed transfer hydrogenative couplings was undertaken. As a critical tool for the construction of organic molecules, modernizing methods for carbonyl addition can contribute to the evolution of synthetic organic methodology.Item Effect of nitrogen doping on the electronic and catalytic properties of carbon nanotube electrode materials(2011-05) Wiggins-Camacho, Jaclyn Dawn; Stevenson, Keith J.; Crooks, Richard M.; Vanden Bout, David A.; Webb, Lauren J.; Manthiram, ArumugamThis dissertation discusses the influence of nitrogen doping (N-doping) on the electronic and catalytic properties of carbon nanotubes (CNTs). These properties have been studied using a variety of techniques, in order to both qualitatively and quantitatively analyze the relationship between the nitrogen concentration and observed properties. Chapter 1 provides a general overview of CNTs and N-doping and details some of the previous research from our group. Chapter 2 discusses the assembly and characterization of free-standing electrode mats, which are used in order to understand the intrinsic physicochemical properties of the material without relying on the secondary influence of another conductive support. Raman microscopy, X-Ray photoelectron spectroscopy, scanning and scanning-tunneling electron microscopy, as well as electrochemical methods were all used to demonstrate the viability of the mat electrodes for further experiments. Chapter 3 addresses the examination of a range of nitrogen concentrations in order to better understand the effects of nitrogen concentration on the electrochemical and electrical properties such as the differential capacitance, density of states at the Fermi level (D(E[subscript F])), bulk conductivity and work function. These properties were studied using a variety of techniques, including UV-photoelectron spectroscopy, electrochemical impedance spectroscopy and conductive four point probe. Chapter 4 investigates the inherent catalysis of the nitrogen doped CNTs (N-CNTs) with respect to O2 reduction, and a complex mechanism is proposed. Electrochemical methods such as cyclic and linear sweep voltammetries as well as thermo-gravimetric analysis and gasometric analysis were all employed to determine heterogeneous decomposition rates as well as to detect intermediates of the O₂ reduction reaction. Chapter 5 discusses the electrocatalytic degradation of free cyanide (CN⁻) at the N-CNT mat electrodes. These results both provide further support for the mechanism discussed in Chapter 4, and present the opportunity for a potential application of N-CNTs for environmental purposes. Specifically, spectroscopic and electrochemical methods, in conjunction with theoretical models show both that the presence of CN⁻ does not inhibit O2 reduction, and that it can be effectively converted to cyanate (OCN⁻) at the N-CNT electrodes. Future work involving the assembly and characterization of transparent N-CNT films is discussed in Chapter 6.Item Electrophilic trapping of enolates in tandem reaction processes and (1,3-diketonato)metal templates for asymmetric catalysis(2004) Bocknack, Brian Matthew; Krische, Michael J.The discovery of methods for the catalytic generation of enolates in the presence of suitable electrophilic partners has led to the development of several effective strategies for the tandem formation of multiple bonds. Typically, enones have been utilized as latent enolates in these tandem processes. For instance, catalytic enone hydrometalation in the presence of an aldehyde or ketone partner allows for the formation of reductive aldol products. Similarly, the presence of an α,β-unsaturated carbonyl acceptor has been shown to give products of a reductive Michael reaction. The historical development of these tandem conjugate reduction–electrophilic trapping processes is reviewed herein. Enolate generation through catalytic enone carbometalation has also been employed as a strategy in the development of novel transformations. This approach has been used to devise an efficient protocol for the desymmetrization of enone-dione substrates via rhodium-catalyzed conjugate addition–enolate trapping. Using this methodology, four contiguous stereocenters can be established in a single manipulation, with high levels of both relative and absolute stereocontrol. This technique has provided a concise route to seco-B-ring steroids possessing a 14-hydroxy cis fused C-D ring junction, as found in naturally occurring cardiotonic steroids derived from digitalis purpurea. Numerous stereogenic processes are catalyzed by transition metal complexes of 1,3-diketonates. Despite this fact, the development of enantioselective variants using chiral (1,3-diketonato)metal templates has been slow. Progress toward the development of a novel family of chiral 1,3-diketonate ligands for asymmetric catalysis is described. These ligands, which all arise from acylation of a common pseudo-planar chiral monoketone precursor, have been used to form a variety of (1,3-diketonato)metal complexes. Additionally, the first known examples of C2-symmetric bis(1,3-diketonate) ligands have been obtained through extension of this modular approach to ligand synthesis. Although highly enantioselective catalytic transformations employing these new (1,3-diketonato)metal complexes have not yet been realized, the knowledge gained from the intial studies presented herein establishes a foundation for future development.Item Elucidating Nucleation and Growth Behavior of Single-Walled Carbon Nanotubes obtained via Catalyzed Synthesis(2014-11-07) Burgos Beltran, Juan CarlosThe catalytic growth of single-walled carbon nanotubes (SWCNTs) is studied using reactive molecular dynamics (RMD) simulations and density functional theory (DFT) calculations. Computational calculations are performed in order to achieve a better understanding of the catalytic reaction mechanism at the initial stages of synthesis, where most of the structural characteristics are defined. Different process variables such as catalyst chemical composition and size, temperature, pressure, and the nature of catalyst support, can be optimized with the purpose of tuning the structure and physical properties of SWCNTs. Controlling the structure of SWCNTs during synthesis and avoiding additional purification and/or separation processes are critical for the direct use of SWCNTs in electronic devices. RMD simulations demonstrate that small catalyst particles favor the growth of lengthy nanotubes over catalyst encapsulation as a result of an increase of the curvature energies of the carbon capsule. Furthermore, simulations performed over deposited catalyst particles demonstrate that the catalyst-support adhesion must be controlled in order to grow nanotubes with high structural quality and avoid catalyst poisoning. Results herein reported suggest that growth conditions must be optimum to minimize the nucleation of topological defects in nanotubes. RMD trajectories prove the vital role played by the catalyst surface in healing defects via adsorption and diffusion. These results significantly impact the field of chirality control since the presence of defects introduce misorientation of hexagons, shifts the overall chiral angle, and therefore, modifies the physical properties of the nanotube. DFT calculations are employed to evaluate the interaction between SWCNTs and the ST-cut quartz substrate. The outstanding performance of CNT-based FET relies on the alignment of the horizontally grown nanotubes on silica substrates, as well as on the selective growth of semiconducting nanotubes. It is demonstrated that finite-length zigzag nanotubes are adsorbed stronger than armchair tubes on the quartz support. This suggests that the nanotube electronic band structure is a key factor on the preferential adsorption of zigzag tubes. DFT calculations suggest that patterns of unsaturated silicon atoms of silica surfaces define the crystallographic directions of preferential alignment. These patterns might be chemically altered in order to favor other directions of alignment.Item Enhanced Catalytic Activities of Nanostructured Materials(2014-10-31) Martinez De La Hoz, Julibeth MilenaCatalysis has enabled the development of very important industrial processes, especially those related to the petroleum and chemical industries. This has led to a significant influence in the worldwide economy, with 20% of it depending on catalysis. Current reliance of the industrial world on catalysis and rapidly increasing worldwide energy prices have motivated the search for improved catalysts allowing more energy-efficient processes. Catalysts performance is affected by the shape, structure, and chemical composition of the catalysts. Fortunately, the development of nanotechnology has allowed researchers to control the structure and morphology of catalyst nanoparticles, as well as that of solid supports. Even though, these approaches have enhanced the reactivity of materials towards specific reactions, there is still much more room for improvement. In this work, the incorporation of electron-rich environments into the structure of nanocatalysts is proposed as a new approach for the enhancement of the catalytic activity of nanomaterials. This study is conducted in its entirety using computational quantum-based simulations. The effect of electron-rich regions on activation barriers for the dissociation of diatomic molecules is studied using metallic slit-type pores, finding that electron-rich environments enhance the reactivity of nanomaterials by reducing activation barriers required for the dissociation of molecules. The influence of electronic and geometric effects in the pores is also evaluated. It is found that local geometric characteristics, such as stacking planes forming the pore, and the presence of step-like defects influence adsorption energies and barriers for dissociation of molecules. Additionally, electrons inside the metallic pores have energies close to the Fermi-energy of the metal surfaces, which may allow tuning their energies for interactions with LUMO anti-bonding orbitals of specific molecules. Subsequently, electron-rich regions are incorporated into a 3D nanostructured material (Pt22/NPG). This proposed catalyst shows enhanced reactivity towards the dissociation of gas-phase molecules. Additionally, Pt22/NPG may display enhanced reactivity, even when electron-rich regions do not interact with the molecules of interest, due to the good dispersion of Pt-clusters. Therefore, the incorporation of electron-rich environments into nanocatalysts is shown to be an efficient approach for the enhancement of the catalytic activity of nanomaterials.Item Enones and enals as latent enolates in catalytic C-C bond forming processes : total synthesis of (-)-paroxetine (Paxil®)(2007-05) Koech, Phillip Kimaiyo, 1974-; Krische, Michael J.Enolates constitute one of the most commonly utilized intermediates in synthetic organic chemistry. However, the regioselective generation of enolates remains a challenge, especially for non-symmetric ketones possessing identical degrees of substitution at the α-positions. Our research has shown that regioselective enolate generation can be achieved by the activation of enones and enals with either 1) nucleophilic phosphine catalysis or 2) transition metal catalysis to generate enolates regioselectively. These enolates can be subsequently trapped with electrophiles. Using nucleophilic phosphine catalysis we have developed the first method for the α-arylation of enones, enals, and nitroalkenes using bismuth(V) reagents. This phosphine-catalyzed arylation methodology is mild in that a strong base is not required. Additionally, the products of this reaction are easily elaborated to complex molecules. This method has been strategically applied in a concise formal and enantioselective total synthesis of the blockbuster antidepressant (-)-paroxetine (PAXIL®). In transition metal catalysis, we have used enantioselective Cu-catalyzed conjugate addition of Grignard reagents to enones to provide magnesium enolates, which can be arylated using bismuth(V) reagents to furnish products of vicinal difunctionalization of enones. These products are obtained in modest to good yields with complete control of both relative and absolute stereochemistry. Another method for regioselective enolate generation is the Rh-catalyzed hydrogenation of enones and enals. Using this method we have developed a reaction that involves addition of metalloaldehyde enolates to ketone acceptors to afford aldol products. This is the first catalytic direct addition of transition metal enolates to ketones.Item Enones and enals as latent enolates in catalytic C-C bond forming processes: total synthesis of (-)-paroxetine (Paxil®)(2007) Koech, Phillip Kimaiyo; Krische, Michael J.Item Gold-surface-mediated hydrogenation chemistry(2013-05) Pan, Ming, active 2013; Mullins, C. B.High surface area catalysts have been studied and applied in a wide range of chemical reactions and processes. The related microscopic details of surface chemistry are important and can be effectively explored employing surface science techniques. My dissertation focuses on investigations of catalytic properties of gold, primarily using vacuum molecular beam techniques, temperature programmed desorption (TPD) measurements, reflection-absorption infrared spectroscopy (RAIRS), and density functional theory (DFT) calculations. I conducted fundamental studies of hydrogenation reactions on a H atoms pre-covered Au(111) single crystal surface with co-adsorption of various chemical compounds, including acetaldehyde (CH₃CHO), acetone (CH₃COCH₃), propionaldehyde (CH₃CH₂CHO), water (H₂O), and nitrogen dioxide (NO₂). These studies allow better understanding of hydrogenative conversions facilitated by gold catalysts, which show great promise in hydrogenation applications but for which relevant fundamental studies are lacking. The experimental results unravel the unique and remarkable catalytic activity of gold in hydrogenation reactions: i) H atoms weakly absorb on the Au(111) surface and have a low desorption activation energy of ~ 28 kJ/mol; ii) acetaldehyde can be hydrogenated to ethanol at a low temperature of < 200 K; iii) propionaldehyde can be hydrogenated to 1-proponal (CH₃CH₂CH₂OH) on H pre-covered Au(111) whereas 2-propanol (CH₃CH(OH)CH₃) cannot be formed in the reaction of acetone with hydrogen atoms; iv) a coupling reaction of aldehyde-aldehyde or aldehyde-alcohol is observed on the H pre-covered Au(111) surface at temperatures lower than 200 K and this reaction can produce various ethers (symmetrical or unsymmetrical) from aldehydes and alcohols with the corresponding chain length; v) co-adsorbed H atoms have a strong interaction with water on the gold model surface and induce the dissociation of the O-H bond in water, which cannot be dissociated on the clean surface; vi) we observed a facile reaction of NO₂ reduction on H covered Au(111) and NO is produced at 77 K, yielding high NO₂ (100 %) conversion and selectivity towards NO (100 %) upon heating the surface to ~ 120 K. These studies indicate the exceptional catalytic activity of gold and enhance the understanding of surface chemistry of classical supported Au-based catalysts at the molecular scale.Item In Situ Polarization Modulation Infrared Reflection Absorption Spectroscopic and Kinetic Investigations of Heterogeneous Catalytic Reactions(2010-01-14) Cai, YunA molecular-level understanding of a heterogeneous catalytic reaction is the key goal of heterogeneous catalysis. A surface science approach enables the realization of this goal. However, the working conditions (ultrahigh vacuum (UHV) conditions) of traditional surface science techniques restrict the investigations of heterogeneous catalysis system under industrial working conditions (atmospheric pressures). Polarization Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRAS) can be operated in both UHV and atmospheric pressure conditions with a wide temperature span while providing high resolution (4 cm-1 is used in this dissertation) spectra. In this dissertation, PM-IRAS has been employed as a major technique to: 1) obtain both electronic and chemical information of catalysts from UHV to elevated pressure conditions; 2) explore reaction mechanisms by in situ monitoring surface species with concurrent kinetic measurements. In this dissertation, NO adsorption and dissociation on Rh(111) have been studied. Our PM-IRAS spectra show a transition of NO adsorption on three-fold hollow sites to atop sites occurs at low temperatures (<275 K). NO dissociation is found to account for this transition. The results indicated the dissociation of NO occurs well below the temperature previously reported. Characterizations of highly catalytically active Au films have also been carried out. Electronic and chemical properties of (1 x 1)- and (1 x 3)-Au/TiOx/Mo(112) films are investigated by PM-IRAS using CO as a probe molecule. The Au overlayers are found to be electron-rich and to have significantly different electronic properties compared with bulk Au. The exceptionally high catalytic activity of the Au bilayer structure is related to its unique electronic properties. CO oxidation reactions on Rh, Pd, and Pt single crystals are explored from low CO pressures under steady-state conditions (less than 1 x 10-4 Torr) to high pressures (0.01-10 Torr) at various gaseous reactant compositions. Surface CO species are probed with in situ PM-IRAS to elucidate the surface phases under reaction conditions. These experimental results are used to correlate reaction kinetics and surface reactant species. It is evident that there is a continuum over the pressure range studied with respect to the reaction mechanism. The most active phase has been shown to be an oxygen-dominant surface. The formation of a subsurface oxygen layer is found to deactivate the reaction.Item Iridium-catalyzed C-C bond formation : development of crotylation and methallylation reactions through transfer hydrogenation(2012-05) Townsend, Ian A.; Krische, Michael J.; Anslyn, Eric V.Under the conditions of transfer hydrogenation utilizing chromatographically purified ortho-cyclometallated iridium C,O-benzoate precatalysts, enantioselective carbonyl crotylation and methallylation can be performed in the absence of stoichiometric metallic reagents and stoichiometric chiral modifiers. In the case of carbonyl crotylation, use of a preformed precatalyst rather than an in situ generated catalyst results in lower reaction temperatures, providing generally higher diastereoselectivity and yields. By utilizing a more reactive leaving group in chloride over acetate on our methallyl donor, the inherently shorter lifetime of the olefin π-complex is compensated for, giving our group’s first report of reactivity utilizing 1,1-disubstituted allyl donors.Item Iron (III) and oxyanion catalysis of some ligand substitution reactions of chromium (III) complexes(Texas Tech University, 1973-12) Choi, Sung NakNot availableItem Metal chalcogenide electrocatalysts for water splitting(2016-08) Mabayoje, Oluwaniyi Olanrewaju; Mullins, C. B.; Brodbelt, Jennifer SOxygen evolution catalysts made out of a metal (Ni, Co, or Fe) and a pnictide or chalcogenide (P, S, or Se) counterion are a promising class of electrocatalysts for the oxygen evolution reaction (OER), an important reaction for the photoelectrochemical splitting of water. We synthesized a nickel-based oxygen evolution catalyst derived from pulse-electrodeposited nickel sulfide. This catalyst was found to produce current densities of 10 mA/cm2 at the relatively low overpotential of 320 mV in alkaline electrolyte (1 M KOH). Importantly, we found that the sulfur anion in the nickel sulfide is depleted in the active form of the electrocatalyst, and that the NiS is converted into an amorphous nickel oxide in the potential range where water is oxidized to oxygen. The superior catalytic activity of this nickel sulfide is thus unrelated to the sulfur anions in the active catalyst, but is instead related to the metal sulfide’s ability to act as a precursor to a highly active nickel oxide OER electrocatalyst. The nickel oxide derived from nickel sulfide was found to be amorphous with a relatively high surface area, two factors that have been previously shown to be important in oxygen evolution electrocatalysis.
- «
- 1 (current)
- 2
- 3
- »