Dissertations / Theses on the topic 'Zeolites characterization'

[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

Zeolites and zeolite membranes are two important advanced chemical materials which are widely used in chemical processes. The manufacture of these materials usually involves the use of expensive chemicals. This study involves the use of Ahoko Nigerian kaolin (ANK) as precursor material for the development of zeolites and zeolite membranes. The synthesis of zeolite A, Y and ZSM-5 was successfully obtained following a sequence, collection of the raw clay from Nigeria, metakaolinization, dealumination and actual hydrothermal synthesis of the zeolites. Raw ANK was refined using sedimentation technique and about 97% kaolin was recovered from the raw sample. A novel metakaolinization technique was developed to convert kaolin into a reactive metastable phase. Amorphous metakaolin was obtained at a temperature of 600°C and exposure time of 10 min. This is a significant result because previous studies use higher temperatures and longer exposure times for the metakaolinization step. The metakaolin was used to prepare a number of different zeolites under various conditions. Highly crystalline zeolite A was obtained at an ageing time of 12 h, crystallization time of 6 h and crystallization temperature of 100oC. Zeolite Y was obtained at an ageing time of 3 h, crystallization time of 9 h and crystallization temperature of 100oC. Zeolite Y was also synthesised by using a dealuminated kaolin and highly crystallized zeolite Y with Si/Al ratio of 1.56 and BET surface area was obtained of 630 m2/g. ZSM-5 was synthesised using an ageing period of 36 h, crystallization time of 48 h and temperature of 140oC. The results obtained from zeolite powder synthesis from ANK were then used as guide to prepare supported zeolite films and membranes by a hydrothermal method. The effect of the support surface (stainless steel) was investigated using two synthesis methods namely modified in-situ and secondary (seeded) growth. Zeolite A, Y and ZSM-5 films were successfully prepared from ANK for the first time and on two modified supports, etched and oxidised. The zeolite films and membranes developed showed complete coverage on the two supports with the oxidised showing better adhesion and intergrowth. The separation performance of the three developed zeolite membrane was tested by pervaporation of water/ethanol mixture. The results of pervaporation of ethanol/water mixture showed that zeolite A membrane is highly selective towards water mainly because of hydrophilic properties occasioned by the high aluminium content. Zeolite Y membrane show a similar response when their separation performance was evaluated but with less selectivity because of reduced aluminium content. ZSM-5 showed selectivity towards ethanol because of it hydrophobicity allowing only ethanol to permeate. In all the zeolite membranes, the flux is lower in comparison to commercial zeolite membranes due mainly to the thickness of the zeolite layer. Oxidised support membranes showed better performance because of their better interaction between the oxide surface and the aluminosilicate gel. The results show that ANK can successfully be used to prepare zeolites and zeolite membrane.

[ES] El Proyecto de investigación aquí descrito se estructura en dos partes. La primera parte se centra en la investigación fundamental con el objetivo de crear un protocolo para la síntesis de zeolitas. La segunda parte se refiere al diseño, síntesis y caracterización de nuevas zeolitas, particularmente utiles para aplicaciones DeNOx,, pero también podría ser útil para aplicaciones MTO. La investigación fundamental sugiere un Nuevo modelo de preparación de zeolitas utilizando otras zeolitas como simiente. Este proceso se llama transformación zeolita-zeolita o también conversión interzeolita. El alto rendimiento obtenido, la rápida cristalización y la mejor utilización y rendimiento de los materiales de partida se han tenido en cuenta para mejorar el proceso en base a un proyecto de doctorado financiado por una empresa. Este método se ha ilustrado utilizando varias zeolitas como semilla, entre otras FAU y CHA, para la preparación de las dos zeolitas objetivo: AEI y AFX. En la segunda parte, la investigación se centra en el diseño de nuevas zeolitas de poro medio. Se han seleccionado tres zeolitas hipotéticas de una base de datos de 933611 estructuras. Esta selección se ha realizado utilizando descriptores específicamente diseñados en base a la aplicabilidad de estas zeolitas en procesos DeNOx zeolitas. A continuación se han buscado los agentes directores de estructura (ADE) más apropiados, con la ayuda de métodos computacionales, algunos de los cuales se han sintetizado posteriormente. El uso de dichos ADE en el gel de síntesis ha permitido la obtención de una zeolita cuya topología (ERI) ha sido identificada mediante análisis por PXRD, y cuya morfología y tamaño de cristal (particularmente pequeño) la hacen muy adecuada para su uso como catalizador en algunos procesos. El trabajo de síntesis también reveló la aparición de una nueva zeolita de alta densidad, llamada 'paracelsio-K'. Este nuevo material se ha obtenido al explorar el espacio de fases que cristalizan al utilizar 1-methyl-DABCO como ADE. La síntesis de esta zeolita tiene un especial interés porque el ADE no se incorpora en los canales de la zeolita, pero más bien influyendo en la nucleación y cristalización. La caracterización reveló que la composición del material es próxima al mineral microcline, estructuralmente cercano al paracelsio, ambos feldespatos. A diferencia de los feldespatos el paracelsio-K contiene moléculas de agua en su interior (1 molécula por cavidad) y puede describirse como el material más simple de la familia de las zeolitas que contiene cadenas del tipo 'doble-cigüeñal'. Utilizando los elementos topológicos correspondientes a esta estructura es posible generar estructuras zeolíticas ya conocidas, como GIS, APC, MER, PHI, SIV y algunas otras zeolitas hipotéticas.
[CAT] El Projecte d'investigació aquí descrit s'estructura en dos parts. La primera part se centra en la investigació fonamental amb l'objectiu de crear un protocol per a la síntesis de zeolites. La segona part es refereix al disseny, síntesis i caracterització de noves zeolites, particularment útils per a aplicacions DeNOx , però també podria ser útil per a aplicacions MTO. La investigació fonamental suggereix un nou model de preparació de zeolites utilitzant altres zeolites com a llavor. Aquest procés s'anomena transformació zeolita-zeolita o també conversió interzeolita. L'alt rendiment obtingut, la ràpida cristal·lització i la millor utilització i rendiment dels materials de partida s'han tingut en compte per millorar el procés en base a un projecte de doctorat finançat per una empresa. Aquest mètode s'ha il·lustrat utilitzant diverses zeolites com a llavor, entre altres FAU i CHA, per a la preparació de les dues zeolites objectiu: AEI i AFX. A la segona part, la investigació se centra en el disseny de noves zeolites de porus mitjà. S'han seleccionat tres zeolites hipotètiques d'una base de dades de 933.611 estructures. Aquesta selecció s'ha realitzat utilitzant descriptors específicament dissenyats sobre la base de l'aplicabilitat d'aquestes zeolites en processos DeNOx zeolites. A continuació s'han buscat els agents directors d'estructura (ADE) més apropiats, amb l'ajuda de mètodes computacionals, alguns dels quals s'han sintetitzat posteriorment. L'ús d'aquests ADE al gel de síntesi ha permès l'obtenció d'una zeolita la topologia (ERI) ha estat identificada mitjançant anàlisi per PXRD, i la morfologia i mida de vidre (particularment petit) la fan molt adequada per al seu ús com a catalitzador en alguns processos. El treball de síntesi també va revelar l'aparició d'una nova zeolita d'alta densitat, anomenada 'paracelsio-K'. Aquest nou material s'ha obtingut a explorar l'espai de fases que cristal·litzen en utilitzar 1-methyl-DABCO com ADE. La síntesi d'aquesta zeolita té un especial interès perquè el ADE no s'incorpora en els canals de la zeolita, però més aviat influint en la nucleació i cristal·lització. La caracterització va revelar que la composició del material és propera al mineral microcline, estructuralment proper al paracelsio, tots dos feldspats. A diferència dels feldspats el paracelsio-K conté molècules d'aigua al seu interior (1 molècula per cavitat) i pot descriure com el material més simple de la família de les zeolites que conté cadenes del tipus 'doble-cigonyal'. Utilitzant els elements topològics corresponents a aquesta estructura és possible generar estructures zeolítiques ja conegudes, com GIS, APC, MER, PHI, SIV i algunes altres zeolites hipotètiques.
[EN] The research project described herein is structured in two parts. The first part is focused on the fundamental research with the aim of creating a toolbox for zeolite preparation. The second part deal with the design, synthesis and characterization of novel zeolites particular useful for DeNOx applications, but could be also useful for MTO applications. The fundamental research is addressing a novel approach of preparing zeolites by using other zeolites as raw materials. This process is known as zeolite-to-zeolite transformation or interzeolite conversion. The high yield obtained, fast crystallization time and the better utilization of the raw materials (e.g. parent zeolite, organic structure directing agent (OSDA)), are important benefits of interzeolite conversion technic, which answer the objectives formulated for an industrial PhD project. The method has been exemplified by using various raw materials as parent zeolites, such as FAU and CHA for the preparation of two target small pore zeolites AEI and AFX. In the second part the focus has been on the design of novel small pore zeolites. Three hypothetical frameworks have been selected by narrowing down a database containing 933611 structures. The selection has been performed by using the general descriptors for the state-of-the-art DeNOx zeolites (e.g. CHA). This was followed by finding suitable OSDAs for the selected frameworks, by using computational methods. The usage of the theoretically predicted OSDAs in synthesis gels made possible the synthesis of a novel high-silica zeolite. PXRD analysis, revealed that the zeolite has the ERI framework topology. The obtained material has a distinct particle morphology and smaller crystallites, which are key parameters for various catalytic processes. The synthesis work revealed also a novel dense zeolite, named K-paracelsian. The new material has been obtained while exploring the phase space using 1-methyl-DABCO as OSDA. The synthesis of this zeolite is especially interesting in the sense that the OSDA is not being incorporated into the zeolite channels, but rather influencing the nucleation and crystallization. Further characterization revealed a material compositionally closely related to the mineral microcline and structurally closely related to the mineral paracelsian, both of which are feldspars. In contrast to the feldspars, K-paracelsian contains intrazeolitic water corresponding to one molecule per cage and can be described as the simplest endmember of a family of dense double-crankshaft zeolite topologies. By applying the identified building principle, a number of known zeolite frameworks (e.g. GIS, APC, MER, PHI, SIV) and hypothetical zeolite topologies can be constructed.
The authors thank Haldor Topsoe A/S and Innovation Fund Denmark for financial support under the Industrial PhD programme (Case no. 1355-0174B). We thank MINECO of Spain for funding (SEV-2016- 0683 and RTI2018-101033-B-100) and ASIC-UPV for the use of computational facilities. We also thank Prof. M. M. J. Treacy for assistance with the Database of Prospective Zeolite Structures.
Boruntea, C. (2020). Design, synthesis and characterization of small-pore zeolites for industrial environmental applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/141094
TESIS

Mesoporous aggregates of nanocrystalline zeolites with MFI and BEA frameworks have been synthesized using a one-pot and single structure directing agent method. The effect of different reaction conditions, such as temperature, time, pH and water content, on the particle size, surface area and mesopore volume has been studied. Nanocrystalline and mesoporous ZSM-5, β and Y zeolites were modified with different transition metals and the resulting single- and double metal containing catalyst materials were characterized. Nanocrystalline Silicalite-1 zeolite samples with varying particle size were functionalized with different organosilane groups and the cytotoxic activity of the zeolite nanocrystals was studied as a function of particle size, concentration, organic functional group type, as well as the type of cell line. Framework stability of nanocrystalline NaY zeolite was tested under different pH conditions. The synthesized zeolites used in this work were characterized using a variety of physicochemical methods, including powder X-ray diffraction, Solid State NMR, nitrogen sorption, electron microscopy, Inductively Coupled Plasma - Optical Emission Spectroscopy and X-ray Photoelectron Spectroscopy.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
The present work deals about the synthesis and characterization of magnetic zeolites obtained by hydrothermal route using kaolin from Brazilian Northeast as silicon and aluminum source. By means of the X-ray diffraction technique it was possible to identify zeolite LTA and zeolite P1 as major crystalline phases for each synthesis, with low intensity peaks referent to unreacted quartz present in the kaolin used, which is in accordance to the. FTIR spectra; the nanoparticles were identified as magnetite, with low intensity peaks referent to goethite. In scanning electron microscopy, however, it was not possible to morphologically identify these minor components, while the zeolites showed well defined morphologies, presenting unchanged morphology when in the composites form, but with nanoparticles dispersed over their surface, as expected. From transmission electron microscopy it was observed that the nanoparticles were of ca. 50 nm. Magnetic measurements indicated magnetite presence with superior diameter to critical diameter to superparamagnetic particles and remanent magnetization. Thermogravimetric analyses showed for the composites, lower mass loss than compared to the pure zeolites what may be associated to the improvement of its thermal stability. Granulometric distribution indicated nanoparticles agglomeration in variable sizes, while zeolites formed agglomerates of ca. 10 Âm. Water softening was accomplished by using both zeolites, with high efficiency on Ca2+ removal and similar behavior between the zeolite and its respective composite, being the best result observed for zeolite A, with efficiency of 97,95%, reaching equilibrium in the first contact minutes. The dependence on mass studies also showed that zeolite A and its composite presented the best efficiency, whereas zeolite P achieved the same removal levels using corresponding zeolite masses (45 mg). This way, the proposed method for zeolites synthesis proved to be efficient, so that the use of a magnet is capable to attract them, leading their excellent separation from the aqueous medium with its ionic exchange capacity unaffected.
O presente trabalho trata da sÃntese e caracterizaÃÃo de zeÃlitas magnÃticas obtidas por impregnaÃÃo de nanopartÃculas de magnetita a zeÃlitas A e P, sintetizadas por mÃtodo hidrotÃrmico utilizando caulim branco do Nordeste brasileiro como fonte de silÃcio e alumÃnio. Por meio da tÃcnica de difraÃÃo de raios-X foi possÃvel identificar como fases cristalinas majoritÃrias a zeÃlita LTA e P1 para cada sÃntese, com picos de baixa intensidade referentes a quartzo, resistente ao processo tÃrmico de tratamento prÃvio do caulim, bem como nos espectros de infravermelho; as nanopartÃculas foram identificadas como magnetita, havendo ainda indÃcios da presenÃa de goethita em pequena quantidade. Nas anÃlises de microscopia eletrÃnica de varredura, entretanto, nÃo foi possÃvel identificar esses componentes minoritÃrios morfologicamente; enquanto que a morfologia das zeÃlitas mostrou-se bem definida, sem alteraÃÃes apÃs a formaÃÃo dos compÃsitos, apenas com nanopartÃculas espalhadas em sua superfÃcie, como desejado. A partir da microscopia eletrÃnica de transmissÃo, pÃde-se observar melhor a variaÃÃo de tamanho das nanopartÃculas, em mÃdia de 50 nm. Medidas magnÃticas das amostras com essa propriedade indicaram a presenÃa de magnetita com diÃmetro superior ao diÃmetro crÃtico para partÃculas superparamagnÃticas e magnetizaÃÃo remanente. As anÃlises termogravimÃtricas mostraram que a adiÃÃo das nanopartÃculas Ãs zeÃlitas diminuiu sua perda de massa diante do aumento de temperatura e as anÃlises de distribuiÃÃo granulomÃtrica indicaram a aglomeraÃÃo das nanopartÃculas em tamanhos variÃveis, enquanto que as zeÃlitas formaram aglomerados de aproximadamente 10 Âm. Os ensaios de abrandamento de Ãguas mostraram alta eficiÃncia das zeÃlitas em remover Ca2+, com comportamento similar entre a zeÃlita e o seu respectivo compÃsito, encontrando para a zeÃlita A o maior percentual de remoÃÃo, de 97,95 %, atingindo equilÃbrio nos primeiros minutos de aplicaÃÃo. Os estudos de massa tambÃm mostraram a eficiÃncia da zeÃlita A e de seu compÃsito, tendo a zeÃlita P se aproximado dos mesmos nÃveis de remoÃÃo em massas referentes a 45 mg de zeÃlita. Assim, o mÃtodo proposto para sÃntese das zeÃlitas magnÃticas mostrou-se eficiente, de modo que a utilizaÃÃo de um Ãmà à capaz de atraÃ-las facilitando a separaÃÃo do meio apÃs a aplicaÃÃo em meio aquoso e sua capacidade de troca iÃnica nÃo foi afetada.

Transition metal containing zeolites (zeolite A and ZSM-5) were prepared by addition of various transition metal containing substrates to zeolite synthesis gels. Crystal growth data were recorded in order to determine the influence of the transition metal species on the rate of crystal growth. X-ray diffraction, oxygen adsorption, FTIR and SEM were utilized to evaluate crystal purity. X-ray photoelectron spectroscopy (XPS), chemical analysis and electron microprobe analysis were performed in order to ascertain the position (intrazeolitic versus surface) and homogeneity of the transition metal. It was concluded that intrazeolitic transition metals were produced by the novel procedure presented in this work. 1-Hexene hydroformylation by rhodium zeolite A showed intrazeolitic rhodium to migrate to the external surface of the zeolite. However, in the presence of a solution and surface rhodium poison, intrazeolitic rhodium was found to hydroformylate 1-hexene exclusively to heptanal. Ruthenium containing zeolite A was evaluated under CO-hydrogenation conditions. No migration of intrazeolitic ruthenium to the external surface of the zeolite was observed over the course of the reaction. The product distribution obtained for this catalyst did not follow a log normal behavior. Also, loss of zeolite crystallinity was observed following the reaction. Cobalt ZSM-5 was evaluated under CO-hydrogenation conditions. No migration of cobalt to the external surface of the zeolite occurred. XPS analysis of the catalyst following various stages of the reaction indicated that intrazeolitic cobalt was not reduced to the zero valent state. Consequently, the non-zero valent cobalt was not capable of hydrogenating carbon monoxide.
Ph. D.

Ce travail visait à développer et à évaluer une nouvelle méthode d'investigation du transport de matière dans les catalyseurs à base de zéolithes. Elle consiste en la combinaison de l'analyse gravimétrique et de la spectroscopie infrarouge. La première permet d'évaluer la diffusion de la phase gazeuse vers toute la porosité, tandis que la spectroscopie IR permet d'évaluer sélectivement la diffusion vers les sites actifs des zéolithes situés dans les micropores, en suivant l'évolution de leur taux couverture par la sonde moléculaire. Une méthode originale de traitement des données, basée sur l'inversion des équations intégrales décrivant les courbes cinétiques d'absorption ou les spectres infrarouges enregistrés au cours de l’adsorption, a également été développée. Ces méthodes ont été appliquées à la caractérisation (i) de mélanges mécaniques modèles de zéolites H-MFI et H-FAU, (ii) de zéolites H-MFI hiérarchisées obtenues par traitement dans un milieu fluorure et (iii) d'un catalyseur composite modèle constitué de Al-MCM-41 et de H-MFI hiérarchisée. Nos résultats montrent que les valeurs relatives des vitesses de diffusion mesurées par analyse gravimétrique et spectroscopie IR sont indicatives de la qualité de la connectivité entre les réseaux méso- et microporeux, et pourraient donc être utilisées pour qualifier les matériaux hiérarchisés à base de zéolithes
This work aimed at developing and benchmarking a new method of investigation of molecular diffusion in zeolite-based materials. It consists in the hyphenation of gravimetric analysis and infrared spectroscopy. The former allows assessing the diffusion from the gas phase to all the porosity, while IR spectroscopy allows for selective assessment of the diffusion to the zeolite active sites located in the micropores by monitoring the evolution of their coverage by the molecular probe. An original method of data processing, based on the inversion of the integral equations describing the uptake curves or infrared spectra has also been developed. These methods were applied to the characterization of (i) model mechanical mixtures of H-MFI and H-FAU zeolites, (ii) hierarchical H-MFI zeolites obtained by treatment in a fluoride medium, and (iii) model composite catalyst made of Al-MCM-41 and hierarchical H-MFI. Our results show that the relative values of diffusion rates as measured by gravimetry and IR spectroscopy are indicative of the quality of connectivity between meso- and microporous networks, and could thus be used to qualify zeolite-based hierarchical materials

L'EU-1 et la MCM-22 sont deux zéolithes à taille de pores intermédiaire, utilisées respectivement pour l'isomérisation de la coupe C8 aromatique et l'alkylation du benzène par des oléfines légères. Leurs propriétés catalytiques originales sont dues à une contribution très importante des sites acides localisés sur leur surface externe. Au cours de ce travail, différentes approches ont été envisagées pour augmenter la quantité ou la proportion de ces sites aux dépends des sites internes. Tout d'abord, une série de zéolithes H-EU-1 partiellement échangées par du sodium a été préparée et caractérisée par voie physicochimique et par des réactions modèles. Comme attendu, l'échange s'accompagne d'une diminution de la concentration en sites acides de Brönsted. Toutefois, une augmentation importante de la quantité de sites acides très forts a été observée pour des taux d'échange de 26 à 35 % et corrélée à l'augmentation de l'activité en craquage du méthylcyclohexane. Par ailleurs, les conversions du m-xylène et du 1,3,5-triméthylbenzène diminuent rapidement pour de faibles taux d'échange, ce qui pourrait s'expliquer par un échange préférentiel des sites acides externes, également mis en évidence dans le cas de zéolithes MCM-22. Enfin, une nouvelle zéolithe de la famille MWW a été synthétisée et caractérisée. Cette zéolithe possède une acidité totale similaire à celle de la MCM-22, mais une proportion de sites acides externes beaucoup plus importante, conduisant à une activité beaucoup plus grande en transformation du m-xylène et du 1,3,5-triméthylbenzène. Cette nouvelle zéolithe pourrait donc constituer une alternative intéressante à la zéolithe MCM-22 en alkylation du benzène
EU-1 and MCM-22 are two 10-ring zeolites used in petrochemical applications such as C8-aromatic cut isomerization and benzene alkylation with short olefins. In all these processes, the original catalytic behaviors of both zeolites are characterized by an important contribution of the acid sites located over the external surface of their crystals. In this work, different methods were investigated in order to increase the amount or the proportion of these acid sites at the expense of those located inside the pores. Firstly, a series of partially Na-exchanged H-EU-1 was prepared and fully characterized through physicochemical techniques and model reactions. As expected, the exchange led to a gradual decrease in the total Brönsted site concentration. Nevertheless, an increase of the concentration in very strong acid sites was obtained for exchange ratio between 26 and 35%, leading to a significant increase of the activity in methylcyclohexane transformation. On the other hand, m-xylene and 1,3,5-trimethylbenzene (135-TMB) conversions decreased rapidly at low exchange ratio, which was attributed to a preferential exchange of the external acid sites. This latter phenomenon was also observed over Na-exchanged H-MCM-22 zeolites. Secondly, a new zeolite belonging to the MWW family was synthesized and characterized. This zeolite was shown to possess the same acid site concentration than MCM-22 zeolite but with a much higher proportion of external sites. In consequence, it exhibited a very high catalytic activity in both m-xylene and 135-TMB transformations. This material could therefore be considered as an alternative to MCM-22 in the benzene alkylation process
EU-1 e MCM-22 são dois zeólitos de poros intermédios utilizados, respetivamente, na isomerização do corte C8 aromático e na alquilação do benzeno com olefinas leves. As suas propriedades catalíticas originais devem-se a uma importante contribuição dos centros ácidos localizados nas superfície externa. Nesta tese, diferentes abordagens foram investigadas com o objetivo de aumentar a quantidade ou a proporção destes centros ácidos em detrimento dos centros internos. Primeiramente, uma série de zeólitos H-EU-1 parcialmente permutados com sódio foi preparada e caracterizada por via físico-química e por reações modelo. Como esperado, a permuta é acompanhada por uma diminuição da concentração em centros ácidos de Brönsted. Contudo, um importante aumento da quantidade de centros ácidos muito fortes foi obtido para taxas de permuta entre 26 e 35% e correlacionado com um aumento da atividade no cracking do metilciclohexano. Por outro lado, as conversões do m-xileno e do 1,3,5-trimetilbenzeno diminuem rapidamente para baixas taxas de permuta, o que pode ser explicado por uma permuta preferencial dos centros ácidos externos. Este último fenómeno foi igualmente observado no caso do zeólito H-MCM-22 permutado com sódio. Por fim, um novo zeólito pertencente à família MWW foi sintetizado e caracterizado. Este zeólito demonstrou possuir uma acidez total semelhante à do zeólito MCM-22, porém com uma muito maior proporção de centros ácidos externos, conduzindo a uma bastante superior atividade nas transformações do m-xileno e do 1,3,5-trimetilbenzeno. Este novozeólito poderá, portanto, representar uma alternativa interessante ao zeólito MCM-22 na alquilação do benzeno

The fibrous zeolite mineral erionite is a concern due to its potential for causing lung disease in humans. Studies have shown that exposure to altered volcanic bedrock containing erionite may be the explanation for a high lung disease rate throughout regions of the world (Metintas et al., 1999). Erionite was reported by Forsman (1986) as occurring in tuffaceous rock units of the Arikaree Formation in the Killdeer Mountains of western North Dakota. Rock and soil samples were collected where zeolite minerals are known or suspected to be present including North and South Killdeer Mountains in Dunn County and West and East Rainy Buttes and White Butte in Slope County. Analysis and identification was carried out using XRD, SEM, and EMPA. Zeolitic material was confirmed in units for both North and South Killdeer Mountains. The chemical compositions of the fibers resulted in a majority being classified as offretite rather than erionite.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Neste trabalho, as zeólitas mordenita, ferrierita e ZSM-5 foram preparadas através de síntese hidrotérmica com a variação dos parâmetros fontes de alumínio e silício, quantidade de água, utilização de sementes, temperatura e tempo de cristalização com a finalidade de obter zeólitas nanocristalinas. As amostras preparadas foram caracterizadas por espectrofotometria de absorção atômica, difração de raios-X com refinamento através do método de Rietveld, adsorção física de N2, microscopia de força atômica, microscopia eletrônica de varredura, microscopia eletrônica de transmissão e ressonância magnética nuclear no estado sólido de 27Al e 29Si. Para se obter um controle do tamanho de cristal foi importante encontrar um equilíbrio entre temperatura e tempo de síntese. A fonte de alumínio mais adequada seria o aluminato de sódio enquanto que a de silício variou de acordo com tipo de zeólita. Foram obtidas amostras de mordenita de tamanho médio de cristalito entre 56 e 292 nm com diferentes percentuais de cristalinidades. As amostras de ferrierita preparadas possuíam tamanho médio de cristalito entre 61 e 82 nm. Já em relação à ZSM-5, foram obtidas uma amostra de tamanho médio de cristalito de 46 nm e uma de 58 nm. Este estudo mostrou a necessidade do conhecimento aprofundado da influência dos diversos parâmetros, individualmente, no processo de cristalização de cada uma zeólitas para se obter um controle eficaz do tamanho da zeólita. Finalmente, foi possível propor um mecanismo de cristalização para cada zeólita estudada.
In this work, the mordenite, ferrierite and ZSM-5 zeolites were prepared by hydrothermal synthesis, modifying the parameters aluminium and silicium sources, water content, seeding, crystallization time and temperature. The objective was to obtain nanocrystalline zeolites. The prepared samples were characterized by atomic absorption spectrophotometry, X-ray diffraction with Rietveld refinement, N2 physical adsorption, atomic force microscopy, scanning electronic microscopy, transmission electronic microscopy and 27Al and 29Si solid state nuclear magnetic resonance. To achieve crystal size control it was important to find the equilibrium between synthesis time and temperature. Sodium aluminate was found to be the most suitable aluminium source. As for the silicium source, each zeolite type had a more suitable source. Mordenite samples with crystallite size between 56 and 292 nm and different crystallinity percentages were obtained. Ferrierite samples with crystallite size between 61 and 82 nm were obtained. Two ZSM-5 samples with crystallite size of 46 nm and 58 nm were prepared. This study showed that to obtain an efficient crystal size control, it is necessary to have a deep knowledge of the influence of all individual parameters in each zeolite`s crystallization process. Finally, it was possible to propose a crystallization mechanism to each zeolite studied.

Transition metal compounds such as Co₂(CO)₈ have often been used to catalyze various organic reactions. Severe difficulties may be encountered when attempts are made to recover and separate the soluble catalysts. A heterogeneous system consisting of Co₂(CO)₈ impregnated on zeolites with faujasitic structure has been designed and investigated using a variety of techniques. In situ FTIR spectroscopy and carbon monoxide evolution were used to identify the major products generated, namely Co₄(CO)₁₂ and Co(CO)_4^-. Disproportionation may be induced thus forming Co(CO)_4^- and an associated cation from the supported subcarbonyls by addition of various ligands such as methanol. The location of the supported cobalt carbonyls is determined by their reactivity toward various phosphines with various kinetic diameters. The materials prepared in this manner were found to be active in catalyzing the methanol carbonylation reaction and following thermolysis were also found to be active Fischer-Tropsch catalysts. Major products observed in the carbonylation of methanol were methyl acetate and an acetaldehyde dimethyl acetal. The supported cobalt catalyst displays greater activity than Co₂(CO)₈ in solution for the carbonylation reaction when conducted under similar conditions. In the Fischer-Tropsch process, selectivity is seen for the production of linear, short-chain hydrocarbons.
Ph. D.

Thesis (M.S.)--Michigan State University. Dept. of Electrical and Computer Engineering, 2008.
Title from PDF t.p. (viewed on Aug. 7, 2009) Includes bibliographical references (p. 58-59). Also issued in print.

This study was carried out on the synthesis of mordenite zeolite and ZSM-5 zeolite. In Chapter 3 reports the growth of ZnS nanoclusters in the pore channels of mordenite zeolite. ZnS as an important wide-band-gap (3.6 eV) semiconductor nanoclusters and have various technological applications such as photocatalysis, nonlinear optics, sensors, solar cells, injection lasers, flat panel displays, ultraviolet light emitting diodes (LED). Zeolites have several different applications in industries, such as in catalysis, ion exchange adsorption and gas separation. Zeolites are mostly used as a catalyst in the petrochemical industry. ZSM-5 zeolite is widely used a heterogeneous catalyst in the petrochemical industry due to its unique porous structure. Special attention has been made to synthesize nano-ZSM-5 in order to improve its catalytic activity. Catalysis depends on the characteristics length scale of the active sites, while the rate depends on the accessible active sites. In order to improve the performance of ZSM-5 zeolite used as a catalyst in the petrochemical industry, the researchers amid to produce nanocrystalline of the ZSM-5 zeolite. That will help to reduce the path length for the reaction and hence will increase the rate of a reaction. Comparative synthesis nano-particles of ZSM-5 zeolite using two different methods of treatment i.e. pre-treatment and interrupted treatment with ultrasound and without ultrasound was studied, its effect on aging and crystal growth during the hydrothermal treatment. In Chapter 4 the pre-treatment with ultrasound and without ultrasound (static) with an increasing time intervals have been reported. The resulting product the particle size is clearly decreased by using ultrasound pre-treatment. While in Chapter 5 using a different method of treatment called interrupted of the hydrothermal process. As in this method, we stopped the hydrothermal process for 20 minutes and treated the gel with ultrasound for 15 minutes. This treatment was repeated after every 2 hours of hydrothermal treatment. Similarly, the same method was applied to the experiment but without the use of ultrasound called a static method of aging. A 3rd method was also applied to investigate the effect of ultrasound on the particle size distribution of the synthesized crystalline powder. All the results showed that the ultrasound not only effects on the particle size but it also affects the crystallinity too i.e. increased the crystallinity and the reduced in the particle size.

Novel open-framework germanates and open low-dimensional structures were synthesized and characterized. Their crystal structures were solved by single crystal X-ray diffraction or X-ray powder diffraction combined with other techniques. Although related open-framework materials, such as zeolites, are of interest for the ability to selectively accommodate guest species in their rings, pores and channels, germanates are primarily of interest for their unique structural properties. Compared to aluminosilicate-based zeolites, germanium oxides readily form frameworks with extra-large rings and low framework density. The formation of elegant germanate architectures is attributed to the unique Ge-O bond geometries compared to Si-O, and the tendency to form large clusters. This thesis is to serve as an introduction to germanate synthesis, structures and characterization. Structures are categorized in accordance to their building units; the Ge7X19 (Ge7), Ge9X25-26 (Ge9) and Ge10X28 (Ge10) (X = O, OH, or F) clusters. Structure determination techniques as well as the characterization techniques used to examine the properties of the materials are presented. While most of the discussed techniques have routinely been used to study crystalline open-frameworks, we introduce the use of infrared spectroscopy for the identification of cluster types, valuable for structure determination by X-ray powder diffraction. Structures and properties of the novel materials ASU-21, SU-62, SU-63, SU-64, SU-65, SU-66, SU-71, SU-72, SU-73, SU-74, SU-75 and SU-JU-14 are described and put into context with previously known structures. The novel structures are all built of the Ge7, Ge9 or Ge10 clusters, and vary from a framework with novel topology to the first open zero-dimensional germanate cavities built of such clusters.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript. Paper 4: Submitted. Paper 6: Submitted. Paper 7: Manuscript. Paper 8. Manuscript. Paper 10: Unpublished book chapter.

 

Mestrado em Engenharia Química
The interest on inorganic membranes has been growing significantly due to their remarkable properties like mechanical, thermal and chemical stabilities, and the ability to perform selective separations based on the kinetic diameter and surface affinity, acting as molecular sieves. The main objectives of this work were: (i) the application of the Maxwell-Stefan (MS) formalism to gas permeation through zeolite-type membranes in order to explore its potential as purely predictive tool; (ii) the development of new MS thermodynamic factors for the Dubinin-Astakhov and Dubinin-Radushkevich isotherms, since they are fundamental in the field of microporous materials; (iii) modeling water permeation through zeolites 13X and 4A membranes after accurate analysis of the influence of isotherm data and effective diffusivity upon permeation; (iv) synthesis and characterization of AM-3 (Aveiro Manchester number 3) titanosilicate membranes for gas separation. Regarding membranes preparation, they were synthesized hydrothermally up to three consecutive times on tubular α-alumina supports through a secondary growth technique. Through X-ray diffraction and scanning electron microscopy it was possible to conclude that after three depositions the AM-3 becomes clearly evident. The influence of pH was also studied and it was verified that a pure phase of AM-3 was not obtained. The dynamic characterization of the membrane disclosed the existence of macro and/or meso-defects, since helium permeances decreased with increasing temperature. The consecutive heating and cooling cycles were able to enhance gas permeance values. Concerning modeling, the MS thermodynamic factors of Dubinin-Astakhov and Dubinin-Radushkevich isotherms were derived for the first time. These factors were successfully validated using published data for methane and ethane on a silicalite-1 membrane. The results showed they are simultaneously able to correlate pure gas permeation and are capable of predicting binary mixture separation, which is a much more important achievement in this field. It was also disclosed that the methane and ethane diffusivities are essentially independent of the fractional occupancy. The water permeation through zeolites 13X and 4A membranes was predicted using MS approach. The influence of temperature and solid loading upon the effective diffusivities was previously modeled, being possible to observe very distinct and non-linear behaviors for both materials. The results evidenced higher fluxes for zeolite 13X, due to its higher pore size. Moreover the flux decreases with increasing temperature, being the opposite verified for the zeolite 4A membrane.
O interesse por membranas inorgânicas tem crescido significativamente devido a propriedades notáveis como a elevada estabilidade mecânica, térmica e química, e a capacidade de efetuarem separações seletivas assentes na afinidade e diâmetro moleculares, atuando como peneiros moleculares. Os objetivos principais deste trabalho foram: (i) a aplicação do formalismo de Maxwell-Stefan (MS) à permeação de gases em membranas zeolíticas de forma a explorar o seu potencial puramente preditivo; (ii) o desenvolvimento de novos fatores termodinâmicos de MS para as isotérmicas de Dubinin-Astakhov e Dubinin-Radushkevich; (iii) a modelação da permeação de água em membranas zeolíticas 13X e 4A, precedida de um estudo rigoroso da influência dos dados de equilíbrio e das difusividades efetivas sobre os resultados; (iv) síntese e caracterização de membranas de titanossilicato AM-3 (Aveiro-Manchester número três) para separação de gases. No que respeita à preparação das membranas de AM-3, estas foram sintetizadas hidrotermicamente em suportes tubulares de α-alumina pelo método de crescimento secundário. Observou-se a formação do filme de AM-3 por difração de raios X e microscopia eletrónica de varrimento. Efetuou-se ainda um estudo de pH tendo-se observado que na gama de concentrações em causa não se conseguiu obter uma fase pura de AM-3. A caracterização dinâmica da membrana de AM-3 mostrou a existência de macro e/ou meso defeitos devido à permeância (do hélio) diminuir com o aumento da temperatura. A realização de ciclos consecutivos de aquecimento e arrefecimento permitiu aumentar os valores de permeância. Relativamente à modelação foram derivados pela primeira vez os fatores termodinâmicos de MS para as isotérmicas de Dubinin-Astakhov e Dubinin-Radushkevich. Estes foram validados com sucesso, usando dados de metano e etano em membrana de silicalite-1. Os resultados mostraram que estes fatores são simultaneamente capazes de correlacionar a permeação de gases puros e prever, a partir deles, a separação de misturas binárias, o que é um feito notável nesta área de investigação. As difusividades do metano e etano são essencialmente independentes da concentração no sólido. A permeação de água através de membranas de zeólitos 13X e 4A foi prevista usando a abordagem de MS. A influência da temperatura e da carga do sólido sobre as difusividades efetivas foi previamente modelada, tendo-se observado comportamentos muito distintos e não lineares nos dois materiais. Os resultados evidenciaram fluxos mais elevados para o zeólito 13X (devido ao maior tamanho de poro), que diminuem com o aumento da temperatura. No caso do zeólito 4A o comportamento foi o oposto.

Microporous materials have a wide range of important applications in separation, gas adsorption, ion-exchange and catalysis. Open-framework germanates are a family of microporous compounds and are of particular interest. This thesis focuses on the synthesis and characterization of new open-framework germanates as well as introducing the transition-metal nickel into germanate structures. One new microporous germanosilicate, SU-78 and four new open-framework germanates, SU-74, SU-75, SU-69 and SU-76 have been obtained by using organic molecules as structure directing agents (SDAs). The incorporation of nickel and organic SDAs in the synthesis resulted in five novel nickel germanates, SUT-1, SUT-2, SUT-3, SUT-4 and SUT-5, in which nickel complexes act either as framework-forming components or as structure directing agents. The general synthesis route is described and the variables that affect the synthesis products are summarized. Different techniques applied on the characterization of chemical and physical properties of the products are also introduced.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Submitted. Paper 2: Submitted. Paper 3: Submitted. Paper 5: Manuscript.

Conventionally, crystalline microporous materials such as zeolites and metal-organic frameworks (MOFs) are synthesized through the hydrothermal route or the trial-and-error approach. Other synthetic strategies may lead to the synthesis of microporous materials with new architectures or interesting properties. The general aim of this thesis is to investigate some new synthetic routes towards crystalline microporous materials. A top-down and post-synthesis method is reported in Chapter 4. Some zeolites are built up by layers and double-4-ring pillars. Germanium is preferentially located in the double-4-ring sites of a zeolite framework and is hydrolytically unstable. The idea of the top-down method is to disassemble these zeolites to the layer structures by dissolving the Ge-containing pillars and reassemble them to a new framework. This method is applied to the germanosilicate IWW and ITH zeolites for the first time. The effects of framework chemical compositions, Ge distributions and disassembling conditions on the top-down treatment process are investigated. The products obtained from the top-down treatment are characterised. An ionic liquid assisted strategy for the synthesis of zeolites is described in Chapter 5. The ionic liquid assisted strategy is a solvent free reaction. The raw materials are transformed to zeolites through a solid state reaction. The ionic liquids are first used as structure-directing agents (SDAs) in this solvent free reaction to replace the expensive quaternary ammonium hydroxide. A TON zeolite is synthesized using 1-ethyl-3-methylimidazolium bromide as the SDA. Moreover, the ionic liquid assisted strategy is considered as a “green chemistry” synthetic route due to the high yield of the zeolites and the minor production of waste water. Many aluminophosphates have been successfully synthesized through ionothermal routes. Most of them are synthesized using 1-alkyl-3-methylimidazolium based ionic liquids. A new ionic liquid, 1-(2-hydroxyl-ethyl)-3-methylimidazolium chloride ([HOEmim]Cl), is prepared and used for the ionothermal synthesis of aluminophosphate materials. A zeolite analogue with the CHA framework has been synthesized. At high synthetic temperatures, the products are large single crystals. The structures of the framework and the SDA are investigated by single crystal diffraction and other characterisation methods. Flexible MOF materials are usually synthesized by a trial-and-error approach. Recently a flexible MOF compound was synthesized using 5-sulfoisophthalic acid (SIP) as the ligand. It was proposed the sulfonate is weakly coordinated to the metal, which brings flexibility to the compound, and the carboxylate groups keep the framework intact. 2-sulfoterephthalic acid (STP) which also contains one sulfonate group and two carboxylate groups is believed to be an alternative ligand for the targeted synthesis of flexible MOFs. In Chapter 7, a MOF compound is synthesized using STP and 4, 4'-bipyridine (Bpy) as ligands to validate the proposed strategy can be generalized. Variable temperature single crystal diffraction analysis solves the structure and reveals a reversible structure transformation upon dehydration and rehydration.

This PhD thesis strives to give an exhaustive characterization of the behaviour of zeolites in nonambient conditions. Zeolites presents a lot of peculiar characteristics, such as shape selectivity, high thermal stability, but the most important is their catalytic activity, which have been evaluated for many petrochemical reactions, such as gas-oil cracking and hydrocracking, aromatic alkylation and isomerisation ecc. The catalytic activity of zeolites is due to their particular structure. These minerals, in fact, are characterized by large pores and channels. Only molecules with determined dimensions, consistent with the pores dimensions, can have access to the acid sites located inside these cavities and can be processed. The importance of a detailed structural characterization is due to the fact that it is necessary to explain the efficiency of these materials, their stability as well as the different types of shape selectivity seen in a wide range of catalytic systems. The understanding of the zeolite behaviour upon heating is of particular importance since the sorptive and catalytic properties, molecular sieve effects are enhanced in the dehydrated/calcined phases. Besides, it is important to study the response to heating because reactions involving hydrocarbons need high temperature (about 300-500°C), so it is important that zeolites used for these reactions have a good thermal stability, and it is important to localize acid sites. The study of the characterization of these materials in non-ambient conditions was carried out starting from structure analysis of diffraction data collected on powder or single crystals, using Xray (conventional source or synchrotron radiation) or neutron diffraction. The main results obtained in this PhD thesis can be summarize as follows: 1) zeolite tschernichite. It has been evaluated how defects due to the simultaneous presence of two different polytypes affect the thermal stability of this material; 2) zeolite gmelinite. The most important results is that it was possible to observe that gmelinite, when heated at T>330°C transform into a new phase (AFI-type) which is very important for catalysis and has a good thermal stability; 3) zeolite omega. It was possible to follow in real time the activation of this important catalyst and its acid sites were localized; 4) zeolite ferrierite and heulandite: protons bonded to framework oxygens were located, and it is put in evidence the importance of water interaction with these catalysts.

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A síntese de zeólitas a partir de cinzas leves e pesadas de carvão mineral foi realizada por tratamento hidrotérmico alcalino, as quais foram nomeadas ZCL e ZCP, respectivamente. As zeólitas organomodificadas ZML e ZMP foram obtidas a partir da modificação superficial de ZCL e ZCP, respectivamente, utilizando o surfactante catiônico brometo de hexadeciltrimetilamônio. A partir das soluções remanescentes geradas na síntese de ZCL e ZCP foi possível sintetizar duas novas zeólitas. As características físicoquímicas dos nanomateriais zeolíticos sintetizados, bem como de suas respectivas matérias primas, tais como: capacidade de troca catiônica, massa específica, área específica, composição química, mineralógica e morfológica, entre outras, foram determinadas. Os adsorventes ZML e ZMP foram utilizados na remoção dos corantes Azul Direto 71 (DB71) e Rodamina B (RB) de soluções aquosas em sistema de batelada. Desta forma, quatro sistemas DB71/ZML, RB/ZML, DB71/ZMP e RB/ZMP foram investigados. Os modelos de pseudoprimeira ordem e pseudo-segunda ordem foram aplicados aos dados experimentais para o estudo da cinética de adsorção. O modelo de pseudosegunda ordem foi o que melhor descreveu o processo de adsorção de todos os sistemas corante/zeólita organomodificada. O equilíbrio da adsorção foi analisado a partir de quatro modelos de isoterma, sendo eles: Langmuir, Freundlich, Temkin e Dubinin-Radushkevich (D-R). Os resultados mostram que os modelos de Freundlich e Langmuir melhor descreveram os dados experimentais dos sistemas DB71/ZML e DB71/ZMP, respectivamente. Para os sistemas com RB, o modelo de D-R foi o que melhor se ajustou para ambos adsorventes ZML e ZMP. O planejamento fatorial 24 foi aplicado para a análise dos seguintes fatores que influenciam o processo de adsorção: concentração inicial do corante (Co), pH, dose de adsorvente (M) e temperatura (T). De acordo com as condições estudadas concluiu-se, com o intervalo de confiança igual a 95%, que para o sistema DB71/ZML, os fatores e suas interações que mais influenciam foram C0, M, pH, pH*M, pH*C0, M*C0, pH*M*C0, nessa ordem. No sistema DB71/ZMP, a ordem de influência foi: M, C0, pH, pH*M, pH*C0, M*C0, pH*M*C0. Para os sistemas RB/ZML e RB/ZMP, os resultados foram: M, C0, M*C0, pH, pH*M e M, C0, M*C0, respectivamente. O equilíbrio de adsorção foi atingido em cerca de 40 min para todas as amostras. As porcentagens de remoção do DB71 estavam na faixa de 50 80% e 20 50% para ZML e ZMP, respectivamente. A faixa de porcentagens de remoção do RB variou entre 60 80% e 30 50% para ZML e ZMP, respectivamente.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Ce travail de thèse porte sur l’optimisation des matériaux zéolithiques à petits pores dans le butd'améliorer leur capacité d'adsorption du CO2 et leur efficacité en séparation des gaz. Dans cecontexte, cette étude se concentre sur l'amélioration des performances des zéolithes à traversl'échange ionique, le contrôle de la taille des cristaux et la synthèse de nouveaux adsorbants. Deszéolithes de type Gismondine (GIS) échangées avec des cations Mg2+ ont été synthétiséesdémontrant une meilleure sélectivités pour CO2/N2 et CO2/CH4 grâce à un échange cationiquespartiel avec Mg2+, ce qui influencé la distorsion de la structure et renforcé à la capacité la sélectivité,mettant en avant leur potentiel pour des applications pratiques de capture du CO2. Une méthode desynthèse assistée par graines a été adaptée pour produire des zéolithes P (GIS) de taillenanométrique améliorant de façon notable la cinétique d’adsorption du CO2 en réduisant leslimitations de diffusion plus rapide, issue d’un mécanisme de diffusion intra-cristalline, a conduità des performances accrues dans la séparation dynamique des gaz, dépassant ainsi celle deszéolithes de taille micrométrique. Les zéolithes Levyne (LEV) sont également introduites danscette thèse comme de nouveaux candidats pour l’adsorption du CO2, où un contrôle rigoureux durapport Si/Al et l’usage des graines de taille nanométrique ont permis un ajustement précis dupropriétés d’adsorption. L’étude met en avant l’importance du rapport Si/Al dans l’optimisation dela sélectivité et de la capacité d’adsorption du CO2 ainsi que du comportementadsorption−désorption positionnant la zéolithe LEV comme un matériau prometteur pour laséparation du gaz. Ces résultats illustrent comment du techniques de synthèse adoptées, associéesà l’optimisation de l’échange cationique, au contrôle de la taille cristalline et l’ajustement durapport Si/Al, peuvent significativement améliorer les performances des zéolithes dans lestechnologies de capture du carbone et la séparation des gaz à haute efficacité énergétique
This thesis is dedicated to optimizing small-pore zeolite materials for efficient CO2 adsorption andgas separation. The work focuses on improving zeolite performance through cation exchange,crystal size control, and the synthesis of novel adsorbents. Mg-exchanged Gismondine (GIS)zeolites were synthesized, demonstrating enhanced CO2/N2 and CO2/CH4 selectivities due to partialcation exchange with Mg2+, which influenced the framework distortion and improved bothadsorption capacity and selectivity, underscoring their potential for practical carbon captureapplications. A seed-assisted synthesis method was also employed to develop nanosized zeolite P(GIS), which significantly improved CO2 adsorption kinetics by reducing diffusion limitations,with faster diffusion resulting from an intracrystalline diffusion mechanism. This superior diffusionwithin the nanosized zeolites led to enhanced performance in dynamic gas separation compared totheir micron-sized counterparts. The thesis also introduces Levyne (LEV) zeolites as novelcandidates for CO2 adsorption, where careful control of the Si/Al ratio and the use of nanosizedseeds allowed for precise tuning of adsorption properties. The study highlights the critical role ofthe Si/Al ratio in optimizing CO2 selectivity, uptake, and adsorption−desorption behaviour,establishing LEV as a promising material for gas separation. These findings demonstrate howtailored synthesis methods, cation exchange optimization, crystal size control, and Si/Al ratioadjustment can significantly enhance the performance of zeolite-based materials in carbon captureand energy-efficient gas separation technologies

Doutoramento em Engenharia Química
Among various methods for the separation of hydrogen containing mixtures, membrane technology has received special attention due to its simplicity of operation, moderate energy consumption, cost effectiveness, it is environmentally friendly and can be easily coupled with other separation methods. In particular, inorganic membranes exhibit relevant advantages such as high thermal, chemical and mechanical stabilities, minor plasticization and better control of pore size distribution. They can be divided into five main families: metallic and ceramic proton conducting membranes (dense phases), and silica, zeolite and carbon molecular sieve membranes (porous materials). With more than 200 framework types, zeolites possess uniform molecular pore dimensions and unique properties for catalytic, ion exchange, adsorption and membrane applications. This thesis is essentially devoted to zeolite (titanosilicate) membranes for hydrogen and light gases separation. Titanosilicates offer important benefits over the remaining zeolites: they are usually synthesized without organic templates, can be prepared under moderate pH conditions, exhibit novel possibilities of isomorphous framework substitution, and generally offer strong alkalinity. The main objectives of this dissertation were: (i) synthesis and characterization of titanosilicate membranes. The materials structure and morphology were examined by X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS); the dynamic characterization of membranes was accomplished by permeation assays with pure gases; (ii) deep analysis of experimental results, with the objective to disclose the mass transport mechanisms that prevail in the membrane; (iii) accurate modeling of permeation data using theoretically sound approaches like the generalized Maxwell-Stefan (MS) formalism; (iv) development of new MS thermodynamic factors to represent the surface diffusion of pure and multicomponent gases through microporous membranes. Here, several important (though less studied) isotherms were tested, the influence of the solid loading upon surface diffusivity was deeply evaluated, and the predictive ability of the whole model was validated. The hydrothermal synthesis and characterization of AM-2 and AM-3 powder and supported membranes have been performed. Altogether, ca. thirty and more than one hundred syntheses of AM-2 and AM-3 powder, respectively, have been accomplished, and eight AM-2 and twenty AM-3 membranes have been prepared on tubular -alumina and stainless-steel supports by seeding and secondary growth. All powders were characterized by XRD and/or SEM, and three AM-2 and seven AM-3 membranes were dynamically tested. The permeation of pure gases at programmed temperature and fixed transmembrane pressure drop ( P) was carried out in order to evaluate the membranes quality and identify the governing transport mechanisms (e.g. viscous flow, Knudsen regime, surface diffusion, activated gaseous diffusion). Additionally, more than one hundred permeance measurements were conducted at various temperatures and pressures using different gases (H2, He, N2, O2 and CO2). The best AM-3 membrane was studied in detail at P=0.5, 1.0 and 1.5 bar, at fixed and programmed temperatures between 304 and 394 K, using H2, He, N2, O2 and CO2. The results provided selectivities towards hydrogen up to 3.5, and disclosed in all cases an activated behavior typical of surface diffusion, a small contribution of viscous flow due to macro-defects, and a minor contribution of Knudsen mechanism due to meso-defects. The gas permeation was accurately modeled using Maxwell-Stefan theory, achieving an average deviation of only 3.42 % for all molecules. The rigorous MS thermodynamic factors of various relevant isotherms – Toth, Dubinin-Astakhov (DA) and Dubinin-Radushkevich (DR) – were derived in this work for the first time, with the objective to model the permeation of pure and mixed gases through zeolite membranes. The DA and DR isotherms received special attention, taking into account they are often adopted to represent the adsorption equilibrium of most industrial adsorbents that possess a welldeveloped porous structure, especially of carbonaceous origin. The MS factors for DA and DR isotherms were validated using equilibrium and flux data for methane/silicalite-1, ethane/silicalite-1 and (methane,ethane)/ silicalite-1 systems according to the following procedure: (i) the unary isotherms were fitted to the corresponding data, while their binary expressions were predicted from the previous ones; (ii) the influence of surface loading upon methane and ethane diffusivities was carefully assessed; (iii) the MS diffusion parameters of each gas were obtained from unary permeation data; (iv) the MS counter-sorption diffusivities were then predicted using the Vignes correlation; (v) the separation of methane/ethane mixtures using the silicalite-1 membrane was totally predicted using the new MS thermodynamic factors combined with the binary isotherms. The results demonstrated the validity of this approach, particularly if DA isotherm is selected. Besides the main focus of this PhD on membranes, ion exchange experiments and modeling were also included. The removal of ionic contaminants (Cd2+ and Hg2+) from aqueous solutions was studied using synthesized stannosilicate AV- 6 and titanosilicate ETS-4. In the case of the Cd2+/K+/AV-6 system, the kinetic removal was modeled with Maxwell-Stefan (MS) and Nernst-Plank (NP) equations, while equilibrium was modeled with mass action law and activity coefficients in both solution (Debye-Hu ckel and Pitzer models) and exchanger (Wilson model) phases. The experimental data proved the ion exchange ability of AV-6 to sorb cadmium(II), and excellent results were achieved for the equilibrium isotherm (deviations around 6.6 %) and kinetic modeling (MS, 3.74 %; NP, 3.71 %). It was shown that the solid phase is clearly non-ideal. The investigation of the ternary system (Cd2+,Hg2+)/Na+/ETS-4 confirmed the large capacity of ETS-4 (5.44 meq g-1) and its selectivity towards both toxic metals, particularly Cd2+. However, the trends of the ion exchange kinetics were very distinct, because the internal diffusivity of cadmium(II) is higher than that of mercury(II). These results are in accordance with the effective ionic radius of both species, namely, 102 pm for Hg2+ and only 95 for Cd2+.
Entre diversos métodos de separação de misturas gasosas contendo hidrogénio, os processos membranares têm recebido uma atenção especial devido à sua simplicidade de operação, consumo moderado de energia, boa relação custo-eficiência, vantagens para o meio ambiente, e podem ser facilmente combinados com outros métodos de separação. Em particular, as membranas inorgânicas exibem vantagens relevantes, podendo citar-se as estabilidades térmica, química e mecânica elevadas, plasticização reduzida e um melhor controlo da distribuição do tamanho dos poros. Estas podem ser divididas em cinco famílias principais: metálicas e cerâmicas densas (membranas densas); e de sílica, zeolíticas e de peneiro molecular de carbono (membranas porosas). Com mais de 200 estruturas, os zeólitos possuem poros uniformes de dimensão molecular e propriedades únicas para aplicações catalíticas, de permuta iónica, de adsorção e membranares. Esta dissertação dedica-se fundamentalmente a membranas zeolíticas (titanossilicatos) para a separação de hidrogénio e gases leves. Os titanossilicatos oferecem vantagens importantes em relação aos restantes zeólitos: são geralmente sintetizados sem agentes orgânicos estruturantes e sob condições moderadas de pH, exibem novas possibilidades de substituição isomórfica da matriz, e oferecem geralmente uma forte alcalinidade. Os objetivos principais desta dissertação foram: (i) síntese e caracterização de membranas de titanossilicatos. A estrutura dos materiais e a sua morfologia foram examinadas por difração de raios-X (DRX) e microscopia eletrónica de varrimento acoplada a espectroscopia de energia dispersiva de raios-X (SEM/EDS). A caracterização dinâmica das membranas foi efetuada com ensaios de permeação utilizando gases puros; (ii) análise aprofundada dos resultados experimentais, com o objetivo de compreender os mecanismos de transporte de massa que prevalecem na membrana; (iii) modelação rigorosa dos dados de permeação, seguindo abordagens como o formalismo de Maxwell-Stefan (MS); (iv) derivação de novos fatores termodinâmicos de MS para representar a difusão superficial de gases puros e misturas através de membranas microporosas. Foram investigadas isotérmicas importantes, (mesmo que pouco utilizadas na literatura), a dependência da difusividade superficial com a concentração no sólido, e a capacidade preditiva de todo o modelo. A síntese hidrotérmica e a caracterização dos titanossilicatos AM-2 e AM-3 foram efetuadas com o material na forma de pó e suportado em membranas. Realizaram-se cerca de trinta sínteses de cristais de AM-2 e mais de uma centena de AM-3, para além de oito membranas de AM-2 e vinte membranas de AM-3 suportadas em tubos de -alumina e de aço inoxidável, recorrendo ao método do crescimento secundário. Todos os cristais obtidos foram caracterizados por DRX e/ou S SEM, e testaram-se dinamicamente três SEM membranas de AM-2 e sete membranas de AM-3. A permeação de gases puros a temperatura programada e a pressão transmembranar fixa ( P) foi realizada com o objetivo de avaliar a qualidade das membranas e identificar os mecanismos de transporte envolvidos (fluxo viscoso, regime de Knudsen, difusão superficial, difusão gasosa ativada). Foram concluídas mais de uma centena de medições de permeação a várias temperaturas e pressões usando gases diferentes (H2, He, N2, O2 e CO2). A melhor membrana de AM-3 foi estudada em detalhe para P = 0,5, 1,0 e 1,5 bar, a temperatura fixa e a temperatura programada entre 304 e 394 K, usando H2, He, N2, O2 e CO2. Os resultados obtidos evidenciaram seletividades para o hidrogénio até 3,5, comportamento ativado típico de difusão superficial em todos os casos, uma pequena contribuição de fluxo viscoso devido a macrodefeitos e uma contribuição residual do mecanismo de Knudsen atribuível a meso-defeitos. A permeação gasosa foi modelada rigorosamente usando o formalismo de Maxwell-Stefan, apresentando um desvio médio de apenas 3,42% para todas as moléculas simultaneamente. Os fatores termodinâmicos de MS para as isotérmicas de Toth, Dubinin- Astakhov (DA) e Dubinin-Radushkevich (DR) foram derivados neste trabalho, com o objetivo de modelar a permeação de gases puros e misturas através de membranas zeolíticas. As isotérmicas de DA e DR receberam uma atenção especial, tendo em conta que são frequentemente adotadas para representar o equilíbrio de adsorção da maioria dos adsorventes industriais que têm uma estrutura porosa bem definida, especialmente com origem carbonácea. Os fatores de Maxwell-Stefan para DA e DR foram validados com dados experimentais de equilíbrio e de fluxo dos sistemas metano/silicalite-1, etano/silicalite-1 e (metano,etano)/silicalite-1 de acordo com o seguinte procedimento: (i) os parâmetros das isotérmicas dos gases puros foram ajustados aos dados correspondentes, e as isotérmicas binárias foram previstas a partir das anteriores; (ii) a influência da concentração do sólido sobre as difusividades superficiais do metano e do etano foi analisada cuidadosamente; (iii) os parâmetros de difusão de MS de cada gás foram obtidos a partir dos dados de permeação mono-componente; (iv) os coeficientes de difusão multicomponente de MS foram estimados com a correlação de Vignes; (v) a separação de misturas metano/etano usando uma membrana de silicalite-1 foi totalmente prevista com recurso aos novos fatores termodinâmicos de MS combinados com as isotérmicas binárias. Os resultados comprovaram a validade desta abordagem, especialmente no caso da isotérmica de DA. Apesar de a área principal deste doutoramento estar relacionada com membranas, foram incluídas experiências de permuta iónica e sua modelação. A remoção de contaminantes tóxicos (Cd2+ e Hg2+) de soluções aquosas foi estudada usando o estanhossilicato AV-6 e o titanossilicato ETS-4. No caso do sistema Cd2+/K+/AV-6, a cinética de remoção foi modelada com as equações de Maxwell-Stefan (MS) e de Nernst-Plank (NP), enquanto o equilíbrio foi modelado com a lei da ação das massas expressa em atividades, usando-se coeficientes de atividade na solução (modelos de Debye-Hückel e Pitzer) e no permutador (modelo de Wilson). Os dados experimentais evidenciaram a capacidade de permuta do AV-6 para sorver cádmio(II) e obtiveram-se resultados excelentes para a isotérmica de equilíbrio (desvios de 6,6 %) e para a modelação cinética (MS = 3,74 %; NP = 3,71%). Ficou ainda demonstrado que a fase sólida é claramente não-ideal. A investigação do sistema ternário (Cd2+,Hg2+)/Na+/ETS-4 confirmou a elevada capacidade do ETS-4 (5,44 meq g-1) e a sua seletividade para os dois metais tóxicos, particularmente para o Cd2+. Contudo, o comportamento das cinéticas de permuta iónica foi muito distinto, uma vez que a difusividade interna do cádmio(II) é superior à do mercúrio(II). Estes resultados estão de acordo com o raio iónico efetivo de ambas as espécies, ou seja, 102 pm para o Hg2+ e apenas 95 pm para o Cd2+.

Zeolite beta has been synthesized using hydrothermal methods. In order to synthesize zeolite beta an aqueous gel having a molar batch composition of 2.2 Na2O&
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Al2O3&
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x SiO2&
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4.6 (TEA)2O&
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444 H2O was utilized. The synthesis parameters were SiO2/Al2O3 ratio (20 &
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x &
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50) and crystallization time (6 &
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t &
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16 days). Pure zeolite beta was crystallized from the experiments which were performed with the batch composition having SiO2/Al2O3 of 20 and 30 in 6 to 16 days period. For SiO2/Al2O3 of 20 and 30, the highest yield was obtained for 12 days. Therefore, the rest of the experiments, in which SiO2/Al2O3 was 40 and 50, were carried out keeping the synthesis time constant (12 days). Pure zeolite beta was also synthesized for SiO2/Al2O3 of 40 and 50. The highest yield and the most crystalline zeolite beta sample were obtained from the experiment performed at SiO2/Al2O3 of 50 with a synthesis time of 12 days. The morphology and crystal size of the zeolite beta samples were identified by using scanning electron microscope (SEM). It was observed that, zeolite beta samples had spheroidal morphology with the crystal size of about 0.5 &
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m. According to the thermogravimetric analyses (TGA), it was found that template molecules and moisture constituted nearly 18 % by weight of the zeolite beta samples. The surface area of the calcined zeolite beta sample was determined by N2 adsorption and was found to be 488 m2/g. Gravimetric sorption analyses yield that, the limiting sorption capacity of Na-Beta for methanol, ethanol, isopropanol and n-butanol at 0°
C was about the same with a value of 0.25 cm3/g. For o-xylene, m-xylene and p-xylene that value was 0.21 cm3/g, 0.22 cm3/g and 0.24 cm3/g, respectively.

Zeolite membranes are attractive materials to separate gas and liquid mixtures. MFI is a widely studied zeolite type due to its ease of preparation and comparable pore size with the molecular size of many substances. In this study MFI type membranes were synthesized over porous &
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-Al2O3 supports and characterized with XRD, SEM and gas permeation measurements. In the first part of this study the effect of soda concentration of the synthesis solution on the membrane morphology and crystal orientation was investigated. The synthesis was carried out from solutions with a molar composition of (0- 6.5)Na2O:25SiO2:6.9TPABr:1136H2O at 150oC. At soda concentrations between 0.45 and 1.8 the membrane layers with (h0h)/c-directed orientation were obtained. At lower and higher soda concentrations membrane layer formed from randomly oriented crystals. The (h0h)/c-oriented membranes showed H2/n-C4H10 ideal selectivities of 478 and 36 at 25°
C and 150°
C, respectively.In the second part, MFI membranes were synthesized from mixtures with different concentrations of template molecules. Tetrapropylammonium hydroxide, tetrapropylammonium bromide or mixture of both types were used as template. The nucleation period, the size of MFI crystals, membrane thickness decreased as the tetrapropylammonium hydroxide concentration increased. Besides conversion of SiO2 in the synthesis solution to MFI passed through a maximum with increasing concentration of tetrapropylammonium hydroxide in the synthesis solution. When tetrapropylammonium bromide was used as template thicker membranes were obtained. In the third part MFI type membranes with a thickness of 1.5-2 &
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m were synthesized by mid-synthesis addition of silica to the synthesis medium. The membranes synthesized with and without mid-synthesis addition of silica have n-C4H10/i-C4H10 ideal selectivities of 47 and 8 at 100oC, respectively. The change of composition during the synthesis increases the crystal growth rate and the size of the crystals forming the membrane, thus better quality membranes can be obtained by mid-synthesis addition of silica to the synthesis medium. In the last part of this study, thin MFI type zeolite membranes were synthesized in a recirculating flow system at 95°
C on the inner side of the tubular &
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- alumina supports. A membrane synthesized by two consecutive synthesis steps had a separation selectivity of 38 and 86 for equimolar mixtures of n- C4H10/CH4 and n-C4H10/N2 at 25oC, respectively. The membrane selectively permeated large n-C4H10 over small CH4 and N2, suggesting that the separation is essentially adsorption-based and the membrane has few nonselective intercrystalline pores.

In this work, a seeding technique was used to synthesize films and membranes of FAU, LTA and MFI type zeolites. In the first part, hydrothermal growth was performed without organic template molecules, which resulted in template-free zeolite films and membranes. The samples were characterized by Scanning Electron Microscopy, X-ray Powder Diffraction and permeation measurements with gaseous probe molecules. Thin films of FAU-type zeolite were prepared on polished single crystals. The thickness and morphology of the films could be controlled by varying the synthesis conditions. Preparation of LTA-type membranes was also attempted. However, the membranes cracked during drying at temperatures above room temperature. Template free MFI membranes with higher quality could be prepared. These membranes had a maximum separation factor alpha of 17.8 at 220°C for a n-butane/i-butane mixture. Cracks formed at temperatures higher than 250°C. Crack formation in zeolite membranes at high temperatures has also been reported by several other groups. Since no model for the crack formation process has been established in the literature, the second part of this work was devoted to study crack formation and to develop a model. Relatively thick (ca 1800 nm) alpha-alumina supported MFI films, prepared using organic template molecules (TPA+), were selected for the study since data on crack formation in the form of SEM images and permeation measurements for these membranes had been obtained in earlier work by the group. These membranes were further studied by in-situ High Temperature X-ray Powder Diffraction experiments in the present work. In addition, MFI powder and a blank alpha-alumina support were also investigated. Data were collected with the aid of a Synchrotron radiation facility as well as with a conventional laboratory instrument for the temperature cycle 25-500-25°C. The Rietveld method was used to determine the unit cell parameters of MFI and alpha-alumina as well as the TPA+ occupancy of MFI. The out-of- plane strain (i.e. strain in the direction perpendicular to the film surface) in the film and the support was calculated. In addition, the microstructure of the support was investigated by pattern decomposition and Williamson-Hall plots. In agreement with previous reports in the literature, it was found that the TPA-MFI structure contracts as a consequence of template removal and possibly also a structure intrinsic mechanism and the alpha-alumina support expands. Hence, a large thermal expansion mismatch occurs in the membranes during heating. An overall out- of-plane compressive strain was observed for the MFI film during heating, which indicates an in-plane tensile stress (i.e. in the direction parallel to the film surface) in the film. This result was explained by the larger expansion of the support, compared to the film. The alpha-alumina support was also found to be under an overall out-of-plane compressive strain at non-ambient temperatures, presumably due to zeolite in the pores of the support. The microstrain for the MFI coated alpha-alumina support increased during heating, and remained during cooling, which indicate the formation of structural defects in the support. Based on these results and results from earlier work, a model for crack formation was proposed: In the thick films (ca 1800 nm) studied in the present work, the crystals are well intergrown. During heating, the MFI crystals contracts and the alpha- alumina support expands. Consequently, a thermal stress develops in the composite which eventually leads to formation of cracks. In addition, part of the stress is also released via formation of structural defects in the alpha-alumina support. In thinner films (ca 500 nm), the crystals are less well intergrown and the thermal expansion mismatch between the crystals in the film and the support leads to opening of grain boundaries in the film rather than cracks.
Godkänd; 2006; 20061130 (pafi)