A celulose é o biopolímero mais abundante na natureza e apresenta grande potencial para ser processada e produzir de maneira sustentável biocombustíveis e produtos químicos. A conversão catalítica é um dos meios mais promissores para transformação da celulose. A separação entre produtos e catalisadores é uma etapa importante para indústria, o que coloca a catálise heterogênea em posição privilegiada como via de conversão, devido à facilidade de separação entre produto e catalisador. A hidrogenólise é uma via de transformação que promove a quebra de ligações C-C e a retirada de átomos de oxigênio, levando a uma gama de combustíveis e produtos químicos. Os carbetos de metais de transição suportados em carvão ativo são efetivos na quebra de ligações C-C, enquanto o paládio atua tanto na quebra de ligações C-C como em etapas de hidrogenação. Assim, este trabalho estudou as propriedades estruturais e catalíticas de catalisadores de carbeto de tungstênio suportados em carvão ativado e promovidos com paládio. Foram preparados e caracterizados catalisadores de WXC sem promotor e com 1 e 2% de Pd. As medidas de fisissorção de N2 revelou que os catalisadores são formados por uma mistura de micro e mesoporos. A análise de difração de raios X revelou predominância da fase W2C nos catalisadores promovidos por Pd, enquanto que nos catalisadores ausentes de Pd ocorreu um misto de fases carbeto. As medidas de XPS revelaram que quanto maior quantidade de Pd na amostra, se tem mais tungstênio exposto na superfície. A seguir, os catalisadores foram aplicados em reações de conversão de celulose sob pressão de hidrogênio. A conversão de celulose foi determinada por gravimetria (balanço de massa) e termogravimetria e os produtos foram identificados e quantificados por cromatografia gasosa GC e por HPLC. Foram obtidos rendimentos em torno de 40% para etileno glicol, com 77% de conversão de celulose, em reações de 120 min a 220°C com o catalisador 2% WXC/C. Além disso, foram testados diferentes substratos e catalisadores para se entender o mecanismo de conversão e o papel de cada componente do catalisador na rota reacional. A obtenção de etileno glicol a partir da celulose se passa através da hidrólise do polissacarídeo em monômeros de glicose, reação retro-aldol produzindo glicolaldeído e hidrogenação para obtenção do etileno glicol. / Cellulose is the most abundant biopolymer in nature and has great potential to be processed and to sustainably produce biofuels and chemicals. The catalytic conversion is one of the most promising ways for processing cellulose. The separation between the products and the catalysts is an important step for the industry, which puts the heterogeneous catalysis in prime position as route of conversion due to the easiness of separation of product and catalyst. Hydrogenolysis is a processing way that promotes breaking C-C bonds and the removal of oxygen atoms, leading to a variety of fuels and chemicals. The carbides of transition metals supported on activated carbon are effectives in breaking C-C bonds, while palladium acts both in breaking C-C bonds and in the hydrogenation steps. So, this work studied the structural and catalytic properties of catalysts of tungsten carbides supported on activated carbon and promoted with palladium. Catalysts WXC without promoter and 1 and 2% Pd were prepared and characterized. The N2 physisorption measurements showed that a mixture of micro and mesopores forms the catalysts. The analysis of X-ray diffraction revealed the predominance of W2C phase in the catalysts promoted with Pd, while in the catalysts absent from Pd a mixture of carbide phases occurred. XPS measurements showed that the greater amount of Pd in the sample, it is more tungsten exposed on the surface. Then, the catalysts were applied in cellulose conversion reactions under hydrogen pressure. The conversion of cellulose was determined by gravimetry (mass balance) and thermogravimetry, and the products were identified and quantified by GC and HPLC. Yields around 40% for ethylene glycol were obtained, corresponding to 77% conversion of cellulose, in reactions performed at 220 °C and 120 min reaction time, with catalyst 2% PdWXC/C. Additionally, different substrates and catalysts were tested for understanding the conversion mechanism and the role of each component of the catalyst in the reaction route. Obtaining ethylene glycol from cellulose goes through hydrolysis of the polysaccharide into glucose monomers, retro-aldol reaction producing glycolaldehyde and hydrogenating to obtain ethylene glycol.

A celulose é o biopolímero mais abundante na natureza e apresenta grande potencial para ser processada e produzir de maneira sustentável biocombustíveis e produtos químicos. A conversão catalítica é um dos meios mais promissores para transformação da celulose. A separação entre produtos e catalisadores é uma etapa importante para indústria, o que coloca a catálise heterogênea em posição privilegiada como via de conversão, devido à facilidade de separação entre produto e catalisador. A hidrogenólise é uma via de transformação que promove a quebra de ligações C-C e a retirada de átomos de oxigênio, levando a uma gama de combustíveis e produtos químicos. Os carbetos de metais de transição suportados em carvão ativo são efetivos na quebra de ligações C-C, enquanto o paládio atua tanto na quebra de ligações C-C como em etapas de hidrogenação. Assim, este trabalho estudou as propriedades estruturais e catalíticas de catalisadores de carbeto de tungstênio suportados em carvão ativado e promovidos com paládio. Foram preparados e caracterizados catalisadores de WXC sem promotor e com 1 e 2% de Pd. As medidas de fisissorção de N2 revelou que os catalisadores são formados por uma mistura de micro e mesoporos. A análise de difração de raios X revelou predominância da fase W2C nos catalisadores promovidos por Pd, enquanto que nos catalisadores ausentes de Pd ocorreu um misto de fases carbeto. As medidas de XPS revelaram que quanto maior quantidade de Pd na amostra, se tem mais tungstênio exposto na superfície. A seguir, os catalisadores foram aplicados em reações de conversão de celulose sob pressão de hidrogênio. A conversão de celulose foi determinada por gravimetria (balanço de massa) e termogravimetria e os produtos foram identificados e quantificados por cromatografia gasosa GC e por HPLC. Foram obtidos rendimentos em torno de 40% para etileno glicol, com 77% de conversão de celulose, em reações de 120 min a 220°C com o catalisador 2% WXC/C. Além disso, foram testados diferentes substratos e catalisadores para se entender o mecanismo de conversão e o papel de cada componente do catalisador na rota reacional. A obtenção de etileno glicol a partir da celulose se passa através da hidrólise do polissacarídeo em monômeros de glicose, reação retro-aldol produzindo glicolaldeído e hidrogenação para obtenção do etileno glicol. / Cellulose is the most abundant biopolymer in nature and has great potential to be processed and to sustainably produce biofuels and chemicals. The catalytic conversion is one of the most promising ways for processing cellulose. The separation between the products and the catalysts is an important step for the industry, which puts the heterogeneous catalysis in prime position as route of conversion due to the easiness of separation of product and catalyst. Hydrogenolysis is a processing way that promotes breaking C-C bonds and the removal of oxygen atoms, leading to a variety of fuels and chemicals. The carbides of transition metals supported on activated carbon are effectives in breaking C-C bonds, while palladium acts both in breaking C-C bonds and in the hydrogenation steps. So, this work studied the structural and catalytic properties of catalysts of tungsten carbides supported on activated carbon and promoted with palladium. Catalysts WXC without promoter and 1 and 2% Pd were prepared and characterized. The N2 physisorption measurements showed that a mixture of micro and mesopores forms the catalysts. The analysis of X-ray diffraction revealed the predominance of W2C phase in the catalysts promoted with Pd, while in the catalysts absent from Pd a mixture of carbide phases occurred. XPS measurements showed that the greater amount of Pd in the sample, it is more tungsten exposed on the surface. Then, the catalysts were applied in cellulose conversion reactions under hydrogen pressure. The conversion of cellulose was determined by gravimetry (mass balance) and thermogravimetry, and the products were identified and quantified by GC and HPLC. Yields around 40% for ethylene glycol were obtained, corresponding to 77% conversion of cellulose, in reactions performed at 220 °C and 120 min reaction time, with catalyst 2% PdWXC/C. Additionally, different substrates and catalysts were tested for understanding the conversion mechanism and the role of each component of the catalyst in the reaction route. Obtaining ethylene glycol from cellulose goes through hydrolysis of the polysaccharide into glucose monomers, retro-aldol reaction producing glycolaldehyde and hydrogenating to obtain ethylene glycol.

Métodos de síntese que viabilizam a obtenção de compósitos contendo xerogéis de óxido de tungstênio e de pentóxido de vanádio pelo método sol-gel foram investigados, bem como a caracterização e propriedades catalíticas nas reações de epoxidação destes materiais. Brometo de cetiltrimetilamina e hexadecilamina foram intercalados nos xerogéis de óxidos vanádio e de tungstênio formando compostos híbridos orgânico-inorgânico ternários. Estas moléculas foram usadas com o objetivo de aumentar a distância interlamelar e conferir caráter hidrofóbico nos compostos híbridos para que facilitasse o acesso dos substratos orgânicos quando utilizados como catalisadores nas reações de epoxidação. Os parâmetros de difração de raios X comprovam a intercalação, com aumento da distância interplanar. Observa-se uma variação na posição da banda M=O para maiores valores de energia devido à interação eletrostática entre as cargas positivas das espécies convidadas com densidade de carga negativa das ligações M=O. O xerogel de óxido de tungstênio e o compósito com xerogel de óxido de vanádio com óxido tungstênio foram dispersos em matrizes de óxido hidróxido de alumínio e de xerogel de óxido de silício. Foi observado que os modos vibracionais no infravermelho não sofreram variações significativas, indicando que pequenas distorções ocorrem quando os xerogéis dos óxidos estão dispersos, ou seja, há interações fracas entre os componentes, corroborando com os padrões de difração de raios X que mostram a manutenção da estrutura inicial dos óxidos. No caso dos compósitos contendo óxido de vanádio em sílica empregando metiltrietóxissilano, houve a formação de partículas esféricas de sílica recobertas por filmes de óxido de vanádio. No entanto, ao utilizar o tetraelilortossilicato como precursor, houve a manutenção da estrutura lamelar dos óxidos, mas não se observou a formação das partículas esféricas de sílica. As propriedades catalíticas destes materiais foram testadas em reações de oxidação do cis-cicloocteno, estireno e ciclo-hexano usando peróxido de hidrogênio (H2O2), terc-butil hidroperóxido (t-BOOH) e ácido meta-cloroperbenzóico (m-CPBA) como agentes oxidantes. De modo geral, os resultados obtidos são satisfatórios e estão de acordo com os resultados apresentados na literatura para sistemas similares, sugerindo uma aplicação potencial destes materiais como catalisadores em reações de epoxidação e oxidação. / Synthetic procedures based on sol-gel process were developed aiming produce xerogel composites of mixed oxides such as tungsten oxide and vanadium oxide, as well as their characterization and catalytic properties in epoxidation reactions. Cetyltrimetylamine bromide and hexadecylamine were intercalated into vanadium oxide and tungsten oxide xerogels resulting in ternary hybrid inorganic-organic compounds. These molecules were used in order to increase the interlamelar distance and confer hydrophobic character facilitating the substrate access in catalyzes epoxidation reactions. X ray diffraction patterns demonstrate the intercalation. It was verified the shift of the M=O vibrational mode towards higher energy region due to electrostatic interaction between positive charges of guest species with negative character of M-O bonding. Tungsten oxide and vanadium and tungsten mixed oxide xerogels were dispersed in oxohydroxiy aluminum and silicon oxide matrices. No significant changes in the infrared vibrational modes were observed, suggesting that few distortions occur when xerogel materials are dispersed, due to weak interactions corroborating previous results. In the case of composites containing vanadium oxide and silica (methyltriethoxysilane as precursor), the final material is formed by sphere particles of silica covered with vanadium oxide film. However, when tetraethylorthosilicate was used as silica precursor, the lamelar structure of metal oxide is retained instead of spherical morphology. The catalytic properties of these materials were verified in oxidation of cis-cyclooctene, styrene, and cyclohexane using hydrogen peroxide (H2O2), terc-butyl hydroperoxide (t-BOOH), and cloroperoxybenzoic acid (m-CPBA) as oxygen donors. From a general point of view, the results are satisfactory and close with those found for similar systems, enabling them as catalysts for epoxidation and oxidation.

There is a considerable interest in the use of tungsten oxide in the research and development of new materials and devices, such as gas sensors and as photocatalysts. In order to improve the photocatalytic properties of WO3, its combination with metals which allows the preparation of WMxOy materials are believed to be promising photocatalysts under visible light. The present work deals with the synthesis of homo- and hetero-metallic tungsten alkoxide and amide compounds using the single source precursor approach for potential chemical vapour deposition precursors of mixed-metal oxide films.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Includes bibliographical references. / by Miriam Zacksenhouse. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by José Converti. / Ph.D.

abstract: ABSTRACT Programmable metallization cell (PMC) technology uses the mechanism of metal ion transport in solid electrolytes and electrochemical redox reactions to form metallic electrodeposits. When a positive bias is applied from anode to cathode, atoms at the anode are oxidized to ions and dissolve in the solid electrolyte. They travel to the cathode under the influence of an electric field, where they are reduced to form electrodeposits. These electrodeposits are filamentary in nature and grow in different patterns. Devices that make use of the principle of filament growth have applications in memory, RF switching, and hardware security. The solid electrolyte under investigation is tungsten trioxide with copper deposited on top. For a standard PMC, these layers are heated in a convection oven to dope the electrolyte. Once the heating process is completed, electrodes are deposited on top of the electrolyte and biased to grow the filaments. What is investigated is the rate of dendritic growth to applied field on the PMC and the composition of the electrolyte. Also investigated are modified three-terminal PMC capacitance change devices. These devices have a buried sensing electrode that senses the increasing capacitance as the filaments grow and increase the upper electrode area. The rate of dendritic growth in the tungsten trioxide and copper electrolyte of different chemistries and applied field to the PMC devices is the important parameter. The rate of dendritic growth is related to the change of capacitance. Through sensing the change in capacitance over time the modified PMC device will function as an odometer device that can be attached to chips. The attachment of these devices to chips, help in preventing illegal recycling of old chips by marking those chips as old. This will prevent would-be attackers from inserting modified chips in systems that will enable them to by-pass any software security precautions. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2019

Aigarchaeota, a deeply branching archaeal lineage with no cultivated representatives, is found in geothermal and hydrothermal systems worldwide and consists of at least 9 genus-level groups, each predicted to have diverse metabolic capabilities. This candidate archaeal phylum is part of the TACK superphylum, members of which possess eukaryotic-signature proteins, thus suggesting that they may represent evolutionary steps along the way to the genesis of the first eukaryotic cells. Cultivating members of Aigarchaeota would elucidate how eukaryotes arose in evolutionary history and provide biotechnological applications. Aigarchaeota Group 4 (AigG4), one genus in Aigarchaeota, was previously found to be abundant in corn stover in situ enrichments in Great Boiling Spring (GBS). AigG4 has been maintained in mixed laboratory cultures, where it composes ~ 0.5-1% of the community. However, these cultures could only be maintained when GBS water, which contains ~300 nM tungsten, was included in the medium. In addition, AigG4 metagenome bins from the in situ enrichments and laboratory cultures contained multiple genes encoding putative tungsten-containing aldehyde:ferredoxin oxidoreductases (TAORs). These observations led to the hypothesis that tungsten was the key component in GBS water that allowed for growth of AigG4. The requirement of tungsten for AigG4 long-term maintenance in mixed culture was tested using three different approaches: (1) Assessing the phylogeny of tungsten transporters and TAORs across the Aigarchaeota lineage, followed by confirmation of transcription of hypothesized AigG4 tungsten-associated genes in lab cultures, (2) Measuring tungsten levels in Great Boiling Spring (GBS) using ICP-OES (Inductively coupled plasma-optical emission spectroscopy), and (3) determining minimum amount of tungsten for long-term AigG4 maintenance in corn stover and in a defined mix of sugars (1% glucose, 1% xylose, 1% D-arabinose, 1% L-arabinose, 1% mannose). In addition, FISH (Fluorescent in situ hybridization) probes were designed to target the AigG4 lineage in the hopes that in conjunction with nanometer-scale secondary ion mass spectroscopy (Nano-SIMS), this would test whether tungsten has indirect or direct effects on AigG4 to track carbon substrate intake. Most Aigarchaeota lineages possess a tungsten transporter complex (TTC). AigG4 TTC groups most closely with the Tup family while other Aigarchaeota group with the Wtp family. Group 4 and Group 5 Aigarchaeota contained TAORs that grouped to other hypothesized TAORs but not to characterized counterparts suggesting diverse functional capabilities. Group 4 and Group 5 TAORs clustered together suggesting that these are conserved within these lineages. Gene expression of predicted AigG4 tungsten-associated enzymes was detected in culture. Tungsten was detected in GBS water as previously observed in 2005. In both corn stover and sugar mix, 1 nM tungsten was sufficient for long term AigG4 maintenance. In corn stover, AigG4 decreased to levels below detection after three 3-week transfer periods in 0 nM and 20 nM tungsten. In sugar mix, AigG4 abundance levels varied wildly in 0 nM tungsten after the fifth transfer period suggesting tungsten contamination. Two newly designed FISH probes exhibited lower fluorescence signal intensity than the previously designed FISH probe suggesting issues with either target site accessibility or conjugation of the fluorescent moiety to oligonucleotide probes.

No description available.

Andrew R. Hutson. / "January 13, 1955"--Cover. "Reprinted from The Physical review, vol. 98, no. 4, 889-901, May 15, 1955." / Includes bibliographical references. / Army Signal Corps Contract DA36-039 sc-42607 Project 132B Dept. of the Army Project 3-99-12-022