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Nancarrow, P. D. "Reaction engineering and separation studies on Friedel-Crafts catalysis in ionic liquids." Thesis, Queen's University Belfast, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426655.
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Winchester, Charles Michael. "Generation and Kinetic Studies of Porphyrin-Manganese(IV)-Oxo Intermediates." TopSCHOLAR®, 2018. https://digitalcommons.wku.edu/theses/3074.
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High-valent metal-oxo complexes are vital as active oxidants in enzymatic and synthetic catalytic oxidations. Inspired by the ubiquitous cytochrome P450 enzyme, researchers have explored the power of metalloporphyrins to mimic one of Nature’s premier catalytic entities.
In this work, four manganese(III)porphyrin systems, including three electronwithdrawing ligands and one electron-donating ligand, were investigated with regard to their ability to form high-valent manganese(IV)-oxo porphyrin systems. The porphyrin ligands studied were 5,10,15,20-tetra(2,6-difluorophenyl)porphyrin [H2(2,6-F2TPP)], 5,10,15,20-tetra(4-trifluoromethylphenyl)porphyrin [H2(4-CF3TPP)], 5,10,15,20-tetra(4- fluorophenyl)porphyrin [H2(4-FTPP)], and 5,10,15,20-tetra(2,6- dimethoxyphenyl)porphyrin [H2(TDMPP)]. All were synthesized purified and characterized spectroscopically. Using the mild oxidant iodobenzene diacetate, manganese(IV)-oxo porphyrins [MnIV(Por)O] were successfully generated in all systems as confirmed through spectroscopic methods. Meanwhile, a new photochemical approach was explored for its efficacy in producing the MnIV-oxo complexes by visible light irradiation of manganese(III) precursors containing the photolabile chlorate as the axial ligand.
More importantly, the MnIV-oxo complexes obtained by chemical generation were tested for their abilities as oxygen atom transfer agents (OATs) with aryl alkenes, alkenes and thioanisoles in CH3CN. The apparent second-order rate constants for sulfoxidation ranged between (2.29 ± 0.08) and (12.9 ± 2.0) M-1s-1 x 10-2 which were, on average, a magnitude larger than the rates for epoxidation of the aryl alkenes. Most notably in reactions with substrate, the order of reactivity of [MnIV(Por)O] was [(4-F)TPP] > [(4- CF3)TPP] > [(2,6-F2)TPP], which is inverted from the expected result based on the electron-demands of the porphyrin ligands. The apparent rate constants for reaction with cyclohexene was found to be 1 to 2 orders of magnitude larger than those with sulfide substrates. The kinetic results are consistent with a reaction model involving disproportionation of MnIV(Por)O to give MnIII(Por) and MnV(Por)O species, the latter of the two being the active oxidant. Alternatively, the results from the sulfoxidations are consistent in part with a direct oxygen atom transfer by [MnIV(Por)O]
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Sharma, Amit. "Catalytic Reaction Engineering using Ionic liquids : Hydroformylation of 1-Octene." Thesis, Toulouse, INPT, 2009. http://www.theses.fr/2009INPT015G/document.
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Une démarche de type génie de la réaction chimique est appliquée à l'hydroformylation modèle d'oct-1-ène par des complexes lipophobes du rhodium préparés à partir de Rh(CO)2(acac) en phase liquide ionique ([Bmim][PF6]) ou en phase liquide ionique supportée sur silice. La réaction étant contrôlée par la concentration des réactifs dans la phase liquide ionique catalytique, une première étape a consisté à mesurer ces concentrations tant pour les deux gaz (H2 et CO) que pour l'oct-1-ène à différentes températures et pressions. Diverses méthodes de mesures sont utilisées pour la solubilité de l'oléfine : thermogravimétrie et chromatographie gazeuse après extraction multiple d’espace de tête, en présence de solvant (décane) et du produit de la réaction (nonanal). Le transfert gaz-liquide, qui peut conditionner la vitesse de réaction dans ces milieux visqueux, est également mesuré par une technique dynamique de variation de pression, en liquide ionique pur et en mélange biphasique liquide ionique-phase organique, dans un réacteur autoclave à autoaspiration de gaz par arbre creux. Une corrélation générale est proposée montrant une forte influence de la vitesse d'agitation.Une étude cinétique est réalisée en conditions de transferts non limitants en gaz-liquide organique-liquide ionique avec la TPPTS comme ligand. Les comportements habituels de l’hydroformylation en phase organique ou en phase aqueuse sont retrouvés : ordre voisin de 1 pour H2, inhibition par CO à forte concentration, énergie d'activation élevée. Si le turnover est convenable (70 h-1), le rapport n/iso est par contre très bas ce qui n'est pas en faveur de ce système catalytique. Quelques résultats permettent aussi une première analyse de la catalyse biphasique avec le ligand sulfoxantphos et de la catalyse en phase liquide ionique supportée sur silice avec la TPPTSA chemical reaction engineering approach is applied to the hydroformylation of 1-octene using lipophobic complexes of rhodium prepared from Rh(CO)2(acac) in ionic liquid phase ([Bmim] [PF6]) or in the ionic liquid phase supported on silica. As the reaction is controlled by the concentration of the reagents in the catalytic ionic liquid phase, the concentrations of both gases (H2 and CO) and also of 1-octene are measured at various temperatures and pressures as an initial step. Different methods are used for the measurement of the olefin solubility inside the ionic liquid: thermogravimetry and multiple headspace chromatography, in the presence of solvent (decane) and reaction product (nonanal). The gas-liquid mass transfer, which can be a rate controlling step in these viscous media, is also measured by a dynamic technique of pressure variation, both in case of pure ionic liquid and biphasic mixture of ionic liquid and organic phase, in an autoclave reactor with self induced stirrer. A general correlation is proposed showing the strong influence of the agitation speed. A kinetic study is realized in no gas–liquid nor organic–ionic liquid mass transfer limiting conditions (chemical regime) with TPPTS as ligand. The usual hydroformylation behaviour is observed, as already found in organic phase or in aqueous phase: order close to 1 for H2, inhibition by CO at large concentration, and high activation energy. If the turnover frequency is suitable (70 h-1), the n/iso ratio is very low which is not favourable to this catalytic system. Some experimental results also allow a first analysis of biphasic catalysis with sulfoxantphos ligand and of ionic liquid phase supported catalysis with TPPTS ligand
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Brown, Darryl Edward. "Kinetic models for the Pt/CeO₂ catalysed water-gas shift reaction." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/27914.
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As the global population grows, so does the world's demand for energy. Consequently, there exists an increased interest in the development of fuel cells for power generation due to their low greenhouse gas emissions. For fuel cells to be a successful power source, a reliable hydrogen source is required. Ultimately, the goal is for hydrogen to be supplied from renewable energy technology however, this type of technology is currently not mature enough to meet the continuous demand of the world's energy systems. Producing hydrogen from fossil fuels can be seen as a temporary solution while further advances are made in developing renewable hydrogen infrastructure. A fuel processing train, therefore, remains an important alternative to producing hydrogen. A fuel processing train converts fossil fuels into hydrogen for use in fuel cells and eliminates the need for hydrogen storage as hydrogen is produced on demand. Currently, the water-gas shift (WGS) reactor is one of the largest components in a fuel processing train and thus opportunity exists to reduce the size of this reactor. To design future WGS catalysts and an optimised fuel processor, the reaction kinetics taking place must be understood and quantified. In this study, kinetic measurements were conducted at 2 bar(a) and across a temperature range of 270 - 300 °C using 16 parallel fixed bed reactors (high throughput experimentation) over a 0.5 wt% Pt/CeO₂ catalyst. The feed composition was varied over the ranges 2 - 12 mol% CO, 20 - 45 mol% H₂O, 4 - 15 mol% CO₂ and 25 - 55 mol% H₂. An online micro gas chromatograph (μGC) was used to analyse the dry gas composition. Fitting of experimental data to various kinetic models was accomplished with the gPROMS software package. An initial evaluation of several Langmuir-Hinshelwood (LH) type mechanisms to two data sets obtained from literature was undertaken to evaluate the strengths and weaknesses of different kinetic expressions. The results of the initial evaluation indicate that a dual-site mechanism with an intermediate species results in the best fit for reducible supports, while a single site mechanism offers a better fit for non-reducible supports. For both kinetic models, the formation of the intermediate species is most likely to be the rate determining step. A power-rate law empirical rate expression and a LH type rate expression were both found to predict the WGS outlet composition well within 10 % error at 2bar(a). The apparent activation energy of the reaction was determined to be 110 kJ/mol. This value was confirmed to be constant, throughout the range of conditions evaluated, by means of a classical Arrhenius analysis. Simulations of increasing total system pressure, using both the empirical and "best fitting" LH model, indicate a significant pressure effect for the LH type equation, whereas the power-rate law empirical equation predicts a small, negative effect on the reaction rate with increaseing pressure. Consequently, further experiments were conducted to determine the true effect of pressure. It was found that increasing system pressure increased the WGS reaction rate, which has also been reported by Twigg (1989:288). Only the LH type rate expression was able to predict this. It is therefore recommended that either the power-rate law empirical rate expression or the LH type rate expression be used to predict the WGS outlet composition when operating below 2 bar(a). Furthermore, when predicting reaction rates outside of the window in which the rate equations were derived, it is recommended that the LH model be used as it is expected to give a better prediction as it is based on fundamental steps.
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Khasu, Motlokoa. "In situ study of Co₃O₄ morphology in the CO-PROX reaction." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/24905.
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The preferential oxidation (PROX) reaction is an effective process for the removal of trace amounts of carbon monoxide from a reformate stream. Tricobalt tetraoxide (Co₃O₄) is the candidate for CO-PROX in a H₂ rich gas and could be an alternative to the rare and expensive PGMs. This study investigates the effect of different Co₃O₄ morphologies in the preferential oxidation of carbon monoxide in H₂ rich gas. Reports have shown morphology dependency in CO oxidation in the absence of hydrogen, no study has investigated the morphology dependency in H₂ rich atmospheres. Different morphologies of nanocubes, nanosheets and nanobelts were prepared using hydrothermal mn and precipitation. Conventional spherical nanoparticles from our group were included to compare the activity of conventional nanoparticles with nanoparticles of different morphology. The model catalysts were supported on silica spheres which were also prepared. The CO-PROX experiments were conducted in the in situ UCT-developed magnetometer and PXRD capillary cell instruments by induced reduction at temperatures between 50 and 450°C. Catalyst tests showed two distinct temperature regions with maximum activity. In the range of 150 – 175ᵒC, activity decreased from nanoparticles > amine nanosheets > nanobelts. However, the surface area specific rate of CO₂ formation displayed an inverse trend. In the region of 225 – 250ᵒC, nanocubes > NaOH nanosheet > HCl nanocubes showed maximum activity. The surface area specific rate was the same for amine nanocubes and NaOH nanosheets. None of the model catalysts retained their morphology after the temperature was ramped from 50ᵒC to 450ᵒC, and back to 50ᵒC. The catalysts were partially reduced to metallic Coo (other phase being CoO). Figure 1: In situ PXRD analysis and kinetics of CH4, CO and CO₂ showing the behaviour of Co₃O₄/SiO₂ (amine nanocubes) under CO-PROX conditions
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Matsutsu, Molefi. "DFT insight into the oxygen reduction reaction (ORR) on the Pt₃Co(111) surface." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/22066.
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Proton exchange membrane fuel cells (PEMFC) are identified as future energy conversion devices, for application in portable and transportation devices. The preferred catalyst for the PEMFC is a Pt-catalyst. However, due to the slow oxygen reduction reaction (ORR) kinetics, high Pt loadings have to be used. The high Pt loadings lead to high costs of the PEMFC. Pt-Co alloys have been identified as catalysts having higher ORR activity higher than of a Pt-catalyst. Therefore, in the present study, the Density Functional Theory (DFT) technique is used to gain fundamental insight into the ORR on the Pt₃Co(111) surface. The calculations have been performed using the plane wave based code, the Vienna ab-initio Simulation Package (VASP). DFT spin-polarized calculations, utilizing the GGA-PW91 functional, have been used to study the adsorption of the ORR intermediates, viz. O₂, O, OOH, OH, H₂O and HOOH on the Pt₃Co(111) surface. The results obtained on the Pt₃Co(111) surface are compared to the results obtained on the Pt(111) surface. The adsorption strength of the ORR intermediates has been shown to be affected by the presence of Co to varying extents on the Pt₃Co(111) surface relative to adsorption on the Pt(111) surface. The most strongly stabilised ORR intermediate on the Pt₃Co(111) surface relative to adsorption on the Pt(111) surface is O: on the Pt₃Co(111) surface O is 0.45 eV more strongly adsorbed than on the Pt(111) surface. The least affected ORR intermediate is H₂O: H₂O adsorption on the Pt₃Co(111) surface is 0.20 eV more stable than on the Pt(111) surface. The energetically favorable, i.e. most strongly bound adsorption configurations for all the ORR intermediates involves a configuration in which the ORR intermediate is bonded to a surface Co atom. Therefore, the surface Co atom stabilizes the adsorption of the ORR intermediates, relative to adsorption on the Pt(111) surface. Coadsorbed configurations have been used to study the formation and dissociation of the ORR intermediates. From the coadsorption studies, it is shown that there is an energy cost associated with moving the adsorbates from their lowest energy sites, while separately adsorbed, to the higher energy coadsorbed state, prior to reaction. Hence, adsorbate-adsorbate interactions are expected to destabilize the coadsorbed state at the coverages considered in the present study. The Climbing Image Nudged Elastic Band (CI-NEB) method has been used to locate the transition states and to calculate the activation energies of the different elementary reaction steps. The calculated dissociation reaction activation energies for the Pt₃Co(111) surface are found to be lower than the dissociation activation energies calculated on the Pt(111) surface. The most lowered dissociation activation energy is for the dissociation of O₂: on the Pt₃Co(111) surface the activation energy is 0.08 eV, whilst on the Pt(111) surface the activation energy is 0.59 eV. For the hydrogenation reaction steps, only the hydrogenation of O to form OH occurs with a lower activation energy of 0.86 eV on the Pt₃Co(111) surface, compared to 0.95 eV on the Pt(111) surface. For other hydrogenation reaction steps, the activation energies on the Pt₃Co(111) surface are higher than those on the Pt(111) surface. Based on the calculated activation energies of the elementary ORR reaction steps, the dissociative and the O-assisted H₂O dissociation mechanisms are identified as the mechanisms most likely to be dominant on the Pt₃Co(111) surface, due to having lower activation energies relative to the associative mechanisms. For both mechanisms, the reaction step with the highest activation energy is the step involving O, i.e. O hydrogenation to form OH for the dissociative mechanism, and the O* + H₂O* --> 2OH* reaction for the O-assisted H₂O dissociation mechanism. Thus, the reaction step involving the reaction of the strongly adsorbed O species, is identified as the potential rate limiting step of the ORR. Both the dissociative and the O-assisted H₂O dissociation mechanisms are expected to be in competition on the Pt₃Co(111) surface, since the potential rate limiting step for both mechanisms have similar activation energies. Hence, the preferred mechanism will depend on the relative abundances of the H species and H₂O on the Pt₃Co(111) surface. A microkinetic analysis would be need needed to fully account for concentration and entropic contributions to the rate of reaction for the different ORR elementary reaction steps.
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Hlabangana, Ntandoyenkosi. "Influence of particle size and morphology of Pt₃Co/C on the oxygen reduction reaction." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/24324.
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Polymer electrolyte fuel cells have shown great potential in providing clean energy with no emissions. The kinetics of the cathode reaction, i.e. the oxygen reduction reaction (ORR) are sluggish necessitating high loadings of the catalyst metal, i.e. platinum. Platinum is a limited resource and expensive. Its price has been one of the major drawbacks in wide scale commercialisation of fuel cells. In an effort to improve the activity of the catalyst and therefore reduce Pt loadings on the catalyst, Pt can be alloyed with transition metal elements (e.g. Ni, Co and Fe) to form bimetallic catalysts. Alloying has been known to improve the activity and stability of a catalyst for the ORR. The enhanced activity of the alloys originates from the modified electronic structures of the Pt in these alloy catalysts which reduces the adsorption of spectator species therefore increasing the number of active sites for the ORR (Wang et al., 2012 (2)). The aim of this study was to gain a better understanding of the influence of Pt alloy particle size and active surface morphology on the ORR activity. The Pt alloy that was investigated was Pt₃Co/C. The surface morphology was modified by varying the Pt/Pt₃Co loading on a carbon support. The catalysts were prepared using thermally induced chemical deposition. The support used was Vulcan-XC-72R. The effects of varying the metal loadings on the ORR was investigated. The loadings that were investigated were 20, 40, 60 and 80 wt. % Pt and Pt₃Co. The alloy catalysts were subjected to annealing at 900 °C and acid leaching. The catalysts were analysed using electrochemical characterisation techniques such as cyclic voltammetry, CO stripping voltammetry, rotating disk electrode and rotating ring disk electrode. Physical characterisation of the catalysts was also implemented. The techniques used were x-ray diffraction, thermogravimetric analysis and transmission electron microscopy. The Pt particles on the carbon support were found not to agglomerate significantly despite the loading being increased. This trend was also observed for the Pt₃Co/C catalysts even after heat treatment and leaching. The lack of agglomeration was credited to a new reactor system developed in this work. The particle growth increased from low loadings to high loadings for both the Pt/C and Pt₃Co/C catalysts. Particle growth was more significant for the Pt₃Co/C catalysts at high loadings. At lower loadings (20 and 40 wt. %) the particle sizes between the Pt/C and Pt₃Co/C catalysts were comparable despite the Pt₃Co/C catalysts undergoing annealing and leaching. The mass specific activity of the Pt/C catalysts was not improved by alloying with the exception of the 20 wt. % catalyst which saw an enhancement factor of 1.66. The surface specific activity of the Pt/C catalysts was improved significantly with factors of 2.40 and 3.11 being recorded for the 20 and 80 wt. % Pt₃Co/C catalysts respectively. The enhancement factors of the intermediate loadings (40 and 60 wt. %) were lower and fairly similar at 1.30 and 1.35 respectively.
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Brinkley, Kendra W. "The Synthesis of Solid Supported Palladium Nanoparticles: Effective Catalysts for Batch and Continuous Cross Coupling Reactions." VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/3959.
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Catalysis is one of the pillars of the chemical industry. While the use of catalyst is typically recognized in the automobile industry, their impact is more widespread as; catalysts are used in the synthesis of 80% of the US commercial chemicals. Despite the improved selectivity provided by catalyst, process inefficiencies still threaten the sustainability of a number of synthesis methods, especially in the pharmaceutical industry. Recyclable solid supported catalysts offer a unique opportunity to address these inefficiencies. Such systems coupled with continuous synthesis techniques, have the potential to significantly reduce the waste to desired product ratio (E-factor) of the production techniques. This research focuses developing sustainable processes to synthesize organic molecules by using continuous synthesis methods. In doing so, solid supported metal catalyst systems were identified, developed, and implemented to assist in the formation of carbon-carbon bonds. Newly developed systems, which utilized metal nanoparticles, showed reactivity and recyclability, comparable to commercially available catalyst.
Nanoparticles are emerging as useful materials in a wide variety of applications including catalysis. These applications include pharmaceutical processes by which complex and useful organic molecules can be prepared. As such, an effective and scalable synthesis method is required for the preparation of nanoparticle catalysts with significant control of the particle size, uniform dispersion, and even distribution of nanoparticles when deposited on the surface of a solid support. This project describes the production of palladium nanoparticles on a variety of solid supports and the evaluation of these nanoparticles for cross coupling reactions.
This report highlights novel synthesis techniques used in the formation of palladium nanoparticles using traditional batch reactions. The procedures developed for the batch formation of palladium nanoparticles on different solid supports, such as graphene and carbon nanotubes, are initially described. The major drawbacks of these methods are discussed, including limited scalability, variation of nanoparticle characteristics from batch to batch, and technical challenges associated with efficient heating of samples.
Furthermore, the necessary conditions and critical parameters to convert the batch synthesis of solid supported palladium nanoparticles to a continuous flow process are presented. This strategy not only alleviates the challenges associated with the robust preparation of the material and the limitations of scalability, but also showcases a new continuous reactor capable of efficient and direct heating of the reaction mixture under microwave irradiation. This strategy was further used in the synthesis of zinc oxide nanoparticles. Particles synthesized using this strategy as well as traditional synthesis methods, were evaluated in the context industrially relevant applications.
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Jayatissa, Kuruppu Lilanthi. "A Metal-Free Approach to Biaryl Compounds: Carbon-Carbon Bond Formation from Diaryliodonium Salts and Aryl Triolborates." PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2229.
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Biaryl moieties are important structural motifs in many industries, including pharmaceutical, agrochemical, energy and technology. The development of novel and efficient methods to synthesize these carbon-carbon bonds is at the forefront of synthetic methodology. Since Ullmann’s first report of stoichiometric Cu-mediated homo-coupling of aryl halides, there has been a dramatic evolution in transition metal catalyzed biaryl cross-coupling reactions.
Our work focuses on the discovery and development of an unprecedented reagent combination for metal-free cross-coupling. It is hypothesized that direct carbon-carbon bond formation occurs via a triaryl-λ3-iodane and that electrophile/nucleophile pairing is critical for success in the reaction. Proof-of-concept for this approach focused on the reaction between bromo 4-trifluoromethylphenyl (trimethoxybenzene)-λ3-iodane and potassium 3-fluorophenyltriolborate. The spectator ligand and counter ions are important parameters for both reactivity and selectivity of the aryl group transfer in this reaction. Moderate to good yields of biaryl products are obtained by this method. Experimental evidence supports the assertion of a metal-free cross-coupling reaction.
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Houlding, T. K. "Application of radiofrequency heating in catalytic reaction engineering." Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.676521.
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Radiofrequency (RF) heating of composite magnetic materials enables direct and efficient transfer of energy to the sites of catalytic reactions within a chemical reactor. The materials consist of an RF heated magnetic component and a catalytic component. The two components can be optimised separately according to the demands of the application. This approach was applied to continuous direct amide formation from amines and carboxylic acids under flow conditions, a reaction of great interest and potential to the pharmaceutical industry. The RF heat generation of NiFe2 04-TiO2 magnetic materials were optimised. Catalyst screening showed sulfated commercial P 25 Ti02 to give good catalytic activity in the reaction of 4-phenylbutyric acid with aniline in xylene. The composite material was prepared mechanochemically from a mixture of the optimised magnetic and catalytic components. A continuous RF heated reactor was developed, consisting of a 6 mm diameter insulated micro packed-bed reactor placed within an RF induction coil. The reactor was operated at 7 bar and up to 200°C for up to 10 hours. The sulfated composite achieved t he highest activity of up to 50% conversion in a single pass and the least deactivation. Temperature profiles obtained from the analytical solutions were combined with a catalyst kinetic model to form a reactor model, which was validated by the experimental results. The concentration profiles obtained from the reactor model gave an insight into the mechanism of the observed process intensification - the temperature rise along the RF heated reactor axis helped to offset the reduction in the reaction rate as a result of depletion of the reactants. This novel type of process is therefore most suited to reactions with high reaction rate orders and it would therefore be of great interest to investigate other processes where this effect could be demonstrated.
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Joshi, Suvid. "MIXED SURFACTANT SYSTEMS: THERMODYNAMICS AND APPLICATIONS IN METAL OXIDE IMPRINTING." UKnowledge, 2014. http://uknowledge.uky.edu/cme_etds/29.
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In this work we study mixtures of cationic surfactant (CTAB) and sugar based surfactant(s) (octyl beta-D-glucopyranoside (C8G1), dodecyl maltoside (C12G2) and octyl beta-D-xylopyranoside (C8X1)) to understand the non-ideal thermodynamic behavior of the mixtures of cationic and non-ionic surfactants in water and synthesis of imprinted materials. The thermodynamics of micellization, mixing and dilution of these systems are studied using Isothermal Titration Calorimetry (ITC) and the experimental data obtained are modeled with a pseudo-phase separation model with non-ideal mixing described by regular solution theory. It is shown that a model accounting for enthalpy of demicellization and enthalpy of dilution based on McMillan-Mayer model is able to fit ITC data set for CTAB-C8G1 system with varying mole fractions.
In addition to measuring non-ideal mixing behavior, mixtures of cationic and saccharide-based surfactants are of interest for the molecular imprinting of oxide materials. Mixtures of CTAB and either C8G1 or C8X1 are utilized to prepare nonporous adsorbent materials which act as selective adsorbents towards the headgroup of the saccharide surfactant. The approach is based on the Stöber silica particle synthesis process in which surfactants are added to soft particles present at the onset of turbidity to imprint their surface. This approach is shown to yield particles displaying selective adsorption for sugars with different number of carbons, but also provide enantioselective adsorption of targeted saccharides. Enantioselectivity of D-glucose, D-xylose and D-maltose is demonstrated by imprinting with C8G1, C8X1 and C12G2, respectively. The imprinting technique provides the first example of selective adsorption based on non-covalent imprinting of silica for sugars.
The mixed surfactant are also used to synthesize templated porous materials incorporating titanium which are used for epoxidation catalysis. The porous materials obtained have high surface area, uniform pore sizes in the mesopore range, and provided high selectivity and activity towards epoxidation of styrene. Titanosilicate thin films are also synthesized using cationic and saccharide surfactant mixtures to understand the incorporation of the titanium into the porous material. It is demonstrated that large amounts of isolated, tetracoordinated titanium sites can be incorporated into mesoporous silica-based materials via the complexation of the titanium precursor with a saccharide-based surfactant.
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Fusion, Joe. "The Role of Environmental Dynamics in the Emergence of Autocatalytic Networks." PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2458.
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For life to arise from non-life, a metabolism must emerge and maintain itself, distinct from its environment. One line of research seeking to understand this emergence has focused on models of autocatalytic reaction networks (ARNs) and the conditions that allow them to approximate metabolic behavior. These models have identified reaction parameters from which a proto-metabolism might emerge given an adequate matter-energy flow through the system. This dissertation extends that research by answering the question: can dynamically structured interactions with the environment promote the emergence of ARNs? This question was inspired by theories that place the origin of life in contexts such as diurnal or tidal cycles. To answer it, an artificial chemistry system with ARN potential was implemented in the dissipative particle dynamics (DPD) modeling paradigm. Unlike differential equation (DE) models favored in prior ARN research, the DPD model is able to simulate environmental dynamics interacting with discrete particles, spatial heterogeneity, and rare events. This dissertation first presents a comparison of the DPD model to published DE results, showing qualitative similarity with some interesting differences. Multiple examples are then provided of dynamically changing flows from the environment that promote emergent ARNs more than constant flows. These include specific cycles of energy and mass flux that consistently increase metrics for ARN concentration and mass focusing. The results also demonstrate interesting nonlinear interactions between the system and cycle amplitude and period. These findings demonstrate the relevance that environmental dynamics has to ARN research and the potential for broader application as well.
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Rodene, Dylan D. "Engineering of Earth-Abundant Electrochemical Catalysts." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6106.
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Alternative energy research into hydrogen production via water electrolysis addresses environmental and sustainability concerns associated with fossil fuel use. Renewable-powered electrolyzers are foreseen to produce hydrogen if energy and cost requirements are achieved. Electrocatalysts reduce the energy requirements of operating electrolyzers by lowering the reaction kinetics at the electrodes. Platinum group metals (PGMs) tend to be utilized as electrocatalysts but are not readily available and are expensive. Ni1-xMox alloys, as low-cost and earth-abundant transition metal nanoparticles (NPs), are emerging as promising electrocatalyst candidates to replace expensive PGM catalysts in alkaline media. Pure-phase cubic and hexagonal Ni1-xMox alloy NPs with increasing Mo content (0–11.4%) were synthesized as electrocatalysts for the hydrogen evolution reaction (HER). In general, an increase in HER activity was observed with increasing Mo content. The cubic alloys were found to exhibit significantly higher HER activity in comparison to the hexagonal alloys, attributed to the higher Mo content in the cubic alloys. However, the compositions with similar Mo content still favored the cubic phase for higher activity. To produce a current density of -10 mA/cm2, the cubic and hexagonal alloy NPs require over-potentials ranging from -62 to -177 mV and -162 to -242 mV, respectively. The cubic alloys exhibited over-potentials that rival commercial Pt-based electrocatalysts (-68 to -129 mV at -10 mA/cm2). The cubic Ni0.934Mo0.066 alloy NPs showed the highest alkaline HER activity of the electrocatalysts studied and therefore a patent application was submitted.
Bulk Ni–Mo phases have been known as electrocatalysts for the HER for decades, while recently transition metal phosphides (TMPs) have emerged as stable and efficient PGM alternatives. Specifically, Ni2P has demonstrated good HER activity and improved stability for both alkaline and acidic media. However, Ni2P electrocatalysts are a compromise between earth-abundance, performance (lower than Ni–Mo and PGMs) and stability. For the first time Ni–Mo–P electrocatalysts were synthesized with varying atomic ratios of Mo as electrocatalysts for alkaline HER. Specific phases, compositions and morphologies were studied to understand the intrinsic properties of TMPs leading to high HER activity. The Ni1.87Mo0.13P and Ni10.83Mo1.17P5 NPs were shown to be stable for 10 h at –10 mA cm-2 with over-potentials of –96 and –82 mV in alkaline media, respectively. The Ni1.87Mo0.13P and Ni10.83Mo1.17P5 NPs exhibited an improved performance over the synthesized Ni2P sample (–126 mV at –10 mA cm-2), likely a result of the overall phosphorous content and hetero-structured morphologies. A strong correlation between phase dependence and the influence of Mo on HER activity needs to be further investigated.
Furthermore, understanding the intrinsic properties of electrocatalysts leading to high water splitting performance and stability can apply electrocatalysts in other research applications, such as photoelectrochemical (PEC) water splitting, water remediation and sustainable chemical processing applications. Contributions to photocatalytic water remediation and electrochemical chlorinated generation to halogenate pyridone-based molecules are reported. Electrochemical techniques were developed and reported herein to aid in understanding electrochemical performance, chemical mechanisms and the stability of electrocatalysts at the electrode-electrolyte interfaces.
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BHATT, SALIL R. "SYNTHESIS, CHARACTERIZATION AND KINETIC STUDIES OF MIXED METAL Mo-V-Nb-Te OXIDE CATALYSTS FOR PROPANE AMMOXIDATION TO ACRYLONITRILE." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1140626212.
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Kong, Caleb J. "Engineering High Reaction Economy or, An Intensification/Scoring Program for the Preparation of Simple and Complex Molecules." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6023.
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Success of newly discovered chemistry in academia is often scored in terms of its novelty and level of scholarship. In industrial settings, cost, safety and quality are often times the ruler by which new processes are measured. Our group has identified that there is a gap between these two measures of success and has sought to develop principles in order formalize an approach to synthetic strategy and developing ready-to-implement manufacturing processes for molecules, simple and complex.
Some of these principles include (1) the development and application of new chemical methods and reactor technologies (2) recognition of globally amenable chemical environments for each chemical step to consolidate unit operations and obviate the need for purification (3) vertical integration of starting materials to generate complexity from the most elementary building blocks in a chemical supply space and (4) the development of new materials that allow for recovery and reuse. These principles are iteratively scored and redeveloped through various metrics that our group has identified as effective tools in maximizing efficiency such as cost of goods (CoG), process mass intensity (PMI) and volume-time output (VTO). The intended benefits of this approach is that these processes become not only cost effective but sustainable and impactful in the manufacturing landscape and increase access of these products to consumers.
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Serbetcioglu, Serpil. "Mass transfer and catalytic reaction in a three-phase monolith reactor." Thesis, University of Bath, 1993. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332665.
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Miller, Jacob. "Modelling the Effect of Catalysis on Membrane Contactor Mass Transfer Coefficients for Carbon Dioxide Absorption Systems." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627662756315225.
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Tien, Ta-Ching. "Catalytic ignition model in a monolithic reactor with in-depth reaction." Case Western Reserve University School of Graduate Studies / OhioLINK, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1059412740.
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Chan, Martin Siu Chun. "Chemical looping for selective oxidations." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/290408.
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This Dissertation describes the development of chemical looping for selective oxidations. Chemical looping is a reactor technology that achieves simultaneous reaction and separation. For a large subset of reactions (viz. abstraction or insertion of oxygen), this technology is based upon the use of oxygen carriers. These materials, typically metal oxides, reversibly store and release oxygen, and there is growing interest in using these materials for selective oxidations. This Dissertation describes work on the development of oxygen carriers for selective oxidations, including foundational work on a method for analysing periodic non-catalytic gas-solid reactions, of which chemical looping selective oxidations are a subset. The oxygen chemical potential of Ca2Fe2O5 was exploited to improve the efficiency of the steam-iron process to produce hydrogen. The ability of reduced Ca2Fe2O5 to convert a higher fraction of steam to hydrogen than chemically unmodified Fe was demonstrated in a packed bed. This demonstrates how the oxygen chemical potential might be manipulated and exploited for chemical looping reactions. The oxygen chemical potential determines the selectivity in thermodynamically-controlled selective oxidations, and, depending on the reaction mechanism, kinetically-controlled selective oxidations. A generic method for enhancing the oxygen-carrying capacity of oxygen carriers for use in selective oxidations is presented, where one material that is selective in the reaction is deposited on the surface of a second material acting as a reservoir of oxygen and as a support. The presence of ceria in the support was found to supply lattice oxygen additional to that provided by the bismuth oxide, without affecting the selectivity of bismuth oxide. The surface chemistry was decoupled from the bulk properties of the support, thus simplifying the design and formulation of composite oxygen carriers. Building upon the concepts of oxygen chemical potential and composite oxygen carriers, chemical looping epoxidation was demonstrated for the first time. The oxygen carrier was composed of Ag, for its unique catalytic properties, and SrFeO3 as the support, for its high oxygen chemical potential at low temperatures. A reaction mechanism was proposed based on the observations. Nonlinear frequency response theory was used to analysis a periodic non-catalytic gas-solid reaction. Generalised frequency response functions (which are higher order analogues to traditional, linear transfer functions) were derived to obtain the nonlinear frequency response of the archetypal reactor. Such a method lies between the traditional frequency response theorem and numerical methods in terms of accuracy and speed. A niche application was proposed for the analysis of experimental kinetics, avoiding convolution of measurements with the response time of measuring equipment. In summary, this Dissertation describes how materials might be formulated for selective oxidations in chemical looping mode. This was demonstrated for an industrially-significant reaction for the production of ethylene. A novel application of nonlinear frequency response theory was also demonstrated for chemical looping reactions.
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Fang, Junchuan. "Electro-catalysis of Oxygen Reduction on Platinum-Bismuth Alloy Nanoparticles and a Study of Nafion Ionomer Impact." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627663391900617.
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Liang, Shunxing. "Catalytic mechanism, multifunctionality and structural design of iron-based metallic glasses." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2019. https://ro.ecu.edu.au/theses/2274.
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Alloys with a well-defined long-range ordered crystalline structure and glasses with a highly disordered amorphous structure as two uncorrelated categories of materials have a long history with a widespread use for different purposes. With the common sense of highly ordered structure in metals/alloys, it is until the 1960s that the first metallic glass (MG, also known as amorphous alloy) has been produced by fast quenching technique to “freeze” their metallic liquid at very high critical cooling rate, realizing glass-like (amorphous/disordered atomic) structure in alloys with extraordinary properties (extreme strength at low temperature, high flexibility at high temperature, etc.) as structural and functional materials. While part of current studies focus on their fundamental and important issues including glass nature and its supercooled liquid state, many application-oriented research endeavors have achieved great successes. Motivated by the pressure of global environmental issues and potential crisis level of fresh water, recently an increasing interest of MGs in attractive catalytic applications has suggested the superior performance of MGs than their crystalline counterparts. Although the application of MGs as catalysts was firstly attempted in almost 40 years ago, their potential value in environmental and energy science has not been recognized until in recent 10 years. As such, studies of catalytic properties of MGs are still very limited and the catalytic mechanism to understand their superior performance is far from easy to achieve. A great effort is still needed for the achievement of the practical catalytic industrialization using massive produced MGs.
Chapter 1 introduces the current challenges of MGs in future development and practical applications, which present as the contradictions between massive production technique and narrow practical application range, between low development as structural materials and high promise as functional materials, and between high catalytic performance and low understanding of mechanism. Accordingly, the significance and innovation of using MGs as functional catalysts will be also described as following: 1) strategies for enhancing catalytic performance of Fe-based MGs without structural change for degradation of organic pollutants; 2) the catalytic application of Fe-based MGs for purifying diversified inorganic contaminants; 3) the potential optimized structure of Fe-based MGs for highly promoting catalytic performance.
Chapter 2 overviews the MGs with structural origin (e.g. short-to-medium-range atomic arrangement with analysis and characterization techniques), glass-forming ability as one of important characteristics for material design, manufacturing methods (i.e. for ribbons, powder and bulk MGs), mechanical and chemical properties, current catalytic properties and applications of MGs (including wastewater treatment, water splitting and fuel cell). The structural heterogeneity in catalysis and strategies to engineer catalytic structure of MGs are also shown in order to develop their future catalytic applications.
Chapter 3 shows the research methods according to different chapters, which contain materials and chemicals, characterization methods, catalytic analysis process, kinetic study methods and other measurements.
Chapter 4 shows the strategies of enhanced catalytic performance of MGs. Fe73.5Si13.5B9Cu1Nb3 MG ribbons are employed for photo-enhanced activation of persulfate (PS), indicating that 100% color removal of malachite green dye can be achieved within 30 min under optimized parameters, and the inclusion of Nb in Fe73.5Si13.5B9Cu1Nb3 MG ribbons promotes enrichment of Si to further improve the surface stability. Yet, the catalytic mechanism of MG ribbons in advanced oxidation processes (AOPs) is not sufficiently understood. As such, Fe78Si9B13 MG ribbons have been applied for the activation of three peroxides: H2O2, PS and peroxymonosulfate (PMS) to investigate catalytic mechanism. The dominant reactive radicals (•OH and/or SO4•−) in AOPs are investigated by competition kinetics using probe reaction. The order of predominant radical generation rate by Fe78Si9B13 under UV-vis irradiation is PS>H2O2>PMS, all with a radical generation rate at least ~2 times higher than other iron-containing materials. The radical evolution mechanism for H2O2, PS and PMS activation has also been investigated. On the other hand, the role of surface to enhance catalytic performance of MGs is suggested. Fe50Ni30P13C7 MG ribbons are found to have the superior corrosion resistance and an effective elimination of surface layer by chemical dealloying can highly promote the catalytic degradation rate of brilliant black BN dye from 20 min to only 10 min, which is attributed to reactivation of surface by chemical dealloying without generating nano-porous structured surface. The reactivation of ribbon surface effectively optimizes active reaction sites and the re-exposure of Fe, Ni and P with zero-valent state forms galvanic cells by atomic clusters leading to the acceleration of catalysis.
Chapter 5 indicates the novel catalytic application of MGs against diversified contaminants. As an advanced alternative of heterogeneous crystalline iron material, low-cost Fe78Si9B13 MG ribbons with mature production by melt spinning is employed in real industrial contaminated water to investigate effective separation of arsenic (As) and reduction of nitrate (NO3−). Fe-based MG ribbons demonstrate attractive high removal rate of As in 30 min with low soluble Fe (1.5 mg/L), which is ascribed to synergistic effect of reduction/adsorption by MG ribbons, precipitation of arsenic sulfide and adsorption of generated iron sulfide. On the other hand, a remarkable sustainability up to 20 reused times of Fe-based MG ribbons for NO3− reduction suggests a promising economic value of MG ribbons in industrial applications. Surface area normalized rate coefficient indicates the superior catalytic capacity of Fe-based MG ribbons compared with other iron materials.
Chapter 6 presents the strategies to engineer catalytic structure correlated to MGs. It is reported that the excellent catalytic behavior in Fe-based MGs goes through a detrimental effect with the partial crystallization but receives a compelling rejuvenation in the full crystallization. Further investigation reveals that multiple crystalline phases with electric potential differences induced by high-temperature annealing facilitate the formation of galvanic cells. The extensively reduced grain boundaries due to grain growth greatly weaken electron trapping and promote inner electron transportation. The relatively homogenous grain-boundary corrosion in the multiphase contributes to well-separated phases after reactions, leading to refreshment of surface active sites, quickly activating H2O2 and rapidly degrading organic pollutants. On the other hand, 3D printing that revolutionizes the way of material manufacturing with functional applications is employed in the manufacturing of an Fe-based MG matrix composite with three-dimensional rhombic dodecahedron microstructure. The 3D-printed porous Fe-based MG matrix composite has been employed into catalytic activation in Fenton-like process and sulfate radical-based reaction. Results demonstrate that extremely high reusability (45 times) is achieved in sulfate radical-based reaction without any apparent efficiency decay. The remarkable catalytic reusability originates from extremely low surface decay. Structural analysis indicates the α-Fe nanocrystals serve as trigger of easy electron transfer but a large amount of α-Fe lead to an inhibitive effect in the MG matrix composite. The overall catalytic ability also demonstrates the excellent catalytic performance of SLM-produced porous Fe-based MG composite in the wastewater remediation.
Chapter 7 concludes the present findings in this thesis and suggests the future challenges and development using MGs as catalysts.
With the investigation of enhanced catalytic performance, catalytic degradation of diversified pollutants and optimization of catalytic structure of Fe-based MGs, this thesis aims to further understand the catalytic mechanism of Fe-based MGs at the atomic size in wastewater treatment, to assess applicability of MGs in practical applications, to provide a novel clue of extending their multifunctional catalytic properties and to suggest the new developing catalyst design with ordered and/or disordered atomic arrangement in the future development.
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Yun, Seonguk. "Sulfur Tolerant Supported Bimetallic Catalysts for Low Temperature Water Gas Shift Reaction." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1573224656177825.
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Chalker, Justin M. "Reaction engineering for protein modification : tools for chemistry and biology." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:52d92917-5c7f-4223-b554-2e1b4fc0b2ea.
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Chemical modification of proteins is critical for many areas of biochemistry and medicine. Several methods for site-selective protein modification are reported in this Thesis that are useful in accessing both natural and artificial protein architectures. Multiple, complementary methods for the conversion of cysteine to dehydroalanine are described. Dehydroalanine is used as a general precursor to several post-translational modifications and glycosylation, polyprenylation, phosphorylation, and lysine methylation and acetylation are all accessible. These modifications and their mimics were explored on multiple proteins, including histone proteins. Unnatural modifications were also explored. The first examples of olefin metathesis and Suzuki-Miyaura cross-coupling on protein substrates are reported. Allyl sulfides were discovered to be remarkably reactive substrates in olefin metathesis, allowing use of this reaction in water and on proteins. For Suzuki-Miyaura cross-coupling, a new catalyst is described that is fully compatible with proteins. Both olefin metathesis and cross-coupling allow the formation of carbon-carbon bonds on proteins. The prospects of these transformations in chemical biology are discussed. Finally, a novel strategy is reported for the installation of natural, unnatural, and post-translationally modified amino acid residues on proteins. This technology relies on addition of carbon radicals to dehydroalanine. This method of "chemical mutagenesis" is anticipated to complement standard genetic manipulation of protein structure.
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Tomaino, Andrew R. "Layer-by-Layer Assemblies for Membrane-Based Enzymatic Catalysis." UKnowledge, 2014. http://uknowledge.uky.edu/cme_etds/38.
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While considerable progress has been made towards understanding the effect that membrane-based layer-by-layer (LbL) immobilizations have on the activity and stability of enzymatic catalysis, detailed work is required in order to fundamentally quantify and optimize the functionalization and operating conditions that define these properties. This work aims to probe deeper into the nature of transport mechanisms by use of pressure-induced, flow-driven enzymatic catalysis of LbL-functionalized hydrophilized poly(vinyldiene) (PVDF)-poly(acrylic acid) (PAA)-poly(allylamine hydrochloride) (PAH)-glucose oxidase (GOx) membranes. These membranes were coupled in a sealed series following cellulose acetate (CA) membranes for the elimination of product accumulation within the feed-side solution during operation. At pH = 6 and T = 21oC, the enzymatic catalysis of LbL-immobilized GOx from Aspergillus niger performed remarkably well in comparison to the homogeneous-phase catalysis within an analogous aqueous solution. On average, the enzymatic turnover was 0.0123 and 0.0076 mmol/(mg-GOx)(min) for the homogeneous-phase catalysis and the LbL-immobilized catalysis, respectively. Multiple consecutive permeations resulted in replicable observed kinetic results with R2 > 0.95. Permeations taking place over the course of a three week trial period resulted in a retention of >90% normalized activity when membranes were removed when not in use and stored at -20oC, whereas the homogenous-phase kinetics dropped below 90% normalized activity in under one day.
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Van, Der Merwe Marianne Werle. "Solution combustion catalysts for the water-gas shift reaction." Master's thesis, Faculty of Engineering and the Built Environment, 2018. http://hdl.handle.net/11427/29988.
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In the context of a growing world population, more sustainable solutions for energy generation are required. Fuel cells supplied with hydrogen generated from fuel processing trains have emerged as a potential medium-term solution due to their improved efficiency and lower greenhouse gas-emissions. This study focuses on the development of a compact, efficient design for fuel processing trains. More specifically, reduction in the size of the largest component, the Water Gas-Shift (WGS) reactor, which could be achieved by an increase in the catalytic activity via alternative catalyst synthesis techniques. Solution combustion synthesis (SCS) is one such technique that could be used since it allows for the preparation of highly-dispersed Pt oxide particles on low surface area CeO2 with a reproducible metal loading and a defined Pt particle size. The aim of this study was to investigate the “conventional” impregnation approach of supports prepared via SCS versus the one-shot SCS approach (support and active metal prepared in one step) for the synthesis of 1 wt.% Pt/CeO2 catalysts for the WGS reaction using a reformate feed stream. It was hypothesized that the preferential formation of metallic Pt species supported on CeO2 can be achieved using a glycine-nitrate combustion system with excess glycine fuel (stoichiometric ratios of glycine to nitrate oxidants > 1) i.e. the Pt is reduced during the one-shot SCS approach. The catalysts were characterized by XRD, N2-physisorption, ICP-AES, TEM and XPS, and their activity towards the WGS reaction was evaluated with a synthetic reformate stream (50 % H2, 6.67 % CO, 6.67 % CO2, 33.3 % H2O, 3.36 % He). Initial characterization results of the catalysts prepared by the one-shot SCS approach confirmed the reproducible synthesis of Pt particles supported on nano-sized CeO2 with low surface areas. Furthermore, TEM and XPS results of the one-shot SCS prepared catalysts indicated that the Pt species were mainly present as Pt oxide particles on the surface of the CeO2 supports. However, for combustion systems with excess fuel, formation of some metallic Pt was observed together with the more prevalent Pt oxide particles. The catalysts prepared by the “conventional” impregnation approach had higher activities towards the WGS reaction than the one shot SCS catalysts. This was attributed to the smaller Pt particles achieved using this “conventional” synthesis approach (approximately 1 nm compared to 3 nm). One-shot SCS is a viable synthesis approach for the preparation of 1 wt.% Pt/CeO2 catalysts as this method allows for the preparation of highly-dispersed Pt oxide particles on low surface area CeO2 with a reproducible metal loading and a defined Pt particle size. However, the characterization results indicated that using a combustion system with excess fuel resulted in the preferential formation of Pt oxide phases as opposed to the desired metallic Pt phase, therefore refuting the hypothesis of this study. Nevertheless, it is recommended to repeat the synthesis of the 1 wt.% Pt/CeO2 catalysts in an inert atmosphere as this has shown to favour the formation of metallic species (Cross et al., 2014). This study was unsuccessful in preparing catalysts using a glycine-nitrate one-shot SCS system that were more active than the “conventionally” prepared catalysts. However, it is recommended that other fuel types, such as urea, also be investigated. These alternative fuel types could combine the good Pt dispersion achieved using the one-shot SCS approach with potentially smaller Pt particle sizes, thereby increasing the catalyst’s activity towards the WGS reaction (Vita et al., 2015a).
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Marfil, Vega Ruth. "Abiotic Transformation of Estrogens in Wastewater." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1289235973.
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Muthukumarasamy, Ayyadurai Subasri. "Optical Sensing of Organic Contaminants through their Immobilization and Reaction Inside Perfluorosulfonic Acid Polymer Membranes." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406821247.
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Brady, Kyle B. "Ignition Propensity of Hydrogen/Air Mixtures in the Presence of Heated Platinum Surfaces." Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1251983992.
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Thesis(M.S.)--Case Western Reserve University, 2009Title from PDF (viewed on 2009-11-23) Department of EMC - Aerospace Engineering Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center
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Mohamed, Rhiyaad. "Electrocatalysis of oxide-based materials for the oxygen reduction and evolution reactions." Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20983.
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Electrochemical devices, such as fuel cells and electrolysers, are said to be at the forefront of a renewable energy technology revolution centred on hydrogen as an energy carrier. These devices rely on the chemical reactions of oxygen, namely the oxidation of water to evolve oxygen (oxygen evolution reaction, OER) and hydrogen , carried out in electrolyser applications or the reverse reaction, the reduction of oxygen to water (oxygen reduction reaction, ORR) producing electricity in the case of fuel cells . Th e reactions of oxygen are however still hindered by extremely slow reaction kinetics. The resultant low efficiencies and associated high cost of electrocatalysts required hinder the widespread commercial success of these devices. In addition, current state - of - the - art electrocatalyst technologies suffer from severe corrosion during operation, presenting an additional barrier to commercialisation and ultimately delaying the successful implementation of a sustainable hydrogen economy. One primary goal of electrocatalysis research is thus the rational design of new materials with higher efficiencies. The fundamental understanding of the behaviour of the electrocatalyst materials towards these reactions will enable greater strides to be achieved in this area. To date much research has been conducted towards this end, however further progress is still required. This thesis details work towards the understanding of a new generation of electrocatalyst technologies for the OER and ORR. This study particularly explore s the use metal oxide based electrocatalyst materials for the oxygen evolution and reduction r eactions as employed in electrolyser and fuel cell applications respectively. The thesis is divided in two parts focusing individually on the OER and ORR respectively. New theoretical and experimental insight into the understanding of oxide electrocataly sts for the OER are discussed in Part I. Part II explores the ORR by studying metal oxides as both catalysts and catalyst support materials in alkaline and acidic environments respectively. Here the emphasis is placed on activity and durability of oxide ma terials under fuel cell operating conditions. The study confirms the promise of oxide based materials and highlights some of the challenges still present in their development for fuel cell applications. The final chapter presents a summary of the thesis. This study provides important insight and contributes towards the further understanding of the use of metal oxides for the OER and ORR. From this study several interesting and promising results were also obtained which warrant further intensive research and investigation. Directions for future research are discussed. [Please note: the full text of this thesis has been deferred until January 2018]
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Brown, Steven M. (Steven Michael). "Catalysis and reactor engineering for the electrochemical conversion of carbon dioxide to carbon monoxide." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/124584.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 163-176).
Carbon dioxide (CO₂) utilization processes have garnered significant interest to both mitigate anthropogenic greenhouse gas emissions and increase the revenue of many chemical and fuel production processes. Low-cost renewable electricity provides impetus for exploring electrochemical methods to recycle CO₂ in cost-competitive and sustainable ways. Researchers have experimentally demonstrated CO₂ transformations into a variety of industrially relevant materials. Techno-economic assessments inform that the simplest transformations, such as generation of carbon monoxide (CO), appear to be the most feasible in the near future. Yet, widespread commercialization of this nascent technology has not occurred due to a number of challenges that include synthesizing stable and active catalyst materials, understanding activity-Ưdriving force relationships, identifying appropriate reactor configurations, and developing comprehensive process models.
This thesis advances both the experiment and theory of CO₂ conversion to CO through electrocatalysis and reactor engineering. A flow reactor was designed and manufactured to understand CO2 reduction in ways that traditional, batch, electroanalytical devices cannot. A key advantage is that, through the use of porous carbon electrodes, the reactor converts gaseous CO₂ to CO at the catalyst-electrolyte interface in a continuous fashion, alleviating the mass transport limitations common to liquid-phase CO₂ delivery systems. To facilitate this transformation, a carbon-supported gold nanoparticle catalyst was synthesized and deposited onto gas diffusion electrodes. These nanoparticles achieved high selectivity (>90%) to CO formation over the competing hydrogen evolution side reaction.
Traditional electrokinetic analyses (e.g., Tafel) were largely unsuccessful at describing the observed current-potential relationship, prompting a rigorous follow-up study on electrokinetics wherein Marcus theory and mass transport convolution, amongst other considerations, were explored. Bayesian statistics concluded that, despite the ubiquitous implementation of Butler-Volmer kinetics in literature, in actuality, a Marcus-Hush-Chidsey model provides the most accurate description of the electrochemical reduction of CO₂ to CO. The implications of this result are significant, potentially resulting in order of magnitude differences in current density projections at high overpotentials.
Overall, this thesis experimentally measured catalysis rates in a specialized electrochemical flow cell, unimpeded by mass transport, and leveraging these results, as well as those from prior literature, advanced electrokinetic descriptions of CO₂ conversion all towards furthering the commercial prospects of this electrochemical technology.
by Steven M. Brown.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemical Engineering
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Singh, Deepika. "Non-Precious Metal Electrocatalysts for the Oxygen Reduction Reaction in Proton Exchange Membrane (PEM) Fuel Cells." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397727211.
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Easterling, Vencon G. "The Effects of Ceria Addition on Aging and Sulfation of Lean NOx Traps for Stand Alone and LNT-SCR Applications." UKnowledge, 2013. http://uknowledge.uky.edu/cme_etds/17.
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THE EFFECTS OF CERIA ADDITION ON AGING AND SULFATION OF LEAN NOx TRAPS FOR STAND ALONE AND LNT-SCR APPLICATIONS
Model powder and fully formulated monolithic lean NOx trap (LNT) catalysts were used to investigate the effect of ceria on desulfation behavior. Temperature-programmed reduction (TPR) experiments (model catalysts) showed each of the oxide phases present is able to store sulfur and possesses distinct behavior (temperature at which desulfation occurs). La-CeO2 or CeO2-ZrO2-containing samples (monoliths) showed a greater resistance to deactivation during sulfation and required lower temperatures to restore the NOx storage efficiency to its pre-sulfation value.
Fully formulated monolithic LNT catalysts containing varying amounts of Pt, Rh and BaO were subjected to accelerated aging to elucidate the effect of washcoat composition on LNT aging. Elemental analysis revealed that residual sulfur, associated with the Ba phase, decreased catalyst NOx storage capacity and that sintering of the precious metals resulted in decreased contact between the Pt and Ba phases.
Spatially-resolved inlet capillary mass spectrometry (SpaciMS) was employed to understand the factors influencing the selectivity of NOx reduction in LNT catalysts degreened and thermally aged) containing Pt, Rh, BaO and Al2O3, and contained La-stabilized CeO2. Stretching of the NOx storage and reduction zone (NSR) zone resulted in increased selectivity to NH3 due to the fact that less catalyst was available to consume NH3 by either the NH3-NOx SCR reaction or the NH3-O2 reaction. Additionally, the loss of oxygen storage capacity (OSC) and NOx storage sites, along with the decreased rate of NOx diffusion to Pt/Rh sites, led to an increase in the rate of propagation of the reductant front after aging, in turn, resulting in increased H2:NOx ratios at the Pt/Rh sites and consequently increased selectivity to NH3.
Finally, a crystallite scale model was used to predict selectivity to NH3 from the LNT catalysts during rich conditions after a fixed amount of NOx was stored during lean conditions. Both the experimental and model predicted data showed that the production of NH3 is limited by the rate of diffusion from the Ba storage sites to the Pt particles at 200 °C. At 300 °C, the process is limited by the rate at which H2 is fed to the reactor.
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Daya, Yatish Surendra. "Performance of gold reference catalysts in the water gas shift reaction." Master's thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/5373.
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Blavo, Selasi Ofoe. "Model Pt- and Pd-based Electrocatalysts for Low Temperature Fuel Cells Applications." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4639.
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In the search for alternative energy technologies, low temperature fuel cells continue to feature as technologies with the most promise for mass commercialization. Among the low temperature fuel cells, alkaline and proton exchange membrane fuel cells are the most popular. Alkaline fuel cells have typically been used for water generation as well as auxiliary power for space shuttles. Their bulkiness however makes them undesirable for other applications, especially in automobiles, where there is a great demand for alternative technologies to internal combustion engines. Proton exchange membrane fuel cells on the other hand possess numerous qualities including their compact size, high efficiency and versatility. Their mass implementation has however been delayed, because of cost among other reasons. Most of this cost is owed to the Pt/C catalyst that accounts for about half of the price of the PEM Fuel Cell. This catalyst is used to drive the sluggish oxygen reduction reaction that occurs at the cathode of the PEM Fuel Cell.
To overcome this obstacle, which is to make PEM Fuel Cell technology more affordable, reducing the amount Pt has traditionally been the approach. Another approach has been to find new ideal catalyst-support combinations that increase the intrinsic activity of the supported material. One more strategy has been to find lower cost alternative materials to Pt through synthetic and kinetic manipulations to rival or exceed the current oxygen reduction reaction activity benchmark.
To this end, Palladium has garnered significant interest as a monometallic entity. Its manipulation through synthetic chemistry to achieve different morphologies - which favor select lattice planes - in turn promotes the oxygen reduction reaction to different degrees. In bimetallic or, in more recent times multimetallic frameworks, geometric and ligand effects can be used to form ideal compositions and morphologies that are synergistic for improved oxygen reduction reaction kinetics.
In this dissertation, we have explored three different approaches to make contributions to the catalysis and electrocatalysis body of literature. In the first instance, we look at the influence of ligand effects through the active incorporation of a PVP capping agent on the stability of ~3nm Pt NPs. Washed (no capping agent) and unwashed (with capping agent) batches of NPs were evaluated via cyclic voltammogram analyses to evaluate differences there might be between them. It was found that the current density measurements for unwashed particle batches were higher. This increase in current density was attributed to the monodentate and bidentate ligand bonding from the PVP, which increased as a function of cycle number and plateaued when the PVP was completely decomposed. The complete decomposition of PVP during the CV experiment was estimated to occur around 200 cycles.
The remaining portion of the dissertation explores the electrocatalytic properties of Palladium based NPs. The first instance, a monometallic study of Palladium cubes and dendrites was aimed at building on a recent publication on the enhanced ORR activity that was achieved with a PdPt bimetallic dendrite morphology. In our work, we sought to isolate the dendritic morphology properties of the monometallic Pd composition in order to understand what advantages could be achieved via this morphology. Pd cubes were used as a comparison, since they could be generated through the combination of a similar set of reagents simply by switching the order of addition. It was found that while there was no significant variation in the ORR activity as a function of morphology / shape, there was an interesting interaction between hydrogen and the palladium NPs in the hydrogen oxidation region that varied as a function of shape. This led to further sorption and ethylene hydrogenation studies, which suggested that, the interaction between hydrogen and Pd depended on the environment. Within the electrochemical environment, the ECSA measured, suggested that hydrogen was being reversibly absorbed into the sub-surface octahedral sites of Pd. The higher ECSA for Pd cubes corroborated with higher sorption for Pd cubes as well. However ethylene hydrogenation showed that the fringes of the Pd dendrites provided additional sites for reaction, which in turn translated to higher conversion. Furthermore, through a Koutecky-Levich analysis, it was found out that the Pd dendrites while exhibiting slightly lower activity, favored the 4-electron oxygen reduction process more than the Pd cubes.
In the last part of this dissertation we explored the electrocatalytic properties of Pd-based bimetallic NPs under different morphologies including nanocages and sub-10nm alloys. With the inclusion of Ag, it was found out, through Koutecky-Levich analysis that the 4-electron process was better observed under alkaline conditions using a 0.1M NaOH(aq) electrolyte solution instead of a 0.1M HClO4 (aq) for acidic media testing. It was found that, for PdAg nanocage morphologies, where the Pd galvanically replaced the Ag to form cages, the four-electron process was suited to thinner Pd shells. Indeed the average electron numbers measured for Ag nanocubes coated with a 6nm shell was in agreement, within reason of literature values for bulk Ag. However, since the binding energy that both metals have for OH is so close, the potential for contributions to the ORR kinetics in alkaline media by Pd is a potential consideration.
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Bloh, Jonathan Zacharias [Verfasser]. "Optimization of Photocatalytic Processes: Catalyst Design, Kinetics and Reaction Engineering / Jonathan Zacharias Bloh." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2021. http://d-nb.info/1238221815/34.
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GOPAL, SRIKANT. "SYNTHESIS, MODIFICATION, CHARACTERIZATION AND CATALYTIC STUDIES OF ZEOLITE BASED BIFUNCTIONAL CATALYSTS FOR HYDROISOMERIZATION REACTION." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1061218813.
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Natesakhawat, Sittichai. "Investigation of active sites and reaction networks in catalytic hydrogen production steam reforming of lower alkanes and the water-gas shift reaction /." Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1110209339.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xiv, 194 p.; also includes graphics Includes bibliographical references (p. 178-188). Available online via OhioLINK's ETD Center
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Demeter, Ethan L. "The Promotion of Base Metal Catalysts for the Electrochemical Oxygen Evolution Reaction." Research Showcase @ CMU, 2013. http://repository.cmu.edu/dissertations/236.
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As the energy needs of society continue to grow, and pressure to produce fewer emissions continues to mount, clean alternatives will be utilized to meet these demands. Conventional renewable technologies (wind and solar, etc.) have great potential, but cannot be used as base-load power, at least not in the traditional sense. Rather, these technologies would require the further adoption of energy storage technologies, such as water splitting, to convert the energy produced into chemical bonds for later use to match demand.
Water splitting currently suffers from large energetic barriers, on the oxygen side, that create a need for catalysts, and high costs associated with the best available catalysts, ruthenium and iridium. This work focuses on developing and understanding ways to promote the catalysis of the oxygen evolution reaction on earth-abundant base metal catalysts. We utilize a combination of electrochemical and in situ surface characterization techniques to correlate changes in the surface chemistry to changes in catalyst activity.
Three systems are examined for their potential effect on the OER. The first two focus on the promotion of NiO materials, examining the effect of changing the alkali cation present in the hydroxide electrolyte, and adding iron to the NiO materials. For the cations, the electrochemical activity is found to increase by a factor of two, switching from a LiOH solution to a CsOH solution of the same concentration. The use of in situ Raman spectroscopy suggests that different phases of the oxidized Ni oxyhydroxides are promoted in the presence of the different cations, with γ-NiOOH promoted in CsOH while β-NiOOH is observed in LiOH. The addition of Fe results in large increases in OER activity up to a loading of 10 mol% Fe, where the further addition of Fe decreases activity. Raman spectra of the electrodes suggest at low Fe loadings, the Ni oxidation to γ- NiOOH is promoted, while further addition of Fe blocks access to active catalyst sites. Finally, we demonstrate the use of Fe-TAML molecular complex as an electrocatalyst for the OER. Fe-TAML is shown to be electrochemically active, and through immobilization, much higher catalyst utilization is achieved.
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Mills, Landon C. "IMPACT OF CONFORMATIONAL CHANGE, SOLVATION ENVIRONMENT, AND POST-TRANSLATIONAL MODIFICATION ON DESULFURIZATION ENZYME 2'-HYDROXYBIPHENYL-2-SULFINATE DESULFINASE (DSZB) STABILITY AND ACTIVITY." UKnowledge, 2019. https://uknowledge.uky.edu/cme_etds/105.
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Naturally occurring enzymatic pathways enable highly specific, rapid thiophenic sulfur cleavage occurring at ambient temperature and pressure, which may be harnessed for the desulfurization of petroleum-based fuel. One pathway found in bacteria is a four-step catabolic pathway (the 4S pathway) converting dibenzothiophene (DBT), a common crude oil contaminant, into 2-hydroxybiphenyl (HBP) without disrupting the carbon-carbon bonds. 2’-Hydroxybiphenyl-2-sulfinate desulfinase (DszB), the rate-limiting enzyme in the enzyme cascade, is capable of selectively cleaving carbon-sulfur bonds. Accordingly, understanding the molecular mechanisms of DszB activity may enable development of the cascade as industrial biotechnology. Based on crystallographic evidence, we hypothesized that DszB undergoes an active site conformational change associated with the catalytic mechanism. Moreover, we anticipated this conformational change is responsible, in part, for enhancing product inhibition. Rhodococcus erythropolis IGTS8 DszB was recombinantly produced in Escherichia coli BL21 and purified to test these hypotheses. Activity and the resulting conformational change of DszB in the presence of HBP were evaluated. The activity of recombinant DszB was comparable to the natively expressed enzyme and was competitively inhibited by the product, HBP. Using circular dichroism, global changes in DszB conformation were monitored in response to HBP concentration, which indicated that both product and substrate produced similar structural changes. Molecular dynamics (MD) simulations and free energy perturbation with Hamiltonian replica exchange molecular dynamics (FEP/λ-REMD) calculations were used to investigate the molecular-level phenomena underlying the connection between conformation change and kinetic inhibition. In addition to the HBP, MD simulations of DszB bound to common, yet structurally diverse, crude oil contaminates 2’2-biphenol (BIPH), 1,8-naphthosultam (NTAM), 2-biphenyl carboxylic acid (BCA), and 1,8-naphthosultone (NAPO) were performed. Analysis of the simulation trajectories, including root mean square fluctuation (RMSF), center of mass (COM) distances, and strength of nonbonded interactions, when compared with FEP/λ-REMD calculations of ligand binding free energy, showed excellent agreement with experimentally determined inhibition constants. Together, the results show that a combination of a molecule’s hydrophobicity and nonspecific interactions with nearby functional groups contribute to a competitively inhibitive mechanism that locks DszB in a closed conformation and precludes substrate access to the active site.
Limitations in DszB’s potential applications in industrial sulfur fixation are not limited to turnover rate. To better characterize DszB stability and to gain insight into ways by which to extend lifetime, as well as to pave the way for future studies in inhibition regulation, we evaluated the basic thermal and kinetic stability of DszB in a variety of solvation environments. Thermal stability of DszB was measured in a wide range of different commercially available buffer additives using differential scanning fluorimetry (DSF) to quickly identify favorable changes in protein melting point. Additionally, a fluorescent kinetic assay was employed to investigate DszB reaction rate over a 48 hr time period in a more focused group of buffer to link thermal stability to DszB life-time. Results indicate a concerningly poor short-term stability of DszB, with an extreme preference for select osmolyte buffer additives that only moderately curbed this effect. This necessitates a means of stability improvement beyond alteration of solvation environment. To this end, a more general investigation of glycosylation and its impact on protein stability was performed.
Post-translational modification of proteins occurs in organisms from all kingdoms life, with glycosylation being among the most prevalent of amendments. The types of glycans attached differ greatly by organism but can be generally described as protein-attached carbohydrate chains of variable lengths and degrees of branching. With great diversity in structure, glycosylation serves numerous biological functions, including signaling, recognition, folding, and stability. While it is understood that glycans fulfill a variety of important roles, structural and biochemical characterization of even common motifs and preferred rotamers is incomplete. To better understand glycan structure, particularly their relevance to protein stability, we modeled and computed the solvation free energy of 13 common N- and O-linked glycans in a variety of conformations using thermodynamic integration. N-linked glycans were modeled in the β-1,4-linked conformation, attached to an asparagine analog, while O-linked glycans were each modeled in both the α-1,4 and β-1,4-linked conformations attached to both serine and threonine analogs. Results indicate a strong preference for the β conformation and show a synergistic effect of branching on glycan solubility. Our results serve as a library of solvation free energies for fundamental glycan building blocks to enhance understanding of more complex protein-carbohydrate structures moving forward.
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Anantharaman, Bharthwaj. "Reaction mechanisms for catalytic partial oxidation systems : application to ethylene epoxidation." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32328.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2005.Includes bibliographical references.
With the rapid advances in kinetic modeling, building elementary surface mechanisms have become vital to understand the complex chemistry for catalytic partial oxidation systems. Given that there is selected experimental knowledge on surface species and a large number of unknown thermochemical, rate parameters, the challenge is to integrate the knowledge to identify all the important species and accurately estimate the parameters to build a detailed surface mechanism. This thesis presents computational methodology for quickly calculating thermodynamically consistent temperature/coverage-dependent heats of formation, heat capacities and entropies, correction approach for improving accuracy in heats of formation predicted by composite G3- based quantum chemistry methods, and detailed surface mechanism for explaining selectivity in ethylene epoxidation. Basis of the computational methodology is the Unity Bond Index- Quadratic Exponential Potential (UBI-QEP) approach, which applies quadratic exponential potential to model interaction energies between atoms and additive pairwise energies to compute total energy of an adsorbed molecule. By minimizing the total energy subject to bond order constraint, formulas for chemisorption enthalpies have been derived for surface species bound to on-top, hollow and bridge coordination sites with symmetric, asymmetric and chelating coordination structures on transition metal catalysts. The UBI-QEP theory for diatomics has been extended for polyatomic adsorbates with empirical modifications to the theory.
(cont.) Formulas for activation energies have been derived for generic reaction types, including simple adsorption, dissociation-recombination, and disproportionation reactions. Basis of the correction approach is the Bond Additivity Correction (BAC) procedures, which apply atomic, molecular and bond- wise modifications to enthalpies of molecules predicted by G3B3 and G3MP2B3 composite quantum chemistry methods available in Gaussian® suite of programs. The new procedures have improved the accuracy of thermochemical properties for open and closed shell molecules containing various chemical moieties, multireference configurations, isomers and degrees of saturation involving elements from first 3 rows of the periodic table. The detailed mechanism explains the selectivity to ethylene oxide based on the parallel branching reactions of surface oxametallacycle to epoxide and acetaldehyde. Using Decomposition Tree Approach, surface reactions and species have been generated to develop a comprehensive mechanism for epoxidation. As a result of these developments in the thesis, chemisorption enthalpies can now be estimated within 3 kcal/mol of experimental values for transition metal catalysts and enthalpies predicted by G3B3 and G3MP2B3 Gaussian methods can be corrected within 0.5 kcal/mol. Examples of heterogeneous reaction systems involving silver-catalyzed ethylene epoxidation demonstrate the effectiveness of the methodologies developed in this work.
by Bharthwaj Anantharaman.
Ph.D.
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Yang, Yuan. "Graphene as a Solid-state Ligand for Palladium Catalyzed Cross-coupling Reactions." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5488.
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Palladium-catalyzed carbon-carbon cross-coupling reactions have emerged a broadly useful, selective and widely applicable method to synthesize pharmaceutical active ingredients. As currently practiced in the pharmaceutical industry, homogeneous Pd catalysts are typically used in cross-coupling reactions. The rational development of heterogeneous catalysts for cross-coupling reactions is critical for overcoming the major drawbacks of homogeneous catalysis including difficulties in the separation, purification, and quality control process in drug production. In order to apply heterogeneous catalysis to flow reactors that may overcome this limitation, the catalyst must be strongly bound to a support, highly stable with respect to leaching, and highly active. While the primary role of supports in catalysis has been to anchor metal particles to prevent sintering and leaching, supports can also activate catalytic processes. In this study, by using a xi combined theoretical and experimental method, we probed the effect of graphene as support in the complex reaction cycle of Suzuki reactions. The density functional theory study provides a fundamental understanding of how a graphene support strongly binds the Pd nanoparticles and act as both an efficient charge donor and acceptor in oxidation and reduction reaction steps. Theoretical investigations prove that the Pd-graphene interaction promotes electron flow between the metal cluster and the defected graphene to reduce reaction barrier. The ability for graphene to both accept and donate charge makes graphene an unusually suitable support for multi-step catalytic processes that involve both oxidation and reduction steps. The computer-aided catalyst design with the atomic precise accuracy demonstrates the Pd/graphene catalyst can be further optimized and the first-row transition metal nanoparticles have great potential to replace Pd to catalyze the Suzuki reaction. The corresponding experimental study shows that the method to immobilize the Pd nanoparticles on the graphene is crucial to increasing the reactivity and stability of the resulted catalyst. A comparison of the activation energy and turn over frequency for a series of supported and homogeneous catalysts indicates that exposing palladium-graphene to defect inducing microwave radiation results in dramatically lower activation energies and higher turnover frequencies. Furthermore, the heterogeneity tests demonstrate the Suzuki reactions are carried out on the surface of the immobilized Pd nanoparticle agreeing with the theoretical results. A method to engineer the 2-D graphene support to a 3-D structure to minimize the re-stacking and agglomeration of the graphene lattice will also be introduced in this study.
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Shi, Zhangsheng. "Strain engineering of Co-N-C catalyst toward enhancing the HER and ORR electrocatalytic activities." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/207078/8/Zhangsheng_Shi_Thesis.pdf.
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This thesis presents a comprehensive review of practical strategies to enhance the catalytic activity of M-N-C materials. The practical strategies can be extended to engineer external factors to break the linear scaling relationships and to further enhance the catalytic performances. In order to design the next-generation higher-performance catalysts, this project was a step forward in developing strain and heterostructure method to achieve a superior HER performance and a ORR performance beyond the limit.
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Zhou, Shanshan. "QUARTZ CRYSTAL MICROBALANCE INVESTIGATION OF CELLULOSOME ACTIVITY FROM CLOSTRIDIUM THERMOCELLUM ON MODEL CELLULOSE FILMS." UKnowledge, 2014. http://uknowledge.uky.edu/cme_etds/31.
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The cost of deconstructing cellulose into soluble sugars is a key impediment to the commercial production of lignocellulosic biofuels. The use of the quartz crystal microbalance (QCM) to investigate reaction variables critical to enzymatic cellulose hydrolysis is investigated here, extending previous studies of fungal cellulase activity for the first time to whole cell cellulases. Specifically, the activity of the cellulases of Clostridium thermocellum, which are in the form of cellulosomes, was investigated. To clearly differentiate the activity of free cellulosome and cell-bound cellulosome, the distribution of free cellulosome and cell-bound cellulosome in crude cell broth at different growth stages of C. thermocellum (ATCC 27405) was quantified. Throughout growth, greater than 70% of the cellulosome in the crude cell broth was unattached to the cell. The frequency response of the QCM was shown to capture adsorption and hydrolysis of amorphous cellulose films by the whole-cell cellulases. Further, both crude cell broth and free cellulosomes were found to have similar inhibition pattern (within 0 - 10 g/L cellobiose). Thus, kinetic models developed for the cell-free cellulosomes, which allow for more accurate interfacial adsorption analysis by QCM than their cell-attached counterparts, may provide insight into hydrolysis events in both systems.
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Shin, Sang Baek. "Catalytic reaction engineering of propene epoxidation with hydrogen peroxide over titanium silicalite (TS-1)." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6951.
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Propene oxide is an important chemical intermediate in the chemical industry. The propene oxide industry has employed two different types of commercial processes for several decades: the chlorohydrin process and the hydroperoxidation process. However, direct epoxidation of propene with hydrogen peroxide has recently attracted much attention as a more environmentally benign and profitable process. This thesis presents the catalytic reaction engineering of the epoxidation of propene to propene oxide using hydrogen peroxide as the oxidant and titanium silicalite (TS-1) as the catalyst under mild conditions. The kinetics of the heterogeneous catalytic epoxidation was studied in an autoclave reactor using methanol/water mixtures as the solvent. The effects of stirring speed, catalyst loading, reactant concentration, reaction temperature, solvent composition and solvent variation on the propene oxidation are presented and discussed. The catalytic performance of TS-1 impregnated with precious metal nanoparticles such as gold and palladium for the propene epoxidation was also investigated. The influences of the kind of precious metal and treatment process adopted in the catalyst preparation on the propene epoxidation and the hydrogen peroxide decomposition were explored. One of the key objectives of this research was to evaluate a new continuous reactor concept for propene epoxidation and other liquid-phase selective oxidation reactions. A conventional monolith and a confined Taylor flow (CTF) reactor were studied for the propene epoxidation. The influences of gas and liquid flow rates on the hydrodynamics of the structured reactors were investigated under Taylor flow regime at atmospheric pressure. It was found that the variation of hydrodynamics had a significant impact on the production of propene oxide. The effect of operating pressure on the propene oxide production was studied in a pressurised system. In addition, the performances of various structures of reactor column were examined to compare.
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Botero, Carrizosa Sara C. "Synthesis, Characterization, and Properties of Graphene-Based Hybrids with Cobalt Oxides for Electrochemical Energy Storage and Electrocatalytic Glucose Sensing." TopSCHOLAR®, 2017. http://digitalcommons.wku.edu/theses/1941.
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A library of graphene-based hybrid materials was synthesized as novel hybrid electrochemical electrodes for electrochemical energy conversion and storage devices and electrocatalytical sensing namely enzymeless glucose sensing. The materials used were supercapacitive graphene-family nanomaterials (multilayer graphene-MLG; graphene oxide-GO, chemically reduced GO-rGO and electrochemical reduced GOErGO) and pseudocapacitive nanostructured transition metal oxides including cobalt oxide polymorphs (CoO and Co3O4) and cobalt nanoparticles (CoNP). These were combined through physisorption, electrodeposition, and hydrothermal syntheses approaches. This project was carried out to enhance electrochemical performance and to develop electrocatalytic platforms by tailoring structural properties and desired interfaces. Particularly, electrodeposition and hydrothermal synthesis facilitate chemically-bridged (covalently- and electrostatically- anchored) interfaces and molecular anchoring of the constituents with tunable properties, allowing faster ion transport and increased accessible surface area for ion adsorption. The surface morphology, structure, crystallinity, and lattice vibrations of the hybrid materials were assessed using electron microscopy (scanning and transmission) combined with energy dispersive spectroscopy and selected-area electron diffraction, X-ray diffraction, and micro-Raman Spectroscopy. The electrochemical properties of these electrodes were evaluated in terms of supercapacitor cathodes and enzymeless glucose sensing platforms in various operating modes. They include cyclic voltammetry (CV), ac electrochemical impedance spectroscopy, charging-discharging, and scanning electrochemical microscopy (SECM).
These hybrid samples showed heterogeneous transport behavior determining diffusion coefficient (4⨯10-8 – 6⨯10-6 m2/s) following an increasing order of CoO/MLG < Co3O4/MLG < Co3O4/rGOHT < CoO/ErGO < CoNP/MLG and delivering the maximum specific capacitance 450 F/g for CoO/ErGO and Co3O4/ rGOHT. In agreement with CV properties, these electrodes showed the highest values of low-frequency capacitance and lowest charge-discharge response (0.38 s – 4 s), which were determined from impedance spectroscopy. Additionally, through circuit simulation of experimental impedance data, RC circuit elements were derived. SECM served to investigate electrode/electrolyte interfaces occurring at the solid/liquid interface operating in feedback probe approach and imaging modes while monitoring and mapping the redox probe (re)activity behavior. As expected, the hybrids showed an improved electroactivity as compared to the cobalt oxides by themselves, highlighting the importance of the graphene support. These improvements are facilitated through molecular/chemical bridges obtained by electrodeposition as compared with the physical deposition.
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De, Oliveira Dominic. "Phase and structural changes of nickel catalysts as a function of reaction conditions." Master's thesis, Faculty of Engineering and the Built Environment, 2019. http://hdl.handle.net/11427/31520.
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Carbon dioxide hydrogenation is a route for the production of methane from hydrogen and carbon dioxide, which has attracted increased attention in recent times. It provides a means for both energy storage through substitute natural gas (SNG) production and as a process for the conversion of carbon dioxide into valuable products. Ni is the most widely used metal for SNG production due to its high activity, high selectivity towards methane and low cost in comparison to the other active metals. Ni catalysts have been extensively studied due to their uses in steam reforming and CO methanation, and it is known that deactivation by sintering, sulphur poisoning and carbon formation are the most common deactivation mechanisms for Ni catalysts. Some deactivation of Ni by oxidation has been reported, despite the fact the oxidation of Ni to NiO is not thermodynamically feasible at reaction conditions relevant to Ni catalysts. This has also been observed with Co catalysts for Fischer-Tropsch synthesis applications, where it has been explained that the size dependent oxidation, by produced water, can occur due to the higher surface energy contributions of smaller crystallites. The aim of this project is to study the phase changes of nickel catalysts, specifically through the oxidation of Ni in the presence of steam using in situ magnetic techniques to identify the loss of metallic Ni. As this oxidation is thought to be a size dependent effect, a set of catalysts with narrow crystallite size distributions and tuneable size is required for the experimental testing. The use of organometallic precursor reduction (OPR) and homogeneous deposition precipitation (HDP) was investigated for the synthesis in this study. OPR produced unsupported nanoparticles with a suitable size, however the occurrence of sintering during the anchoring and supporting of these nanoparticles on silica spheres, due to the high temperature calcination step, made these catalysts unsuitable for use in the oxidation study. The catalysts synthesised by HDP produced supported nickel catalysts with high loadings and sizes of 3.6 and 7.5 nm, with minimal overlap of size distributions, making them suitable for oxidation testing. The size of these nanoparticles was controlled by varying the reduction temperature. The HDP catalysts were tested at model conditions (i.e. in the absence of CO2) where the partial pressure ratios of steam to hydrogen, simulating different conversion levels, were increased up to a steam to hydrogen ratio of 400, to determine at what ratio the catalysts would begin to oxidise. The smaller catalysts showed significant oxidation at lower partial pressure ratios and to a greater extent than the larger particle size. These results showed the size dependence of the oxidation, with the large particles showing greater resistance to oxidation. These results were compared to iii thermodynamic calculations made for the size dependent oxidation of Ni, and good agreement between the experimental and predicted results was observed. The use of magnetic characterisation of the particle size was conducted by application of the Langevin equation as well as by a dispersion measurement, carried out by the titration of the Ni surface with H2. These in situ characterisation techniques showed consistency with the conventional external characterisation techniques and also showed that no size changes occurred throughout the testing, indicating that the results are truly due to size effects. Upon re-reduction of the oxidised catalysts, the full recovery of oxidised Ni was achieved with the large sample, whereas the smaller sample only achieved 60 % recovery of oxidised material. This is thought to be due to the formation of a less reducible phase, specifically metal-support compounds such as nickel silicate.
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Smith, Bradley Joseph. "Steam-Assisted Catalysis of n-Dodecane as a Jet Fuel Analogue in a Flow Reactor System for Hypersonic Thermal Management." University of Dayton / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1577978953025703.
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Mai, Trang. "FUNCTIONALIZATION OF IRON OXIDE NANOPARTICLES AND THE IMPACT ON SURFACE REACTIVE OXYGEN SPECIES GENERATION FOR POTENTIAL BIOMEDICAL AND ENVIRONMENTAL APPLICATIONS." UKnowledge, 2019. https://uknowledge.uky.edu/cme_etds/102.
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Iron oxide nanoparticles (IONPs) have been widely studied for a variety of applications, from biomedical applications (e.g., cell separation, drug delivery, contrast agent for magnetic resonance imaging and magnetically mediated energy delivery for cancer treatment) to environmental remediations (e.g., heavy metal removal and organic pollutants degradation). It has been demonstrated that IONPs can induce the production of reactive oxygen species (ROS) via Fenton/Haber-Weiss reactions which has been shown to be one of the key underlying mechanisms of nanoparticles toxicity. This inherent toxicity of nanoparticles has been shown to enhance the efficacy of traditional cancer therapies such as chemotherapy and radiation. In addition, the generation of ROS induced by IONPs has been also studied as advanced oxidation processes (AOP) for wastewater treatment. Recent research has also shown that exposure to an alternating magnetic field can significantly enhance the generation of ROS induced by IONPs. Moreover, the coatings of IONPs play an important role on the surface reactivity of nanoparticles since it can prevent the generation of ROS via Fenton chemistries at the surface of the nanoparticles.
In this work, co-precipitated IONPs were functionalized with small molecules including citric acid, sodium phosphate, amino silane and dopamine. The impact of coating on surface reactivity of the as-synthesized particles was studied using methylene blue dye degradation assay under AMF exposure. With the coatings of these small molecules, the IONPs induced ROS generation was significantly decreased because of the dense surface coverage. To study the effect of polymeric coatings, a degradable poly (beta amino ester) (PBAE) polymer coating was synthesized with dopamine as an anchor to bind to nanoparticles. The surface reactivity of the particles was expected to be recovered once the polymer coating was degraded. Furthermore, the impact of non-degradable PEG-based polymer coating on surface reactivity via ROS generation was also investigated using methylene blue decolorization assay with the presence of AMF. The retention of surface reactivity of PEG-based polymer coated IONPs shows promise for cancer treatment.
The application of IONPs as heterogeneous catalyst for organic contaminant degradation was investigated. Bisphenol A (BPA) was used as a model compound, and Fenton reactions were induced by IONPs with the presence of hydrogen peroxide and hydroxylamine as well as alternating magnetic field exposure. The kinetics of BPA degradation under water bath and AMF exposure at 37oC was also studied, and the results showed potential applications of IONPs for organic pollutants remediation.
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Ledung, Greger. "Heterogenization of a Cobalt Porphyrin Catalyst Investigated by Scanning Probe Microscopy and X-Ray Photoelectron Spectroscopy: The Effect on Catalysis of Oxidation Reactions." Doctoral thesis, Västerås : School of sustainable Development of Society and technology, Mälardalen university, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-492.
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Li, Hsin-Fen. "APPLICATION OF THIN FILM ANALYSIS TECHNIQUES AND CONTROLLED REACTION ENVIRONMENTS TO MODEL AND ENHANCE BIOMASS UTILIZATION BY CELLULOLYTIC BACTERIA." UKnowledge, 2012. http://uknowledge.uky.edu/cme_etds/13.
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Cellulose from energy crops or agriculture residues can be utilized as a sustainable energy resource to produce biofuels such as ethanol. The process of converting cellulose into solvents and biofuels requires the saccharification of cellulose into soluble, fermentable sugars. However, challenges to cellulosic biofuel production include increasing the activity of cellulose-degrading enzymes (cellulases) and increasing solvent (ethanol) yield while minimizing the co-production of organic acids. This work applies novel surface analysis techniques and fermentation reactor perturbations to quantify, manipulate, and model enzymatic and metabolic processes critical to the efficient production of cellulosic biofuels.
Surface analysis techniques utilizing cellulose thin film as the model substrate are developed to quantify the kinetics of cellulose degradation by cellulase as well as the interactions with cellulase at the interfacial level. Quartz Crystal Microbalance with Dissipation (QCM-D) is utilized to monitor the change in mass of model cellulose thin films cast. The time-dependent frequency response of the QCM simultaneously measures both enzyme adsorption and hydrolysis of the cellulose thin film by fungal cellulases, in which a significant reduction in the extent of hydrolysis can be observed with increasing cellobiose concentrations. A mechanistic enzyme reaction scheme is successfully applied to the QCM frequency response for the first time, describing adsorption/desorption and hydrolysis events of the enzyme, inhibitor, and enzyme/inhibitor complexes. The effect of fungal cellulase concentration on hydrolysis is tested using the QCM frequency response of cellulose thin films. Atomic Force Microscopy (AFM) is also applied for the first time to the whole cell cellulases of the bacterium C. thermocellum, where the effect of temperature on hydrolysis activity is quantified.
Fermentation of soluble sugars to desirable products requires the optimization of product yield and selectivity of the cellulolytic bacterium, Clostridium thermocellum. Metabolic tools to map the phenotype toward desirable solvent production are developed through environmental perturbation. A significant change in product selectivity toward ethanol production is achieved with exogenous hydrogen and the addition of hydrogenase inhibitors (e.g. methyl viologen). These results demonstrate compensatory product formation in which the shift in metabolic activity can be achieved through environmental perturbation without permanent change in the organism’s genome.