Thesis (Master)--İzmir Institute of Technology,İzmir, 2005 / Includes bibliographical references (leaves. 75).

Thesis (Ph.D. (Physics)) --University of Limpopo, 2003 / Refer to the document / National Research Foundation, and the Standard Bank

Thesis (M.Sc. (Chemistry)) -- University of Limpopo, 2015 / This dissertation investigated the properties of ferrierite synthesised using different SiO2 sources under identical conditions. The SiO2 sources used were TEOS, water-glass, Aerosil 200 and Ludox LS-30. The synthesis procedure comprised preparation of a gel with molar composition: 20 Na2O : Al2O3 : 37 pyrrolidine : 66:5 SiO2 : 6:3 H2SO4 : 1460 H2O. This was followed by hydrothermal treatment at 160 oC in a stainless steel autoclave for 72 h. The solid products were characterised by XRD, SEM, NH3-TPD and BET techniques. The ferrierite prepared using sodium silicate was more crystalline than ferrierite zeolites synthesised using Ludox LS-30, Aerosil 200 and tetraethyl orthosilicate as SiO2 sources. An amorphous phase was produced when ferrierite was synthesised using unhydrolysed TEOS as a sole SiO2 source. The physicochemical properties of the materials were not only affected by the nature of the SiO2 source, but also some synthesis manipulations such as acid-hydrolysis and water-glass addition when TEOS was used as a primary silica source. There were improvements in the materials produced when the TEOS was pre-hydrolysed with HCl and also mixed with water-glass in equal proportions. The SEM images of ferrierite materials synthesised using water-glass and Ludox LS-30 were uniform. The water-glass-based materials were thin sheets, flake-like images and Ludox LS-30-based produced thin-plate-like morphologies. The micrograph of ferrierite synthesised using TEOS as the SiO2 source showed hexagonal-type morphology and aggregates of smaller particles. There were two types of shapes in the ferrierite synthesised using Aerosil 200 as the silica source, namely, octagonal prismatic and hexagonal type morphologies. An equimolar mixture of TEOS and water-glass showed octagonal prismatic shape with triangular faces along certain edges of the material. The NH3-TPD acid site distribution profiles showed two peaks of weak acid strength at low temperatures (≤ 350 oC) for the representative H-ferrierite investigated. The ferrierite materials synthesised using unhydrolysed TEOS and Ludox LS-30 as SiO2 sources, showed NH3 desorption peaks at higher temperatures (≥ 350 oC). These peaks correspond to ammonia eluted from strong acid sites. The BET surface area of ferrierite synthesised using water-glass was high, while the material synthesised using unhydrolysed TEOS had the lowest surface area. Novel crystal shapes, comprising octagonal prisms with additional triangular phases, were observed in ferrierite samples prepared by the use of TEOS/water-glass mixture as silica source. The zeolitic materials prepared in this study were tested for the efficiency in the removal of Cu2+ from simulated wastewater, using a batch method. The effects of initial pH, initial concentration, contact time and adsorbent dose on Cu2+ adsorption were studied. All the materials showed maximum metal uptake efficiency at pH 5, and this pH was fixed in further studies involving other variables. It was observed that the metal uptake from aqueous solution increased with contact time and adsorbent dose. The Na-form of ferrierite synthesised using water-glass was the poorest Cu2+ adsorbent with respect to the four variables investigated (pH, contact time, adsorbent dose and initial metal ion concentration). KEY CONCEPTS Acidity, Adsorption, Ferrierite, Morphology, Silica source.

Une pénurie de C4 s'est produite au cours des dernières années en partie à cause de la révolution naissante du gaz de schiste. Le faible coût et la grande abondance de cette source d'énergie nouvellement découverte sont rapidement devenues un facteur de changement pour l'industrie chimique. Bien que la concurrence avec cette source d'énergie non renouvelable ne soit pas une tâche facile, ses lacunes, telles qu'une production minimale en C3 et en C4, créent de nouvelles opportunités pour les molécules biosourcées. Dans ce travail, nous rapportons la conversion nouvellement découverte du (bio) isobutanol en n-butènes sur un catalyseur zéolitique. Ce catalyseur conduit à un rendement exceptionnel en butènes linéaires, ce qui est paradoxal car la FER est un catalyseur bien connu pour l'isomérisation squelettale des butènes. Bien que la recherche sur le dernier ait débuté il y a 30 ans, aucune conclusion définitive n'a encore été faite sur le mécanisme dominant : une réaction de monomoléculaire ou un mécanisme de "carbon pool". Acquérir des connaissances plus approfondies sur ce sujet est alors nécessaire pour expliquer la sélectivité inattendue en n-butène de cette réaction.Un criblage de catalyseurs a confirmé la sélectivité supérieure de FER pour les n-butènes (81%). Ceci est une augmentation significative par rapport aux catalyseurs de déshydratation couramment utilisés, alumine  (1%) et MFI (23%). Comme la sélectivité en n-butène pour les deux zéolites est significativement plus élevée que pour l’alumine un premier indice est que l'environnement confiné et cristallin de la porosité de la zéolite est crucial pour la sélectivité du n-butène. Cependant nous avons démontré que l'isobutanol est incapable d'accéder aux micropores de la structure FER; sa déshydratation doit donc se produire sur la surface externe de la zéolithe, en particulier sur ses sites acides de Brønsted.Nous avons déterminé l'identité du site actif responsable de l'isomérisation. En raison des similitudes avec la réaction d'isomérisation squelettale de du butène 1 à l'isobutène, un mécanisme de "carbon pool" a dû être envisagé. Cependant, aucun lien n'a été trouvé entre ces espèces et l’évolution de la sélectivité du n-butène, ne permettant pas de conclure quant à la participation de ces espèces carbonées comme sites actifs d'isomérisation. Par la suite, nous avons cherché à déterminer si les n-butènes sont formés directement ou via un mécanisme de type râteau dans lequel l'isobutène serait un intermédiaire. Nous avons établi que les constantes de vitesse pour l'isomérisation individuelle des butènes sont très inférieures à la constante de vitesse globale, excluant ainsi le mécanisme de type râteau. Par conséquent, le site actif d'isomérisation doit être identique ou situé à proximité du site actif de déshydratation pour éviter la désorption des espèces intermédiaires de surface sous forme d’isobutène. Nous avons ensuite démontré la nécessité d'une densité minimale d'acidité de Brønsted externe pour une sélectivité élevée en n-butène, également valable pour différentes zéolites, (10 MR ZSM-5 et ZSM-22 et 8 MR Erionite). Ces résultats nous ont ainsi amener à conclure que la sélectivité exceptionnelle des zéolithes de type FER en n-butène est le résultat de leur forte densité de sites acide de Brønsted externes. Cependant, une trop forte densité a un effet indésirable en terme de désactivation.L’ensemble de ces résultats nous permet de conclure que le catalyseur idéal doit présenter une densité de site d'acide de Brønsted externe très spécifique, suffisamment importante pour produire une sélectivité élevée en n-butène tout en évitant une désactivation excessive. Alors que les sites acides de Brønsted internes ne semblent pas jouer le rôle de site actifs pour la transformation de l'isobutanol en butènes linéaires, il n’est pas exclus qu’elle ait un impact sur le taux de formation des espèces carbonées. / A C4-shortage has been arising during the recent years partly as a result of the nascent shale gas revolution. The low cost and vast abundance of this newly discovered energy source rapidly became a game changer for the chemical industry. Although competing with this non-renewable energy source is not an easy task, its shortcomings such as a minimal C3 and C4 production, are creating new opportunities for bio-based molecules. In this work, we report on the newly discovered conversion of (bio)isobutanol to n-butenes over a zeolitic (ferrierite, FER structure) catalyst. It displays an exceptional yield in linear butenes. However, this is remarkable since FER is a well-known catalyst for the skeletal isomerisation of n- towards iso-butene. Although research on the n- to iso-butene skeletal isomerisation started 30 years ago, no firm conclusion has yet been made on the prevailing mechanism: a monomolecular reaction or a carbon pool mechanism. Acquiring deeper knowledge on this topic is required to explain the unexpected n-butene selectivity of this reaction. A screening of catalysts confirmed the superior selectivity of FER for n-butenes (~ 80 %). This is a significant increase compared to the commonly used dehydration catalysts, γ-alumina (~ 1 %) and MFI (~ 25 %). Since n-butene selectivity for both zeolites is significantly higher, a first hint is found that the confined and crystalline zeolite environment should be crucial for n-butene selectivity. However, we have demonstrated that isobutanol is unable to access the micropores of the FER structure; its dehydration must therefore occur on the external surface, in particular its acidic Brønsted sites.We have determined the identity of the active site responsible for isomerisation. Due to similarities with the 1- to isobutene skeletal isomerisation reaction, a carbon pool mechanism had to be considered. However, no correlation was found, hence allowing to exclude the carbonaceous species as possible isomerisation active sites. Next, we have investigated whether the n-butenes are formed directly or via a rake-type mechanism where isobutene is an intermediate. We have established that the rate constants for the individual butene isomerisation are lower than the over-all rate constant of iso-butanol transformation to n-butenes, thus excluding the rake-type mechanism. Hence, either dehydration-isomerisation occur in the same site or isomerisation occurs on a site located in the immediate neighbouring of the dehydration site in order to avoid the desorption of intermediate species as isobutene. With this respect, we have subsequently demonstrated the requirement of a minimal external Brønsted acid density for a high n-butene selectivity. Strikingly, the latter held also for different zeolites, (10 MR ZSM-5 and ZSM-22 and 8 MR Erionite) which suggests a general trend relating the n-butene selectivity to the density of external Brønsted acid sites with the existence of a “critical threshold” of external BAS density beneath which the selectivity towards n-butene is severely degraded. We concluded that the exceptional n-butene selectivity of FER is a result of its high external Brønsted acid density. However, an adverse effect was observed on isobutanol conversion as a high density of external sites is also linked to a faster deactivation. Additionally, we have determined that the selectivity for a secondary set of products, octenes, decreased with increasing the external Brønsted sites density; isolated external Brønsted acid sites should therefore function as active sites for octene formation.Finally, we conclude that the ideal catalyst should contain a very specific external Brønsted acid site density, sufficiently dense to produce high n-butene selectivity while avoiding excessive deactivation. While internal Brønsted acidity does not function as active sites for the one-step transformation, it is not excluded that they can impact the rate of carbonaceous species formation

Thesis (doctoral)--Technische Universiteit Delft, 2002. / Vita. Includes bibliographical references.

Thesis (doctoral)--Technische Universiteit Delft, 2002. / Vita. Includes bibliographical references.

Zeolites are crystalline aluminosilicates of natural or synthetic origin, with a structure consisting of an extensive microporous three-dimensional network, routinely used as catalysts, ion exchange and adsorbents. The production of ferrierite and other zeolites are limited due to the high cost of the organic structure-directing agents used in synthesis. Many studies are conducted with the goal of finding a viable and more economical route to the possibility of industrial scale production. The purpose of this study was to obtain a methodology for synthesis of ferrierite without using organic structure-directing agents, by hydrothermal method, inserting seeds during the crystallization gel preparation and varying the alkaline concentration of the mixture in order to achieve shorter times of crystallization and lower cost production at a temperature of 200°C. For the synthesis of materials prepared in this work were used: fumed silica as silicon source, pseudoboehmite as a source of aluminum, sodium and potassium hydroxide as sodium and potassium sources, respectively. As seeds to crystallization, samples of commercial ferrierita were used. The synthesized samples were characterized by X-ray diffraction (XRD), spectroscopy of the Fourier transform infrared (FT-IR) and thermal analysis (TG/DTA). The X-ray diffraction patterns showed characteristic peaks of zeolite desired in all conditions of synthesis. The infrared spectra showed bands characteristic of ferrierite, as a further indication of the formation of zeolite. TG curves showed a mass loss of up to 10% in the temperature range from 23 to 400°C. The results of the analysis confirmed the formation of zeolite ferrierite with good crystallinity and purity, proving the efficiency of the methodology. / As zeólitas são aluminossilicatos cristalinos, de origem natural ou sintética, com estrutura constituída por uma extensa rede tridimensional microporosa, rotineiramente utilizadas como catalisadores, trocadores iônicos e adsorventes. A produção da ferrierita, e outras zeólitas, são limitadas devido ao alto custo do direcionador orgânico utilizado na síntese. Muitos estudos são realizados com o objetivo de encontrar uma rota mais econômica e viável para a possibilidade de produção em escala industrial. O objetivo deste trabalho foi obter uma metodologia para síntese da ferrierita sem utilizar direcionador orgânico, pelo método hidrotérmico, inserindo sementes de cristalização durante o preparo do gel e variando a concentração alcalina da mistura reacional, a fim de alcançar menores tempos de cristalização e menor custo de produção, numa temperatura de 200°C. Para a síntese do material preparado neste trabalho foram utilizados: sílica fumed como fonte de silício, pseudoboehmita como fonte de alumínio, e hidróxido de sódio e potássio como fontes de sódio e potássio, respectivamente. Já para sementes de cristalização, foram utilizadas amostras de ferrierita comercial. As amostras sintetizadas foram caracterizadas por difração de raios X (DRX), espectroscopia na região do infravermelho por transformadas de Fourier (FT-IR) e análises térmicas (TG/DTA). Os difratogramas de raios X mostraram picos característicos da zeólita desejada em todas as condições de síntese. Os espectros de infravermelho apresentaram bandas características da ferrierita, sendo mais um indício da formação da zeólita. As curvas de TG mostraram uma perda de massa de no máximo 10% numa faixa de temperatura de 23 a 400°C. Os resultados das análises realizadas comprovaram a formação da zeólita ferrierita com boa cristalinidade e pureza, comprovando a eficiência da metodologia proposta.

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

[pt] Existe uma crise energética devido ao excessivo consumo do petróleo e à contaminação em suas diversas formas. Há enormes reservas de gás natural e a conversão deste gás em combustíveis líquidos a partir do gás de síntese, que vem do gás natural, via metanol, e posterior transformação do metanol em hidrocarbonetos é uma interessante alternativa. Catalisadores híbridos formados por um catalisador de síntese de metanol e um material ácido poroso, geralmente uma zeólita, são empregados para esta síntese direta. Seis famílias de catalisadores híbridos foram sintetizadas onde diversas variáveis foram testadas como: método de preparação do catalisador híbrido, método de preparação do catalisador de síntese de metanol, fase ativa, razão catalisador de síntese de metanol/zeólita, acidez da zeólita e diferente promotor. A zeólita empregada em todos os sistemas foi a H-ferrierita. O método de preparação influenciou nas propriedades estruturais, texturais, morfológicas, ácidas e catalíticas do catalisador híbrido. O melhor método de preparação do catalisador híbrido foi o método de coprecipitação-sedimentação que se mostrou mais ativo em temperaturas acima de 300°C. Observaram-se diferenças morfológicas nas partículas do catalisador de síntese de metanol (CSM) quando diferentes métodos de preparação foram empregados. O cobre, entre as fases ativas, mostrou-se a melhor na síntese direta de hidrocarbonetos a partir do gás de síntese em temperaturas acima de 300°C. A melhor razão catalisador de síntese de metanol/zeólita, nesta síntese direta, foi de 2:1. O cromo no sistema Cu-Zn-Al favoreceu a atividade em 250°C. Baixas razões acidez total/área de Cu(0) e altas temperaturas (350 e 400°C) favoreceram maiores conversões e seletividades em propano e butano, baixas temperaturas (300°C) favoreceram a formação de DME. Altas razões acidez total/área de Cu(0) favoreceram a formação de etano. A distribuição dos produtos na síntese direta de hidrocarbonetos a partir do gás de síntese foi dependente da temperatura de reação. Éter dimetílico apresentou um máximo em 300ºC. A síntese do metanol, parece ser a etapa limitante do processo. / [en] An energy crisis due to the extreme consumption of the oil and to the contamination in its diverse forms exists. There are enormous natural gas reserves and the conversion of this gas in liquid fuels from the synthesis gas, through methanol, and posterior transformation of methanol in hydrocarbons is an interesting alternative. Hybrid catalysts based in methanol synthesis catalyst and an acidic porous material such as zeolites, are used for this direct synthesis. Six groups of hybrid catalyst were prepared and several properties studied such: preparation method of the hybrid catalyst, preparation method of the methanol synthesis catalyst, active site, CuO-ZnO-Al(2)O(3)/H- ferrierite ratio, acidity of the zeolite and different promoter. The zeolite used in all the systems was the ferrierite. The preparation method influenced the structural, textural, morphologic, acid and catalytic properties of the hybrid catalyst. The coprecipitationsedimentation method was more active in temperatures above 300°C. Morphologic differences in particles of the catalyst of methanol synthesis were observed when different preparation methods were used. The copper as active site was the better in the direct synthesis of hydrocarbons from synthesis gas in temperatures above 300°C. The best CuO-ZnO-Al(2)O(3)/H- ferrierite catalyst ratio, in this direct synthesis, was 2:1. The chromium in the Cu-Zn- Al system favored the activity in 250°C. Low acidity/metallic area Cu(0) ratio and high temperatures (350 and 400°C) favored higher activities and selectivities in propane and butane, lower temperatures (300°C) favored the DME formation. High acidity/metallic area Cu(0) ratio favored the formation of ethane. The hydrocarbons distribution was dependent on the reaction temperature. Dimethyl ether showed a maximum at 300°C. The methanol, seens to be the limitant step of the process.

[pt] A síntese direta de dimetil éter (DME) a partir de gás de síntese é catalisada a partir de catalisadores bifuncionais que possuem duas propriedades: uma hidrogenante que catalisa a formação de metanol a partir de gás de síntese e a outra desidratante que se encarrega da formação do dimetil éter a partir do metanol. Catalisadores bifuncionais com componente hidrogenante baseado em Cu, Zn e Al e componente desidratante baseado na zeólita H-ferrierita foram sintetizados, avaliando-se, o método de preparação, a influência do alumínio no componente hidrogenante e a razão componente desidratante versus componente hidrogenante. Dos diferentes métodos de preparação utilizados: precipitação-deposição, coprecipitação-impregnação e coprecipitação-sedimentação foram os dois últimos que apresentaram melhores resultados na conversão de gás de síntese além de apresentar a formação do precursor do catalisador de síntese de metanol. Os catalisadores foram caracterizados por: absorção atômica, análise térmica gravimétrica, adsorção de N2, difração de raios-x, redução com temperatura programada (RTP), dessorção com temperatura programada de amônia (DTPNH3), dessorção com temperatura programada de hidrogênio (DTP-H2) e microscopia eletrônica de transmissão. Verificou-se que o catalisador bifuncional apresenta um entupimento no volume de poros de aproximadamente 50 por cento. Os resultados dos raios-x identificaram a formação das fases auricalcita, hidrozincita, malaquita e rosacita nos catalisadores com componente hidrogenante baseado em Cu e Zn dos catalisadores com componente hidrogenante baseado em Cu, Zn e Al, e razão atômica Cu/Zn/Al:55/30/15, se observou somente a fase hidrotalcita. A inclusão de alumínio no componente hidrogenante favoreceu a formação de partículas de CuO muito pequenas, conforme observado na microscopia eletrônica de transmissão e difração de raios-x. A análise da DTP-H2 mostrou que os catalisadores preparados por coprecipitação-impregnação apresentam áreas de cobre um pouco maiores. A DTP-NH3 identificou a presença de sítios ácidos de Lewis e de Bronsted que ainda permanecem na H-ferrierita após a preparação do catalisador bifuncional. Sítios ácidos de Bronsted diminuem em maior proporção no catalisador bifuncional quando é preparado pelo método de coprecipitação-impregnação. Os testes catalíticos mostraram não existem grandes diferenças entre os catalisadores bifuncionais preparados por ambos os métodos e que o alumínio no componente hidrogenante não melhora a atividade catalítica destes catalisadores na síntese direta de DME. Concluiu-se que a etapa limitante do processo é a hidrogenação e que esta é dominada pelo cobre e que a H-ferrierita é um excelente componente desidratante pela sua elevada acidez. / [en] The direct synthesis of dimethyl ether from syngas is catalyzed by bifunctional catalysts: the hydrogenation function that catalyzes the methanol formation and the dehydration function to produce dimethyl ether from methanol. Bifunctional catalysts with Cu, Zn and Al as hydrogenation component and Hferrierite zeolite as dehydration component had been synthesized. It was evaluated the method of preparation, the influence of aluminum present in the hydrogenation component and dehydration/hydrogenation component ratio. The coprecipitating impregnation and coprecipitating sedimentation methods were used to form the precursor of hydrogenation component. The catalysts had been characterized by atomic absorption, thermal gravimetry analysis, N2 adsorption, xrays diffraction, TPR, ammonia TPD, hydrogen TPD and transmission electronic microscopy. It was verified that the bifunctional catalyst lost 50 percent of its pore volume. The results of x-rays identified the formation of aurichalcite, hydrozincite, malachite and rosacite phases in the catalyst based on Cu and Zn. However, in the catalyst based on Cu, Zn and Al (for an atomic ratio, Cu/Zn/Al:55/30/15) only the hidrotalcite phase was found. It was observed that the aluminum introduction in the hydrogenation component favors the formation of very small particles of CuO as verified in transmission electronic microscopy and x-rays diffraction. The NH3-TPD identified the presence of Lewis and Bronsted acid sites that still remain in the H-ferrierite after the preparation of the bifunctional catalysts. Bronsted acid sites had an importante decrease in the bifunctional catalysts when it is prepared by the method of coprecipitating impregnation. The catalytic tests showed that the catalysts prepared by the coprecipitating sedimentation method, present higher conversions and DME selectivitys than the prepared by coprecipitating impregnation. The presence of Al in the hydrogenation component doesn`t improve the catalytic activity. It can be concluded that the H-ferrierite is an excellent dehydration component for its high acidity and that the methanol synthesis can be limitant in the process of direct synthesis of DME from syngas.