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.

[ES] Las zeolitas son materiales cristalinos microporosos con canales y tamaños de poro de dimensiones moleculares. La estructura y composición de las zeolitas les confiere interesantes propiedades que permiten su aplicación en una amplia gama de aplicaciones industriales como adsorción, separación o catálisis. La síntesis de zeolitas es la etapa más importante para el control de la estructura y composición de las zeolitas y, por tanto, crítica para la optimización de sus propiedades. Esta tesis se ha centrado en la síntesis de zeolitas utilizando compuestos que contienen fósforo (cationes fosfonio y aminofosfonio) como Agentes Directores de Estructura (P-ADE). El uso de compuestos fosforados influye en la cristalización y propiedades de las zeolitas obtenidas en comparación con las zeolitas obtenidas con cationes de amonio clásicos. Los compuestos fosforados se eligieron debido a su diferente química y estabilidad con respecto a los cationes de amonio clásicos comúnmente usados en la síntesis de zeolitas. Estos aspectos se estudiaron con un estudio comparativo de diferentes cationes de amonio y fosforados. Los compuestos de fósforo utilizados en este trabajo han dado lugar a nuevas estructuras cristalinas (ITQ-58 e ITQ-66) y han abierto nuevas vías de síntesis de zeolitas ya conocidas (RTH, IWV y DON), ampliando su gama de composiciones químicas. La descomposición térmica de los P-ADE confinados dentro de las zeolitas da lugar a la formación de especies de fósforo extra-red que permanecen dentro de los canales y cavidades de las zeolitas. Estas especies modulan las propiedades ácidas y de adsorción de los materiales finales dependiendo de los tratamientos post-síntesis. En este trabajo se ha estudiado una ruta para la incorporación de cantidades controladas de fósforo durante la etapa de síntesis. Esto ha permitido controlar la adsorción y las propiedades ácidas en las zeolitas de poro pequeño, lo que no se puede lograr mediante metodologías de post-síntesis. / [CA] Les zeolites són materials cristal·lins microporosos amb canals i mides de porus de dimensions moleculars. L'estructura i composició de les zeolites els confereix interessants propietats que permeten la seua aplicació en una àmplia gamma d'aplicacions industrials com adsorció, separació o catàlisi. La síntesi de zeolites és l'etapa més important per al control de l'estructura i composició de les zeolites i, per tant, crítica per a l'optimització de les seues propietats. Aquesta tesi s'ha centrat en la síntesi de zeolites utilitzant compostos que contenen fòsfor (cations fosfoni i aminofosfoni) com a agents directors d'estructura (P-ADE). L'ús de compostos fosforats influeix en la cristal·lització i propietats de les zeolites obtingudes en comparació amb les zeolites obtingudes amb cations d'amoni clàssics. Els compostos fosforats es van triar a causa de la seua diferent química i estabilitat pel que fa als cations d'amoni clàssics utilitzats en la síntesi de zeolites. Aquests aspectes s¿estudiaren amb un estudi comparatiu de diferents cations d'amoni i fosforats. Els compostos de fòsfor utilitzats en aquest treball han donat lloc a noves estructures cristal·lines (ITQ-58 i ITQ-66) i han obert noves vies de síntesi de zeolites ja conegudes (RTH, IWV i DO), ampliant la seua gamma de composicions químiques. La descomposició tèrmica dels P-ADE atrapats dins de les zeolites dona lloc a la for-mació d'espècies de fòsfor extra-xarxa que romanen dins dels canals i cavitats de les zeolites. Aquestes espècies modulen les propietats àcides i d'adsorció dels materials finals depenent dels tractaments post-síntesi. En aquest treball s'ha estudiat una ruta per la incorporació de quantitats controlades de fòsfor durant l'etapa de síntesi. Això ha permés controlar l'adsorció i les propietats àcides en les zeolites de porus petit, el que no es pot aconseguir mitjançant metodologies de post-síntesi. / [EN] Zeolites are microporous crystalline materials with channels and pore openings of molecular dimensions. The structure and composition of zeolites confers them interesting properties that allow their application in a wide range of industrial applications as adsorption, separation or catalysis. The synthesis of zeolites is the most important stage to control the structure and composition of zeolites, and thus, critical to optimize their properties. This thesis has been focused on the synthesis of zeolites using phosphorous containing compounds (phosphonium and aminophosphonium cations) as Organic Structure Directing Agents (P-OSDA). The use of these phosphorous compounds influence the crystallization and properties of the obtained zeolites compared to zeolites obtained with classical ammo-nium cations. Phosphorous compounds were chosen because of their different chemistry and stabil-ity properties respect to classical ammonium cations commonly used in the synthesis of zeo-lites. These aspects were studied in a comparative study with different ammonium and phosphorous cations. The phosphorous compounds used in this work have yielded new crystalline structures (ITQ-58 and ITQ-66) and opened new routes for the synthesis of already known zeolites (RTH, IWV and DON), widening their chemical composition range. The thermal decomposition of the P-OSDAs entrapped inside the zeolites yields to the formation of extra-framework phosphorus species that remain inside the channels and voids of the zeolites. These species modulate the adsorption and acid properties of the final materials depending on the post-synthesis treatments. In this work, a route for the incorporation of controlled amounts of phosphorus during the synthesis stage has been studied. This has allowed to control the adsorption and acid properties in small pores zeolites, which cannot be achieved by post-synthesis methodologies. / I wish to firstly acknowledge the Spanish Government for the necessary funding for the FPI pre-doctoral fellowship (BES-2013-062999). Also, this thesis would not have been possible without the infrastructures provided by the UPV and the CSIC staff, fused into the ITQ. Furthermore, I want to acknowledge the Microscopy Service of the UPV for their support in sample microscopy characterization / Simancas Coloma, J. (2021). Synthesis and Characterization of Zeolitic Materials Using Phosphorous Organic Structure Directing Agents [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/171267 / TESIS

Für die hochselektive technische Trennung von Stoffen hält die Natur eine optimale Lösung namens Zeolithe bereit. In dieser Arbeit wurden Zeolith 4A in Form von Partikeln und wenig permeables Polymer in einer Membran kombiniert. Die Partikel lagen dabei in einer Monolage vor und wurden lediglich seitlich vom Polymer eingefasst, sodass sie beide Oberflächen der Polymerschicht durchbrachen. Diese Einbettung zu so genannten Zeolithkompositmembranen erlaubt einen Stofftransport ausschließlich durch die hochselektiven Zeolithpartikel. Die Herstellung und Charakterisierung der Zeolithkompositmembranen stehen im Mittelpunkt der vorliegenden Arbeit. Für die Membranherstellung kam das Prinzip der partikelassistierten Benetzung einer Wasseroberfläche zum Einsatz. Hierfür wurden die Zeolithpartikel beschichtet und anschließend das unverändert zugängliche Porensystem mittels Thermogravimetrie in Wasseradsorptions-Desorptionsmessungen nachgewiesen. Aus beschichteten Partikeln und passendem Monomer konnten schichtdickenoptimierte Zeolithkompositmembranen hergestellt werden. Es wurde eine Permeabilität P für Wasserdampf von 49 barrer festgestellt, während die Gase Stickstoff und Sauerstoff keinen Transportnachweis zuließen (P < 0,03 barrer). Daraus ergeben sich Selektivitäten von über 1600. Die Durchlässigkeit für Wasser beweist ein offenes Porensystem, die Impermeabilität für Stickstoff und Sauerstoff deutet auf eine sehr geringe Defektdichte hin, was beste Voraussetzungen für Trennmembranen darstellt. Das Herstellungsprinzip soll als Vorlage für die Präparation maßgeschneiderter Kompositmembranen mit wählbarer Porengröße dienen. Vergleiche zu konventionellen Zeolithmembranen belegen, dass die partikelassistierte Benetzung die Methode der Wahl ist, partikelförmiges hochselektives Material optimal einzubetten, ohne die begehrten Permeationseigenschaften zu beeinträchtigen. / An optimal material for highly selective separation processes can be found in zeolites. We prepared composite membranes composed of zeolite 4A particles and a polymer of low permeability. The particles formed a dense monolayer which were embedded into the polymer sheet in such a way that each particle prenetrates both the top and the bottom surface of the sheet. Only this embedding offffers a transport through the highly selective particles exclusively. This work focusses on these so called zeolite composite membranes, on their preparation and characterization. The preparation of the membranes was done via particle assisted wetting on a water surface. Therefore the zeolite particles were coated by a suitable silane agent and a blocking of the pore openings by the coating process was disproved by water adsorption-desorption measurements via TGA. Using the coated particles and a suitable monomer composite membranes could be formed and the optimum thickness was found. The membranes were permeable for water vapor (permeability P = 49 barrer), but impermeable for nitrogen and oxygene (P < 0,03 barrer (detection limit)). This results in a selectivity of above 1600. The permeability for water indicates that the molecules are transported through the zeolite channels. The impermeability for nitrogene and oxygene indicates a very low amount of defects. Furthermore the composite nature of the membrane reduces brittleness thus rendering it a promising candidate for separation technology with tailoring the pore size.

As cinzas leves e pesadas de carvão foram utilizadas na síntese das zeólitas (ZCL e ZCP) por tratamento hidrotérmico alcalino. As zeólitas modificadas de cinzas leves e pesadas (ZMSL e ZMSP) foram preparadas pela mistura de ZCL e ZCP com o surfactante brometo de hexadeciltrimetilamônio. Os adsorventes foram caracterizados por diferentes técnicas, tais como: métodos físico-químicos, fluorescência de raios-X, espectroscopia na região do infravermelho, difração de raios-X e microscopia eletrônica de varredura. O processo de adsorção dos corantes cristal violeta (CV) e do ácido laranja 8 (AL8) foi realizado em sistema de batelada com o objetivo de investigar o equilíbrio e a dinâmica dos materiais zeolíticos no tratamento de efluentes. Os modelos de cinética de pseudo-primeira-ordem e pseudo-segunda-ordem foram aplicados aos dados experimentais e a cinética de pseudo-segunda-ordem descreveu a adsorção dos corantes sobre os adsorventes. Estudos da difusão intrapartícula revelaram que as velocidades de adsorção não eram controladas somente pela etapa de difusão. O modelo de Freundlich ajustou-se melhor aos dados experimentais para todos os sistemas estudados, com exceção do sistema CV/ZCL, que seguiu o modelo de Langmuir. As capacidades máximas de adsorção das zeólitas modificadas foram maiores do que aquelas obtidas para as zeólitas não modificadas. Este melhor desempenho é devido ao ambiente hidrofóbico proporcionado pela adsorção do surfactante catiônico na superfície do adsorvente. Os parâmetros das isotermas de adsorção foram usados para prever o design do equipamento para a realização de processo de adsorção descontínuo de estágio simples. / The coal fly and bottom ashes were used in the synthesis of zeolites (ZFA and ZBA) by alkaline hydrothermal treatment. The modified zeolites from coal fly ash and botton ash (ZMSF and ZMSB) was performed by mixing ZFA e ZBA with the surfactant hexadecyltrimethylammonium bromide. The adsorbents were characterized by different techniques such as: physico-chemical methods, X-ray fluorescence spectroscopy, infrared, X-ray diffraction and scanning electron microscopy. The adsorption of the dye crystal violet (CV) and acid orange 8 (AO8) was carried out in batch system with the purpose of investigating the equilibrium and dynamics of zeolitic materials in wastewater treatment. Pseudo-first- and second-order kinetic models have been applied to the experimental data and pseudo-second-order kinetic was found to describe the adsorption of the dyes on the adsorbents. Intra-particle diffusion studies revealed that the adsorption rates were not solely controlled by the diffusion step. The Freundlich model was better ajusted to the experimental data for all systems studied, except system CV/FTA, which followed the Langmuir model. The maximum adsorption capacities of the modified zeolites were higher than those obtained for the unmodified zeolites. This best performance is due to the hydrophobic ambient provided by the adsorption of cationic surfactant on the surface of the adsorbent. The parameters of adsorption isotherms were used to predict the design of the equipment for performing adsorption discontinuous single stage.

Made available in DSpace on 2014-12-17T15:42:06Z (GMT). No. of bitstreams: 1 ReusTR_DISSERT.pdf: 4094188 bytes, checksum: 4969fc6bf4243a6e241302a399783473 (MD5) Previous issue date: 2013-07-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The synthesis of MFI-type zeolite membranes was carried by the process in situ or hydrothermal crystallization. We studied the homogenization time of the room temperature and gel filtration just before the crystallization step performed out in an oven, thus obtaining a more uniform zeolite film. The powder synthesized zeolite (structure type MFI, Silicalite) was characterized by several complementary techniques such as Xray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis, temperature programmed desorption (TPD), Fourier Transform infrared spectroscopy (FTIR) and textural analysis by nitrogen adsorption (specific surface area). For the purpose of evaluating the quality of the layer supported on the ceramic support, N2 permeation tests were carried starting from room temperature to 600 ?C, where values were observed values more appropriate permeation from 200 ?C. With the data obtained, it was made into a graph of temperature versus permeation function, the curve of surface diffusion was found. For scanning electron microscopy, we observed the formation of homogeneous crystals and the zeolite film showed no fissures or cracks, indicating that the process of synthesis and subsequent treatments not damaged the zeolite layer on the support. Carried permeation studies were found values ranging from 3.64x10-6 to 3.78x10-6, 4.71x10-6 to 5.02x10-6, to pressures 20 and 25 psi, respectively. And the mixture xylenes/N2 values were between 5.39x10-6 to 5.67x10-6 and 8.13x10-6 to 8.36x10-6, also for pressures of 20 and 25 psi. The values found for the separation factor were 15.22 at 400 ?C in the first experiment and 1.64 for the second experiment at a temperature of 150 ?C. It is concluded that the Silicalite membrane was successfully synthesized and that it is effective in the separation of binary mixtures of xylenes / A s?ntese de membranas zeol?ticas do tipo MFI foi realizada pelo processo de cristaliza??o in situ ou hidrot?rmica. Foi estudado o tempo de homogeneiza??o do gel em temperatura ambiente e filtra??o do mesmo antes da etapa de cristaliza??o efetuada em estufa, obtendo-se um filme zeol?tico uniforme. O p? da ze?lita sintetizada (estrutura tipo MFI, Silicalita) foi caracterizado por diversas t?cnicas complementares, como: difra??o de raios X (DRX), microscopia eletr?nica de varredura (MEV), an?lise t?rmica, dessor??o a temperatura programada (TPD), infravermelho por transformada de Fourier (FTIR) e an?lise textural por adsor??o de nitrog?nio (?rea espec?fica). Com a finalidade de avaliar a qualidade da camada suportada sobre o suporte cer?mico, testes de permea??o com N2 foram efetuados partindo da temperatura ambiente at? 600 ?C, onde foram observados valores mais adequados de permea??o a partir dos 200 ?C. Com os dados obtidos confeccionou-se um gr?fico em fun??o da temperatura versus a permea??o, a curva encontrada foi de difus?o superficial. Por microscopia eletr?nica de varredura, observouse a forma??o de cristais homog?neos e que o filme zeol?tico n?o apresentava fissuras ou rachaduras, indicando que o processo de s?ntese e tratamentos posteriores n?o danificaram a camada de ze?lita sobre o suporte. Realizando estudos de permea??o foram verificados valores que variam entre 3,64x10-6 a 3,78x10-6 e 4,71x10-6 a 5,02x10-6, para press?es de 20 e 25 psi, respectivamente. Para a mistura xilenos/N2 os valores foram de 5,39x10-6 a 5,67x10-6 e 8,13x10-6 a 8,36x10-6, tamb?m para press?es de 20 e 25 psi. Os valores encontrados para o fator de separa??o foram de 15,22 em 400 ?C no primeiro experimento e 1, 64 para o segundo experimento em uma temperatura de 150 ?C. Conclui-se que a membrana Silicalita foi sintetizada com sucesso e que a mesma ? efetiva na separa??o de misturas bin?rias de xilenos

Zeolite nucleation and growth is a complex problem that has been widely investigated but still not completely understood. However, a full understanding of this process is required in order to develop predictive models for the rational design and control of the zeolite properties. The primary objective of this dissertation is to determine the strength of organicinorganic interactions (i.e., the adsorption Gibbs energy) in transparent synthesis mixtures using PFG NMR spectroscopy, in order to provide more information for a better understanding of zeolite nucleation and growth. Three main tasks were conducted in this work. The first was an investigation of the organocation role in precursor mixtures of silicalite-1, where the Gibbs energy of the organocation adsorption on the silica particles was determined at 25 degrees C. The findings showed that small changes in the adsorption Gibbs energy resulting from the differences in the molecular structure of the organocations lead to large changes in both the stability of the precursor particles and the rate of silicalite-1 formation. The second was an in situ PFG NMR investigation of silicalite-1 synthesis mixtures, where the adsorption Gibbs energy was determined at 25 degrees C and 70 degrees C, and the time evolution of silicalite-1 was monitored at synthesis conditions. The findings showed similar adsorption Gibbs energies at 25 degrees C and 70 degrees C. Also, a maximum in the organocation diffusion coefficients was observed during the time evolution of silicalite-1, which was associated with the exothermicendothermic transition occurring during the synthesis. The third was a systematic investigation of silicalite-1 precursor mixtures with varying degrees of dilution, where the effect of the composition of the mixtures on their conductivity, pH and particle size distribution (PSD) was studied. The results showed that conductivity, pH, and PSD are strongly affected by the mixture composition. The main conclusion of this research is that the strength of the organic-inorganic interactions in transparent synthesis mixtures can be determined from experimental data of the organocation self-diffusion coefficients obtained with PFG NMR spectroscopy. The outcome information of this research should contribute to the development of a more detailed molecular-level description of the zeolite nucleation and growth, which is expected to allow the emergence of a new generation of materials by design.

LTA-type zeolites with narrow window apertures coinciding with the approximate size of small gaseous molecules such as CO2 and N2 are interesting candidates for adsorbents with swing adsorption technologies due to their molecular sieving capabilities and otherwise attractive properties. These sieving capabilities are dependent on the energy barriers of diffusion between the zeolite pores, which can be fine-tuned by altering the framework composition. An ab initio level of theory is necessary to accurately describe specific gas-zeolite interaction and diffusion properties, while it is desirable to predict the macroscopic scale diffusion for industrial applications. Hence, a multiscale modeling approach is necessary to describe the molecular sieving phenomena exhaustively. In this thesis, we use several different modeling methods on different length and time scales to describe the diffusion driven uptake and separation of CO2 and N2 in Zeolite NaKA. A combination of classical force field based modeling methods are used to show the importance of taking into account both thermodynamic, as well as, kinetic effects when modeling gas uptake in narrow pore zeolites where the gas diffusion is to some extent hindered. For a more detailed investigation of the gas molecules’ pore-to-pore dynamics in the material, we present a procedure to compute the free energy barriers of diffusion using spatially constrained ab initio Molecular Dynamics. With this procedure, we seek to identify diffusion rate determining local properties of the Zeolite NaKA pores, including the Na+-to-K+ exchange at different ion sites and the presence of additional CO2 molecules in the pores. This energy barrier information is then used as input for the Kinetic Monte Carlo method, allowing us to simulate and compare these and other effects on the diffusion driven uptake using a realistic powder particle model on macroscopic timescales. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Les zéolithes représentent une importante classe de catalyseurs hétérogènes largement utilisées dans l’industrie. En effet, ce sont des catalyseurs de choix pour de multiples réactions grâce à leurs propriétés uniques largement modulables, à savoir leur forte acidité de Brønsted, leur grande surface spécifique, leur stabilité hydrothermique et leur sélectivité de forme. Cependant, la taille de leur micropores engendre des difficultés en terme de diffusion, réduisant ainsi leur potentiel catalytique. Ainsi, la conception sur mesure, en fonction de l’application finale, semble être une méthode très intéressante pour le développement de nouveaux catalyseurs zéolithiques.Les travaux réalisés au cours de cette Thèse ont pour objectif la conception de zéolithes à trois échelles : (i) au niveau du site actif en jouant sur la force acide et sur leur accessibilité, (ii) au niveau macroscopique par la taille des cristaux et (iii) au niveau du réacteur en les déposant sur divers supports. Ces différentes zéolithes ont été évaluées dans deux réactions acides : la chloration d’aromatiques et la conversion du méthanol en oléfines légères (MTO).Des zéolithes hiérarchisées ont été synthétisées selon diverses méthodes pré- ou post-Synthétiques et testées dans la chloration du nitrobenzène et du chlorobenzène. De plus, des cristaux « géant » de ZSM-5, préparés par voie fluorure, ont été évalués dans le MTO.La corrélation directe entre l’activité catalytique et les propriétés intrinsèques des zéolithes a permis de souligner les propriétés indispensables à chaque réactions. / Zeolites are aluminosilicate catalysts of great importance for the chemical industries. Their unique properties, i.e., strong Brønsted acidity, high surface area, high hydrothermal stability, and shape selectivity, combined with an extensive tunability, render them the candidate of choice in various reactions. Nevertheless, often only a fraction of their potential is exploited, due to access and diffusion limitation to/in their micropores. In this field, the rational design appears as a valuable method to design new zeolite catalysts, according to their targeted application.The work described in this Thesis aims in the design of zeolites at three levels: (i) acid site by playing on the acid strength and on the accessibility, (ii) microscopic scale by adapting the crystal size and (iii) reactor level by coating zeolite crystals on different supports. These as-Prepared zeolites were evaluated in two acid-Catalyzed reactions: the aromatics chlorination and the conversion of methanol in light olefins (MTO).Hierarchical zeolites were synthesized according to several pre- or post-Synthetic modifications and evaluated in nitro- and chlorobenzene chlorinations. Besides, “giant” ZSM-5 zeolites, prepared according to fluoride-Mediated route, as well as zeolite coatings on β-SiC, were tested in the MTO reaction.Thanks to a direct correlation between catalytic activities and intrinsic properties, optimal catalyst properties were highlighted in both reactions.

As cinzas leves e pesadas de carvão foram utilizadas na síntese das zeólitas (ZCL e ZCP) por tratamento hidrotérmico alcalino. As zeólitas modificadas de cinzas leves e pesadas (ZMSL e ZMSP) foram preparadas pela mistura de ZCL e ZCP com o surfactante brometo de hexadeciltrimetilamônio. Os adsorventes foram caracterizados por diferentes técnicas, tais como: métodos físico-químicos, fluorescência de raios-X, espectroscopia na região do infravermelho, difração de raios-X e microscopia eletrônica de varredura. O processo de adsorção dos corantes cristal violeta (CV) e do ácido laranja 8 (AL8) foi realizado em sistema de batelada com o objetivo de investigar o equilíbrio e a dinâmica dos materiais zeolíticos no tratamento de efluentes. Os modelos de cinética de pseudo-primeira-ordem e pseudo-segunda-ordem foram aplicados aos dados experimentais e a cinética de pseudo-segunda-ordem descreveu a adsorção dos corantes sobre os adsorventes. Estudos da difusão intrapartícula revelaram que as velocidades de adsorção não eram controladas somente pela etapa de difusão. O modelo de Freundlich ajustou-se melhor aos dados experimentais para todos os sistemas estudados, com exceção do sistema CV/ZCL, que seguiu o modelo de Langmuir. As capacidades máximas de adsorção das zeólitas modificadas foram maiores do que aquelas obtidas para as zeólitas não modificadas. Este melhor desempenho é devido ao ambiente hidrofóbico proporcionado pela adsorção do surfactante catiônico na superfície do adsorvente. Os parâmetros das isotermas de adsorção foram usados para prever o design do equipamento para a realização de processo de adsorção descontínuo de estágio simples. / The coal fly and bottom ashes were used in the synthesis of zeolites (ZFA and ZBA) by alkaline hydrothermal treatment. The modified zeolites from coal fly ash and botton ash (ZMSF and ZMSB) was performed by mixing ZFA e ZBA with the surfactant hexadecyltrimethylammonium bromide. The adsorbents were characterized by different techniques such as: physico-chemical methods, X-ray fluorescence spectroscopy, infrared, X-ray diffraction and scanning electron microscopy. The adsorption of the dye crystal violet (CV) and acid orange 8 (AO8) was carried out in batch system with the purpose of investigating the equilibrium and dynamics of zeolitic materials in wastewater treatment. Pseudo-first- and second-order kinetic models have been applied to the experimental data and pseudo-second-order kinetic was found to describe the adsorption of the dyes on the adsorbents. Intra-particle diffusion studies revealed that the adsorption rates were not solely controlled by the diffusion step. The Freundlich model was better ajusted to the experimental data for all systems studied, except system CV/FTA, which followed the Langmuir model. The maximum adsorption capacities of the modified zeolites were higher than those obtained for the unmodified zeolites. This best performance is due to the hydrophobic ambient provided by the adsorption of cationic surfactant on the surface of the adsorbent. The parameters of adsorption isotherms were used to predict the design of the equipment for performing adsorption discontinuous single stage.

>Magister Scientiae - MSc / Millions of tonnes of fly ash are generated worldwide every year to satisfy the large demand for energy. Management of this fly ash has been a concern and various approaches for its beneficial use have been investigated. Over the last two decades, there has been intensive research internationally that has focused on the use of different sources of fly ash for zeolite synthesis.However, most of the studies have concentrated on class C fly ash and very few have reported the use of South African class F fly ash as feedstock for zeolite synthesis.Class F fly ash from South Africa has been confirmed to be a good substrate for zeolite synthesis due to its compositional dominance of aluminosilicate and silicate phases. However, because differences in quartz-mullite/glass proportions of fly ash from different sources produces impure phases or different zeolite mineral phases under the same activation conditions, the present study focused on optimization of synthesis conditions to obtain pure phase zeolite Na-P1 from class F South African coal fly ash. Synthesis variables evaluated in this study were; hydrothermal treatment time (12 - 48 hours), temperature (100 – 160 oC) and addition of varying molar quantities of water during the hydrothermal treatment step (H2O:SiO2 molar ratio ranged between 0 - 0.49).Once the most suitable conditions for the synthesis of pure phase zeolite Na-P1 from fly ash were identified, a statistical approach was adopted to refine the experiments, that was designed to evaluate the interactive effects of some of the most important synthesis variables. In this case, the four synthesis variables; NaOH concentration (NaOH: SiO2 molar ratio ranged between 0.35– 0.71), ageing temperature (35 oC – 55 oC), hydrothermal treatment time (36 - 60 hours) and temperature (130 oC – 150 oC) were studied. The response was determined by evaluating the improvement in the cation exchange capacity of the product zeolite.The starting materials (fly ashes from Arnot, Hendrina and Duvha power stations) and the synthesized zeolite product were characterized chemically, mineralogically and morphologically by X-Ray fluorescence spectrometry, X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. Other characterization technique used in the study were Fourier transform infrared spectroscopy to provide structural information and also monitor evolution of crystallinity during synthesis, as well as cation exchange capacity to determine the amount of exchangeable positively charged ions. Nitrogen adsorption was used to determine the surface area and porosity, and inductively coupled mass spectrometry for multi-elemental analysis of the post-synthesis supernatants.The results from the X-ray diffraction spectroscopy showed that the most pure zeolite Na-P1 phase was achieved when the molar regime was 1 SiO2 : 0.36 Al2O3 : 0.59 NaOH : 0.49 H2O and at synthesis conditions such that ageing was done at 47 oC for 48 hours while the hydrothermal treatment time and temperature was held at 48 hours and 140 oC, respectively. Results from statistically designed experiments show that there was a distinct variation of phase purity with synthesis conditions. From the analysis of linear and non linear interactions, it was found that the main effects were ageing temperature and hydrothermal treatment time and temperature, which also showed some interactions. This experimental approach enabled a clearer understanding of the relationship between the synthesis conditions and the purity of the zeolite Na-P1 obtained.The quality of zeolites is a major determinant in the efficiency of toxic element removal from waste water. Preliminary experiments conducted using optimised zeolite Na-P1 obtained in this study with a cation exchange capacity of 4.11 meq/g showed a high percentage removal of Pb,Cd, Ni, Mn, V, As, B, Fe, Se, Mo Sr, Ba and Zn from process brine obtained from Emalahleni water reclamation plant.In summary, a pure phase of zeolite Na-P1 was obtained from South African class F fly ash feedstock at relatively mild temperature. The systematic approach, incorporating statistical design of experiments, developed in this study resulted in a better understanding regarding the relationships of synthesis parameters in the formation of zeolites from fly ash. The zeolite Na-P1 synthesized with a high cation exchange capacity was effective for removal of toxic elements from brine.