Dissertations / Theses on the topic 'Mechanism of reaction'

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Growing awareness of climate change and the risks associated with our society's dependence on fossil fuels has motivated global initiatives to develop economically viable, renewable energy sources. However, the transportation sector remains a major hurdle. Although electric vehicles are becoming more mainstream, the transportation sector is expected to continue relying heavily on combustion engines, particularly in the freight and airline industries. Therefore, research efforts to develop cleaner combustion must continue. This includes the development of more efficient combustion engines, identification of compatible alternative fuels, and the streamlining of existing petroleum resources. These dynamic systems have complex chemistry and are often difficult and expensive to probe experimentally, making detailed chemical kinetic modeling an attractive option for simulating and predicting macroscopic observables such as ignition delay or CO₂ concentrations. This thesis presents several methods and applications towards high fidelity predictive modeling using Reaction Mechanism Generator (RMG), an open source software package which automatically constructs kinetic mechanisms. Several sources contribute to model error during automatic mechanism generation, including incomplete or incorrect handling of chemistry, poor estimation of thermodynamic and kinetics parameters, and uncertainty propagation. First, an overview of RMG is presented along with algorithmic changes for handling incomplete or incorrect chemistry. Completeness of chemistry is often limited by CPU speed and memory in the combinational problem of generating reactions for large molecules. A method for filtering reactions is presented for efficiently and accurately building models for larger systems. An extensible species representation was also implemented based on chemical graph theory, allowing chemistry to be extended to lone pairs, charges, and variable valencies. Several chemistries are explored in this thesis through modeling three combustion related processes. Ketone and cyclic ether chemistry are explored in the study of diisoproyl ketone and cineole, biofuel candidates produced by fungi in the decomposition of cellulosic biomass. Detailed kinetic modeling in conjunction with engine experiments and metabolic engineering form a collaborative feedback loop that efficiently screens biofuel candidates for use in novel engine technologies. Next, the challenge of modeling constrained cyclic geometries is tackled in generating a combustion model of JP-10, a synthetic jet fuel used in propulsion technologies. The model is validated against experimental and literature data and succeeds in capturing key product distributions, including aromatic compounds, which are precursors to polyaromatic hydrocarbons (PAHs) and soot. Finally, oil-to-gas cracking processes under geological conditions are studied through modeling the low temperature pyrolysis of the heavy oil analog phenyldodecane in the presence of diethyldisulfide. This system is used to gather mechanistic insight on the observation that sulfur-rich kerogens have accelerated oil-to-gas decomposition, a topic relevant to petroleum reservoir modeling. The model shows that free radical timescales matter in low temperature systems where alkylaromatics are relatively stable. Local and global uncertainty propagation methods are used to analyze error in automatically generated kinetic models. A framework for local uncertainty analysis was implemented using Cantera as a backend. Global uncertainty analysis was implemented using adaptive Smolyak pscudospcctral approximations to efficiently compute and construct polynomial chaos expansions (PCE) to approximate the dependence of outputs on a subset of uncertain inputs. Both local and global methods provide similar qualitative insights towards identifying the most influential input parameters in a model. The analysis shows that correlated uncertainties based on kinetics rate rules and group additivity estimates of thermochemistry drastically reduce a model's degrees of freedom and can have a large impact on model outputs. These results highlight the necessity of uncertainty analysis in the mechanism generation workflow. This thesis demonstrates that predictive chemical kinetics can aid in the mechanistic understanding of complex chemical processes and contributes new methods for refining and building high fidelity models in the automatic mechanism generation workflow. These contributions are available to the kinetics community through the RMG software package.
by Connie W. Gao.
Ph. D.

The chemical evolution with respect to time of complex macroscopic mixtures such as interstellar clouds and Titan’s atmosphere is governed via a mutual competition between thousands of simultaneous processes, including thousands of chemical reactions. Chemical kinetic modeling, which attempts to understand their macroscopic observables as well as their overall reaction mechanism through a detailed understanding of their microscopic reactions and processes, thus require thousands of rate coefficients and product distributions. At present, however, just a small fraction of these have been well-studied and measured; in addition, at the relevant low temperatures, such information becomes even more scarce. Due to the recent developments in both theoretical kinetics as well as in ab initio electronic structure calculations, it is now possible to predict accurate reaction rate coefficients and product distributions from first-principles at various temperatures, often in less time, than through the running of an experiment. Here, the results of a first principles theoretical investigation into both the reaction rate coefficients as well as the final product distributions for the reactions between the ground state CH radical (X2Π) and various C1-C3 hydrocarbons is presented; together, these constitute a set of reactions important to modeling efforts relevant to mixtures such as interstellar clouds and Titan’s atmosphere.

Abstract A theoretical study of the Kolbe-Schmitt reaction mechanism, performed using a DFT method, reveals that the reaction between sodium phenoxide and carbon dioxide proceedswith the formation of three transition states and three intermediates. In the first step of the reaction, a polarized ONa bond of sodium phenoxide is attacked by the carbon dioxide molecule, and the intermediate NaPh-CO2 complex is formed. In the next step of the reaction the electrophilic carbon atom attacks the ring primarily at the ortho position, thus forming two new intermediates. The final product, sodium salicylate, is formed by a 1,3-proton shift from C to O atom. The mechanism agrees with the experimental data related to the Kolbe-Schmitt reaction.

An in-depth knowledge of the structure formation process and the resulting dependency of the morphology on the reaction mechanism is a key requirement in order to design application-oriented materials. For twin polymerization, the basic idea of the reaction process is established, and important structural properties of the final nanoporous hybrid materials are known. However, the effects of changing the reaction mechanism parameters on the final morphology is still an open issue. In this work, the dependence of the morphology on the reaction mechanism is investigated based on a previously introduced lattice-based Monte Carlo method, the reactive bond fluctuation model. We analyze the effects of the model parameters, such as movability, attraction, or reaction probabilities on structural properties, like the specific surface area, the radial distribution function, the local porosity distribution, or the total fraction of percolating elements. From these examinations, we can identify key factors to adapt structural properties to fulfill desired requirements for possible applications. Hereby, we point out which implications theses parameter changes have on the underlying chemical structure.

Gas phase ab initio, semi-empirical and density functional theory (DFT) quantum mechanical (QM) calculations are used to investigate key steps in the conversion of farnesyl diphosphate to aristolochene by the sesquiterpene synthase, aristolochene synthase (AS-PR), from P. roquefort Molecular docking and a combined quantum mechanics / molecular dynamics (QM/MM) are then used to simulate the reaction in silico. A total of three models of AS-PR are considered, one with two magnesium ions docked and two models containing three magnesiums ions docked in different positions. Gas phase results indicate that an intramolecular proton transfer, either directly or via a water molecule, during a key step in the mechanism is feasible with a maximum barrier height of ca. 22 kcal mol-1. Such a mechanism would avoid the generation, quenching and regeneration of a high energy carbocation intermediate. However, experimental evidence obtained contemporaneously with these results suggest that AS does indeed utilise an alternative mechanism involving the formation of a neutral intermediate (germacrene A) but the identity of the acid capable of protonating this intermediate has yet to be determined. Molecular docking experiments performed in this work reject a previous suggestion that diphosphate ion can perform this role. A series of QM/MM free energy sampling simulations demonstrate no significant lowering of the energetic barrier to intramolecular proton transfer over the gas phase suggesting that AS-PR does not catalyse this step of the reaction mechanism in vivo. Additional data also seemingly rule out Lys 206 as a possible active site acid. The condensed phase data also support gas phase results which suggest the formation of intermediate eudesmane cation occurs via a concerted process but that subsequent steps axe not concerted and that there are further true on-path intermediates in the reaction mechanism catalysed by AS-PR. By considering a number of different models for the AS-PR holoenzyme the role of the magnesium in causing favourable substrate binding and acting as a 'trigger' for the cyclisation cascade are presented and computational results support the tentative evidence obtained by X-ray crystallography. The results presented in this work add weight to the developing theories in sesquiterpene chemistry in which the biosynthesis of these molecules is achieved by enzymes whose role is the act as chaperones guiding their universal substrate into appropriate conformation, triggering catalysis by the binding of magnesium and preventing premature quenching of reactive carbocations by solvent.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
BOLSA NOTA 10
Este trabalho apresenta os resultados de um modelo matemático proposto para a carbocloração de pentóxido de nióbio com uma corrente de cloro gasoso em presença de carbono sólido como agente redutor. O modelo é baseado na equação de conservação de massa unidimensional em regime transitório. Soluções desta equação, acompanhada das condições de contorno e inicial, foram obtidas através do método de diferenças finitas. Uma análise estatística por distribuição t-student, dos valores obtidos utilizando o modelo de otimização Nelder e Mead, foi empregado neste estudo. O modelo representa resultados obtidos experimentalmente em um estudo anterior, referentes à conversão do pentóxido de nióbio em pentacloreto de nióbio gasoso por meio de um programa computacional para PC utilizando a linguagem Visual Basic for Applications (VBA). Os resultados experimentais apresentam uma boa concordância com os obtidos com o modelo e permitem representar de forma satisfatória o mecanismo reacional observado, incorporando os efeitos das variáveis envolvidas. Foram ainda determinadas a constante cinética e a difusividade efetiva para as diferentes variações de teor de carbono e porosidade nas temperaturas de 700 graus Celsius e 800 graus Celsius, para um fluxo de gás e altura da amostra constante. Observou-se que a melhor conversão do pentóxido de nióbio (96,5 por cento) obtém-se para 800 graus Celsius, 28 por cento de porosidade e 9 por cento de carbono. O tipo de controle é por difusão.
This study presents the results of a mathematical model proposed for carbochlorination of niobium pentoxide under a stream of chlorine gas in the presence of solid carbon as reducing agent. The model is based on one-dimensional unsteady state regime considering kinetic, diffusion and mass conservation. Solutions for this equation, associated with initial and boundary conditions were obtained using the method of finite differences. In this study, the Nelder and Mead optimization model was used and t-Student’s statistics was applied for goodness of fit analysis. The data obtained experimentally in a previous study, concerning the conversion of niobium pentoxide into niobium pentachloride gas, was processed using a computer software written for an Excel platform on Visual Basic for Applications (VBA). It was found that the experimental results were in accordance with the models outputs, allowing satisfactory representation of the observed reaction mechanism, incorporating the effects of the intervening variables. It was also determined the kinetic constant and the effective diffusivity for the different levels of carbon content and porosity, at temperatures of 700 Celsius degrees and 800 Celsius degrees for a specified gas flow and sample height. It was observed that the best conversion of the niobium pentoxide (96.5 per cent) is obtained at 800 Celsius degrees for 28 per cent porosity and 9 per cent carbon, for diffusion control.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2006.
Includes bibliographical references (leaves 38-44).
The process of building accurate chemical mechanisms for hydrocarbon oxidation systems is difficult since these mechanisms can have hundreds of species and thousands of reactions. Computer programs have recently been developed to construct these models automatically, but until this work, these programs did not include tools for the propagation of uncertainty. Rate constants and thermodynamic properties are not known precisely, and this can lead to large errors in model predictions. This work presents tools for sensitivity analysis and uncertainty propagation within an automatic reaction mechanism generator. A function for calculating first-order sensitivity coefficients with respect to rate and thermodynamic parameters and initial conditions is implemented in the MIT Reaction Mechanism Generator (RMG). An algorithm for generating error bounds on model output using first-order sensitivity coefficients and uncertainties in model parameters is also implemented. These tools are applied to an automatically generated model for the oxidation of the neopentyl radical, and results are compared to experimental observations.
(cont.) Comparison of the model with experimental data allowed identification of two rate constants. At 673 K and 60 Torr, kC5H11+O2-->OH+C5HI0O = 1.9x 10-14 ± 6x 10-15 cm3/molecule-s, and kOH+C5H1I-C5HOI+H20 = 3.1 x 10-12±1 .5 x 10-2 cm3/molecule-s.The computer-generated model is consistent with two prior literature studies.
by Sarah V. Petway.
S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 169-186).
Chemical kinetic modeling plays an important role in the study of reactive chemical systems. Thus, an automated means of constructing chemical kinetic models forms a useful tool in the engineering and science surrounding such systems. This document describes work to further develop one such tool, known as RMG (Reaction Mechanism Generator). Focus is placed on improving the accuracy of parameter estimation in the mechanism generation process and expanding the scope of applicability of the tool. In particular, effort has targeted the generation and use of explicit three-dimensional molecular structures for chemical species considered during reaction mechanism generation. This work has resulted in the generation of a software system integrated with RMG that can automatically generate and use such structures with quantum chemistry or force field codes to obtain more reliable thermochemistry estimates for cyclic structures without human intervention. Ultimately, the result of these updates is improved usefulness and reliability of the software system as a predictive tool. An application of the tool to the high temperature oxidation of JP-10, a jet fuel often used in military applications, is described. Using the newly refined RMG system, a detailed chemical kinetic model was constructed for this system. The resulting model represents a significant improvement upon existing work for JP- 10 oxidation by capturing detailed chemistry for this system. Simulations with this model have been found to produce results for ignition delay and product distribution that compare favorably with experimental results. The successful application of the refined RMG software system to this system demonstrates the practical utility of these updates.
by Gregory Russell Magoon.
Ph.D.

En aquesta tesi s'ha dissenyat i aplicat diferents eines teòriques i computacionals per a l'estudi de la reactivitat de l'enzim Mandelat Racemasa.
L'enzim Mandelat Racemasa catalitza la interconversió dels dos enantiòmers (S) i (R) de l'àcid mandèlic a una velocitat semblant. El mecanisme de reacció que es postula experimentalment passa per l'abstracció d'un protó molt poc àcid. Aquesta reacció molt poc favorable en medi aquós l'enzim la catalitza a una velocitat sorprenentment alta.
Fent un estudi Mecànica Quàntica / Mecànica Molecular (QM/MM) de la reactivitat de l'enzim s'han trobat els intermedis i les barreres de reacció que permeten deduir tres mecanismes a través dels quals el substracte natural mandelat i altres dos substractes anàlegs poden racemitzar. Expliquem de quina manera l'enzim pot fer la catàlisi tant efectiva i equivalent per als dos enantiòmers.
Partint de la necessitat de millorar l'estudi QM/MM anterior, sobretot pel què fa a l'acurada localització dels estats de transició (barreres reacció), s'ha dissenyat un mètode d'optimització d'estructures per ser aplicat a sistemes de milers d'àtoms com ho és el nostre enzim.
El mètode anomenat micro-iteratiu es basa en una cerca segons les equacions Rational Function Optimization (RFO) en una zona reduida mentre es minimitza l'entorn amb un mètode computacionalment barat com el LBFGS. Aquest mètode micro-iteratiu ha estat formulat, implementat i testejat en sistemes moleculars grans i petits. Se n'ha estudiat les diferents opcions donant una recepta pràctica per al seu ús en altres reaccions. També se n'ha justificat el seu desenvolupament posant de relleu les millores obtingudes amb aquest nou mètode quan es comparen els nous resultats amb els obtinguts en l'estudi QM/MM inicial.
Finalment, l'energia lliure de la reacció enzimàtica s'ha calculat amb tècniques de la dinàmica molecular i de l'Umbrella Sampling. Per aquest tipus de càlcul és imprescindible escollir a priori una coordenada de reacció que permeti anar de reactius a productes, en altres paraules, és necessari saber com té lloc la reacció. Gràcies a la prèvia localització d'estats de transició amb el mètode micro-iteratiu podem conèixer el mecanisme de reacció. I per tant podem emprar una coordenada de reacció adequada que ens permet calcular l'energia lliure de reacció de forma efectiva.
In this thesis several theoretical techniques to study the Mandelate Racemase enzyme reactivity are designed and used.
The Mandelate Racemase enzyme catalyses the interconversion of both enantiomers (S) and (R) of mandelic acid at apparently the same rate. Experimental results suggest that the reaction mechanism takes place through the abstraction of a non-acid hydrogen. This reaction is very low in aqueous media but the enzyme catalyzes it at an extremely fast rate.
We carry out a QM/MM study of the enzyme reativity. We have found the intermediate structures and the energy barriers corresponding to three proposed mechanisms that the natural substrate mandelate and two other substrate analogues may undergo. We are able to explain how the the efficient catalysis is performed for the two enantiomers.
Due to the lack in the previous QM/MM study of an efficient method to locate transition state structures (energy barriers) we have designed an structure optimization method to be applied to systems constituted by thousands of atoms such as our enzyme.
The so-called micro-iterative method consists in a search based on the Rational Function Optimization (RFO) equations applied in a core zone while the environment is minimized through a computationally affordable method such as LBFGS. The micro-iterative method has been formulated, implemented and tested for small and big molecular systems. We have studied several possible options giving as a result a practical guide for its usage in other reactions. Comparing the results coming from the initial QM/MM study with the ones found by this micro-iterative method we show an improvement that justifies the development.
Finally, the free energy corresponding to the enzymatic reaction is calculated by means of Molecular Dynamics and Umbrella Sampling techniques. The free energy computation requires the a priori election of a reaction coordinate that allows the system to go from reactants to products. In other words, it is essential to know how the reaction takes place. Thanks to the accurate search of transition states performed previously by the micro-iterative we can find the reaction mechanism. In this sense we can use an adequate reaction coordinate that permits us an efficient calculation of the reaction free energy.

Master of Science
Department of Chemical Engineering
Keith Hohn
The study will utilize a probabilistic reaction modeling method for ring-opening reactions of epoxide. In particular, to elucidate the reaction mechanism by the methods presented, focus will be placed on the nucleophillic attack of ethylene oxide by ammonia and its anion. This focus was chosen because of the potential to gain significant advantage in computational intensity required to model the epoxy-amino macromolecular curing reactions and resulting thermochemical and physical properties of the cured resin. The method employed utilizes the combinatorial probability that 1. Two molecules will approach a transition state with sufficient energy to drive reaction 2. Any reaction will occur for a given penetration into the potential energy surface. The concept of a transition state is relaxed to allow a dynamic probability that any reaction will proceed given a position on the intrinsic reaction coordinate (IRC) rather than searching for a specific transition state of theoretical reaction probability. 3. The reaction that occurs yields a desired stable or semi-stable molecular complex This study will focus on identifying possible stable and semi-stable products and corresponding rate constants. The technique developed here is novel in that it provides an unsupervised method to identify all structures corresponding to minima on the potential energy surface. The technique provides a pragmatic and efficient approach to sample a molecular system for different reaction mechanisms and provides a relative energy requirement to achieve these mechanisms with no presupposition of the mechanism, product, or transition state. It is possible from this data to derive rate constants for a reacting system, however, the rate constant derived for the EO/NH2 molecular system yielded significantly understated reaction probabilities and therefore rate constants.

Since the field of wireless technology is growing rapidly, security is becoming a major concern. A variety of security problems are being addressed, and much research work is taking place in order to provide adequate security to prevent hackers from disrupting network service. Wireless networks follow the IEEE 802.11 standard to transmit and receive packets. The IEEE 802.11 MAC protocol is designed in such a way to provide an equal share of throughput among all nodes in a network. Users who misbehave could modify the IEEE 802.11 MAC protocol, thus causing major security threats including substantial bandwidth degradation of other users. This thesis addresses the misbehavior of a node caused by altering the packet size. For a node to acquire higher throughput compared to other genuine nodes in the network, its packet size could be set higher than that of the genuine nodes. In order to protect against this sort of misbehavior, a special algorithm, which is a slight modification of the IEEE 802.11 MAC protocol, was developed. This algorithm is based on the notion of receiver-assigned backoff, which has already been used to deal with other types of misbehavior. The packet size-based misbehavior was modeled mathematically using queuing theory, and an appropriate reaction strategy was deduced from the analytical results. It was shown that the proposed approach reduces the effectiveness of misbehavior and leads to fairness in the network.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science.

La aplicación de los métodos de la química computacional ha llevado a una mejor comprensión del mecanismo de la reacción de Pauson-Khand para la síntesis de ciclopentenonas, en especial en su variante enantioselectiva.
Se han analizado tres métodos distintos para introducir enantioselectividad en esta reacción, que en su modelo original no es selectiva. Se han estudiado tres casos: a) la activación del catalizador convencional dicobalto octacarbonilo mediante un N-óxido quiral, b) la modificación de este mismo catalizador mediante la sustitución de dos ligandos carbonilo por una difosfina quiral, y c) la sustitución del catalizador dinuclear de cobalto por un catalizador mononuclear de rodio con ligandos quirales.
El estudio teórico ha llevado a la caracterización de aspectos mecanísticos que son inaccesibles al estudio puramente experimental, y contribuye así al desarrollo de métodos catalíticos más eficientes para esta importante reacción.
The application of computational methods has lead to a better understanding of the mechanism of the Pauson-Khand reaction (PKR) for the synthesis of cyclopentenone compounds. In particular the enantioselective PKR has been considered.

Different methods for inducing enantioselectivity in this originally unselective reaction have been analyzed. Three cases have been considered: a) Activation of the conventional dicobalt octacarbonyl catalyst by a chiral N-oxide, b) A modification of the dicobalt catalyst by means of a substitution of two carbonyl ligands by a chiral diphosphine ligand. and c) the substitution of the dinuclear cobalt catalyst by a mononuclear rhodium catalyst with chiral ligands.

The theoretical study has lead to the characterization of mechanistic aspects that would be inaccessible from a purely experimental study. The study therefore contributes to the development of more efficient catalytic methods for this important reaction.

[EN] The present thesis focuses on the rationalization of the zeolite synthesis for catalysis by understanding the nature of active sites and their microenvironments, together with their influence on the mechanisms of catalyzed reactions. In the first part of the thesis, efforts have been put on attempting to achieve the regioselective locating of active sites in zeolite catalyst and, more specifically, on tunning acid site locations in zeolite framework. The development of a zeolite synthesis strategy and an indicator that can describe the aluminum distribution in the zeolite framework is important to evaluate if the final objective has been achieved. In this part, in order to evaluate aluminum distribution in MFI framework, an indicator based on monomolecular and bimolecular mechanisms of n-hexene catalytic cracking was proposed. First, several ZSM-5 samples were synthesized, which have been reported in the literature to have different aluminum distributions. These samples were characterized to be analogous in physicochemical properties and, then, tested in the n-hexene cracking to justify the usefulness of the indicator proposed in this work. Using 27Al MAS NMR, the aluminum locations were proved to be different, which was also reflected by the indicator in this thesis, justifying its applicability to evaluate aluminum locations. Afterward, this indicator has been employed to check the zeolite synthesis methodology that could potentially lead to different aluminum distribution in zeolite frameworks. Then, a boron-assisted synthesis is proposed considering that boron and aluminum may have competitive positioning in ZSM-5 framework. Then, and by means of DFT calculations, we have studied if the unit cell of MFI shows different stabilities when substituted by aluminum and/or boron in different T positions. It has been found that boron location is less favored when introduced in 10-ring channels of the MFI framework, while aluminum shows no preference for positioning among all the T-sites. ZSM-5 samples with different Si/Al and Si/B were synthesized and their physicochemical properties as well as the relative proportion of paired and isolated states of aluminum was characterized. Characterization includes n-hexene cracking, for which the samples showed different preference toward monomolecular and bimolecular reactions. Finally, once the materials were proved to have different aluminum distribution, they were employed in methanol-to-propene (MTP) reactions to show the influence of aluminum distribution on an industry-relevant reaction where the spatial confinement has an important impact. Indeed, the samples with aluminum preferentially positioned in 10-ring channel favored more monomolecular cracking and less bimolecular side reactions such as oligomerization and hydrogen transfer, giving higher propene yield and lower amount of alkanes and aromatics. The second part of the thesis focuses on rationalizing the synthesis of zeolites with cavities for catalyzing “a priory” selected reaction. More specifically, zeolite synthesis was carried out using OSDAs that mimic the transition state (TS) or a relevant intermediate in the target reaction. Ethylbenzene production by transalkylation between diethylbenzene and benzene was selected as the reaction to be catalyzed. A potential reaction TS was established and a diaryldimethylphosphonium OSDA was synthesized that mimicks the transition state in the diaryl-mediated mechanism of transalkylation between benzene and diethylbenzene. Then, the OSDA successfully led to the formation of the largepore zeolite ITQ-27. This ITQ-27 was tested in the reaction of transalkylation between benzene and diethylbenzene. The catalytic performance of this material was benchmarked to be superior than other commercially employed zeolites, such as USY, mordenite or Beta with similar physicochemical properties. Finally, Methanol to olefins (MTO) reaction was chosen as another target catalytic system, where the reaction pathways are more complicated than transalkylation between benzene and diethylbenzene but nevertheless they have been well established in the literature. Thus, several OSDAs were synthesized mimicking the intermediates and transition states of the paring pathway, which produces more propene and butenes, which are highly demanded among all products. The OSDAs led to formation of several cage-based small pore zeolites, such as CHA, RTH and AEI. All the zeolites obtained were tested in MTO reactions to evaluate their catalytic activity and gave high selectivity toward light olefins, which appeared to selectively depend on the zeolite tested. The tendency of each structure toward certain product distributions was related to the reaction mechanism by establishing a structure-reactivity correlation, when the experiment results were combined with theoretical calculations. It is proposed that different shape of the cavities stabilize different precursor intermediates present in the paring or side-chain pathways and this indicates the reaction preference between each pathway and therefore the product distributions. A linear correlation was obtained between the shape of cavities and the C3 = /C2 = molar ratios being possible. In this way, ITQ-3 (ITE structure) was predicted that should also give higher selectivity toward paring pathway, which has been demonstrated experimentally
[ES] La presente tesis se centra en la racionalización de la síntesis de zeolitas para su aplicación como catalizadores mediante la comprensión de la naturaleza de los sitios activos y sus microambientes, junto con su influencia en los mecanismos de las reacciones catalizadas. En la primera parte de la tesis, se han realizado esfuerzos para intentar lograr la ubicación regioselectiva de los sitios activos en el catalizador zeolítico y, más específicamente, en la ubicación controlada de sitios ácidos en la red cristalina de la zeolita. El desarrollo de una estrategia de síntesis adecuada junto con un indicador que pueda describir la distribución de aluminio en la red de la zeolita es importante para evaluar si se ha logrado el objetivo final. En esta parte, para evaluar la distribución de aluminio en la red de la zeolita MFI, se ha propuesto un indicador basado en los mecanismos monomoleculares y bimoleculares asociados a la reacción de craqueo catalítico de n-hexeno. En primer lugar, se sintetizaron varias muestras de ZSM-5, que según la literatura tienen diferentes distribuciones de aluminio. Estas muestras se caracterizaron por ser análogas en propiedades fisicoquímicas y, posteriormente, se analizaron en la reacción de craqueo de n-hexeno para justificar la utilidad del indicador propuesto en este trabajo. A partir de RMN MAS de 27Al se demostró que las ubicaciones de aluminio eran diferentes, lo que también se reflejó en el indicador propuesto en esta tesis, lo que justifica su aplicabilidad para evaluar distribuciones de aluminio. Posteriormente, este indicador se ha empleado para verificar la nueva metodología de síntesis de zeolitas que podría conducir a una distribución de aluminio diferente en sus estructuras cristalinas. En este sentido, se propone la síntesis de la zeolita ZSM-5 asistida por boro, considerando que el boro y el aluminio podrían tener un posicionamiento competitivo en la estructura MFI. Mediante cálculos de DFT, se ha estudiado si la celda unidad de MFI muestra diferente estabilidad cuando se introduce aluminio y/o boro en diferentes posiciones cristalográficas T. Se ha encontrado que la ubicación del boro está menos favorecida cuando se introduce en los canales de 10 miembros de la estructura MFI, mientras que el aluminio no muestra preferencia por el posicionamiento entre todos los sitios T. Se sintetizaron muestras de ZSM-5 con diferentes Si/Al y Si/B y se caracterizaron sus propiedades fisicoquímicas, así como la proporción relativa de estados emparejados y aislados de aluminio. La caracterización incluye el craqueo de n-hexeno, para el cual las muestras mostraron una preferencia diferente hacia las reacciones monomoleculares y bimoleculares. Finalmente, una vez demostrada la distinta distribución de aluminio en los materiales sintetizados, estos catalizadores se estudiaron en la reaccióde metanol a propeno (MTP) para mostrar la influencia de la distribución de aluminio en una reacción relevante a nivel industrial, donde el confinamiento espacial tiene un impacto importante. De hecho, las muestras con aluminio posicionadas preferentemente en un canal de 10 miembros favorecen reacciones de craqueo monomolecular frente a reacciones secundarias bimoleculares, como por ejemplo reacciones de oligomerización y de transferencia de hidrógeno, dando un mayor rendimiento a propeno y una menor cantidad de alcanos y compuestos aromáticos. La segunda parte de la tesis se centra en racionalizar la síntesis de zeolitas con cavidades para catalizar una reacción seleccionada "a priori". Más específicamente, la síntesis de zeolita se llevó a cabo utilizando agentes directores de estructura orgánicos (ADEO) que mimetizan el estado de transición (ET) o el intermedio relevante en la reacción objetivo. La producción de etilbenceno por transalquilación entre dietilbenceno y benceno se ha seleccionado como una reacción objetivo a catalizar. Se estableció el ET determinante de la reacción y se sintetizó un ADEO tipo diarildimetilfosfonio que mimetiza el estado de transición del mecanismo de la reacción de transalquilación entre benceno y dietilbenceno. Dicho ADEO permitió la cristalización de la zeolita de poro grande ITQ-27, cuyo comportamiento catalítico se estudió en la reacción de transalquilación entre benceno y dietilbenceno. La actividad catalítica de la zeolita ITQ-27 se mostró claramente superior al de otras zeolitas empleadas comercialmente, como USY, mordenita o Beta, todas ellas con propiedades fisicoquímicas similares a la ITQ-27. Finalmente, la reacción de metanol a olefinas (MTO) se eligió como otro sistema catalítico objetivo, donde los mecanismos de reacción son mucho más complicados que en el caso de la reacción de transalquilación entre benceno y dietilbenceno, pero, sin embargo, están bien establecidos en la literatura. Se sintetizaron varios ADEOs que mimetizan los intermedios y los estados de transición de la ruta “paring”, que produce más propeno y butenos, y que son posiblemente los productos más demandados. Dichos ADEOs mímicos permitieron la formación de varias zeolitas de poro pequeño basadas en cavidades, como las zeolitas CHA, RTH y AEI. Todas las zeolitas obtenidas se probaron en la reacción MTO para evaluar su actividad catalítica, obteniéndose una alta selectividad hacia distintas olefinas ligeras, cuya selectividad depende de la forma y tamaño de la cavidad de cada zeolita. La tendencia de cada estructura hacia ciertas distribuciones de productos se ha relacionado con el mecanismo de reacción, pudiendo establecer una correlación estructura-reactividad al combinar los resultados experimentales con cálculos teóricos.
[CA] La present tesi es centra en la racionalització de la síntesi de zeolites per a la seva aplicació com a catalitzadors mitjançant la comprensió de la naturalesa dels centres actius i els seus microambientes, juntament amb la seva influència en els mecanismes de les reaccions catalitzades. A la primera part de la tesi, s'han realitzat esforços per intentar aconseguir la ubicació regioselectiva dels centres actius en el catalitzador zeolític i, més específicament, en la ubicació controlada de centres àcids en la xarxa cristal·lina de la zeolita. El desenvolupament d'una estratègia de síntesi adequada juntament amb un indicador que descriga la distribució d'alumini a la xarxa de la zeolita és important per avaluar si s'ha aconseguit l'objectiu final. En aquesta part, per avaluar la distribució d'alumini a la xarxa de la zeolita MFI, s'ha proposat un indicador basat en els mecanismes monomoleculares i bimoleculars associats a la reacció de craqueig catalític de n-hexé. En primer lloc, es van sintetitzar diverses mostres de ZSM-5, que segons la literatura tenen diferents distribucions d'alumini. Aquestes mostres es van caracteritzar per ser anàlogues en propietats fisicoquímiques i, posteriorment, es van analitzar en la reacció de craqueig de nhexéper justificar la utilitat de l'indicador proposat en aquest treball. A partir dels espectres de RMN MAS de 27Al es va demostrar que les ubicacions d'alumini eren diferents, el que també es va reflectir en l'indicador proposat en aquesta tesi, justificant la seva aplicabilitat per avaluar distintes distribucions d'alumini. Posteriorment, aquest indicador s'ha emprat per verificar la nova metodologia de síntesi de zeolites que podria conduir a una distribució d'alumini diferent al llarg de les seves estructures cristal·lines. En aquest sentit, s’ha proposat la síntesi de la zeolita ZSM-5 assistida per bor, considerant que el bor i l'alumini podrien tenir un posicionament competitiu en l'estructura MFI. Mitjançant càlculs de DFT, s'ha estudiat si la cel·la unitat de MFI mostra diferent estabilitat quan s’introdueix alumini i/o bor en diferents posicions cristal·logràfiques T. S'ha trobat que la ubicació dels àtoms de bor està menys afavorida als canals de 10 membres de la estructura MFI, mentre que l'alumini no mostra preferència pel posicionament entre tots els llocs T. Es van sintetitzar mostres de ZSM-5 amb diferents relacions de Si/Al i Si/B i es van caracteritzar les seves propietats fisicoquímiques, així com la proporció relativa d'estats aparellats i aïllats d'alumini. La caracterització inclou la reacció de craqueig de n-hexé, on les mostres van mostrar una preferència diferent cap a les reaccions monomoleculares i bimoleculars. Finalment, un cop demostrada la diferent distribució d'alumini en els materials sintetitzats, aquests catalitzadors es van estudiar a la reacció de metanol a propè (MTP) per mostrar la influència de la distribució d'alumini en una reacció rellevant a nivell industrial, on el confinament espacial té un impacte important. De fet, les mostres amb alumini posicionades preferentment en un canal de 10 membres afavoreixen reaccions de craqueig monomolecular enfront de reaccions secundàries bimoleculars, com ara reaccions d'oligomerització i de transferència d'hidrogen, donant un major rendiment a propè i una menor quantitat d'alcans i compostos aromàtics. La segona part de la tesi es centra en racionalitzar la síntesi de zeolites amb cavitats per catalitzar una reacció seleccionada "a priori". Més específicament, la síntesi de zeolita es va dur a terme utilitzant agents directors d'estructura orgànics (ADEO) que mimetitzen l'estat de transició (ET) o l'intermedi rellevant en la reacció objectiu. La producció de etilbenzèper transalquilació entre dietilbenzè i benzè s'ha seleccionat com una reacció objectiu a catalitzar. Es va establir l'ET determinant de la reacció i es va sintetitzar un ADEO tipus diarildimetilfosfoni que mimetitza eixe estat de transició. Eixe ADEO va permetre la cristal·lització de la zeolita de porus gran ITQ-27, i el seu comportament catalític es va estudiar en la reacció de transalquilación entre benzè i dietilbenzè. L'activitat catalítica de la zeolita ITQ-27 es va mostrar clarament superior a la d'altres zeolites emprades comercialment, com la USY, mordenita o Beta, totes elles amb propietats fisicoquímiques similars a la ITQ-27. Finalment, la reacció de metanol a olefines (MTO) es va triar com un altre sistema catalític objectiu, on els mecanismes de reacció són molt més complicats que en el cas de la reacció de transalquilació entre benzè i dietilbenzè, però que, al mateix temps, estan ben establerts en la literatura. Es van sintetitzar diversos ADEOs que mimetitzen alguns dels intermedis i dels estats de transició de la ruta "paring", que produeix més propè i butens, i que són possiblement els productes més demandats. Aquests ADEOs mímics van permetre la formació de diverses zeolites de porus petit basades en cavitats, com les zeolites CHA, RTH i AEI. Totes les zeolites obtingudes es van provar en la reacció MTO per avaluar la seva activitat catalítica, obtenint una alta selectivitat cap a diferents olefines lleugeres, on la selectivitat cap a cada olefina lleugera depèn de la forma i mida de la cavitat de cada zeolita. La tendència de cada estructura cap a certes distribucions de productes s'ha relacionat amb el mecanisme de reacció, i s´ha pogut establir una correlació estructura-reactivitat al combinar els resultats experimentals amb càlculs teòrics.
Li, C. (2020). Rationalize the synthesis of zeolite catalysts by understanding reaction mechanism [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/147115
TESIS

Lithium-oxygen batteries, also known as Lithium-air batteries, could possibly revolutionize energy storage as we know. By letting lithium react with ambient oxygen gas very large theoretical energy densities are possible. However, there are several challenges remaining to be solved, such as finding suitable materials and understanding the reaction, before the lithium-oxygen battery could be commercialized. The scope of this thesis is focusing on the latter of these challenges. Efficient ion transport between the electrodes is imperative for all batteries that need high power density and energy efficiency. Here the mass transport properties of lithium ions in several different solvents was evaluated. The results showed that the lithium  mass transport in electrolytes based on the commonly used lithium-oxygen battery solvent dimethyl sulfoxide (DMSO) was very similar to that of conventional lithium-ion battery electrolytes. However, when room temperature ionic liquids were used the performance severely decreased. Addition of Li salt will effect the oxygen concentration in DMSO-based electrolytes. The choice of lithium salt influenced whether the oxygen concentration increased or decreased. At one molar salt concentration the highest oxygen solubility was 68 % larger than the lowest one. Two model systems was used to study the electrochemical reaction: A quartz crystal microbalance and a cylindrical ultramicroelectrode. The combined usage of these systems showed that during discharge soluble lithium superoxide was produced. A consequence of this was that not all discharge product ended up on the electrode surface. During discharge the cylindrical ultramicroelectrodes displayed signs of passivation that previous theory could not adequately describe. Here the passivation was explained in terms of depletion of active sites. A mechanism was also proposed. The O2 and Li+ concentration dependencies of the discharge process were evaluated by determining the reactant reaction order under kinetic and mass transport control. Under kinetic control the system showed non-integer reaction orders with that of oxygen close to 0.5 suggesting that the current determining step involves adsorption of oxygen. At higher overpotentials, at mass transport control, the reaction order of lithium and oxygen was zero and one, respectively. These results suggest that changes in oxygen concentration will influence the current more than that of lithium. During charging not all of the reaction product was removed. This caused an accumulation when several cycles was examined. The charge reaction pathway involved de-lithiation and bulk oxidation, it also showed an oxygen concentration dependence.
Litiumsyrebatteriet, även känt som litiumluftbatteriet, kan potentiellt revolutionera vårt förhållande till energilagring. Genom att låta litium reagera med syrgas från luften kan teoretiskt höga energitätheter uppnås. Dock så behöver många problem lösas, så som att hitta lämpliga elektrod- och elektrolytmaterial samt att få en ökad förståelse för reaktionsmekanismen, innan litiumsyrebatteriet kan kommersialiseras. Den här avhandlingen behandlar de sistnämnda av dessa problem. För att ett batteri ska kunna leverera hög effekttäthet och energieffektivitet krävs en effektiv jontransport mellan elektroderna. Här utvärderades masstransporten hos flera olika elektrolyter. Resultatet visade att masstransporten av litium i en litiumsyrebatterielektrolyt (baserad på dimetylsulfoxid (DMSO)) är likvärdig med en konventionell litiumjonbatterielektrolyt. När elektrolyter baserade på jonvätskor användes uppvisades väldigt stora energiförluster. När litiumsalt tillsattes påverkades lösligheten av syre i DMSO-baserade elektrolyter. Vilken sorts litiumsalt som användes påverkade om lösligheten av syre ökade eller minskade. Vid en saltkoncentration på en molar var den högsta syrelösligheten 68 \% större än den lägsta. Två olika modellsystem används för att studera den elektrokemiska reaktionen: En elektrokemisk kvartskristallmikrovåg och en cylindrisk ultramikroelektrod. Vid kombinerad användning av dessa system påvisades att löslig litiumsuperoxid bildades vid urladdningen. Följden av detta blev att endast delar av urladdningsprodukten hamnade på elektroden. Vid urladdning visade ultramikroelektroderna tecken på passivering som inte kunde beskrivas av tidigare teori. Här föreslås att passiveringen uppstår på grund av en blockering av de aktiva säten där reaktionen fortskrider. För denna process föreslås även en detaljerad mekanism. Urladdningsprocessens koncentrationsberoende utvärderades genom att bestämma reaktionsordningen för syre och litium under kinetisk- och masstransport kontroll. Under kinetisk kontroll fanns inga heltalsreaktionsordningar, för syre var reaktionsordningen nära 0.5 vilket föreslår att det reaktionssteg som bestämmer strömstorleken innefattar en adsorption av syre. Vid högre överpotentialer, då systemet var under masstransportkontroll, var reaktionsordningarna för litium och syre noll respektive ett. Detta föreslår att ändringar i syrekoncentration påverkar strömmen betydligt mer än vad det gör för litium. Under uppladdning kunde inte all reaktionsprodukt avlägsnas från elektroden. Detta ledde till en ackumulation då flera cykler studerades. Uppladdningens delsteg innefattade en delitiering följt av en oxidation av reaktionsproduktbulken. Denna process uppvisade även ett syrekoncentrationsberoende.

QC 20171114

Chemical reactivity hazards have posed a significant challenge for industries that manufacture, store, and handle reactive chemicals. Without proper management and control of reactivity, numerous incidents have caused tremendous loss of property and human lives. The U.S. Chemical Safety and Hazard Investigation Board (CSB) reported 167 incidents involving reactive chemicals that occurred in the U.S. from 1980 to 2001. According to the report, 35 percent of the incidents were caused by thermal runaway reactions, such as incidents that involved hydroxylamine and hydroxylamine nitrate. The thermal stability of hydroxylamine system under various industrial conditions was studied thoroughly to develop an understanding necessary to prevent recurrence of incidents. The macroscopic runaway reaction behavior of hydroxylamine system was analyzed using a RSST (Reactive System Screening Tool) and an APTAC (Automatic Pressure Tracking Calorimeter). Also, computational chemistry was employed as a powerful tool to evaluate and predict the measured reactivity. A method was proposed to develop a runaway reaction mechanism that provides atomic level ofinformation on elementary reaction steps, in terms of reaction thermochemistry, activation barriers, and reaction rates. This work aims to bridge molecular and macroscopic scales for process safety regarding reactive chemicals and to understand macroscopic runaway reaction behaviors from a molecular point of view.

Emission control of greenhouse gases especially CO2 has become an environmental challenge. CO2 capture by absorption in amine is so far the only CCS technique that has been industrially acknowledged. Chemical absorption of CO2 in amine solution is a complex process and needs investigation for better understanding.An experimental study has been conducted to understand the kinetics of CO2 absorption in non-aqueous DEA solution at 293K in a stirred cell reactor with a smooth and flat gas liquid interface. Experiments were repeated to ensure the reproducibility of data and the results were compared with literature to ensure the validity of this work. Physio-chemical properties of all chemicals like density, diffusivity and viscosity were taken from literature whereas solubility data was generated by experimentation. Solubility data was also validated by comparison with literature.Experimental data for reaction kinetics was treated with both zwitterion and termolecular mechanism. Based on the findings from this work, the order of reaction is 1.78 with respect to amine. Furthermore, Parity plot between calculated and experimental CO2 fluxes have been generated to elaborate the argument and it could be concluded that for non-aqueous system both studied mechanisms shows less than 10% deviation and hence can give satisfactory results. It is recommended to continue this work at different temperatures for better understanding.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 281-292).
Nearly two-thirds of the United States' transportation fuels are derived from non-renewable fossil fuels. This demand of fossil fuels requires the United States to import ~ 60% of its total fuel consumption. Relying so heavily on foreign oil is a threat to national security, not to mention that burning all of these fossil fuels produces increased levels of CO₂, a greenhouse gas that contributes to global warming. This is not a sustainable model. The United States government has recently passed legislation that requires greenhouse gas emissions to be reduced to 80% of the 2005 level by the year 2050. Furthermore, new legislation under the Energy Independence and Security Act (EISA) requires that 36 billion gallons of renewable fuel be blended into transportation fuel by 2022. Solving these types of problems will require the fuel industry to shift away from petroleum fuels to biomass-derived oxygenated hydrocarbon fuels. These fuels are generated through different biological pathways, using different "bugs." The question of which fuel molecules should we be burning, and thus, which bugs should we be engineering, arises. To answer that question, a detailed understanding of the fuel chemistry under a wide range of operating conditions, i.e. temperature, pressure, fuel equivalence ratio, and fuel percentage, must be known. Understanding any fuel chemistry fully requires significant collaboration: experimental datasets that span a range of temperatures, pressures, and equivalence ratios, high-level ab initio quantum chemistry calculations for single species and reactions, and a comprehensive reaction mechanism and reactor model that utilizes the theoretical calculations to make predictions. A shortcoming in any of these three fields limits the knowledge gained from the others. This thesis addresses the third field of the collaboration, namely constructing accurate reaction mechanisms for chemical systems. In this thesis, reaction mechanisms are constructed automatically using a software package Reaction Mechanism Generator (RMG) that has been developed in the Green Group over the last decade. The predictive capability of any mechanism depends on the parameters employed. For kinetic models, these parameters consist of species thermochemistry and reaction rate coefficients. Many parameters have been reported in the literature, and it would be beneficial if RMG would utilize these values instead of relying on estimation routines purely. To this end, the PrIMe Warehouse C/H/O chemistry has been validated and a means of incorporating said data in the RMG database has been implemented. Thus, all kinetic models built by RMG may utilize the community's reported thermochemical parameters.
(cont.) A kinetic model is evaluated by how accurately it can predict experimental data. In this thesis, it was shown that the RMG software, with the PrIMe Warehouse data collaboration, constructs validated kinetic models by using RMG to predict the pyrolysis and combustion chemistry of the four butanol isomers. The kinetic model has been validated against many unique datasets, including: pyrolysis experiments in a flow reactor, opposed-flow and doped methane diffusion flames, jet-stirred reactors, shock tube and rapid compression machine experiments, and low-pressure and atmospheric premixed laminar flames. The mechanism predicts the datasets remarkably well across all operating conditions, including: speciation data within a factor of three, ignition delays within a factor of two, and laminar burning velocities within 20% of the experimental measurements. This accurate, comprehensivelyvalidated kinetic model for the butanol isomers is valuable itself, and even more so as a demonstration of the state-of-the-art in predictive chemical kinetics. Although the butanol kinetic model was validated against many datasets, the model contained no nitrogen-containing species, and also had limited pathways for benzene formation. These limitations were due to the RMG software, as RMG was initially written with only carbon, hydrogen, and oxygen chemistry in mind. While this functionality has been sufficient in modeling the combustion of hydrocarbons, the ability to make predictions for other chemical systems, e.g. nitrogen, sulfur, and silicon compounds, with the same tools is desired. As part of this thesis, the hardcoded C/H/O functional groups were removed from the source code and database, enabling our RMG software to model heteroatom chemistry. These changes in the RMG software also allows for robust modeling of aromatic compounds. The future in the transportation sector is uncertain, particularly regarding which fuels our engines will run on. Understanding the elementary chemistry of combustion will be critical in efficiently screening all potential fuel alternatives. This thesis demonstrates one method of understanding fuel chemistry, through detailed reaction mechanisms constructed automatically using the RMG software. Specifically, a method for data collaboration between the RMG software and the PrIMe Warehouse has been established, which will facilitate collaboration between researchers working on combustion experiments, theory, and modeling. The RMG software's algorithm of mechanism construction has been validated by comparing the RMG-generated model predictions for the combustion of the butanol isomers against many unique datasets from the literature; many new species thermochemistry and reaction rate kinetics were calculated and this validation shows RMG to be a capable tool in constructing reaction mechanisms for combustion. Finally, the RMG source code and database have been updated, to allow for robust modeling of heteroatom and aromatic chemistry; these two features will be especially important for future modeling of combustion systems as they relate to the formation of harmful pollutants such as NOx and soot.
by Michael Richard Harper, Jr.
Ph.D.

Afin de mieux comprendre et de dépasser les limites actuelles des systèmes métal-air non-aqueux, le mécanisme de réduction de l’oxygène (ORR) a été étudié en présence de cation alcalins dans divers solvants aprotiques. Sur la base de caractérisations électrochimiques sur électrode statique et d’électrodes tournantes disque-anneau, un mécanisme unique a été proposé afin de rendre compte de l’ORR en présence de cations alcalins. De plus, les différences observées d’un solvant à l’autre ont été expliquées en termes de capacité du solvant à solvater à la fois le cation alcalin en présence et l’anion superoxyde, mais aussi à sa capacité à séparer les paires d’ions. Un modèle cinétique basé sur ce mécanisme a montré un excellent accord avec les résultats expérimentaux
In order to better understand and overcome the current limitations of non-aqueous metal-air batteries, the oxygen reduction reaction (ORR) mechanism has been studied in presence of different alkali metal cations in several aprotic solvents. Based on electrochemical characterizations on static electrode and rotating ring-disk electrode, a unique mechanism has been proposed to account for ORR in presence of alkali metal cations. It has been further showed that the differences observed from one solvent to another could be linked to the solvent’s ability to solvate both the alkali metal cation and the superoxide anion, as well as its capability to separate ion-pairs. A kinetic model based on this mechanism has shown very good agreement with experimental results

京都大学
新制・課程博士
博士(人間・環境学)
甲第23286号
人博第1001号
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 内本 喜晴, 教授 田部 勢津久, 教授 高木 紀明
学位規則第4条第1項該当
Doctor of Human and Environmental Studies
Kyoto University
DFAM

Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第16947号
人博第590号
新制||人||141(附属図書館)
23||人博||590(吉田南総合図書館)
29622
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 内本 喜晴, 教授 杉山 雅人, 教授 田部 勢津久, 准教授 藤原 直樹, 准教授 雨澤 浩史
学位規則第4条第1項該当

碩士
長庚大學
化學工程研究所
90
Methanol is a raw material for the production of hydrogen and carbon monoxide from its direct decomposition reaction. Decomposition of methanol at 200 to 300OC yields two moles of hydrogen, one mole of carbon monoxide and small amount of carbon dioxide, methane and methyl formate. The objective of this research is to study the kinetics and the mechanisms of methanol decomposition reaction using Cu/Cr/Mn as the catalyst. In the course of this study, we modified the parent catalyst with 1% of and the promoters, La, Ce and Pt to improve catalystic reactivity and selectivity. Furthermore, a fixed amount of oxygen was co-fed with methanol to adjust H2/CO ratio and to reduce energy requirement of the endothermic reaction by converting carbon monoxide into carbon dioxide. The amount of oxygen was fixed to be 20% of the methanol feed. Methyl formate is the key intermediate of the methanol decomposition reaction. In the decomposition of methyl formate under the same reaction conditions, we found that it had a higher activation energy than that of methanol decomposition reaction (14.75 Kcal/mol for methyl formate; 10.23 Kcal/mol for methanol) and a 190 time larger frequency factor, ko than that of methanol. It was found that addition of 1% La and Ce promoters to the parent Cu/Cr/Mn catalyst increased the reactivity of the parent catalyst. However, addition of Pt to the parent catalyst gave poor reactivity against our original expectation of its ability to promote hydrogen spillover. Part of the reason was attributed to the growth of copper crystal size and the reduction of copper surface area by the incorporation of Pt metal onto the parent catalyst. The exact course of this de-activation by Pt metal, however, was not clear yet at this moment. All three catalysts, Cu/Cr/Mn, La/Cu/Cr/Mn, Ce/Cu/Cr/Mn were found to the selective catalysts for the hybrid reaction of partial oxidation and decomposition reaction of methanol; carbon monoxide was selectively oxidized into carbon dioxide with these three catalysts. Therefore, partial oxidation with these catalysts can be used as a mean to help adjust H2/CO ratio and to supply reaction heat to the endothermic reaction of methanol decomposition.

碩士
中原大學
化學系
87
ABSTRACT Calcium Phosphate glass-ceramic have a potential in application of biomaterials, due to their composition was as like human’s, nontoxic and bio-compatible. In our study, in order to improve the crystallizability of glass-ceramic addition of the nucleus agents to calcium phosphate glass was performed. It is excepted to increase mechanical properties. Application of calcium phosphate glass was limited, because of their higher melting point and absorption. Generally, matrix glass with Ca/P molar ratios lower than 0.7 was comfortable. In this work, six kinds of matrix glass were selected with molar ratios ranging from 0.3 to 0.6. By addition of calcium pyrophosphate and calcium metaphosphate, the detail reaction mechanism in solid state will be gotten. Using DTA, XRD and SEM, the effects of addition of nucleus agent were investigated. Adding calcium pyrophosphate to matrix glass with higher molar ratios, the forming temperature of bata-calcium metaphosphate nuclide decreased with additions. However, the crystal growth did not concern with nucleus agent directly. After addition, crystallization reaction was fast more than non-addition. In additional, the crystal phase own thermal stableness well. According to the result of thermal analysis, adding procedure make exothermic peak of the crystal growth symmetric. Further, in the investigation on thermodynamic, the lower value of growth activity energy, Ea=243.75 KJ/mole, was gotten. The crystal morphology was small and distributed well in bulk of glass. Adding calcium metaphosphate to matrix glass with lower molar ratios, the forming temperature of bata-calcium metaphosphate nuclide also was decreased and the crystallization raising, but have lower reaction rate. The crystal morphology was network differ to higher molar ratio glass and non-additional glass. Unexpectedly, a mirror product, Ca2P6O17 poor crystal, was find besides the major phase β-Ca(PO3) 2 by XRD studying.

碩士
國立中興大學
材料科學與工程學系所
100
Cu2ZnSnS4 (CZTS) powders have been synthesized from aqueous solutions consisting of copper (II) chloride, zinc (II) chloride, stannic (IV) chloride, and thioacetamide (TAA) dissolved in mixtures of deionized water and ethanol. The CZTS powders were obtained when the precursor solutions were held isothermally at 65 oC followed by annealing at 550 oC in Ar atmosphere. When the reaction temperature was held at 35 to 55 oC, a pronounced formation of intermediate Cu3(TAA)3Cl3 prisms resulted which produced Cu2S at elevated temperatures as an impurity. In addition, rounded particles were obtained from the CZTS precursor solutions by filtering removal of the Cu3(TAA)3Cl3 prisms. Since Zn was present as Zn2+ ions in the reaction solution, Cu2SnS3 (CTS) resulted rather than the formation of CZTS when the rounded particles were annealed at 450 ¬oC. Therefore, a successful synthesis of the CZTS powders requires annealing of the solution containing Zn2+ and the precipitate in the same pot. From thermal analyses, crystalline CZTS powders began to form as the annealing temperature was raised above 210 oC. XRD pattern revealed that the CZTS diffraction peaks appeared when the annealing temperature was raised to 250 oC and no other phases were observed. We have also conducted separate experiments involving CuCl2, ZnCl2, SnCl4, CuCl2+ZnCl2, CuCl2+SnCl4 mixture with the TAA respectively and reacted isothermally at 65 oC for 1 h. After the reaction, the solutions were annealed at 190 oC and 250 oC, respectively. When the annealing temperature was increased, following reaction steps resulted: (1) Cu2+ ions were firstly reduced to Cu+ which facilitated Cu2S formation；(2) (NH4)2ZnCl4 → ZnS；(3) (NH4)2SnCl6 → SnS2. The Cu2S reacted with SnS2 to form CTS first, and then CTS reacted with ZnS to form the CZTS powders.

We have combined the tools of organometallic chemistry with those of organic chemistry, and explored methodology and mechanism of palladium and copper-based catalysis. Organometallic chemistry plays a prominent role in industrial and academic laboratories, and developments in this field continue to expand our fundamental understating of chemical reactions. Herein, we report on a specific failure of a palladium-catalyzed coupling reaction, and the subsequent development of alternative copper-based methodologies. We have developed a new cross coupling protocol for the synthesis of unsymmetrical triarylphosphines, using copper-based catalysis. Furthermore, we conducted a thorough investigation into the mechanism of the centuryold Ullmann coupling. Our mechanistic research is based on rational experimental design intended to address fundamental questions regarding copper-based catalysis. One such question is: what is the nature of the reaction intermediate( s); our data is inconsistent with copper(III) intermediates.