Using complexing-agent assisted sol-gel routes, mixed Pd/ceria-alumina and Pd/terbia-ceria-alumina catalysts were prepared. The materials have been characterised by means of ICP-MS, TEM, EDX, XPS, XRD, BET, TPR, TPO and TPD. Catalytic testing was carried out in a temperature programmed mode as well as isothermally, using synthetic exhaust gas mixtures with different air-to-fuel ratios. The obtained results were compared with those of traditionally impregnated Pd/ceria-alumina and PtRh/ceria-alumina. Evaluating the catalysts potential as three-way converters, it has been shown that as a result of the sol-gel preparation chosen, highly homogeneous materials were produced. These had (i) much higher oxygen storage potential (especially at low temperatures, T ≈ 400 - 500K), (ii) improved metal support interactions and (iii) lower CO and propane light-off temperatures (T50%(CO) ≈ 423K, T50%(C3H8) ≈ 593K for R ≥ 1). Under fuel-rich conditions an improved low temperature NO activity was shown for the ceria-containing materials. This was attributed to a ceria-mediated redox mechanism and an improved Pd-ceria interaction for these sol-gel-derived samples. The addition of terbia was found to promote the catalysts propane activity, especially under fuel-rich conditions. The application of the different catalysts as three-way converters has been discussed, with special emphasis on their potential during the cold-start period. In a further set of catalytic experiments, using less complex gas mixtures, a more comprehensive view of the detailed Pd chemistry involved in these new three-way catalysts was obtained.

<p> A computer model is developed to simulate the emulsion copolymerization of styrene/butadiene in perfectly stirred batch, semi-batch or continuous flow reactors. The model considers free radical initiation by a redox mechanism, micellar particle nucleation, radical concentration as -a function of particle size, radical entry rate and termination rate and diffusion controlled termination and propagation reactions. It predicts conversion, copolymer composition, particle number, number and mass average molecular masses and tri- and tetra-functional branch frequencies. A simple method of estimating the particle size distribution is included in the model. Heat balances over the reactor and cooling jacket are considered and proportional-integra control of the reactor temperature is simulated.</p> <p> The model is used to simulate SBR copolymerization and styrene homopolymerization experimental data from the literature. These simulations tested only certain parts of the model and it is concluded that a more complete verification of the model can only be achieved by running a series of designed experiments. Qualitatively, the molecular mass, particle size distribution and reactor temperature predictions appear to be reasonable. The lack of appropriate temperature dependent rate constants currently limits the molecular mass predictions to isothermal conditions.</p> <p> A comparison of semi-batch operating policies designed to control copolymer composition is presented to illustrate the potential application of the model.</p> / Thesis / Master of Engineering (ME)

Molecular electrochemistry has proved to be very useful for characterizing redox reactions and deciphering chemical reaction mechanisms that are associated with electron transfer. It correlates strongly with redox-based medicine. In this study, we investigated the electrochemical behavior of pterocarpanquinones and selenoquinones, in protic and aprotic media, in the absence and presence of oxygen, in order to obtain data regarding their reduction mechanisms, reactivity with oxygen, the analysis of the stability of the electrogenerated intermediates and interactions with biological targets, like DNA. In typical measurements, CVs were recorded in aprotic medium (DMF + TBAPF6) to resemble the cell membrane environment. On the other hand, protic medium mimics the hydrophilic regions of the biological matrixes. This work shows cases of successful pharmacoelectrochemical investigations. In the first case, we investigate the electrochemical behavior of LQB-118, a pterocarpanquinone, which is anticancer and parasiticidal, with biological mechanisms of action related to the formation of ROS and interaction with DNA, among others. The cyclic voltammogram (VC) for LQB-118 in aprotic medium exhibits, at least, four waves. The first two are related to the usual reduction of quinones. The presence of additional waves suggests the clivage of the heterocyclic rings and the generation of additional reducible systems. A spectroelectrochemical investigation revealed the appearance of new absorption bands, which suggest the formation of the transient quinonamethide (QM). The QM was captured with thiophenol. In addition, electrochemical experiments were performed in the presence and absence of oxygen to verify the reactivity with oxygen, after the reduction of LQB-118 and its derivatives, with positive results. Studies with the ssDNA biosensor in solution showed positive interaction with LQB-118 and its electrogenerated products. The interaction of LQB-118 with CT-DNA was also evidenced by the fluorescence quenching technique. In the second case, CV was used to investigate the electrochemical behaviour of the antitumor selenoquinones. The obtained profiles confirmed the presence of two individual redox centres. All the compounds had shown electrochemical activity in the cathodic and anodic portions of the CVs. We also studied the behaviour of the compounds in protic medium. Electrochemical methods do well to predict the mechanism for adduct formation, structural rearrangement, generation of reactive oxigen species of pterocarpanquinones and appear well-adapted to explore redox pathways of all the compounds in vitro to be correlated to in vivo studies. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A eletroquímica molecular tem se mostrado muito útil para caracterizar reações redox e decifrar mecanismos reacionais associados à transferência de elétrons. Relaciona-se fortemente com a medicina redox. Neste estudo, investigou-se o comportamento eletroquímico de quinonas híbridas, tais como pterocarpanoquinonas e selenoquinonas, em meios prótico e aprótico, na ausência e presença de oxigênio, a fim de obter dados sobre seus mecanismos de redução e oxidação, reatividade com oxigênio, análise da estabilidade dos intermediários eletrogerados e interações com alvos biológicos importantes, como os tióis e o DNA. Em medidas típicas, os voltamogramas cíclicos (VCs) foram registrados em meio aprótico (DMF + TBABF6), para se assemelhar ao ambiente lipofílico, típico de membranas celulares. Por outro lado, o meio prótico mimetiza regiões hidrofílicas das matrizes biológicas. Este trabalho descreve dois casos de investigações farmacoeletroquímicas bem-sucedidas. No primeiro caso, investigou-se o comportamento eletroquímico da LQB-118, uma pterocarpanoquinona antitumoral e parasiticida, com mecanismos de ação relacionados à formação de espécies reativas de oxigênio (EROs) e interação com DNA, entre outros. Estudou-se também as pterocarpanoquinonas derivadas da LQB-118, mais precisamente seus derivados clorado, bromado e nitrado. O voltamograma cíclico (VC) para a LQB-118, em meio aprótico, exibe, pelo menos, quatro ondas catódicas. As duas primeiras são relacionadas com a redução habitual de quinonas. A presença de ondas adicionais sugere a quebra de anel heterocíclico e a geração de sistemas redutíveis adicionais. Investigação espectroeletroquímica revelou o surgimento de novas bandas de absorção, as quais sugerem a formação do quinonametídeo (QM) transiente. O QM foi capturado com tiofenol. Além disso, experimentos eletroquímicos foram realizados na presença e na ausência de oxigênio para verificar a reatividade com oxigênio, após a redução de LQB-118 e seus derivados, com resultados positivos. Estudos com o sensor de ssDNA, em solução, mostrou interação positiva com LQB-118 e seus produtos eletrogerados. A interação de LQB-118 com CT-DNA também foi evidenciada através da técnica de quenching de fluorescência. No segundo caso, a voltametria cíclica foi utilizada para investigar o comportamento eletroquímico de selenoquinonas antitumorais. Os perfis obtidos confirmam a presença de dois centros redox individuais. Todos os compostos mostraram atividade eletroquímica nas regiões anódica e catódica dos VCs. Estudou-se também o comportamento dos compostos em meio prótico e foi observada a formação de selenóxidos. Métodos eletroquímicos se mostraram adequados para prever rearranjos estruturais, formação de adutos, geração de espécies reativas de oxigênio, no caso de pterocarpanquinonas e para explorar caminhos redox in vitro das outras séries, correlacionando-se aos estudos in vivo.

Despite their increasing usefulness in a wide variety of applications, organic electrochemical transistors still lack a comprehensive and unifying physical framework able to describe the current-voltage characteristics and the polymer/electrolyte interactions simultaneously. Building upon thermodynamic axioms, we present a quantitative analysis of the operation of organic electrochemical transistors. We reveal that the entropy of mixing is the main driving force behind the redox mechanism that rules the transfer properties of such devices in electrolytic environments. In the light of these findings, we show that traditional models used for organic electrochemical transistors, based on the theory of field-effect transistors, fall short as they treat the active material as a simple capacitor while ignoring the material properties and energetic interactions. Finally, by analyzing a large spectrum of solvents and device regimes, we quantify the entropic and enthalpic contributions and put forward an approach for targeted material design and device applications.

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