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

Zeolites are well-known aluminosilicate minerals that have been widely used as adsorbents in separation, purification processes and environmental pollution control. Zeolites are used in various industrial applications due to their high cation-exchange ability, molecular sieve and cataltic properties. In order to reduce the costs of acquisition and minimise the disposal of adsorbents, both modified natural zeolite and synthetic zeolite (derived from kaolinite) were used for the purification of wastewater. The characteristic properties and applications of adsorbents are also discussed including the advantages and disadvantages of each technique. The present work involves the study of the removal of Cu2+, Fe3+, Pb2+ and Zn2+ from synthetic metal solutions using natural zeolite. Laboratory experiments were used to investigate the efficiency of adsorbents in the uptake of heavy metals from industrial wastewater. These include equilibrium tests, kinetic studies and regeneration studies. The physical and chemical characterization of the zeolites was carried out using different analytical techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X - Ray Diffraction (XRD), X - Ray Fluorescence (XRF), Thermogravimetric Analysis (TGA), Fourier Transform Infrared (FT-IR) Spectroscopy and Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). The kinetic study indicated the suitability of the natural zeolite for the removal of Cu2+, Fe3+, Pb2+ and Zn2+ ions from synthetic wastewater. Batch experiments were used to identify the effect of parameters that affect the rate of adsorption such as the effect of adsorbent mass, effect of adsorbent particle size, effect of initial solution pH, effect of initial solution concentration, effect of agitation speed and effect of pre-treatment of adsorbent and evaluated their impact on the efficiency of the zeolite in the removal of heavy metals from industrial wastewater. The kinetic studies showed that the capacity of the adsorbents for the removal of heavy metals increased with a greater mass of absorbent, increased initial solution pH, increased agitation speed, higher solution concentration as well as the application of a pre-treatment. The results from the equilibrium studies positively demonstrated that natural zeolite can be used as an excellent adsorbent for removing heavy metals from multi-component solutions. The equilibrium experiments indicated that the capacities of natural zeolite for the uptake of heavy metals increased when the initial solution pH increased. The results indicated that the maximum removal capacities Q were 22.83, 14.92, 14.49 and 17.54 mg/g natural zeolite for copper, iron, zinc, and lead respectively. Both the Langmuir and Freundlich isotherm models were used to characterize the experimental data and to assess the adsorption behaviour of natural zeolite for copper, iron, lead and zinc. The experimental data were slightly better suited to the Langmuir isotherm than the Freundlinch isotherm. The value of the correlation coefficients r2 ranged from 0.93 to 0.99 for the Langmuir isotherm and from 0.90 to 0.99 for the Freundlich isotherm. The present work also involved the study of synthetic zeolite A, which was derived from natural kaolinite. The conversion of the raw materials into zeolitic materials was carried out in two ways: first, conventional hydrothermal synthesis and second, alkaline fusion prior to hydrothermal synthesis. The results from both routes show that zeolite A was synthesised successfully. Finally, the experiments show that both natural and synthetic zeolites can be available in commercial quantities. Synthetic zeolites are more attractive for some specific applications, while the cheapness of natural zeolite may favour its use.

The diesel engine is growing in popularity due to its energy efficiency and solving the emissions issues associated with diesel engine exhaust would clear the way for further growth. The key pollutants are NOx, particulate matter and unburned hydrocarbons. Selective catalytic reduction (SCR) catalysis is likely the best choice for NOx control. In SCR, NH3 selectively reacts with NOx to form N2 – the selectivity refers to NH3 reacting with NOx instead of the abundant O2. Urea is used as the NH3 source, being injected into the exhaust as an aqueous solution where the urea decomposes and NH3 is generated. Spatial resolution characterization techniques have been gaining attention in the catalysis field because of the higher level of information provided. In this thesis, a new spatial resolution technique, called SpaciFTIR (spatially-resolved, capillary-inlet Fourier transform infra-red spectroscopy), was developed, which overcomes the interference of water in the detection of NH3 in an earlier developed technique, SpaciMS (spatially-resolved, capillary-inlet mass spectrometry). With the new test method, three SCR topics were addressed. First, the three key SCR reactions were spatially resolved. These are the standard SCR reaction (2NO + 2NH3 + 1/2O2 = 2N2 + 3H2O), the fast SCR reaction (NO + NO2 + 2NH3 = 2N2 + 3H2O), and NO2-SCR, (6NO2 + 8NH3 = 7N2 + 12H2O). Results show that in the presence of NO2, but at a NO2/NOx ratio < 0.5, the fast SCR reaction proceeds followed by the standard SCR reaction, i.e. in series. If the NO2/NOx ratio exceeds 0.5, the NO2-SCR and fast SCR reactions occur in parallel. Compared to the standard integral test method, this spatial resolution technique clearly showed such trends. Secondly, the spatial resolution technique was used to characterize the effects of thermal aging on catalyst performance. It was found that for a highly aged catalyst, there was a radial activity profile due to an inhomogeneous temperature distribution in the process of aging. Aging effects on various key SCR reactions, i.e. NO oxidation, NH3 oxidation, and the reduction reactions, were studied. Last but not least, for the purpose of passive SCR system development, transient NH3 storage profiles along the monolith channel were measured with SpaciFTIR. Passive SCR is a system where the NH3 is generated on an upstream catalyst, such as a three-way catalyst or lean-NOx trap, instead of via urea injection. In such a system, NH3 is therefore not constantly being fed to the SCR catalyst, but “arrives” in pulses. Factors such temperature, NH3 concentration, pulsing time, flow rate and thermal aging were investigated. For the first time, NH3 migration was observed and its effect on SCR reactions along the length of catalyst was studied.

Zeolites are a well-known class of crystalline oxide materials with tunable compositions and nanoporous structures, and have been used extensively in catalysis, adsorption, and ion exchange. The zeolite MFI is one of the well-studied zeolites because it has a pore size and structure suitable for separation or chemical conversion of many industrially important molecules. Modification of zeolite structures with organic groups offers a potential new way to change their properties of zeolites, beyond the manipulation of the zeolite framework structure and composition. The main goals of this thesis research are to study the organic-modification of the MFI pore structure, and to assess the effects of such modification on the adsorption and transport properties of zeolite MFI sorbents and membranes. In this work, the internal pore structure of MFI zeolite particles and membranes has been modified by direct covalent condensation or chemical complexation of different organic molecules with the silanol defect sites existing in the MFI structure. The organic molecules used for pore modification are 1-butanol, 1-hexanol, 3-amino-1-propanol, 1-propaneamine, 1,3-diaminopropane, 2-[(2-aminoethyl)amino]ethanol, and benzenemethanol. TGA/DSC and 13C/29Si NMR characterizations indicated that the functional groups were chemically bound to the zeolite framework, and that the loading was commensurate with the concentration of internal silanol defects. Gas adsorption isotherms of CO2, CH4, and N2 on the modified zeolite materials show a range of properties different from that of the bare MFI zeolite. The MFI/3-amino-1-propanol, MFI/2-[(2-aminoethyl)amino]ethanol, and MFI/benzenemethanol materials showed the largest differences from bare MFI. These properties were qualitatively explained by the known affinity of amino- and hydroxyl groups for CO2, and of the phenyl group for CH4. The combined influence of adsorption and diffusion changes due to modification can be studied by measuring permeation of different gases on modified MFI membranes. To study these effects, I synthesized MFI membranes with [h0h] out-of-plane orientation on α-alumina supports. The membranes were modified by the same procedures as used for MFI particles and with 1-butanol, 3-amino-1-propanol, 2-[(2-aminoethyl)amino]ethanol, and benzenemethanol. The existence of functional groups in the pores of the zeolite was confirmed by PA-FTIR measurements. Permeation measurements of H2, N2, CO2, CH4, and SF6, were performed at room temperature before and after modification. Permeation of n-butane, and i-butane were measured before and after modification with 1-butanol. For all of the studied gases, gas permeances decreased by 1-2 orders of magnitude compared to bare MFI membranes for modified membranes. This is a strong indication that the organic species in the MFI framework are interacting with or blocking the gas molecule transport through the MFI pores. A detailed fundamental study of the CO2 adsorption mechanism in modified zeolites is necessary to gain a better understating of the adsorption and permeation behavior of such materials. Towards this end, an in situ FTIR study was performe.For the organic molecules with only one functional group (1-butanol, benzenemethanol, and 1-propaneamine), physical adsorption was found - as intuitively expected - to be the only observed mode of attachment of CO2 to the modified zeolite material. Even in the case of MFI modified with 1,3-diaminopropane, only physical adsorption is seen. This is explained by the isolated nature of the amine groups in the material, due to which only a single amine group can interact with a CO2 molecule. On the other hand, chemisorbed CO2 species are clearly observed on bare MFI, and on MFI modified with 3-amino-1-propanol or 2-[(2-aminoethyl)amino]ethanol. Specifically, these are carbonate-like species that arise from the chemisorption of CO2 to the silanol group in bare MFI and the alcohol groups of the modifying molecule. The possibility of significant contributions from external surface silanol groups in adsorbing CO2 chemisorbed species was ruled out by a comparative examination of the FTIR spectra of 10 μm and 900 nm MFI particles modified with 2-[(2-aminoethyl)amino]ethanol.

Zeolite A-type membranes are usually synthesized from hydrogels and rarely synthesized from clear solutions mostly in batch systems. Few studies were carried out using semi-continuous systems for zeolite A membrane synthesis. Zeolite A membranes are mainly used in pervaporation processes for separation of water from water/organic mixtures because of their hydrophilic property. In this study, zeolite A membranes were synthesized on -alumina supports from a clear solution with a molar composition of 49Na2O: 1Al2O: 5SiO2: 980H2O. Synthesis was done both in a batch system and in a flow system in which solution was circulated through the support under atmospheric pressure. Effects of synthesis temperature, time, flow rate and seeding on membrane formation were investigated. The membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), single gas permeation measurements and pervaporation tests. In batch system, pure zeolite A membranes having cubic form of zeolite A was obtained for the syntheses carried out at 60&deg / C for 24 h and 80&deg / C for 8 h. Thicknesses of the membranes synthesized at 80&deg / C and 60&deg / C were about 2 &micro / m and 4 &micro / m, respectively. N2 permeances were 2*10-8 mol/m2sPa and 8*10-8 mol/m2sPa for of the membranes synthesized in the batch system at 60&deg / C and 80&deg / C, respectively. When synthesis was carried out in flow system pure and continuous zeolite A membranes were obtained for all conditions. Membranes synthesized at 60&deg / C and 80&deg / C had thicknesses of about 1.5 and 2 &micro / m, respectively. Lower N2 permeations were obtained for the membranes synthesized in flow system. It was observed that flow rate and seeding did not significantly affect the thickness of the membrane layer. The membranes synthesized in this study are significantly thinner than the membranes reported in the literature. Single gas permeation tests at 25&deg / C for the membranes showed that comparable membranes with the ones in literature were obtained in this study. For a double layer membrane synthesized in flow system at 80&deg / C for 8h separation factor about 3700 was obtained for the separation of 92:8 (wt.%) ethanol/water mixture at 45&deg / C.

Zeolites are microporous crystallines with well defined structures. Zeolites are used in variety of applications because of their properties such as high temperature stability, ion-exchange capacity, adsorption capacity and stability to harsh conditions. Some major applications of zeolites are ion-exchange, catalysis, adsorption and separation. Synthetic zeolites are normally produced as fine crystalline powder. Prior to their use, the powder is usually formed into spheres, tablets and extrudates by addition binder. Since binders present in the zeolite can block the pores and decrase the adsorption properties, preparation binderless zeolite agglomerates with high mechanical stability has great technological importance. Objective of the study is to synthesize binderless zeolite X tubular macrobodies by using the developed methods for the synthesis of zeolite A bars and tubes. Main steps of the study are synthesis of the tubular binderless zeolite X macrobodies, characterization of the macrobodies, determination the effect of hydrogel composition on zeolite phase and analyzing effect of time on the crystallinity of macrobodies. Experimental method for synthesizing the binderless tubular zeolite X macrobodies includes the following steps / preparing hydrogel by mixing sodium aluminate and sodium silicate solutions, filtration of the hydrogel, paste preparation from solid phase of the hydrogel, extrusion of green tubes from paste, calcination of green tubes and crystallization of calcined tubes in filtered liquid of the hydrogel. In this study, synthesis of binderless tubular pure zeolite X macrobodies with high crystallinity was achieved. Micropore volume and BET surface area of the zeolite X tubular macrobody I&Ccedil / S-18, which has 99.9 % crystallinity were determined as 0.178 cm3/g and 631.2 m2/g, respectively. Pure zeolite X, pure zeolite A and zeolite A, X mixtures were obtained after the crystallization of the calcined extrudates which were obtained from different hydrogel compositions. Ternary diagram which was based on the hydrogel compositions and the obtained zeolite phases was plotted.

Zeolite A membranes have great potential in pervaporation separation of ethanol/water mixtures with high flux and selectivity. Zeolite membranes usually synthesized from hydrogels in batch systems. In recent years, zeolite membranes are prepared in semicontinuous, continuous and recirculating flow systems to allow the synthesis of zeolite membranes with enlarged surface areas and to overcome the limitations of batch system at industrial level production. The purpose of this study is to develop a synthesis method for the preparation of good quality zeolite A membranes in a recirculated flow system from hydrogels and to test the separation performance of the synthesized membranes by pervaporation of ethanol/water mixture. In this context, three different experimental synthesis parameters were investigated with zeolite A membranes synthesized in batch system. These parameters were the composition of the starting synthesis hydrogel, silica source and the seeding technique. Syntheses were carried out using hydrogels at atmospheric pressure and at 95 &deg / C. The membranes were characterized by X-ray diffraction, scanning electron microscopy and pervaporation of 90 wt% ethanol-10 wt% water mixtures. v Pure zeolite A membranes were synthesized both in batch and flow systems. The membranes synthesized in batch system have fluxes around 0.2-0.3 kg/m2h and selectivities in the range of 10-100. Membranes with higher selectivities were obtained in batch system by using waterglass as silica source, seeding by dip-coating wiping method, and with a batch composition of 3.4Na2O:Al2O3:2SiO2:155H2O. The membranes prepared in flow system have higher pervaporation performances than the ones prepared in batch system in considering both flux and the selectivity. Fluxes were around 0.3-3.7 kg/m2h and selectivities were in the range of 102-104 for the membranes prepared in flow system which are comparable with the data reported in literature for batch and flow systems. A high quality zeolite A membrane was also synthesized from 3.4Na2O:Al2O3:2SiO2:200H2O hydrogel at 95 &deg / C for 17 hours in flow system. Pervaporation flux of this membrane was 1.2 kg/m2h with a selectivity &gt / 25,000 at 50&deg / C. Although the synthesis method is resulted with high quality membrane, reproducibility of the synthesis method is poor and it should be improved.

The diesel engine is growing in popularity due to its energy efficiency and solving the emissions issues associated with diesel engine exhaust would clear the way for further growth. The key pollutants are NOx, particulate matter and unburned hydrocarbons. Selective catalytic reduction (SCR) catalysis is likely the best choice for NOx control. In SCR, NH3 selectively reacts with NOx to form N2 – the selectivity refers to NH3 reacting with NOx instead of the abundant O2. Urea is used as the NH3 source, being injected into the exhaust as an aqueous solution where the urea decomposes and NH3 is generated. Spatial resolution characterization techniques have been gaining attention in the catalysis field because of the higher level of information provided. In this thesis, a new spatial resolution technique, called SpaciFTIR (spatially-resolved, capillary-inlet Fourier transform infra-red spectroscopy), was developed, which overcomes the interference of water in the detection of NH3 in an earlier developed technique, SpaciMS (spatially-resolved, capillary-inlet mass spectrometry). With the new test method, three SCR topics were addressed. First, the three key SCR reactions were spatially resolved. These are the standard SCR reaction (2NO + 2NH3 + 1/2O2 = 2N2 + 3H2O), the fast SCR reaction (NO + NO2 + 2NH3 = 2N2 + 3H2O), and NO2-SCR, (6NO2 + 8NH3 = 7N2 + 12H2O). Results show that in the presence of NO2, but at a NO2/NOx ratio < 0.5, the fast SCR reaction proceeds followed by the standard SCR reaction, i.e. in series. If the NO2/NOx ratio exceeds 0.5, the NO2-SCR and fast SCR reactions occur in parallel. Compared to the standard integral test method, this spatial resolution technique clearly showed such trends. Secondly, the spatial resolution technique was used to characterize the effects of thermal aging on catalyst performance. It was found that for a highly aged catalyst, there was a radial activity profile due to an inhomogeneous temperature distribution in the process of aging. Aging effects on various key SCR reactions, i.e. NO oxidation, NH3 oxidation, and the reduction reactions, were studied. Last but not least, for the purpose of passive SCR system development, transient NH3 storage profiles along the monolith channel were measured with SpaciFTIR. Passive SCR is a system where the NH3 is generated on an upstream catalyst, such as a three-way catalyst or lean-NOx trap, instead of via urea injection. In such a system, NH3 is therefore not constantly being fed to the SCR catalyst, but “arrives” in pulses. Factors such temperature, NH3 concentration, pulsing time, flow rate and thermal aging were investigated. For the first time, NH3 migration was observed and its effect on SCR reactions along the length of catalyst was studied.

Clinoptilolite is the most abundant zeolite mineral in nature. In this study a reproducible synthesis recipe for clinoptilolite was established and the limits of the crystallization field were developed by changing synthesis parameters such as temperature, composition and the nature of reactants. Clinoptilolite was reproducibly synthesized as a pure phase and in high yield at 140oC using a benchmark batch composition of 2.1 Na2O:Al2O3:10SiO2:110.1 H2O. Clinoptilolite was crystallized from 10wt% or 28wt% seeded systems while it was not formed if no seeds were present. Clinoptilolite was also crystallized as a pure phase when the cation in the benchmark batch composition was Na,K mixture, or when alkali salts such as carbonates or chlorides were used besides alkali hydroxides, or when the SiO2/Al2O3 ratio was in the range of 10-12. Clinoptilolite was still crystallized as a single phase when alkali hydroxides in the batch were reduced by 20%. With the benchmark batch composition, clinoptilolite was crystallized in pure phase form at 100oC, 120oC, 140oC and 160oC while synthesis at 175oC resulted in the formation of pure mordenite. At 140oC clinoptilolite was crystallized together with Linde L when cation in the benchmark composition is only potassium. Phillipsite crystallized together with clinoptilolite at SiO2/Al2O3 ratio of 8 to 9. At SiO2/Al2O3 ratios of 6 or 4, phillipsite or analcime was formed as pure phase respectively. When the alkali hydroxides in the batch was increased by 20%, sanidine was formed. Use of reactive aluminosilicate gels enhanced the formation of clinoptilolite while attempts to use mineral raw materials were unsuccessful. For both Na and (Na,K)-clinoptilolite, Si/Al ratio of products were greater than four. Thermal stability of synthetic clinoptilolites were comparable with natural clinoptilolite and potassium ion increased thermal stability of clinoptilolite.

Made available in DSpace on 2014-12-17T14:07:07Z (GMT). No. of bitstreams: 1 AlexandreFMC_DISSERT.pdf: 2018035 bytes, checksum: dd77e9d37e80465172d8dc362ca0200a (MD5) Previous issue date: 2011-11-25 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The synthesis of zeolites from natural sources of silicon and aluminum are promising alternative routes to obtain porous or zeolite MCM family. Such materials are typically used in catalytic processes and / or adsorption is to obtain new products or for separation and purification processes thereof. Environmental legislation is becoming stricter and requires the use of materials more efficient, aiming to achieve pollution prevention, by gas or liquid contaminants in the environment. In order to obtain a material with environmentally friendly features, this study aimed at the synthesis of zeolite A, from an amorphous sediment, diatomite, which is found in abundance in the northeast region of Brazil, may be substituted for conventional products the production of zeolite, involving higher costs. The methodology for obtaining the "Zeolite A" using as a source of silica and alumina diatomite is simple, since this is a source of silicon, not requiring therefore a structural driver, but also by heat treatment, only drying conventional to remove water. The "zeolite A" was obtained from diatomite, but as an intermediate step we obtained the sodalite. The characterization was made by the following techniques: EDX, XRD, FT-IR, SEM and determining a specific area by the BET method and the BJH method for checking the diameter of pores. By characterization of the obtained material was first demonstrated the achievement of sodalite and after modification of the same, there was obtained zeolite A / A s?ntese de ze?litas a partir de fontes naturais de Sil?cio e Alum?nio s?o rotas alternativas promissoras para a obten??o de materiais porosos da fam?lia MCM ou ze?litas. Tais materiais normalmente s?o usados em processos catal?ticos e/ou adsortivos seja para obten??o de novos produtos ou para processos de purifica??o e separa??o dos mesmos. A legisla??o ambiental ? cada vez mais rigorosa e exige o uso de materiais cada vez mais eficientes, com intuito de realizar preven??o de polui??o, por gases ou a l?quidos contaminantes do meio ambiente. Visando a obten??o de um material com caracter?sticas ambientalmente corretos, esse estudo teve como objetivo a s?ntese de ze?lita A, a partir de um sedimento amorfo, diatomita, o qual ? encontrado em abund?ncia na regi?o nordeste do Brasil, podendo vir a substituir produtos convencionais para a produ??o de ze?lita, envolvendo custos mais altos. A metodologia utilizada para obten??o da ze?lita A usando como fonte de s?lica e alumina a diatomita ? simples, uma vez que esta ? uma fonte de sil?cio, n?o necessitando, portanto de um direcionador estrutural, como tamb?m de um tratamento t?rmico, apenas secagem convencional para retirada da ?gua. A ze?lita A foi obtida a partir da diatomita, por?m como etapa intermedi?ria obteve-se a sodalita. As caracteriza??es foram feitas pelas seguintes t?cnicas: EDX, DRX, FT-IR, MEV e determina??o de ?rea espec?fica pelo m?todo BET e o m?todo BJH para verifica??o do di?metro de poros. Atrav?s da caracteriza??o do material obtido comprovou-se primeiramente a obten??o da sodalita e ap?s modifica??o da mesma, obteve-se a ze?lita A