The ability of natural zeolite and synthetic ion-exchange resin for ammonia removal from aqueous solution was studied through batch experiments. The results showed that both zeolite and ion-exchange resin were effective (up to 87% of removal) in eliminating ammonia from aqueous solution. Factorial design and response surface methodology were applied to evaluate and optimize the effects of pH, dose, contact time, temperature and initial ammonia concentration. Low pH condition was preferred with the optimum pH found to be 6 for both zeolite and ion-exchange resin. High dose generated high removal rate and low exchange capacity. Results of factorial design and response surface methodology showed that temperature was not a significant parameter. The model prediction was in good agreement with observed data (R2 = 0.969 for zeolite and R2 = 0.957 for resin, respectively). For zeolite, the optimum Qe was 22.90 mg/g achieved at pH=7 and initial ammonia concentration of 3000 mg/L. For ion-exchange resin, Qe of 28.78 mg/g was achieved at pH=6 and initial TAN concentration of 3000 mg/L. The reaction kinetics for both of them followed the Pseudo-second order kinetic model (R2=0.998 and R2=0.999, respectively). Equilibrium data were fitted to Langmuir and Freundlich isotherm models with Freundlich model providing a slightly better predication for zeolite (R2=0.992) and Langmuir providing more accurate prediction for ion-exchange resin (R2=0.996). The ion-exchange resin can be completely regenerated by 2N H2SO4.

Zeolite membranes are considered to be a promising alternative to polymeric membranes and they have the potential to separate gases under harsh conditions. Silicalite-1 membranes in particular are easy to prepare and suitable for several industrial applications. In this research project, silicalite-1/ceramic composite membranes were prepared using the pore plugging hydrothermal synthesis method and supports with zirconium oxide and/or titanium oxide as active layers. The effect of the support’s pore size on the morphology and permeation performance of the prepared membranes was investigated using five supports with different active layer pore sizes in the range of 0.14 – 1.4 m. The prepared membranes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), electron diffraction spectrometer (EDS), single gas and binary gas mixtures permeation tests. The results confirmed the presence of a typical silicalite-1 zeolite structure with a high internal crystalline order grown inside the pores of the active layer of the supports, with a dense film covering most of the supports active layers. Silicalite-1 crystals in the prepared membranes were preferably oriented with either a- or b-axes perpendicular to the support surface. Single gas permeation results illustrated that the observed permeances were not directly related to the kinetic diameter of permeants. Instead, the transport of the studied gases through the prepared membranes occurred by adsorption followed by surface diffusion mechanism. Binary gas tests performed with CO2 and N2 mixtures showed that the prepared membranes were selective and very permeable with CO2/N2 permselectivities up to 30 and a CO2 permeances in the order of 10-6 mol m-2 Pa-1 s-1. A model was developed, based on Maxwell−Stefan equations and Extended Langmuir adsorption isotherm, to describe the transport of binary CO2 and N2 mixtures through the prepared silicalite-1 membranes. The model results showed that the exchange diffusivities (D12 and D21) were less dependent on the feed pressure and feed composition compared to the permeances and the permselectivities. Hence, they are more appropriate to characterize the intrinsic transport properties of the prepared silicalite-1 membranes.

La conversion du méthanol par les zéolithes est l'une des applications les plus prometteuses pour l'obtention d'hydrocarbures (oléfines, essences, gasoils) à partir de sources alternatives au pétrole (gaz naturel, charbon, biomasse). Dans cette thèse, un procédé catalytique multi-étapes permettant la conversion du méthanol en hydrocarbures à longue chaîne a été imaginé.Le méthanol est converti en oléfines légères par différents catalyseurs zéolithiques dans un réacteur à lit fixe sous flux continu et en phase gazeuse. L'utilisation de la ferrierite dessilicatée, de la chabazite désaluminée, de la MCM-22 et de la MCM-36 est détaillée. Les oléfines inférieures sont ensuite oligomérisées. L'oligomérisation de l'éthylène catalysée par des solides mésoporeux de type MCM-41 échangés au nickel et la co-oligomérisation des oléfines inférieures par catalyse acide sur H-MCM-41 ont été étudiées. Ces réactions ont été mises en oeuvre dans un autoclave semi-continu de type slurry. / Methanol conversion into hydrocarbons (olefins, gasoline and diesel fuel) over zeolites is one of the most promising applications involving non-oil based sources (natural gas, coal, and biomass). In this thesis, a multi-step catalytic process for converting methanol into long-chain hydrocarbons has been designed.Methanol was converted into light olefins by different zeolitic catalysts in a fixed bed reactor under continuous flow in gas phase. The use of dessilicated ferrierite, dealuminated chabazite, MCM-22 and MCM-36 has been investigated. Then, the lower olefins were oligomerized. The oligomerization of ethylene catalyzed by nickel exchanged mesoporous MCM-41 and co-oligomerization of lower olefins by H-MCM-41 acid catalyst were studied. These reactions were performed in a gas-slurry reactor operating in semi-batch mode.

This thesis focuses on developing an alternative system for membrane electrode assembly (MEA) formation to use with a direct methanol fuel cell (DMFC). The approach involves incorporating inorganic fillers with an industry standard Nafion polymer as part of a methanol resistant composite barrier layer at the anode/membrane interface of MEA featuring Nafion 117 membranes. This procedure is used to reduce the fuel cell losses related to the crossover of un-oxidised methanol through the membrane and prevent its subsequent reaction at the cathode. The inorganic filler used within this study was mordenite that has Si/Al ratio of 5 and by incorporating this into the barrier layer a superior DMFC performance has been achieved in comparison to a standard MEA featuring a Nafion 117 membrane. The voltage, current density and power density used as a measure of DMFC performance under a range of methanol molarities (1M-4M) and cell temperatures (40°C-70°C) have been taken for both the novel and standard MEA. Linear sweep voltammetry (LSV) and AC impedance spectroscopy (ACIS) were used to give some insight into what was occurring within the MEA with regards to methanol crossover current and the proton conductivity within the DMFC. To obtain the best possible DMFC performance a range of mordenite loadings from 0wt%1.0wt% were utilised and an optimum loading of 0.5wt% was reached. MEA which featured mordenite that had undergone ion exchange into a protonated form (from the sodium form) and had a silane functional group (glycidoxypropyltrimethoxysilane) grafted onto the surface, gave DMFC performances that were as much as 50% better than the standard. The highest power density obtained with this MEA was 43.6mW/cm-2 compared to the 35mW/cm-2 obtained using the standard. Values obtained for the methanol crossover current and proton conductivity under working DMFC operating conditions showed that this novel MEA had as much as 16% lower methanol permeability compared to the standard combined with comparable proton conductivity when using a 1M methanol feed. The durability of a novel MEA featuring the 0.5wt% functionalised H-mordenite composite barrier layer was tested in the DMFC and compared to a standard MEA at a constant current of 50mA/cm-2 over 100 hours. The cell potential fell by 0.1mV/h in comparison to a 0.23mV/h loss observed with the standard. The work reported within this study aims to show that by incorporating a thin Nafion/mordenite composite layer at the anode/membrane interface within an MEA will result in improvements in DMFC performance. The development of this technology has led to the application for a patent due to the potential for the commercial development of DMFC using this novel approach.

Les problèmes de pollution chimique de l'eau sont devenus une source de préoccupation importante et un enjeu prioritaire pour les industriels du nucléaire. L'objectif principal de cette thèse est d'étudier certains minéraux échangeurs ioniques utilisables pour une décontamination liquide en strontium (radioisotope toxique pour l'homme). Mais également de relier les propriétés physico-chimiques de ces matériaux avec leurs propriétés de rétention du radioisotope. Ce mémoire présente donc la synthèse de deux matériaux choisis pour leurs propriétés de sorption spécifique et quantitative du strontium : le nonatitanate de sodium et la zéolithe A. Une seconde partie du travail est dédiée à l'étude des capacités d'échange spécifique de ces matériaux vis-à-vis du strontium en présence d'autres éléments comme le sodium et le calcium. Le nonatitanate de sodium et la zéolithe A ont également été testés sur des effluents réels. Les performances d'un monolithe de zéolithe A ont été évaluées pour un procédé de traitement en colonne. Ce matériau semble prometteur pour la décontamination d'effluents car il permet de cumuler les avantages de la poudre de zéolithe A avec ceux d'un transfert de matière sans perte de charge du solide. / The problems of chemical pollution of water have become a major concern and a priority for the nuclear industry.The aim of this work is to study some ion exchangers used for the removal of strontium ions because 90Sr is one of a major pollutant in nuclear liquid wastes. This study allows linking the physical and chemical properties of these materials and their sorption properties. This work presents therefore the synthesis of two materials - sodium nonatitanate and zeolite A - selected for their specific sorption properties of strontium: A second part of this work is dedicated to the study of specific exchange capacities of these materials for the strontium in presence of other elements such as sodium and calcium. Batch experiments were performed and kinetic and ion exchange models have been applied to understand the selectivity of the materials for strontium removal. Sodium nonatitanate and zeolite A are also studied in actual effluents.Monoliths of zeolite A have been also tested in dynamic ion exchange process. This material is promising for the treatment of radioactive effluents in continuous flow because it joins the sorption properties of the zeolite powder with the advantage of a solid with a macroporous network.

The energy consumption in the world is increasing at the same time as the fossil fuel resources are limited. This is causing a rising interest in renewable energy sources over the world. To reduce dependency on fossil fuel sources biomass is an excellent alternative.SCA Östrand pulp mill in Timrå is having one of the largest industrial investments made in Sweden. The production capacity will double, resulting in the largest production line for bleached softwood kraft pulp in the world. This level will be reached in 2020. The large expansion has given an interest for a possible localization of a biorefinery in connection with the existing pulp mill. This project was one of the first investigations towards building a biorefinery at SCA Östrand pulp mill.The aim of this project was to investigate liquefaction of bark from spruce from SCA Ortviken paper mill by solvent solubilization of lignin. It was desirable to hydrolyze all cellulose in the media used, with or without the use of solid catalyst. Many different catalysts together with solvents were investigated with the goal to find the best suitable combination to be used in a biorefinery of softwood bark. The investigated solvents were para-toluenesulfonic acid and methanol. Today bark is usually burned for heat recovery at the pulp and paper mill.Analysis of extractives, ash metals and carbohydrates of the bark were performed before any trials. Reactions took place in a 0.3 L stainless steel Parr reactor with high temperature and pressure. Several trials (21 in total) were made with or without catalyst and most of them with methanol as solvent. Two catalysts were studied in more detail, zeolite ZSM-5 and zeolite Beta_250. For ZSM-5 mainly methyl esters and steroid hydrocarbons were formed. Reactions with Beta_250 resulted in monolignols, shorter methyl esters and shorter organic acids compared with ZSM-5.The result showed most liquid product and lowest bark and coke residue from zeolite ZSM-5 and Ni/C-catalyst with 0.16 g respectively 0.21 g bio-oil, both from 1 g of softwood bark.

Este trabalho objetivou estudar a síntese de zeólita NaA sob condições hidrotérmicas e aplicála na adsorção de metais pesados. Para a síntese de zeólita NaA, caulim do município de Ipixuna, Pará, foi calcinado a 700 °C por 3 horas para obtenção de metacaulim e usado como fonte de sílica e alumina. Para efeito de comparação, cloreto de alumínio e metassilicato de sódio também foram utilizados na síntese de zeólitas como precursores de Si e Al. A influência da alcalinidade na síntese dos produtos zeolíticos foi avaliada utilizando-se diferentes concentrações de NaOH. Todas as sínteses foram realizadas a 110 °C em autoclaves. Visando à compreensão da influência do tempo na quantidade e tipo de fase formada, foram realizadas sínteses com diferentes tempos de cristalização. Os produtos de reação foram caracterizados por difração de raios X, espectroscopia na região do infravermelho, análise termogravimétrica, análise térmica diferencial, microscopia eletrônica de varredura e adsorção de nitrogênio para cálculo de área específica pelo método BET. A amostra que apresentou maior proporção de zeólita NaA foi utilizada como adsorvente em soluções de Cu2+, Ni2+ e Cd2+ com concentrações iniciais de 25 a 400 mg/L. A concentração de equilíbrio desses metais, após remoção pela zeólita NaA, foi determinada por espectrofotometria de absorção atômica. Os resultados mostraram que o aumento da alcalinidade e do tempo de cristalização favoreceu a obtenção de sodalita, uma fase zeolítica concorrente à Zeólita A, nos produtos de síntese. A zeólita NaA provou ser um excelente adsorvente para remoção dos metais analisados, apresentando uma capacidade de adsorção máxima de aproximadamente 79, 65 e 32 mg/g para Cd2+, Cu2+ e Ni2+, respectivamente. O modelo de isoterma de adsorção que melhor descreveu a remoção de metais pela zeólita NaA foi o de Langmuir. / The aim of this work was to study the synthesis of zeolite NaA under hydrothermal conditions and use it as adsorbent of heavy metals. To synthesize zeolite NaA, kaolin from the city of Ipixuna, Pará, was calcined at 700 °C for 3 hours and used as source of silica and alumina. For comparison purposes, aluminum chloride and sodium metasilicate were also used in the synthesis of zeolites as precursors of Si and Al. The influence of alkalinity on the synthesis of the zeolitic products was evaluated using different NaOH concentrations. All the syntheses were performed at 110 °C by autoclaving. To understand the influence of time on the type and relative amount of the obtained phases, syntheses with different crystallization times were carried out. The reaction products were characterized by means of X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, thermal differential analysis, scanning electron microscopy and nitrogen adsorption for calculating surface area by the BET method. One of the samples, which exhibited the highest content of zeolite NaA, was used as adsorbent of Cu2+, Ni2+ and Cd2+ solutions with initial concentrations ranging from 25 to 400 mg/L. The equilibrium concentration of these heavy metals, after removal by zeolite NaA, was determined by atomic absorption spectrophotometry. The results showed that increasing alkalinity of the reaction medium led to the formation of sodalite, a concurrent zeolitic phase, in the products. Zeolite NaA turned out to be an excellent adsorbent for removing heavy metals, with an adsorption capacity of 79, 65 and 32 mg/g for Cu2+, Cd2+ and Ni2+, respectively. The Langmuir isotherm model was the most appropriate to describe the removal of metals by zeolite A.

Previous studies have successfully used near and supercritical water (SCW) for cracking and desulfurization of heavy crude oil and bio-oil, suppressing coke formation as a low-value by-product. Some of these studies benefited from using zeolite catalysts to increase the activity and selectivity toward targeted products; however, in depth studies are required to identify the role of water on zeolite catalysis under supercritical condition. Using three common zeolites, ZSM-5, HY, and β for supercritical water cracking of dodecane at 400°C, 24±2 MPa (in a 100 ml batch reactor), we showed that ZSM-5 is the only catalyst that partially retains its crystalline structure and activity under hydrothermal conditions. Further characterization of the ZSM-5 (used under 50/50 wt% SCW/dodecane feed) revealed 95% decrease in Brønsted acid site (BAS) density and 80% decrease in microporous area after 2 h reaction time. However, compared to the runs where SCW was absent, the apparent dodecane cracking rate constant in SCW decreased only by a factor of 2.6. Examining catalytic activity of ZSM-5 degradation products and re-using ZSM-5 showed that the unexpected activity cannot be ascribed to ZSM-5 degradation products. Using a group-type model, we showed that SCW accelerated gas and suppressed coke formations. Additionally a coke gasification pathway was suggested to account for formation of CO and CO2 in the presence of SCW. Additional experiments with two different ZSM-5 particle sizes suggested that dodecane cracking reaction is diffusion-limited in the absence of SCW and reaction-limited in its presence. Zero length chromatography of calcined and hydrothermally treated ZSM-5 showed 10 times greater apparent diffusivity for un-treated catalyst. This, according to Weisz-Prater analysis, suggested a 250 times greater dodecane surface concentration in the absence of SCW. We successfully optimized the water content of feed (5-15 wt%) to decrease the destructive effects of SCW on the structure, increase the selectivity toward BTEX products and eliminate coke formation.

Las especies de metal con diferentes tamaños (átomos individuales, nanocristales y nanopartículas) muestran un comportamiento catalítico diferente para diversas reacciones catalíticas heterogéneas. Se ha demostrado en la bibliografía que muchos factores que incluyen el tamaño de partícula, la forma, la composición química, la interacción metal-soporte, la interacción metal-reactivo / disolvente, pueden tener influencias significativas sobre las propiedades catalíticas de los catalizadores metálicos. Los desarrollos recientes de metodologías de síntesis bien controladas y herramientas de caracterización avanzada permiten correlacionar las relaciones a nivel molecular. En esta tesis, he llevado a cabo estudios sobre catalizadores metálicos desde átomos individuales hasta nanoclusters y nanopartículas. Al desarrollar nuevas metodologías de síntesis, el tamaño de las especies metálicas puede modularse y usarse como catalizadores modelo para estudiar el efecto del tamaño sobre el comportamiento catalítico de los catalizadores metálicos para la oxidación del CO, la hidrogenación selectiva, la oxidación selectiva y la fotocatálisis. Se ha encontrado que, los átomos metálicos dispersados por separado y los grupos subnanométricos de metal pueden aglomerarse en nanoclusters o nanopartículas más grandes en condiciones de reacción. Para mejorar la estabilidad de los catalizadores subnanométricos de metal, he desarrollado una nueva estrategia para la generación de átomos individuales y clusters en zeolitas. Esas especies subnanométricas de metales son estables en tratamientos de oxidación-reducción a 550 oC. Siguiendo esta nueva metodología de síntesis, este nuevo tipo de materiales puede servir como catalizador modelo para estudiar la evolución de especies subnanométricas de metales en condiciones de reacción. La transformación estructural de las especies subnanométricas de Pt ha sido estudiada mediante microscopía electrónica de transmisión in situ. Se ha demostrado que el tamaño de las especies de Pt está fuertemente relacionado con las condiciones de reacción, que proporcionan importantes conocimientos para comprender el comportamiento de los catalizadores de metales subnanométricos en condiciones de reacción. En la otra línea de investigación para catalizadores de metales no nobles, he desarrollado varias estrategias generales para obtener catalizadores de metales no nobles, ya sea soportados sobre óxidos metálicos o protegidos por capas delgadas de carbono. Estos materiales muestran un rendimiento excelente para varias reacciones importantes, como la hidrogenación quimioselectiva de nitroarenos, incluso cuando se comparan con los catalizadores de metales nobles convencionales. En algunos casos, los catalizadores de metales no nobles pueden incluso alcanzar selectividades para productos inviables que no ha sido posible conseguir en catalizadores de metales nobles convencionales, que es causado por la diferente ruta de reacción en catalizadores de metales no nobles. Sin embargo, la espectroscopía fotoelectrónica de rayos X a presión ambiente ha revelado que la irradiación de la luz puede modular la selectividad a los alcoholes y los hidrocarburos C2 +, lo que abre una nueva posibilidad para ajustar el comportamiento catalítico de los catalizadores metálicos. Con base en los trabajos anteriores de diferentes aspectos relacionados con catalizadores metálicos heterogéneos, las perspectivas sobre las direcciones futuras hacia una mejor comprensión del comportamiento catalítico de diferentes entidades metálicas (átomos individuales, nanoagrupamientos y nanopartículas) de una manera unificadora también se han dado en esta tesis. / Les espècies metàl·liques de diferents dimensions (àtoms individuals, nanoclusters i nanopartícules) mostren diferents comportaments catalítics per a diverses reaccions catalítiques heterogènies. S'ha demostrat a la literatura que, molts factors que inclouen la mida de la partícula, la forma, la composició química, la interacció amb el suport metàl·lic, la reacció metàl·lica i la interacció amb dissolvents poden tenir influències significatives sobre les propietats catalítiques dels catalitzadors metàl·lics. Els desenvolupaments recents de metodologies de síntesi ben controlades i eines de caracterització avançada permeten relacionar les relacions a nivell molecular. En aquesta tesi, he realitzat estudis sobre catalitzadors metàl·lics d'àtoms únics a nanoclústers i nanopartícules. Mitjançant el desenvolupament de noves metodologies de síntesi, la mida de les espècies metàl·liques es pot modular i utilitzar com a catalitzadors model per estudiar l'efecte de mida sobre el comportament catalític dels catalitzadors metàl·lics per a l'oxidació de CO, hidrogenació selectiva, oxidació selectiva i fotocatàlisi. S'ha trobat que, els àtoms metàl·lics dispersos individualment i els clústers metàl·lics subnanomètrics poden aglomerar-se en nanoclústeres o nanopartícules més grans en condicions de reacció. Per millorar l'estabilitat dels catalitzadors subnanomètrics de metall, he desenvolupat una nova estratègia per a la generació d'àtoms i racimos en zeolites. Aquestes espècies metàl·liques subnanométricas són estables en tractaments de reducció d'oxidació a 550 oC. Després d'aquesta nova metodologia de síntesi, aquest nou tipus de materials poden servir com a model de catalitzador per estudiar l'evolució de les espècies metàl·liques subnanométricas en condicions de reacció. La transformació estructural de l'espècie Pn subnanométrica ha estat estudiada per microscòpia electrònica de transmissió in situ. S'ha demostrat que la mida de les espècies de Pt està fortament relacionada amb les condicions de reacció, que proporcionen idees importants per comprendre el comportament dels catalitzadors de subnanometria en condicions de reacció. En l'altra línia de recerca dels catalitzadors de metalls no nobles, he desenvolupat diverses estratègies generals per obtenir catalizadors de metalls no nobles recolzats en òxids metàl·lics o protegits per capes de carboni primes. Aquests materials presenten un excel·lent rendiment per a diverses reaccions importants, com la hidrogenació quimioelectiva de nitroarenes, fins i tot quan es comparen amb els catalitzadors convencionals de metall noble. En alguns casos, els catalitzadors de metalls no nobles poden fins i tot aconseguir selectivitats a productes no factibles que no s'han pogut assolir en catalitzadors de metall noble convencionals, que es deuen a la via de reacció diferent en catalitzadors de metalls no nobles. No obstant això, s'ha observat una espectroscòpia de fotoelèctria de raigs X amb pressió d'atmosfera que la irradiació lleugera pot modular la selectivitat als alcohols i hidrocarburs C2 +, la qual cosa obre una nova possibilitat per sintonitzar el comportament catalític dels catalitzadors metàl·lics. A partir d'aquests treballs de diferents aspectes relacionats amb els catalitzadors metàl·lics heterogenis, també s'ha donat en aquesta tesi perspectives sobre les futures orientacions cap a una millor comprensió del comportament catalític de diferents entitats metàl·liques (àtoms individuals, nanoclústers i nanopartícules). / Metal species with different size (single atoms, nanoclusters and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that, many factors including the particle size, shape, chemical composition, metal-support interaction, metal-reactant/solvent interaction, can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow to correlate the relationships at molecular level. In this thesis, I have carried out studies on metal catalysts from single atoms to nanoclusters and nanoparticles. By developing new synthesis methodologies, the size of metal species can be modulated and used as model catalysts to study the size effect on the catalytic behavior of metal catalysts for CO oxidation, selective hydrogenation, selective oxidation and photocatalysis. It has been found that, singly dispersed metal atoms and subnanometric metal clusters may agglomerate into larger nanoclusters or nanoparticles under reaction conditions. To improve the stability of subnanometric metal catalysts, I have developed a new strategy for the generation of single atoms and clusters in zeolites. Those subnanometric metal species are stable in oxidation-reduction treatments at 550 oC. Following this new synthesis methodology, this new type of materials can serve as model catalyst to study the evolution of subnanometric metal species under reaction conditions. The structural transformation of subnanometric Pt species has been studied by in situ transmission electron microscopy. It has been shown that the size of Pt species is strongly related with the reaction conditions, which provide important insights for understanding the behavior of subnanometric metal catalysts under reaction conditions. In the other research line for non-noble metal catalysts, I have developed several general strategies to obtain non-noble metal catalysts either supported on metal oxides or protected by thin carbon layers. These materials show excellent performance for several important reactions, such as chemoselective hydrogenation of nitroarenes, even when compared with conventional noble metal catalysts. In some cases, non-noble metal catalysts can even achieve selectivities to unfeasible products which has not been possible to achieve on conventional noble metal catalysts, which is caused by the different reaction pathway on non-noble metal catalysts. Nevertheless, it has been revealed by ambient-pressure X-ray photoelectron spectroscopy that light irradiation can modulate the selectivity to alcohols and C2+ hydrocarbons, which opens a new possibility for tuning the catalytic behavior of metal catalysts. Based on the above works from different aspects related with heterogeneous metal catalysts, perspectives on the future directions towards better understanding on the catalytic behavior of different metal entities (single atoms, nanoclusters and nanoparticles) in a unifying manner have also been given in this thesis. / Liu, L. (2018). Heterogeneous Metal Catalysts: From Single Atoms to Nanoclusters and Nanoparticles [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/113169 / TESIS

Catalytic conversion of methanol to hydrocarbons (MTH) provides an alternative route to the production of fuels and important industrial chemicals that are currently mainly produced from the refinery of petroleum. The ability to control the product distribution of MTH according to the demands of specific applications is of crucial importance, which relies on the thorough understanding of the reaction pathways and mechanisms. Despite the significant research efforts devoted to zeolite-catalyzed MTH, it remains a challenge to establish a firm correlation between the physicochemical properties of zeolites and their catalytic activity and selectivity. In this dissertation, we designed a series of experiments to gain fundamental understanding of how the structural and compositional parameters of zeolites influence their catalytic performances in MTH. We investigated different types of zeolites, covering large-pore Beta, medium-pore ZSM-5, and small-pore DDR zeolites, and tune their crystallite size/diffusion length, hierarchical (mesoporous) structure, and Si/Al ratio (density of acid sites) by controlled synthesis or post-synthesis treatments. The influence of mesoporosity of a zeolite catalyst on its catalytic performance for MTH, with zeolite Beta, was first investigated. The shorter diffusion length associated with the hierarchical structure results in a lower ethylene selectivity but higher selectivity towards C4-C7 aliphatics. Then we investigated the correlation between the Al content and the ethylene selectivity by ZSM-5 zeolites with similar crystal sizes but varied Si/Al ratios. We realized that ethylene selectivity is promoted with the increase of aluminum content in the framework. These two observations can be explained by the same mechanistic reason: the ethylene selectivity is associated with the propagation degree of the aromatics catalytic cycle and essentially determined by the number of the acid sites that methylbenzenes would encounter before they exit the zeolite crystallite. Last we explored how to maximize the propylene selectivity by tuning the physicochemical properties of DDR zeolites. Due to the confined pore space in DDR, the propagation of olefins-based catalytic cycle can be preferentially promoted in a tunable manner, which cannot be realized with zeolites having larger pores. Thus, the propylene selectivity increases with increasing the Si/Al ratio and decreasing the crystallite size.