Browsing by Subject "Nickel"
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Item Hierarchical three-dimensional Fe-Ni hydroxide nanosheet arrays on carbon fiber electrodes for oxygen evolution reaction(2014-05) O'Donovan-Zavada, Robert Anthony; Manthiram, ArumugamAs demands for alternative sources of energy increase over the coming decades, water electrolysis will play a larger role in meeting our needs. The oxygen evolution reaction (OER) component of water electrolysis suffers from slow kinetics. An efficient, inexpensive, alternative electrocatalyst is needed. We present here high-activity, low onset potential, stable catalyst materials for OER based on a hierarchical network architecture consisting of Fe and Ni coated on carbon fiber paper (CFP). Several compositions of Fe-Ni electrodes were grown on CFP using a hydrothermal method, which produced an interconnected nanosheet network morphology. The materials were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrochemical performance of the catalyst was examined by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The best electrodes showed favorable activity (23 mA/cm², 60 mA/mg), onset potential (1.42 V vs. RHE), and cyclability.Item Mechanistic investigations of the A-cluster of acetyl-CoA synthase(Texas A&M University, 2006-04-12) Bramlett, Matthew RichardThe A-cluster of acetyl-CoA synthase (ACS) catalyzes the formation of acetyl- CoA from CO, coenzyme-A, and a methyl group donated by a corrinoid iron-sulfur protein. Recent crystal structures have exhibited three different metals, Zn, Cu, and Ni, in the proximal site, which bridges a square-planar nickel site and a [Fe4S4] cubane. Contradicting reports supported both the nickel and copper containing forms as representing active enzyme. The results presented here indicate that copper is not necessary or sufficient for catalysis and that copper addition to ACS is deleterious. Several proposed mechanisms exist for the synthesis of acetyl-CoA, the two most prominent are the ??paramagnetic?? and ??diamagnetic?? mechanisms. The ??diamagnetic?? mechanism proposes a two electron activation that precedes methylation to produce an EPR silent Ni2+-CH3 species. This then reacts with CO and coenzyme-A to form acetyl- CoA and regenerate the starting species. The ??paramagnetic?? mechanism assumes a one electron activation prior to the methylation of the paramagnetic Ni1+-CO state to form an unstable Ni3+-acetyl species. This is immediately reduced by an electron shuttle. Results are presented here that no shuttle or external redox mediator is necessary for catalysis. This supports the ??diamagnetic?? mechanism, specifically that a two-electron reductive activation is necessary and that the Ni1+-CO species is not an intermediate. The two-electron reductive activation required by the ??diamagnetic?? mechanism results in an unknown electronic state. Two proposals have been made to describe this form of the A-cluster. The first hypothesis from Brunold et al involves a one-electron reduction of the [Fe4S4]2+ cube and a one-electron reduction of the Nip 2+. This should result in a spin-coupled state that is S = integer. The Ni0 hypothesis requires both electrons to localize on the Nip 2+ forming a zero-valent proximal nickel. M??ssbauer spectroscopy has been used to probe the oxidation state and spin state of the [Fe4S4] cube in the reduced active form. No integer spin system is found and this is interpreted as supporting the Ni0 hypothesis. Additionally, spectra are presented that indicate the heterogeneous nature of the A-cluster is not caused by the occupancy of the proximal site.Item Superalloys created by the self-propagating high-temperature synthesis of nano-composite nickel aluminide(Texas Tech University, 2005-05) Hunt, Emily M.; Pantoya, Michelle; Bennett, Harold R.; Levitas, Valery; Simon, Sindee L.; Burton, Thomas D.Advancements in nanotechnology for material processing via combustion synthesis have spurred the development of superalloys that provide improved protective properties. Nano-scale reactant particles offer unique thermal properties and increased homogeneity that improve the micro-structural features and macroscopic properties of the synthesized product. The ignition and combustion behaviors of Nickel (Ni) and Aluminum (Al) thermites were studied as a function of Al particle size. In particular, nano-scale Ni/Al composites were compared to micron-scale Ni/Al composites. Laser ignition experiments were performed on pressed Ni/Al pellets to determine ignition time and temperature as a function of Al particle size. Flame propagation behavior and burn rates were also examined using high-speed diagnostics. Results show that nano-scale composites have significantly reduced ignition times over micron-scale composites owing primarily to the unique thermal properties associated with nano-particles. Flame propagation and overall burn rate was also influenced by Al particle size and physical properties. Electron micrographs of the products reveal the formation of whiskers in nano-scale composites but not in micron-scale composites. In order to examine the effects of a nano-scale additive on the Ni/Al alloy, nano-scale molybdenum tri-oxide (MoO3) particles were added to micron scale Ni and Al. The goal was to incorporate a nano-scale additive within the reactant matrix that would produce a superalloy by generating excessively high heating rates and creating controlled quantities of Al2O3 (a strengthening agent) within the microstructure of the alloy. Ignition and flame propagation were examined using a CO2 laser and imaging diagnostics that include a copper-vapor laser coupled with a high-speed camera. Product microstructure was examined using micro-XRD analysis and scanning electron microscopy. Abrasion testing was performed to evaluate the wear resistance properties of the superalloy. Results show that adding MoO3 increases the flame temperature, results in greater ignition sensitivity, produces a more homogeneous microstructure and increases the overall wear resistance of the product. Ignition behaviors associated with nano and micron scale particulate composite thermites were studied experimentally and modeled theoretically. The experimental analysis utilized a CO2 laser ignition apparatus to ignite the front surface of compacted Ni and Al pellets at varying heating rates. Ignition delay time and ignition temperature as a function of both Ni and Al particle size were measured using high speed imaging and micro-thermocouples. The activation energy was determined from this data using a Kissinger isoconversion method. This is the first study to show that the activation energy is significantly lower for nano- compared with micron-scale particulate media (i.e., as low as 17.4 compared with 162.5 kJ/mol, respectively). Two separate Arrhenius-type mathematical models were developed that describe ignition in the nano- and the micron- composite thermites. The micron-composite model is based on a heat balance while the nano-composite model incorporates the energy of phase transformation in the alumina shell theorized to be an initiating step in the solid-solid diffusion reaction and uniquely appreciable in nano-particle media. These models were found to describe the ignition of the Ni/Al alloy for a wide range of heating rates. A highly porous intermetallic alloy was created through self-propagating high-temperature synthesis. The reactants are composed of nano-scale particles of Ni, micron-scale particles of Al, and nano-scale Al particles passivated with a gasifying agent, C13F27COOH. The concentration of nm Al particles present in the reactant matrix was controlled according to the wt % of gasifying agent. The reactant mixture was cold-pressed into cylindrical pellets with a constant density equal to 70% of the theoretical maximum density. Once ignited, flame propagation was observed to transition from normal to convectively dominant burning as more gasifying agent became present in the reactants. A critical Andreev number of 6 was determined to represent this transition. Ignition delay times were reduced by two orders of magnitude when only 2.24 wt % nm Al particles were present. The product alloy expanded by a factor of 14 in the axial direction with 1.6 wt % nm Al (corresponding to 10 wt % gasifying agent). Total porosity of the pellets was also measured and found to increase with increasing wt % of the nm Al and gasifying agent.Item Superalloys created by the self-propagating high-temperature synthesis of nano-composite nickel aluminide(2005-05) Hunt, Emily M.; Pantoya, Michelle; Bennett, Harold R.; Levitas, Valery; Simon, Sindee L.; Burton, Thomas D.Advancements in nanotechnology for material processing via combustion synthesis have spurred the development of superalloys that provide improved protective properties. Nano-scale reactant particles offer unique thermal properties and increased homogeneity that improve the micro-structural features and macroscopic properties of the synthesized product. The ignition and combustion behaviors of Nickel (Ni) and Aluminum (Al) thermites were studied as a function of Al particle size. In particular, nano-scale Ni/Al composites were compared to micron-scale Ni/Al composites. Laser ignition experiments were performed on pressed Ni/Al pellets to determine ignition time and temperature as a function of Al particle size. Flame propagation behavior and burn rates were also examined using high-speed diagnostics. Results show that nano-scale composites have significantly reduced ignition times over micron-scale composites owing primarily to the unique thermal properties associated with nano-particles. Flame propagation and overall burn rate was also influenced by Al particle size and physical properties. Electron micrographs of the products reveal the formation of whiskers in nano-scale composites but not in micron-scale composites. In order to examine the effects of a nano-scale additive on the Ni/Al alloy, nano-scale molybdenum tri-oxide (MoO3) particles were added to micron scale Ni and Al. The goal was to incorporate a nano-scale additive within the reactant matrix that would produce a superalloy by generating excessively high heating rates and creating controlled quantities of Al2O3 (a strengthening agent) within the microstructure of the alloy. Ignition and flame propagation were examined using a CO2 laser and imaging diagnostics that include a copper-vapor laser coupled with a high-speed camera. Product microstructure was examined using micro-XRD analysis and scanning electron microscopy. Abrasion testing was performed to evaluate the wear resistance properties of the superalloy. Results show that adding MoO3 increases the flame temperature, results in greater ignition sensitivity, produces a more homogeneous microstructure and increases the overall wear resistance of the product. Ignition behaviors associated with nano and micron scale particulate composite thermites were studied experimentally and modeled theoretically. The experimental analysis utilized a CO2 laser ignition apparatus to ignite the front surface of compacted Ni and Al pellets at varying heating rates. Ignition delay time and ignition temperature as a function of both Ni and Al particle size were measured using high speed imaging and micro-thermocouples. The activation energy was determined from this data using a Kissinger isoconversion method. This is the first study to show that the activation energy is significantly lower for nano- compared with micron-scale particulate media (i.e., as low as 17.4 compared with 162.5 kJ/mol, respectively). Two separate Arrhenius-type mathematical models were developed that describe ignition in the nano- and the micron- composite thermites. The micron-composite model is based on a heat balance while the nano-composite model incorporates the energy of phase transformation in the alumina shell theorized to be an initiating step in the solid-solid diffusion reaction and uniquely appreciable in nano-particle media. These models were found to describe the ignition of the Ni/Al alloy for a wide range of heating rates. A highly porous intermetallic alloy was created through self-propagating high-temperature synthesis. The reactants are composed of nano-scale particles of Ni, micron-scale particles of Al, and nano-scale Al particles passivated with a gasifying agent, C13F27COOH. The concentration of nm Al particles present in the reactant matrix was controlled according to the wt % of gasifying agent. The reactant mixture was cold-pressed into cylindrical pellets with a constant density equal to 70% of the theoretical maximum density. Once ignited, flame propagation was observed to transition from normal to convectively dominant burning as more gasifying agent became present in the reactants. A critical Andreev number of 6 was determined to represent this transition. Ignition delay times were reduced by two orders of magnitude when only 2.24 wt % nm Al particles were present. The product alloy expanded by a factor of 14 in the axial direction with 1.6 wt % nm Al (corresponding to 10 wt % gasifying agent). Total porosity of the pellets was also measured and found to increase with increasing wt % of the nm Al and gasifying agent.Item The design of new ligands and transition metal compounds for the oxidation of organic compounds(2009-06-02) Grill, Joseph MichaelA review of metal-mediated epoxidation is given. Jacobsen's catalyst and the Sharpless asymmetric epoxidation catalyst are discussed. The origins of enantioselectivity are explained using stereochemical models. Several new salen-type ligands were synthesized based on biphenol and binaphthol. The synthesis of these ligands and their subsequent coordination to transition metals were described. The transition metal complexes were structurally characterized by X-ray diffraction of single crystals. The manganese (III) complexes were evaluated for catalytic activity in epoxidation reactions. Despite the fact that these many of these complexes were optically active, little asymmetric induction was observed in any of the epoxidation reactions. The investigation of a soluble nickel salen complex for the epoxidation of olefins led to the discovery of a new heterogeneous catalyst for the epoxidation of ?,?- unsaturated carboxylic acids. Nickel salen complexes, upon reaction with commercial bleach, yield a fine black powder, which we identified as nickel oxide hydroxide-a known but poorly characterized nickel peroxide containing species. The reaction of an aqueous nickel (II) source with commercial bleach also yields nickel oxide hydroxide. This material was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Extremely broad peaks in the X-ray diffraction pattern suggested that this material consisted of particles with a very small diameter and this was confirmed by TEM. This insoluble material was found to function as a heterogeneous catalyst for the epoxidation of ?,?-unsaturated carboxylic acids in the presence of sodium hypochlorite. The high activity of this catalyst in the epoxidation of certain olefins is due in part to its small particle size, which increases the overall surface area of this heterogeneous catalyst. Large particles of nickel oxide hydroxide were prepared and the catalytic activity was comparatively less. The oxidation of several other organic substrates was also explored using this catalyst. Both primary and secondary alcohols can be oxidized with our nickel-based system. Primary alcohols go through an aldehyde intermediate which is then in turn oxidized to the carboxylic acid.Item The kinetics of nickel molybdate formation(Texas Tech University, 1962-08) Garner, Richard LewisNot availableItem Transition metal catalyzed regioselective carbon-carbon bond formation mediated by transfer hydrogenation(2015-05) Sam, Brannon; Krische, Michael J.; Anslyn, Eric V; Dong, Guangbin; Keatinge-Clay, Adrian T; Kerwin, Sean MOne of the more formidable challenges in the synthesis of complex organic molecules remains the efficient formation of carbon-carbon bonds. The development of a broad class of reactions to achieve this goal involves the addition of carbon based nucleophiles to carbonyl and imine compounds. Until recently, classical approaches to carbon-carbon bond formation generally required the use of stoichiometric pre-formed organometallic reagents to serve as nucleophiles, which translate into stoichiometric organometallic byproducts. In an effort to minimize nucleophile pre-activation and byproduct formation, our lab has developed efficient methods for carbonyl and imine additions via in situ formation of alkyl metal nucleophiles from π-unsaturates. The research reported herein describes our advances in an assortment of transition metal-catalyzed carbon-carbon bond forming reactions mediated by transfer hydrogenation, including regioselective hydrohydroxymethylation, hydrohydroxyfluoroalkylation, and hydroaminomethylation. Additionally, the investigation of regioselective carbonyl vinylation is reported.