Thesis (M.Ch.E.)--University of Delaware, 2005. / Principal faculty advisors: Jingguang Chen, Raul F. Lobo, Dept. of Chemical Engineering. Includes bibliographical references.

Master of Science / Department of Chemical Engineering / Jennifer L. Anthony / Zeolite refers to a microporous material, which is also called a molecular sieve. There are three major industrial applications of zeolites: adsorbents, ion exchangers, and catalysts; and many other minor applications including: sensors, agriculture, medicine, veterinary, hydrogen storage, fuel cells, microreactors, membrane reactors, and racemic separations. Today, zeolite is not limited to aluminosilicate. Researchers are attempting to use other species (such as B, Ga, Ge, Ti, and Zn) to replace aluminum in zeolites framework to accomplish particular applications. In 1991, the first zincosilicate zeolite was synthesized by Annen et al.. Currently, only four zincosilicate zeolites have been synthesized. Theoretically, zincosilicate should balance divalent cations better than aluminosilicate zeolites to provide a stronger acid site especially for hydrogen cracking reactions. Large pore VET type VPI-8 (Li₁.₉₁₄Zn₁.₉₁₄Si₁₅.₀₈₆O₃₄) is the most thermal stable of all the zincosilicate zeolites and has low chemicals cost, however, a high crystallinity VPI-8 required prohibitively long synthesis times or seeded synthesis procedures. In this work, a seed-free short time synthesis zincosilicate zeolite VPI-8 is presented. Methane, also known as natural gas, had become the largest abundant carbon reserve today, more than the amount of the fossil fuel including conventional gas, oil, and coal. Unlike fossil fuel, methane can be recycled from landfill. Methane could be used to produce useful and/or expensive chemicals via syngas conversion to fuel, paraffin, methanol, alcohol, and dimethoxyethane. In addition to pathways via a syngas intermediate, methane could react directly to ethylene, formaldehyde, and aromatics. Because syngas preparation and compression usually expends 60-70% of the capital cost and consumes almost all the energy of operation, more and more researchers are exploring direct methane activation. However, the high stability of methane is one of the limitations, and coking is another limitation. In this work, methane dehydroaromatization (MDA) over zincosilicate zeolite Li-VPI-8 and ion exchanged Ni/Li-VPI-8 are investigated, due to the stronger acid site in zincosilicate than aluminosilicate zeolites. This is the first time to study using zincosilicate as catalyst, capitalizing on the more efficient synthesis methods demonstrated in this work.

Orientador: Gilson Herbert Magalhães Dias / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-13T19:09:25Z (GMT). No. of bitstreams: 1 Forner_Ricardo_D.pdf: 4146958 bytes, checksum: e310cb4a554e926b949b24daf9b0a2a9 (MD5) Previous issue date: 2008 / Resumo: Esta tese teve como objetivo o estudo dos efeitos estéricos e eletrônicos dos zeólitos faujasita HY, LiY, NaY e CsY na estrutura, reatividade e comportamento térmico do organometálico [MnCp(CO)3]ocluído. As diversas formas alcalinas do zeólito Y foram preparadas por troca iônica no zeólito Na56Y comercial e os estudos das interações, do comportamento térmico e da reatividade do complexo ocluído nos zeólitos foram feitos por espectroscopia de infravermelho com transformada de Fourier (FTIR) em um sistema especialmente construído para essa finalidade. O organometálico [MnCp(CO)3] adsorvido nos zeólitos apresentou, no mínimo, cinco bandas nos espectros FTIR, que foram atribuídas a diferentes sítios de ancoramentos localizados na superfície e na supercavidade. A decomposição do convidado ocluído ocorre com velocidades maiores nos sítios de ancoramento que possuem interações cátion-carbonila mais fracas. Os espectros obtidos para a oclusão do organometálico em zeólitos parcialmente hidratados mostraram que as interações carbonilas-cátions no zeólito parcialmente hidratado são tão intensas quanto às interações do convidado no hospedeiro desidratado. Os cálculos computacionais, que simularam as interações entre o zeólito e o organometálico, forneceram informações sobre energias de interações, comprimentos e ângulos de ligação. Os espectros simulados exibiram bandas de estiramentos de carbonilas próximas às bandas dos espectros obtidos experimentalmente / Abstract: This thesis aimed to study the steric and electronic effects of faujasita zeolites HY, LiY, NaY and CsY on the structure, reactivity and thermal behavior of [MnCp(CO)3] organometallic compound occluded. Various alkaline forms of zeolite Y were prepared by ion exchange in the zeolite Na56Y. Study of the interactions, the thermal behavior and reactivity of the organometallic compound occluded in zeolites were done using FTIR spectroscopy in a system especially constructed for this purpose. The FTIR spectra of [MnCp(CO)3] compound adsorbed in zeolites displays at least 5 bands that were attributed to different anchoring sites located on the surface and in the supercages. The decomposition of the occluded guest was faster in the anchoring sites where the interactions cation-carbonyl were weaker. The occluded organometallic spectra in partially hydrated zeolites have showed the same strength for carbonyl-cation and water-cation interactions. The computational calculations, that have simulated the interactions of the organometallic with zeólito, provided information on interaction energy, lengths and angles of bonds. The simulated spectra have showed carbonyl stretching bands in similar way to experimental spectra / Doutorado / Quimica Inorganica / Doutor em Ciencias Quimicas

M. Tech. / Gold (Au) mining in South Africa resulted in vast volumes of hazardous waste being generated. Poor management of most of the tailings dams has resulted in the release of acid mine drainage, which caused stream water and soil contamination with their run-offs. The consequence of mine closure has not only been observed in large-scale land degradation, but also in widespread pollution of surface water and groundwater in the Wonderfonteinspruit Catchment Area (WCA). Thus, clean-up methods must be developed in order to remove heavy metals from contaminated water bodies in this area. The efficacy of algae, zeolite and zeolite functionalized with humic acid in reducing the concentration of the heavy metals iron (Fe3+), zinc (Zn2+), manganese (Mn2+) and nickel (Ni2+) to acceptable levels in WCA was investigated in this study. It is also envisaged that the heavy metals to be removed from contaminated water can be useful in various industries. A sampling exercise was undertaken with the aim of identifying the heavy metals that contaminate the water in the catchment, as well as identify the priority heavy metals for laboratory sorption tests. Batch experiments were conducted to study the adsorption behavior of natural zeolite clinoptilolite and algae Desmodesmus sp. with respect to Fe3+, Mn2+, Ni2+, and Zn2+. The data was analysed using the Langmuir and Freundlich isotherms. Two kinetic models namely, pseudo-first order and pseudo second order were also tested to fit the data. It was found that the concentration of Fe3+, Mn2+, Ni2+ and Zn2+ was 115 mg/L, 121 mg/L, 26.5 mg/L and 6.9 mg/L from the sampled water bodies in the WCA, respectively. The Langmuir isotherm was found to correlate the adsorption of Fe3+, Mn2+, Ni2+, and Zn2+ better, with the adsorption capacity of 11.9 mg/g, 1.2 mg/g, 1.3 mg/g, and 14.7 mg/g, for the functionalized zeolite (FZ), respectively. The algae system gave adsorption capacities of 1.523 mg/g, 144 mg/g and 71.94 mg/g for Fe3+, Mn2+ and Ni2+; respectively. Pseudo second-order equation was found to be the best fit for the adsorption of heavy metals by unfunctionalized zeolite (UFZ) and the algae system. Zeolite functionalization with humic acid increased its uptake ability. The best results for kinetic study was obtained in concentration 120 ppm for Fe3+ and Mn2+, whilst for Ni2+ was at 20 mg/L , which is about the same concentrations found in contaminated water in the WCA (Fe3+ 115 mg/L, Mn2+121 mg/L and Ni2+ 26.5 mg/L).

[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 no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/147115 / TESIS

>Magister Scientiae - MSc / The use of diesel engines in vehicles and heavy machinery throughout the world has been slowly increasing in the past few decades. This has led to high demand for diesel and gasoline with high octane number. Diesel and gasoline are in high demand due to its qualities as fuels containing low or no sulfur and nitrogen compounds, making them environmentally friendly and the anti- knocking properties respectively. With these reasons and more, researchers have been studying processes like the catalytic oligomerization of olefins to produce synthetic fuels with augmented qualities and properties. The effectiveness of the process will depend on the quality of the catalyst.

With demand for gasoline and diesel expected to decline in the near future, crude-tochemicals technologies have the potential to become the most important processes in the petrochemical industry. This trend has triggered intense research to maximize the production of light olefins and aromatics at the expense of fuels, which calls for disruptive processes able to transform crude to chemicals in an efficient and environmentally friendly way. Simultaneously, the production of high-demand chemical commodities such as olefins, aromatics and gasoline from alternative feedstocks such as methanol has been central to research in both academia and industry. In both conversions, catalyst composition and formulation play a key role. In principle, shaping and optimal compositional formulation are major challenges in the successful industrial application of heterogeneous catalysts. Herein, we evaluate the application of the spray-drying shaping technique to manufacture spherical zeolite-based catalysts and their applicability in the direct crude-to-chemicals and the methanol-to-hydrocarbons processes. A thorough study of the effect of formulated fluid catalytic cracking catalyst composition on the one-step cracking of Arabian light crude oil was studied in the present thesis. Our results demonstrate that over a 35wt.% yield to light olefins can be achieved on spray-dried catalysts containing 1:1 mixtures of ZSM-5 and FAU zeolites. On the other hand, the nature of the selected clay, one of the key components in formulated catalysts, has a significant influence in modifying the final acidity of the composite, which, when applied in methanol to hydrocarbons, results in the propagation of either the alkene or arene cycles. The present PhD thesis also has been dedicated to the study of optimal conditions for the highly selective and stable production of aromatics during methanol to aromatics at high pressure. High selectivity to aromatics (~50%) can be achieved on a commercial high silica ZSM-5 at 400° and 30 bar total pressure. The high partial pressure of primary olefins and the promoted methanol-induced hydrogen transfer pathway result in an exponential increase in aromatization, while the high partial pressure of steam generated via dehydration of methanol leads to in situ coke removal and, therefore, to a slower deactivation of the zeolite.

Zeolite-supported transition metal catalysts, which couple the unique size- and shape-selectivity arising from the well-defined microporous structure of zeolites with the inherent high activity of metal species, have demonstrated remarkable performance in numerous catalytic reactions. Conventionally, such catalysts are prepared by loading metal species in the micropores of zeolites in the form of clusters (each containing only several atoms). Despite their high catalytic activity, the ultra-small clusters are usually highly mobile, and tend to migrate from the micropores to the crystal surfaces of zeolite during the reaction, where they agglomerate and deactivate. In this dissertation, we attempted to solve this issue by encapsulating metal nanoparticles (NPs) in zeolite crystals, based on the following considerations: (i) compared to clusters, nanoparticles have similar catalytic activity but much less mobility; and (ii) as long as the active sites are inside the zeolite crystals (not necessarily in the micropores that are too small to accommodate nanoparticles), they can exhibit selectivity associated with the zeolite structure. In the first chapter, we gave a general introduction to zeolites and zeolite supported catalysts, focusing on the preparation of hierarchical zeolites that are the main catalyst support materials used in the research projects of this dissertation. In the second chapter, we encapsulated highly dispersed Pd NPs (~2.6 nm) in zeolite ZSM-5 crystals, and used the obtained catalyst (Pd@SG-ZSM-5) for the hydrogenation of cinnamaldehyde. The confinement effect gave rise to an interesting catalytic behavior: compared with the traditional supported Pd catalyst prepared by impregnation, Pd@SG-ZSM-5 showed a 2.5-fold enhancement in the selectivity of hydrocinnamaldehyde (73% vs. 30%). Liquid adsorption combined with infrared spectroscopy characterization revealed that Pd@SG-ZSM-5 catalyst adsorbs much less reactant and product molecules than traditional catalyst, thereby suppressing the formation of by-products and leading to high selectivity. In chapter three, we developed a new method to encapsulate in situ produced molybdenum carbide (MoCx) in zeolite ZSM-5 for the methane dehydroaromatization (MDA) reaction. In this method, the structure-directing agent used to synthesize hierarchical zeolite ZSM-5 was utilized to reduce molybdenum precursor through a calcination process in an inert atmosphere. The zeolite subsequently underwent a secondary growth process to achieve encapsulation. The catalytic behavior of the as prepared catalyst in MDA consolidate our previous conclusion that MoCx particles outside the microporous channels can also act as the active sites for MDA, whereas it is traditionally viewed that only MoCx clusters inside the micropores are active sites. In addition, the encapsulation strategy allowed us to design experiments to answer one open question related to MDA, namely whether the Brønsted acid (BA) sites of the zeolite play a catalytic role in the conversion of methane to aromatics or only promote the dispersion of the Mo species. We encapsulated MoCx particles, which had proven to be active sites, in pure siliceous zeolite (Silicalite-1) that does not contain BA sites. The catalyst did not exhibit MDA activity even when aromatic compounds were introduced into the system by pre-adsorption or co-feeding, indicating that the BA sites are responsible for the oligomerization/cyclization step during MDA. Finally, in chapter five, we summarized the dissertation and gave our perspectives and outlooks on the further development of encapsulated catalysts based on zeolites.

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Today, zeolites play a considerable role in many industrial fields, especially in heterogeneous catalysis. Well-defined microporous structure combined with acidity provides exceptional size and shape selectivity, making zeolites indispensable in petrochemistry. However, the micropores can cause diffusion limitations and, in turn, a drop in reaction rate and selectivity. Hence, the development of modification methodologies on zeolite textural properties is one of the attention-grabbing research topics nowadays. For example, to overcome transport limitations in zeolites, the particle size can be reduced, or a system of larger auxiliary pores can be introduced [1]. One of the most promising methods for introducing secondary pores on a large scale is desilication since it is low-cost, versatile, and easy [2]. Despite its simplicity, the desilication mechanism is still a matter of discussion. In detail, it is not well-understood: 1. The influence of different species on mesopore formation kinetics 2. How aluminum is assembled back into the zeolite 3. Which types of aluminum species form throughout the treatment. The present study tries to answer these questions by relating ex-situ and in-situ NMR. The proposed ex-situ 29Si MAS NMR approach allows monitoring the development of mesoporosity and silicon extraction by analyzing Q3 and Q4 changes. The combination of ex-situ with in-situ 29Si MAS NMR study showed that the limiting step of Si extraction is the transformation of Q3 into Q2. 27Al MAS NMR combined with MQMAS showed the formation of new aluminum species after desilication. It was shown that some of the Al framework T-sites might dissolve during alkaline treatment. In-situ 27Al NMR indicates redistribution of dissolved aluminum upon desilication.