Made available in DSpace on 2016-08-19T12:56:32Z (GMT). No. of bitstreams: 1 GILVAN PEREIRA DE FIGUEREDO.pdf: 11579757 bytes, checksum: dda638ee3ac748c09fb726ca60cc9e98 (MD5) Previous issue date: 2010-03-12 / The State of the Maranhão, Northeast of Brazil, has large occurrences of clays and zeolites. Nevertheless, these materials are not commercially exploited, due to lack of studies on its mineralogical and chemical composition. In this context, the objective this paper has as to study the physico-chemical features, particularly textural and structural properties and surface acidity of some natural clays and zeolites from the State of Maranhão. Thirteen samples of clays and four of zeolites were collected in Governador Edson Lobão, Montes Altos, Barra do Corda, Presidente Dutra, Grajaú, Codó and Carolina. All materials were characterized by X ray diffraction (XRD), X ray fluorescence (XRF), thermal analysis (TGA/DTA/DSC), N2 and n-butylamine adsorption/desorption. The obtained results revealed that the clays are, under a mineralogy view point, constituted by, basically, smectites and kaolinites, being some of these solid composites for 100% of sand and another one for a mixture of minerals of iron and clay, showing diversified chemical compositions and specific areas which varying from 2 m2/g until 85 m2/g. The zeolites showed to be structurally similar with a mixed mineralogical composition, presenting stilbite phases as well as smectite, with quite low specific areas (5 m2/g until 13 m2/g). Zeolites revealed to be more acidic than the clays. However, it should be emphasized that the surface acidity of all clays is also significant, being characterized by strong acid sites. In the particular case of the smectites, mainly of A5 sample, it was verified that the chemical activation, through acid treatment, modified its crystalline structure and increased its specific area for 136,53 m2/g. The adsorption capacity of the acid-activated clays had been more of natural clays and in some cases, these values had been similar to those gotten when using commercial clays. In a general way, this study indicates that the evaluated solids can be applied as adsorbents, as catalysts and as raw materials for refractory and ceramics production. / O Estado do Maranhão, Nordeste do Brasil, possui diversas ocorrências de argilas e de zeólitas. Apesar disso, esses materiais não são explorados comercialmente, devido à falta de estudos sobre sua composição mineralógica e química. Diante disso, este trabalho tem como objetivo estudar as características físico-químicas, especialmente as propriedades texturais e estruturais e acidez superficial de algumas argilas e zeólitas naturais do Estado do Maranhão. Foram coletadas treze amostras de argilas e quatro de zeólitas, nos municípios de Governador Edson Lobão, Montes Altos, Barra do Corda, Presidente Dutra, Grajaú, Codó e Carolina. Os materiais foram caracterizados por DRX, FRX, TGA/DTA/DSC, adsorção/dessorção de N2 e de n-butilamina. Os resultados obtidos revelaram que as argilas são mineralogicamente constituídas por, basicamente, esmectitas e caulinitas, sendo alguns desses sólidos compostos por quase 100% de areia e outro por uma mistura de minerais de ferro e argila, apresentando composições químicas variadas e áreas específicas que vão de 2 a 84 m2/g. As zeólitas são estruturalmente semelhantes, de composição mineralógica mista, apresentado estruturas de estilbita cálcica e esmectita, com áreas específicas bastante baixas (5 m2/g a 13 m2/g). As zeólitas mostraram-se muito mais ácidas do que as argilas. Porém, deve-se ressaltar que a acidez superficial das argilas é também apreciável, possuindo sítios ácidos mais fortes. No caso particular das esmectitas, principalmente da amostra A5, verificou-se que a ativação química, através de tratamento ácido, modificou sua estrutura cristalina e aumentou sua área específica para 136,53 m2/g. A capacidade de adsorção das argilas ativadas foram superiores a das argilas naturais e em alguns casos, esses valores foram semelhantes àqueles obtidos ao empregar argilas comerciais. De um modo geral, este estudo indica que os sólidos avaliados podem ser aplicados tanto como adsorventes e catalisadores quanto como matérias-primas para a produção de material cerâmico e refratário.

O objetivo deste trabalho consistiu na caracterização das zeólitas Y e ZSM-5, usando a técnica de Espectroscopia de Alta resolução em sólidos por Ressonância Magnética Nuclear (RMN). Os espectros de alta resolução do 13C e 27Al foram obtidos usando, simultaneamente, as técnicas de desacoplamento em alta potência (DEC) e rotação da amostra em torno de ângulo mágico (MAS). Utilizamos os espectros de alta resolução dos núcleos de 27Al para analisarmos a coordenação e a quantificação dos alumínios estruturais e extra-estruturais em zeólitas Y e de 13C para analisarmos o posicionamento de moléculas direcionadas localizadas nos canais da ZSM-5 / The objective of this work consisted of the characterization of zeolites Y and ZSM-5, using Solid State High Resolution Nuclear Magnetic Resonance Spectrsocopy. The 13C and 27Al high resolution spectra were obtained using simultaneously, High Power Decoupling (DEC) and Magic Angle Spinning (MAS). The high resolution 27Al spectra were used to distinguish and quantify framework and non-framework aluminium in zeolites Y. The high resolution 13C spectra were used to probe the position and configuration of the guest organic molecules within the framework of the ZSM-5 zeolite

Orientador: Heloise de Oliveira Pastore / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-21T05:07:04Z (GMT). No. of bitstreams: 1 Pietre_MendelssolmKisterde_D.pdf: 10147011 bytes, checksum: bc8b63b205099dec1b50bf41ce37c4ef (MD5) Previous issue date: 2012 / Resumo: O presente trabalho descreve a síntese e esfoliação dos precursores lamelares [V,Al]-PREFER e [V,Al]-Nu-6(1), onde os elementos Al e V foram inseridos diretamente na síntese. Difração de raios-X, fisissorção de N2 e Si-MAS-RMN confirmaram o sucesso da esfoliação. A manutenção da entidade zeolítica foi observada por FTIR, através da presença dos anéis duplos, enquanto que a presença de Al tetraédrico, responsáveis pelos fortes sítios ácidos de Bronsted, foi confirmado por Al-MAS-RMN. Através das técnicas espectroscópicas, V-MAS-RMN e UV-Vis, observa-se que diferentes tratamentos conduzem a formação de espécies com ambientes distintos de vanádio. Para os catalisadores obtidos a partir do tratamento em meio alcalino, observou-se somente espécies de vanádio tetracoordenado com a estrutura. Por outro lado, os materiais derivados do processo em meio ácido, geram sítios octaédricos de vanádio, localizados fora da rede. A questão do acesso foi confirmada pela reação de desidratação da xilose. Os materiais esfoliados foram mais eficientes do que os respectivos zeólitos Nu-6(2) e ferrierita, evidenciando que os sítios ácidos estão mais facilmente acessíveis a moléculas volumosas. A sondagem da bifuncionalidade dos catalisadores [V,Al]-lTQ-6 e [V,Al]-lTQ-18 foi feita através da reação de oxidação e desidratação da molécula de etanol. Observou-se a formação majoritária de produtos de desidratação (éter etílico + etileno) mostrando a maior atividade dos sítios ácidos. Nos sólidos [V,Al]-lTQ-6(B), o processo que governa a formação do acetaldeído é o tipo de sítio de vanádio presente e não a composição química como se esperava. Por outro lado, na reação do etanol com os sólidos [V,Al]-lTQ-6(B), mesmo apresentando maior teor de vanádio, a seletividade ao acetaldeído é menor do que observado para os catalisadores [V,Al]-lTQ-6(B). Nesse caso, há a provável contribuição das ligações V-O-Si que conduz a reação para a formação de éter etílico, diminuindo a seletividade ao acetaldeído / Abstract: This work describes the synthesis and delamination of the [V,Al]-PREFER and [V,Al]-Nu-6(1) layered zeolites, where Al and V were directly inserted into the zeolitic framework. X-ray diffraction, N2 physisorption and Si-MAS-NMR confirmed the delamination success. The maintenance of zeolitic entities was verified by FTIR through double rings presence, whereas the tetrahedral Al sites presence, responsible by strong Bronsted acid sites, was confirmed by Al-MAS-NMR. Such observed by V-MAS-NMR and UV-Vis spectra, different treatments leads to the formation of distinct vanadium sites. Tetrahedral vanadium sites are obtained for the catalysts from alkaline treatment only. In the other hand, extraframework vanadium sites are generated for the samples derivates from acid treatment. As observed by xylose dehydration reaction, delaminated solids were more efficient than Nu-6(2) and ferrierite zeolite, showing that the acid sites are more exposed and, consequently, easily accessible to bulky molecules. The bifunctionality of the [V,Al]-lTQ-6 and [V,Al]-lTQ-18 catalysts were probed by ethanol oxidation and dehydration. It was observed the majority formation of dehydration product (diethyl ether + ethylene) showing the best activity of the acid sites. It was verified, for [V,Al]-lTQ-6(B) catalysts, that specific structural arrangements of the vanadium sites present in the delaminated layers is determining for catalysts activity than just chemical composition, particularly the amount of vanadium, which could be expected as responsible for the generation of redox sites potentially active. In the other hand, for [V,Al]-lTQ-18(B) catalysts, presented lower acetaldehyde selectivity, even with higher amounts of vanadium. One possible explanation can be due the contribution of Si-O-V bonds leading the reaction to the diethyl ether formation, lowering the acetaldehyde selectivity / Doutorado / Quimica Inorganica / Doutor em Ciências

Nous avons exploré les potentialités de la RMN 14N à l'état solide pour étudier l'ordre et le désordre local dans les zéolithes structurées à l'aide des cations de tétraalkylkammoniums. Cette étude est effectuée en combinant les approches expérimentales et théoriques. Les halogénures de tétraalkylkammonium CnH2n+1+X- (n : 1–4 ; X : Br, I) considérés comme des cristaux modèles, sont étudiés dans une première partie. Nous avons pu corréler des aspects structuraux spécifiques (distorsion des angles CNC, répartition spatiale des anions) aux paramètres spectroscopiques de l'interaction quadripolaire 14N.Dans une deuxième partie, nous décrivons l'ordre local dans la silicalite-1 (MFI), en nous basant notamment sur les paramètres de l'interaction quadripolaire 14N. Des variations chimiques au niveau des agents minéralisateurs ou structurants ont des effets mesurés sur ces paramètres qui peuvent être corrélés à l'ordre local au niveau de l'agent structurant et de la charpente minérale. Des modélisations théoriques effectuées à T = 0 et 300 K ont permis de mieux comprendre ces systèmes.Enfin, dans une troisième partie nous avons démontré la sensibilité des paramètres RMN de l'azote-14 à la distribution des sites actifs (Al, B) dans la zéolithe ZSM-5 en utilisant une large palette d'expériences RMN et de calculs théoriques.Ce travail a permis pour la première fois d'établir l'intérêt de la RMN 14N pour l'étude de l'ordre local dans les zéolithes et de montrer les principales informations qui peuvent en être tirées. / We explored the 14N solid state NMR potential to study the local order and disorder in zeolites structured using tetraalkylkammonium cations. This study is performed by combining experimental and theoretical approaches.Tetraalkylkammonium halides CnH2n+1+X- (n: 1-4, X: Br, I) considered as crystal models are studied in the first part. We were able to correlate specific structural aspects (CNC angles distortions, anions spatial distribution) to the 14N NMR parameters. In the second part, we describe the local order in the silicalite-1 (MFI), based in particular on the 14N quadrupolar parameters. Chemical variations in mineralizing or structure directing agents have effects on these measured parameters which can be correlated to the organic and inorganic local orders. Theoretical modeling carried out at T = 0 and 300 K led to a better understanding of these systems. Finally, in the third part we have demonstrated the sensitivity of 14N NMR parameters to the distribution of active sites (Al, B) in ZSM-5 zeolites using a wide range of NMR experiments and theoretical calculations.This work allowed to establish for the first time the interests of 14N NMR to study the local order in zeolites and display key information that can be extracted.

A l’heure actuelle, la réduction de l’impact environnemental de l’industrie chimique est un enjeu majeur. Pour parvenir à ce but, le concept de Chimie Verte, né dans les années 90, cherche à promouvoir les réactions catalysées et notamment l’utilisation de catalyseurs hétérogènes. L’objectif de cette thèse a été d’utiliser des zéolithes, aluminosilicates microporeux, dopées avec un métal, pour des applications en synthèse organique, et notamment dans une synthèse multi-étapes. Ce type de catalyseur hétérogène est intéressant car il est potentiellement recyclable, facile à séparer du milieu réactionnel et stable.Afin d’atteindre notre objectif, la synthèse totale de l’acortatarine A a été effectuée en utilisant lors d’une étape, une zéolithe dopée avec du cuivre pour former un N-alcynylpyrrole et lors d’une autre étape, une zéolithe dopée avec de l’argent pour effectuer une spirocétalisation. Dans un premier temps, les méthodologies liées à ces deux réactions ont été étudiées puis dans un second temps, en se basant sur les connaissances acquises, la synthèse totale de l’acortatarine A a été effectuée avec succès. Il est à noter que lors de cette synthèse, deux étapes additionnelles ont été réalisées avec des zéolithes acides. A travers cette synthèse nous avons montré que les zéolithes dopées avec des métaux qui entrent pleinement dans le cadre de la Chimie Verte, peuvent être des outils très attractifs dans les synthèses multi-étapes. / Nowadays, reduction of the environmental impact of the chemical industry is a major challenge. To reach this goal, Green Chemistry was born in the 90s where catalysis plays an essential role especially with heterogenous catalysts. The aim of this PhD thesis was to use a support (zeolite) doped with a transition metal in organic synthesis and more specifically in a multi-step synthesis. These heterogeneous catalysts are interesting because they are potentially recyclable, easy to separate from reaction medium and stable. In order to reach our goal, we have performed the total synthesis of acortatarin A performing a step with a copper doped zeolite to form a N-alcynylpyrrole and in another step, a silver doped zeolite was used in a spiroketalization. The methodology linked to these two steps was firstly studied and then gained knowledge was successfully applied in the total synthesis of acortatarin A. Moreover, two additional steps were carried out with acidic zeolites during the synthesis. Through this total synthesis, we have demonstrated that metal-doped zeolites can be very attractiveto perform multi-step synthesis.

Les zéolithes, aluminosilicates cristallins poreux, sont des catalyseurs acides hétérogènes très largement utilisés dans l’industrie chimique. Ces catalyseurs permettent de répondre très précisément à de nombreuses exigences économiques et environnementales contemporaines. Pour cela, les zéolithes s’appuient sur des propriétés uniques, comme la sélectivité de forme, ou encore la présence d’une double acidité de Lewis et de Brønsted, pour offrir de nouveaux outils à la synthèse organique. Ce sont plus de 230 structures qui ont été décrites à ce jour mais ce sont bien des centaines de milliers d’assemblages possibles, ce qui laisse un vaste choix quant à l’expansion de cette recherche. Dans ce travail, nous avons cherché à (i) mieux comprendre la cristallisation des zéolithes en présence d’un déchet issu de l’industrie sucrière, la bagasse de canne à sucre ; (ii) pour cela, différentes techniques ont été employées et développées afin de permettre une caractérisation précise de chaque zéolithe, notamment leur acidité, paramètre clé de leur réactivité ; (iii) une fois bien identifiés, ces catalyseurs ont été engagés dans des réactions modèles, une réaction de Diels-Alder ainsi qu’une acylation de Friedel-Crafts. Ainsi, un catalyseur le plus « idéal » possible regroupant toutes les propriétés requises aura pu être conçu sur mesure. Cette thèse s’essaie à une meilleure compréhension de la croissance cristalline des aluminosilicates poreux, et cela, via la synthèse de différentes zéolithes dont les propriétés intrinsèques sont optimisées puis utilisées de façon à obtenir les meilleurs résultats dans des réactions de catalyse acide ; en accord avec la chimie verte et ses préceptes. / Zeolites are crystalline porous aluminosilicates and useful heterogeneous catalysts in chemical industries. They represent one of the significant solutions to main environmental concerns. Thanks to their particular properties like shape selectivity and intrinsic acidities of Lewis and Brønsted, zeolites offer unbeatable abilities in organic synthesis. More than 230 structures have already been discovered, which afford thousands discovery and offer a lot of possibilities.This work was focused on (i) a better understanding of zeolite crystallisation in the presence of an additional component from sugar industry, sugarcane bagasse; (ii) several characterization techniques have been used for a precise structure – properties understanding, mainly for their acidity; (iii) tailored-made catalysts have been tested in model reactions like Diels-Alder and Friedel-Crafts acylation. Hence, optimal catalysts exhibiting required properties could be prepared. This Thesis also aimed to explain zeolite crystallization thanks to sacrificial additional template.BEA, MFI, FAU and LTA zeolites have been prepared then optimized for catalytic testing in different reactions, while keeping in mind the Green Chemistry concept.

Dans le cadre de cette thèse, des techniques avancées de Microscopie électronique à transmission (MET)ont été utilisées dans le but de caractériser et de fabriquer de nouveaux nanomatériaux pour des applications dans les domaines de la nanoélectronique et de la catalyse. Trois types de matériaux fonctionnalisés sont étudiés: le graphène multifeuillets (FLG– Few-Layer Graphene) avec des nanomotifs,des nanotubes de carbone (CNTs - Carbon Nanotubes en anglais) et des zéolithes mésoporeux. La formation de nanomotifs de tranchées et de tunnels sur des flocons de FLG à l’aide de nanoparticules(NPs) de fer est étudiée dans une approche qui combine la tomographie électronique et la MET environnementale. Le rôle des facettes de la nanoparticule et des paramètres topographiques de FLG a été déterminé du point de vue quantitatif, ce qui a mené à la mise en évidence du mécanisme de formation des nanomotifs de tranchées et de tunnels. Le transfert de nanoparticules à base de métal entre deux nanostructures de carbone a été également étudié, en temps réel, en employant un porte-échantillon MET couplé avec un dispositif STM (Scanning Tunneling Microscope en anglais). Le protocole de contrôle du transfert des nanoparticules, les transformations chimiques et structurales subies par celles-ci, le mécanisme de croissance de nouvelles nanoparticules et d’autres phénomènes liés à ces effets ont été étudiés avec attention. La dernière partie de la thèse est centrée sur l’étude de la tomographie électronique à faible dose de la porosité induite dans deux classes de zéolithes, ZSM-5 et zéolithe Y, en utilisant un traitement chimique novateur à base de fluor. / In this thesis, advanced Transmission Electron Microscopy (TEM) techniques are used to characterize and fabricate new nanomaterials with applications in nanoelectronics and catalysis. Three types of functionalized materials are investigated: nanopatterned few-layer graphene (FLG), carbon nanotubes(CNTs) and mesoporous zeolites. The nanopatterning process of FLG flakes by iron nanoparticles (NPs) is studied using an approach combining electron tomography (ET) and environmental TEM. The role of the nanoparticle faceting and of the FLG topographic parameters has been quantitatively determined leading to the first determination of the operating mechanism of the patterning process. The mass transfer of metallic-based NPs between two carbon nanostructures was studied as well in real-time by using a TEMSTMholder. The protocol of controlling the mass transfer, the chemical and structural transformations of the NPs, the growth mechanism of the new NPs and other related phenomena were carefully investigated.The last part deals with the low-dose ET investigation of the porosity induced in two classes of zeolites,ZSM-5 and zeolite Y, by an innovative fluoride-based chemical treatment.

Diffusion is a fundamental process which occurs in a wide variety of phases. It plays an important role in chemistry, physics, biology, materials science etc. In recent times, diffusion in confined systems has been widely investigated. Porous aluminosilicates such as zeolites, carbon nano tubes and metal organic frameworks(MOF) provide confined regions within which small molecules can diffuse. Indeed, diffusion within these materials have attracted considerable attention in the past few decades (see for example, “Diffusion in Zeolites and Other Microporous Solids”, J. Ka¨rger and D..M. Ruthven, John Wiley &Sons, NewYork,1992). Diffusion in confined spaces exhibits rich variety. For example, single file diffusion, window effect, levitation effect (LE), super-and sub-diffusive motion have all been observed in confined regions. Levitation effect provides an explanation for the dependence of self-diffusivity on the diameter of the diffusant. Consider a diffusant diffusing within a porous material. The pore network provided by the pore material may be characterized by the void and the neck distribution where the necks are the narrower regions interconnecting larger voids. It has been seen that diffusivity is maximum when the size of the diffusant is large and when it is comparable to the diameter of the bottleneck of the pore network. Recently it has been demonstrated that the levitation effect also exists in dense liquids such as water and dense solids. These developments essentially unify our understanding of diffusion in widely differing condensed matter phases. These results show that there is fundamentally no difference between porous substances and dense media at least with regard to dependence of self-diffusivity on the diameter of the diffusant. Chapter 1 provides a brief introduction to the subject of hydrocarbons confined within zeolites and ionic conductivity in polar solvents. We have given a description of the different applications of zeolites in the area of catalysis, separation etc. Window effect, single file diffusion, levitation effect and enhancement of viscosity of confined fluids are described. A brief review of various computational studies of hydrocarbons confined within zeolites is given. This is followed by a discussion of different experimental techniques and their use in the study of diffusion and adsorption within zeolites by many different groups in the last few decades. In the last section of the chapter we have discussed the anomalous size dependence of ionic conductivity in polar solvents which presumably has its origin in the Levitation Effect(LE). We have explained different theories proposed previously to understand the non-monotonic behavior of ionic conductivity as a function of ionic radius. A molecular dynamics(MD) investigation and quasi-elastic neutron scattering (QENS) study of pentane isomers in zeolite NaY is pre-sented in Chapter 2. QENS provides the first direct experimental evidence for LE. In an earlier study, a maximum in diffusivity as a function of the diameter of the diffusant for monatomic sorbates confined within zeolite NaY was observed by MD simulation. Since LE has been invoked to explain the diffusion in a wide variety of condensed matter phases, an experimental evidence of the levitation effect would be of great value. QENS measurements were carried out by Dr. Herve Jobic. Surprisingly we found that neopentane shows higher diffusivity than n-pentane and isopentane although its cross-sectional diameter perpendicular to the long molecular axis is larger compared to isopentane and n-pentane in agreement with predictions of LE. There is an excellent agreement between QENS results and MD simulation. LE predicts that the isomer with high diffusivity has low activation energy. The activation energies have been calculated from the Arrhenius plots using QENS as well as MD data. These follow the order Ea(n−pentane)>Ea(isopentane)>Ea(neopentane). Various other properties such as potential energy barrier at the bottleneck, velocity auto correlation function, intermediate scattering function, k dependence of the width of the dynamic structure factor have been computed. These provide additional insights into the nature of the motion of these isomers. They suggest that the barrier at the 12-ring window depends on the molecular diameter and levitation parameter of isomer. In Chapter 3, we report molecular dynamics simulation study of n-hexane and 2,2-dimethylbutane(DMB) mixture confined within the pores of zeolite NaY. We have taken an equimolar composition of the mixture consisting of n-hexane and DMB. The total number of hydrocarbon molecules in the system is 128. The simulations were carried out at various temperatures of 170, 200, 250 and 300 K. We have computed the self-diffusivities from the slope of the mean square displacement. It is found that the diffusivity of DMB is 0.82 ×10−9 m2/sec and that of n-hexaneis0.38 ×10−9 m2/sec. All previous studies of linear hydrocarbon and its branched analogue in different zeolites in the literature suggest that it is the linear member which has higher self-diffusivity. The cross-sectional diameter of DMB perpendicular to the long molecular axis is higher than that of n-hexane. Thus, DMB should have lower diffusivity. In order to understand this behavior of diffusivity we have computed the activation energies from the Arrhenius plots. The activation energy of DMB is found to be lower than that of n-hexane. This is inconformity with the levitation effect which states that the molecule with larger diameter comparable to that of the bottleneck diameter has low activation energy. We have also computed the potential energyprofileatthe12-ring window. The potential energy profile shows a barrier for n-hexane and a minimum for DMB at the window. This is in agreement with the previous results on monatomic species. We have computed other properties such as velocity auto correlation function, intermediate scattering function as well as wave number dependence of full width at half maximum of dynamic structure factor. These properties explain in detail the motion of n-hexane and DMB within NaY zeolite. In Chapter 4 molecular dynamics investigation into diffusion of n-decane and 3-methylpentane mixture within zeolite NaY. We have studied an equimolar mixture of n-decane and 3-methylpentane (36 of each) in the supercages of NaY zeolite in such a way that the con-centration is one molecule for every three cages. Simulations were performed at four different temperatures : 300, 350, 400 and 450 K. The distribution and orientation of the molecules inside the cage and at the window plane have been studied. Inside the cage, 3-methylpentane stays more close to the inner surface of the zeolite whereas n-decane prefers to stay close to the center of the cage. Both the species prefer to stay with their long molecular axis parallel to the surface of the zeolite. During passage through the window, 3-methylpentane is closer to the window center than n-decane. The distribution of the angle subtended by the end-to-end vector of the molecule with the normal to the window plane, while the molecular center is in the window plane, shows that 3-methylpentane samples a larger range of orientation than n-decane. This may lead to an entropic barrierfor n-decane. We have computed the diffusivity of both the molecules. Diffusivity of 3-methylpentane is found to be higher than n-decane. This behavior is consistent with the observations made in the last two chapters. The activation energy of 3-methylpentane is found to be 3.17 kJ/mol and forn-decaneitis6.0kJ/mol. This agrees with the prediction of levitation effect. The energy profile a the window shows shallow minimum for both n-decane and 3-methylpentane. Therefore, the energy profile does not describe the nature of motion of the molecules. We have computed the the dihedral angle distribution when the molecule is at the adsorption site and when it is at the window plane. The distributions essentially remain same for 3-methylpentane whereas a considerable change in the distributions is seen for n-decane. The gauche population of n-decane increases at the cost of trans population when it goes from the adsorption site to the window. The lower diffusivity of n-decane can be partly attributed to the change in the dihedral angle. Also, the orientational entropic barrier may be another cause of the slow motion of n-decane. Thus, in the present study the slow motion of n-decane is partly explained by levitation effect and partly by the change in the dihedral angle as well as the entropic barrier. Overall, the results in the last three chapters leads to the main conclusion that the branched isomer will diffuse faster than a linear hydrocarbon in zeolites with 12-ring window such as zeolite NaY. In Chapter 5, diffusion of pentane isomers in zeolites NaX and NaY has been investigated using pulsed field gradient nuclear magnetic resonance(PFG-NMR) and molecular dynamics(MD) techniques respectively. Temperature as well as concentration dependence of diffusivity have been studied. The diffusivities obtained from NMR are roughly an order of magnitude smaller than those obtained from MD. The dependence of diffusivity on loading at high temperatures exhibits a type I behavior according to the classification of K¨arge rand Pfeifer. NMR diffusivities of the isomers exhibit the order D(n−pentane)>D(isopentane)>D(neopentane). The results from MD are in agreement with the QENS results where the diffusivities of the isomers follow the order D(n-pentane)<D(isopentane)<D(neopentane). The activation energies from NMR show Ea(n-pentane)<Ea(isopentane) <Ea(neopentane) whereas those from MD suggest the order Ea(n-pentane) >Ea(isopentane) >Ea(neopentane). The latter follows the predictions of levitation effect whereas those of NMR appears to be due to the presence of defects in the zeolite crystals. The differences between NMR and MD are attributed to the long time and length scales over which NMR samples are probed compared to MD or QENS. Th eresults from these studies suggests that although branched isomer intrinsically have higher diffusivities than linear hydrocarbons in zeolites such as NaY, the presence of defects can effectively annul this higher diffusivity of the branched isomer. Correlation of self-diffusivity and entropy of monatomic sorbates con-fined within zeolite NaY has been investigated in Chapter 6. We have carried out molecular dynamics simulation on monatomic sor-bates within zeolite NaY at 150, 110 and 90 K. As suggested by the Levitation Effect, the self-diffusivity shows a non-monotonic behavior as a function of the diameter of the sorbates. We have computed the entropy of the sorbates of various sizes ranging from 3.07˚ A to 7.0˚ A using the method proposed by Goddard and his co-workers as well as from the radial distribution function. The variation of entropy with the diffusant diameter exhibits a behavior similar to that of the self-diffusivity on diffusant diameter, thereby showing a strong correlation between the entropy and diffusivity. The loss of entropy on adsorption is a minimum for the diffusant with maximum diffu-sivity. This is in agreement with the experimental measurements of Kemball. Thus, entropy follows the prediction of the levitation effect. With decrease in temperature both self-diffusivity as well as entropy show more pronounced maximum as a function of the diameter of the sorbate. The dimensionless diffusivity from three different isotherms follow a Rosenfeld type of excess entropy scaling rule, D∗= Aexp(αSe) where A and α are the scaling coefficients. In Chapter 7 we have investigated the self-diffusivity as well as cor-rected diffusivity of pure methane in faujasite NaY combining quasi elastic neutron scattering experiment and molecular dynamics simu-lation. The QENS experiment carried out at 200 K led to an unex-pected dependence of self-diffusivity on loading for pure methane with the presence of a maximum at 32 CH4/unit cell. This is at variance with previous reports. Typically, diffusivity of a polar species such as methane in a zeolite such as NaY exhibits a monotonic decrease with loading. Molecular dynamics simulation was performed to reproduce this experimentally observed behavior. We could reproduce the diffusivity behavior qualitatively with a maximum at 16 CH4/unit cell. The corrected diffusivities obtained from both experiment as well simulation show similar behavior as the self-diffusivity with maximum at an intermediate loading. The experimental behavior was reproduced only when the interaction of methane with the sodium cation is in-creased suggesting that this interaction may be important. In Chapter8 we have investigated the role of attractive interaction on size dependent diffusivity maximum of ions in water. We have per-formed molecular dynamics simulation of mode lions in water. Earlier study of systems interacting only through van der Waals interaction shows that the size dependent diffusivity maximum or the levitation effect disappears when the attractive term(r−6 term) of the Lennard-Jones potential is put equal to zero. It is not clear whether the absence of the dispersion interaction in a system where there is electrostatic attraction will lead to a size dependent diffusivity maximum. There-fore, two sets of simulations with and without dispersion interaction between the ion and water have been carried out at700Kinorderto understand the influence of the attractive interaction. It is found that the self-diffusivity of the ions indeed exhibits an anomalous maximum as a function of the vanderWaals diameter for both the sets, viz., with dispersion and without dispersion interaction. In fact, the diffusivity maximum is seen to be more pronounced when there is no dispersion interaction. This existence of the maximum in self diffusivity when there is no dispersion interaction between the ion and the water is attributed to the attractive term from electrostatic interactions. De-tailed analysis shows that the solvent shell is more well defined in the presence of dispersion interactions. The velocity auto correlation function shows undulation at short times for the smaller ions indicating rattling motion inside the cage formed by the surrounding water molecules. Smaller ion exhibits a bi-exponential decay while a single exponential decay is seen for the ion with maximum diffusivity in the intermediate scattering function. The solvent structure appears to determine much of the dynamics of the ion. Interesting trends are seen in the activation energies and these can be understood in terms of the Levitation Effect.

Carbochlorination, a solvent-free top-down process, is a novel pathway for the hierarchization of zeolites. In contrast to other methods no further washing steps are required. The employed method should serve as a model system for the “upcycling” of coked and deactivated zeolites accumulated by the industry. In order to establish a basic understanding of the process, zeolite H-Y was taken as a model system and a thorough investigation of important reaction parameters, like chlorination temperature, time and concentration, carbon loading, and Si/Al ratio, was performed. Under optimized conditions, we have been able to hierarchize H-Y with high yield, doubling the mesopore volume while maintaining the crystallinity and surface area.

Philosophiae Doctor - PhD / Coal combustion accounts for 95% of electricity generation in South Africa while globally coal combustion for energy generation stands at 42%. It has been predicted that coal utilization for energy generation will continue due to its low cost and availability in huge quantities in different parts of the world. Additionally brine and gaseous emissions are produced in the power generation and coal combustion processes. In fact, it has been established that CO2 emissions from power plants are the main cause of the green-house effect leading to global warming. Mitigation of the effects of disposal of fly ash, brine and CO2 emissions is critical for sustainable energy generation from coal and environmental protection. The study investigated whether South African coal fly ash could be used for brine remediation and CO2 capture using fly ash based hydrotalcites and zeolites. Four main objectives were investigated. These were; firstly, to compare the natural CO2 capture potential of a power station ash dam with an accelerated ex-situ mineral carbonation process. Secondly, to probe the effect of accelerated ex-situ mineral carbonation on brine quality with regards to major, minor and trace elements concentration. Furthermore, the study investigated the feasibility of synthesizing hydrotalcites from fly ash by optimizing the synthesis parameters such as acid concentration, aging time, aging temperature, pH during aging, crystallization time and crystallization temperature. Finally the study compared the CO2 adsorption capacities of the fly ash based hydrotalcites with fly ash based zeolites NaA, and NaX. The natural carbonation potential of the wet disposed ash dam at Secunda was investigated by coring a 20 year old dam. Three cores (SI, S2 and S3) were obtained by air flush coring the dam along a geophysical line and establishing the geophysical profile of the three cores. The surface of the three cores was of medium resistivity with values between 9.3 and 12.2 nm while the midsections were of low resistivity with values ranging between 4 and 7 nm. The base section of core SI had a resistivity of 28.3 nm, that of S2 was between 16.2 and 21.4 nm and that of S3 between 12.2 and 16.2 nm; implying that SI had the lowest salt load while S3 had the highest salt content. Moisture content was observed to be high deeper down the profiles of S2 and S3 with samples appearing water logged while SI had the highest moisture content at the surface showing the inhomogeneity of the ash dam. The morphology of fresh fly ash taken from the ash collection hoppers at Secunda was observed to be spherical. Weathered ash from the ash dam showed irregularly agglomerated particles while accelerated ex-situ mineral carbonation resulted in the formation of acicular particles of calcite. Fresh ash, weathered ash and the accelerated carbonated ash were all class F with a sum total of silica, alumina and iron oxide totaling more than 70%. A reduction in silica and alumina content with instability of fly ash. Dumping of spent iron catalyst (resulting from the petrochemical operations as Sasol) on the ash dam led to an increase in Fe203 content of the weathered ash. Enrichment of Nb, Sr, Y, Th, Na, Cl, S04, K and S with natural carbonation as well as during accelerated ex-situ mineral carbonation was observed and was due to the contact of ash with brine during these two processes. Reduction of Zr, Rb, Pb, Ni, Co and V content of ash was observed with weathering. Mineralogically, all the ash samples had main phases of mullite, quartz, magnetite and hematite, with weathered and accelerated carbonated ash having additional phases of calcite. The aluminosilicious nature of the three ashes was identified by structural evaluation using Fourier transform infrared analysis which revealed that, bands associated with C-O in-plane and out of plane bending of carbonates was only visible in weathered and carbonated ash.