Tesi sul tema "Molybdenum carbides"
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1
Clark, Christopher H. "Characterization and investigation of molybdenum carbides on activated carbon as hydrogenation catalysts". Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4281.
Abstract (sommario):
Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains viii, 76 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 54-57).
2
McCauley, Robert Lowry. "The effects of molar flux, pressure, and product gases on the stability of molybdenum carbide during steam methane reforming". Online access for everyone, 2005. http://www.dissertations.wsu.edu/Thesis/Fall2005/r%5Fmccauley%5F120105.pdf.
3
Susanto, Benny Laurensius Materials Science & Engineering Faculty of Science UNSW. "Kinetics of carbide dissolution in chromium + molybdenum steels during oxidation". Awarded by:University of New South Wales. Materials Science and Engineering, 2004. http://handle.unsw.edu.au/1959.4/19385.
Abstract (sommario):
Iron-based alloys containing 15% chromium, 2-3% molybdenum and 0.02-1.7% carbon, consisting of M23C6 and M6C carbides in an austenitic matrix were oxidised at 8500C to study their oxidation resistance and a precipitate-free zone formation. Alloy design was carried out using a thermodynamic software Thermo-Calc. Carbides in these alloys were expected to dissolve during oxidation, releasing chromium required for the protective oxide formation. Decarburisation of the matrix was expected to trigger the carbide dissolution, and form a precipitate-free zone. Transformation of the austenitic into ferritic matrix in the precipitate-free zone was expected be essential for providing a fast chromium supply to the oxide/alloy interface. Upon exposure to pure oxygen, most of the alloys oxidised non-protectively due to the fast oxidation attack and low chromium content in the matrix, while carbide dissolution was too slow. The alloys were then pre-oxidised in H2+10%H2O to grow a purely chromia scale. In this low oxygen partial pressure environment, carbides in the alloy's sub-surface dissolved and formed a ferritic precipitate-free zone. The precipitate dissolution model developed by previous investigators was then tested and proven to be valid in this iron-based alloy system. The endurance of the pre-formed chromia scale with its underlying precipitate-free zone was then tested in pure oxygen environment. All of the alloys that had successfully developed a ferritic precipitate-free zone in the pre-oxidation stage, survived the subsequent oxidation in pure oxygen up until 3 weeks observation. Although x-ray diffraction found some minor iron oxides, the oxide consisted of mainly Cr2O3. Since iron activity had increased and iron oxides had become stable after the pure oxygen gas was introduced, the growth of the precipitate-free zone had to compete with the rate at which it was consumed by oxidation. It was concluded that the transformation from austenite to ferrite at the subsurface region of the alloy could be achieved provided that the volume fraction of the carbides did not exceed 0.2. Evidence indicated that the chromia scale grew by chromium provided by the dissolving carbides. Pre-oxidation led to a promising use of the alloys at atmospheric oxygen pressure.
4
Perret, Noemie. "New catalyst formulations based on gold and molybdenum nitrides and carbides : application in selective hydrogenation". Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2657.
Abstract (sommario):
The development of selective heterogeneous catalytic systems is of fundamental importance for the realisation of sustainable green chemical processes. In this thesis, the hydrogenation of nitroarene, aldehyde and carboxylic acid compounds is examined in continuous gas phase operation, for the synthesis of a target functionalised aromatic amine and alcohol. Novel catalysts based on Mo nitride, carbide and supported Au have been synthesised and subjected to an array of complementary characterisation measurements that provide catalyst structure/performance correlations with detailed kinetic and mechanistic analysis. The use of Mo2N and Mo2C as catalysts served to promote the selective hydrogenation of nitrobenzene to aniline and p-chloronitrobenzene to p-chloroaniline where the incorporation of nano-scale Au increased reaction rate. Activity has been correlated to hydrogen adsorption/release capacity, which shows a dependence on the degree of nitridation and crystallographic structure. In contrast, hydrogenation of benzaldehyde is limited by C=O activation, which is facilitated by the Mo component. Alumina supported Au has exhibited 100% selectivity in the hydrogenation of benzaldehyde and 4-nitrobenzaldehyde to the target alcohol, where Au particle size and surface Lewis acidity play crucial roles. The hydrogenation of benzoic acid over Au supported on a CeO2-ZrO2 mixed oxide has shown promising results with the possibility of a one step transformation to the alcohol. The results presented in this thesis establish feasible catalytic routes to high value amines and alcohols where critical process optimisation is demonstrated in terms of catalyst composition/surface structure and reaction conditions.
5
Cunha, Adilto Pereira Andrade 1981. "Caracterização mecânica e microestrutural de aços médio carbono microligados ao nióbio e molibdênio". [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265015.
Abstract (sommario):
Orientador: Paulo Roberto MeiTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Neste trabalho foi estudada a influência da adição de molibdênio e nióbio na microestrutura e propriedades mecânicas de aços com 0,5 e 0,6 %C, utilizado na fabricação de rodas ferroviárias. A deformação dos aços foi aplicada através da laminação, em escala de laboratório, simulando o forjamento no processo real de fabricação. As amostras foram aquecidas a 1250 °C para solubilização do nióbio, sendo então laminadas em 4 passes, a partir de 1200 °C, sofrendo uma deformação total (redução em altura) de 67%, seguida de resfriamento ao ar. Posteriormente, os aços C5 e C5Nb foram submetidos a um tratamento térmico de têmpera e revenimento. Foram analisadas amostras dos aços por microscopia óptica, eletrônica de varredura e transmissão e também foram realizados ensaios mecânicos em todas as condições. Após a laminação entre 1200 e 1120 °C, observou-se que a adição de molibdênio e nióbio promoveu um aumento da resistência mecânica em 171 e 119 MPa no limite de escoamento e 61 e 66 MPa no limite de resistência à tração, nos aços C5Nb e C6Nb, respectivamente, devido à precipitação de carbonetos de nióbio, mantendo a mesma ductilidade e tenacidade para o aço C5Nb, mas houve uma queda dessas propriedades para os aço C6Nb. Após a laminação com posterior têmpera e revenimento a 500°C, simulando o mesmo tratamento feito na roda ferroviária, o aço C5 apresentou dureza, resistência mecânica e alongamento iguais à do aço da MWL, porém com redução de área e energia absorvida maiores que o aço da MWL. O aço C5Nb apresentou maiores valores de resistência mecânica, ductilidade e tenacidade que o aço da MWL, o que demonstra seu potencial para melhorar a qualidade das rodas ferroviárias atualmente produzidas
Abstract: The influence of molybdenum and niobium addition on the microstructure and mechanical properties of 0,5 and 0,6 %C steels used in railway wheels was studied. The deformation was applied by rolling, in a thermo mechanical processing laboratory, simulating the forging in the real process of manufacture. The samples were heated to 1250 °C to ensure dissolution of niobium and hot rolled in four passes, starting at 1200 °C, undergoing a total reduction of 67%, followed by air cooling. Steels were water quenched and tempered (heat treatment). Steel samples, before and after rolling and heat treated were analyzed by optical and scanning electron microscopy. Mechanical tests were performed on the all conditions. After rolling between 1200 and 1120 ° C, it was found that the addition of molybdenum and niobium resulted in an increase of mechanical strength at 171 and 119 MPa in yield strength and 61 and 66 MPa in tensile strength, respect due to precipitation of niobium carbides, while maintaining the same ductility and toughness for C5Nb steel, but there was a decrease of these properties for C6Nb. After rolling with subsequent quenching and tempering at 500 ° C, simulating the same treatment done in the railway wheel, steel C5 showed the same toughness, strength and elongation in comparison with MWL rail wheels steel, but with reduced area and absorbed energy greater than the MWL steel. C5Nb steel showed higher strength, ductility and toughness than MWL steel, which demonstrates its potential to improve the quality of railway wheels currently produced
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica
6
Posada, Pérez Sergio. "Heterogeneous catalysis of green chemistry reactions on molybdenum carbide based catalysts". Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/552405.
Abstract (sommario):
Our society has a problem with the use of fossil fuels, due to the vast and exceeding emissions derived from human activities. Two ways could be consider to mitigate these harmful effects. On the one hand, the capture, activation, and conversion of these hazardous gases towards valuable compounds, and on the other hand, the substitution of fossil fuels for renewable energies. This thesis encompasses the study of two different green chemistry reactions to convert the most abundant greenhouse gas in Earth's atmosphere and the production of a new environmental friendly fuel, the hydrogen.
In the current search for new catalysts, Transition Metal Carbides (TMCs) have arisen as an appealing alternative, because their exhibit broad and amazing physical and chemical properties and their low cost. In particular, titanium carbide (001) was proposed from experimental and theoretical points of view as active catalyst and support of small metal particles for CO2 hydrogenation to methanol and water gas shift reaction. However, given that titanium carbide is a cumbersome support to be used in applications due to the difficulty of obtaining nanoparticles on working conditions, we have carried out these reactions on cubic δ-MoC (001) and orthorhombic β-Mo2C (001) surfaces.
The adsorption and activation of a CO2 molecule on cubic δ-MoC (001) and orthorhombic β-Mo2C (001) surfaces have been investigated by means of periodic density functional theory based calculations using the Perdew-Burke-Ernzerhof exchange-correlation functional showing that both surface are promising catalyst for CO2 conversion because they are able to activate and bend the CO2 molecule. The β- Mo2C (001) surface is able to dissociate the CO2 molecule easily, with a low energy barrier, whereas δ-MoC (001) surface activates CO2 but it does not promote its direct dissociation. Experiments accomplished by the group of Dr. Jose Rodriguez revealed that CO and methane are the main products of the CO2 hydrogenation using β-Mo2C
(001) as catalyst, and the amount of methanol is lower. On the other hand, only CO and methanol are produced using δ-MoC (001).
Experiments revealed that the deposition of small copper particles on the carbide surfaces increase drastically the catalysts' activity and selectivity, which was demonstrated by theoretical calculations. On β-Mo2C, the amount of CO and methanol
increase whilst the amount of methane decrease, since copper blocks reactive sites on surface. This is a positive fact since copper avoid the excessive oxygen deposition, which deactivated the catalysts. On the other hand, the deposition of copper on δ-MoC
(001) increases a lot the amount of CO and methanol. In summary, our combining DFT- experimental study proposed the Cu/δ-MoC as promising catalyst for CO2 hydrogenation due to its activity (the amount of products is superior than other TMCS, metals, and the model of commercial catalysts), selectivity (only CO and methanol are produced), and stability ( this catalysts is not deactivated by the oxygen deposition).
The results obtained in the first part of the thesis were used to study the water gas shift reaction. Given that the excellent features, experiments proposed Au supported on δ-MoC (001) as catalysts. Our theoretical calculations demonstrated that clean δ-MoC (001) is not a good catalysts for WGS, due to the fact that the reverse reactions are favorable respect the direct ones, which implies that the amount of products is lower. Nevertheless, the deposition of Au clusters change the reaction mechanism, favoring the direct barriers instead of reverse ones, and increasing the amount of produced H2.
In summary, this thesis has displayed the prominent role of molybdenum carbides as support of small metal particles to catalyze green chemistry reactions.En aquesta tesi es mostra un treball computacional sobre l'ús de catalitzadors econòmics per a la conversió de CO2, un perillós gas d'efecte hivernacle i també per a la producció d'hidrogen, el combustible del futur. En la recerca actual de nous catalitzadors, els carburs de metalls de transició (TMC) han sorgit com una alternativa atractiva pel el seu baix cost i per exhibir excel·lents propietats físiques i químiques. En aquest treball utilitzarem com a catalitzadors les superfícies cúbica δ-MoC (001) i ortoròmbica β-Mo2C (001). L'adsorció de la molècula de CO2 mostra que ambdues superfícies són capaces d'activar i doblegar la molècula. La superfície β-Mo2C (001) és capaç de dissociar fàcilment la molècula de CO2, mentre que la superfície δ-MoC (001) activa CO2 però no la dissocia. Els experiments realitzats pel grup del Dr. Jose Rodriguez van revelar que el CO i el metà són els principals productes de la hidrogenació de CO2 utilitzant β-Mo2C (001) com a catalitzador, i la quantitat de metanol és menor. D'altra banda, només es produeixen CO i metanol utilitzant δ-MoC (001). La deposició de partícules de coure a les superfícies del carbur augmenta dràsticament l'activitat dels catalitzadors, cosa que es va demostrar mitjançant càlculs teòrics. A la superfície β-Mo2C, la quantitat de CO i metanol augmenten mentre que la quantitat de metà disminueix. D'altra banda, la deposició de coure a δ-MoC (001) augmenta molt la quantitat de CO i metanol. En resum, el nostre estudi proposa el Cu/δ-MoC com a prometedor catalitzador de la hidrogenació de CO2 a causa de la seva activitat (la quantitat de productes és superior a la resta de TMCS, metalls i el model de catalitzadors comercials), selectivitat (només el CO i el metanol es produeixen) i l'estabilitat (aquests catalitzadors no es desactiven per la deposició d'oxigen). Tenint en compte els resultats previs, es va proposar la deposició d'or en la superfície δ-MoC per a la producció d'hidrogen. Els càlculs teòrics demostren que la superfície δ-MoC (001) no és un bon catalitzador per WGS, però la deposició dels clústers d'or canvia el mecanisme de reacció i augmenta la quantitat d'H2 produïda.
7
Fonseca, Solange Tamara da 1978. "Efeito de adições de vanádio, nióbio e molibdênio na estrutura e propriedades mecânicas de aços com 0,7 % C utilizados na fabricação de rodas ferroviárias". [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265830.
Abstract (sommario):
Orientadores: Paulo Roberto Mei , Amilton SinatoraTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Uma das maneiras de se reduzir os custos no transporte de cargas é aumentando a quantidade de carga transportada por vagão, isto eleva a tensão no eixo do vagão e, consequentemente, a roda deve possuir maior dureza sem perda da tenacidade para suportar o desgaste. Para atingir os níveis de dureza necessários estão sendo desenvolvidas rodas ferroviárias com aços microligados que são definidos como aços carbono-manganês contendo pequenos teores (menores que 0,5% em massa) de elementos de liga, que são fortes formadores de carbonetos como o nióbio (Nb), vanádio (V), molibdênio (Mo) e titânio. Em 2008, a MWL do Brasil iniciou o desenvolvimento de rodas ferroviárias fabricadas com aços microligados, e a partir de 2012, com a colaboração da EPUSP foi necessário o desenvolvimento de uma máquina de ensaio de desgaste tipo disco contra disco que atendesse as especificações da norma AAR (Association of American Railroads). Além disso, havia interesse em se conhecer o comportamento desses aços, sendo assim, seria necessário obter as curvas de resfriamento contínuo (CRC) dos mesmos. A análise destas mostrou que a adição dos elementos microligantes refinou o grão austenítico por formação de finos carbonetos de Nb e V, retardou a formação de ferrita e perlita, o que reduziu o espaçamento interlamelar da perlita; e elevou a temperabilidade dos aços. Entretanto, a adição de microligantes não alterou as temperaturas de início de formação de martensita, mas melhorou a temperabilidade. A formação de martensita não foi finalizada até a temperatura ambiente e todos os aços apresentaram austenita retida junto com a martensita. A análise de corpos de prova retirados das pistas de rolamento das rodas ferroviárias prontas para uso, com estrutura ferrítica-perlítica, revelou que o aço ao V apresentou os melhores resultados em todos os ensaios (tração na temperatura ambiente e 540 ºC, energia absorvida no ensaio Charpy e KIC) quando comparado ao aço sem microligantes ou com a adição de Nb+Mo. O melhor desempenho do aço ao V foi atribuído ao seu menor tamanho de grão austenítico e espaçamento interlamelar da perlita mais refinado. No ensaio de desgaste por deslizamento, a perda de massa foi maior no aço Nb. O primeiro protótipo construído da máquina de desgaste tipo disco contra disco forneceu resultados confiáveis até 250.000 ciclos, não atingindo o valor minímo especificado pela AAR. Entretanto a experiência adquirida foi essencial para projetar um novo protótipo que está em comissionamento
Abstract: One of the main strategies to reduce cost in load transportation is through the increase of the load transported a railroad car. This increase of tension in the wagons axes, require wheels with higher hardness but without loss of ductility and toughness. Thus, to achieve the required levels of hardness, the developments are now focusing on railway wheels composed by microalloyed steels that are defined as carbon-manganese steels containing a small amount (less than 0.5% by mass) of strong carbide-forming elements such as niobium (Nb), vanadium (V), molybdenum (Mo) and/or titanium. The MWL Brazil began in 2008, together with Unicamp, a research project on the development of railway wheel made of microalloyed steel and, later on 2012, EPUSP joined to the project reinforcing the importance of the project. During this work, project developed a disk-on-disk wear test machine that would attend the specifications of the standard AAR (Association of American Railroads). Besides, there was also an interest on further knowing the behavior of these steels, that is, it would be necessary to obtain the continuous cooling curves (CCC). In this work, the analysis of CCC showed that the addition of microalloying elements contributed in refining the austenitic grain size due to fine Nb and V carbides formation; delayed the formation of ferrite and pearlite, which reduced the interlamellar spacing of pearlite; and increased the hardenability of steels. However, the addition of microalloying did not change the starting martensite formation temperature, but increased the hardenability. It was also observed that the formation of martensite was not finished at room temperature and all studied steels presented retained austenite. The analysis of samples taken from the tread of railway wheels, with ferritic-pearlitic structure revealed that the vanadium steel showed the best results in all tests of strength (at room temperature and 540 °C), K1C and Charpy test if compared to steels without microalloying or with the addition of Nb+Mo. The superior performance vanadium steel was attributed to the smallest austenite grain size and the finest interlamellar spacing of the pearlite. In the wear test, the weight loss was greater in the niobium microalloyed steel. The developed prototype of the disk-on-disk wear test machine only provided reliable results up to 250,000 cycles; it not reached the minimum value specified by the AAR. However, the experience was essential to enhance a new prototype that is commissioning
Doutorado
Materiais e Processos de Fabricação
Doutora em Engenharia Mecânica
8
Sosa, Letícia. "Hydrodésoxygénation du furfural en 2-methylfurane à l’aide de catalyseurs à base de carbures de molybdène". Electronic Thesis or Diss., Centrale Lille Institut, 2023. http://www.theses.fr/2023CLIL0004.
Abstract (sommario):
Des carbures de molybdène ont été synthétisés, caractérisés et évalués pour la réaction d'hydrodésoxygénation du furfural en 2-méthylfurane à 30 bar de H2, 200 °C dans le 2-butanol et le cyclopentyl méthyl éther. Dans cette thèse, plusieurs facteurs concernant la nature des carbures ont été évalués : (i) l'effet des phases cristallographiques (α-MoC et β-Mo2C) ; (ii) l'effet de l'addition des promoteurs Ni et Cu ; (iii) l'effet de la passivation et de la réactivation ; (iv) l'effet du support (SiO2, TiO2, ZrO2, ZSM-5). Les résultats montrent que la phase β-Mo2C est plus active que la phase α-MoC, mais la même distribution des produits est observée en iso-conversion. L'ajout de Ni et de Cu a eu un effet positif et négatif, respectivement, sur l'activité du carbure. Différents degrés d'oxydation ont eu lieu pendant la passivation des carbures, ce qui était lié à leur dispersion et la réactivation ne les a pas régénérés. Les différents supports ont principalement affecté la première étape de la réaction ainsi que l'état final des carbures de MoMolybdenum carbides were synthesized, characterized, and evaluated for the hydrodeoxygenation reaction of furfural to 2-methylfuran at 30 bar of H2 and 200 °C in 2-butanol and cyclopentyl methyl ether. In this thesis, several factors concerning the nature of carbides were evaluated: (i) the effect of crystallographic phases (α-MoC and β-Mo2C); (ii) the effect of the addition of Ni and Cu promoters; (iii) the effect of passivation and reactivation; (iv) effect of support (SiO2, TiO2, ZrO2, ZSM-5). The results show that the β-Mo2C phase is more active than the α-MoC phase, but the same distribution of products is observed in iso-conversion. The addition of Ni and Cu had a positive and negative effect, respectively, on the carbide activity. Different degrees of oxidation occurred during the passivation of carbides, which was related to their dispersion and reactivation did not regenerate them. The different supports mainly affected the first step of the reaction, as well as the final state of the Mo carbides
9
Murugappan, Karthick. "Molybdenum trioxide and molybdenum carbide as promising hydrodeoxygenation catalysts for biomass conversion". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111404.
Abstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 171-176).
Growing concerns due to rising CO2 emissions have made biomass an indispensable source of renewable fuels and chemicals. However, biomass inherently has high oxygen content, which translates to low energy density, thereby necessitating a deoxygenation step before being utilized as fuels. Recently, MoO3 and Mo2C have emerged as promising earth-abundant cheap catalysts that perform hydrodeoxygenation (HDO) at relatively low temperatures ( 673 K) and ambient H2 pressures wherein oxygen is selectively removed as water. However, there exists a significant knowledge gap in understanding the stability and the active phases responsible for HDO of these catalysts. Furthermore, their applicability for real biomass conversions has not been largely demonstrated. In this thesis, first, HDO of m-cresol, a biomass-derived model compound, is investigated over bulk and supported MoO 3 catalysts. Detailed reactivity and characterization studies reveal that Mo5+ species plays a critical role during HDO. Specifically, TiO2 and ZrO2 are identified as ideal supports as they feature superior HDO reactivity and stability over bulk MoO3 by stabilizing intermediate Mo oxidation states (i.e. Mo5+) while bulk MoO 3 over-reduces to inactive metallic Mo. Translating from model compound studies, supported MoO3 catalysts are demonstrated to be effective in converting biomass (pine) pyrolysis vapors to hydrocarbons (ca. 30 % yield). In comparison with MoO 3, Mo2C is significantly more stable and selective for HDO of 4-methylanisole to toluene under identical reaction conditions. Mo2C predominantly breaks the stronger phenolic C-0 bond while MoO 3 also breaks the weaker aliphatic C-0 bond, likely due to the presence of Bronsted acid sites. To gain insights into the surface active sites, operando near-ambient XPS is employed during HDO and this technique revealed that HDO seems to operate via distinct active sites over both these materials. Finally, Mo2C is shown to be effective in upgrading real lignin streams to a single product propylbenzene, a precursor for renewable polymer. Overall, this thesis demonstrates the applicability of MoO3 and Mo2C in real biomass conversions and provides insights on the working nature of these catalysts, which will enable the design of more effective HDO catalysts.
by Karthick Murugappan.
Ph. D.
10
Yu, Jenwei Roscoe. "Methane activation over molybdenum disulfide, molybdenum carbide, and silver(110). Molecular orbital theory". Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1059138320.
11
Lugge, John J. "Molybdenum carbide synthesis using plasmas for fuel cells". Monterey, California: Naval Postgraduate School, 2013. http://hdl.handle.net/10945/34700.
Abstract (sommario):
Approved for public release; distribution is unlimitedCurrently, carbon is the preferred support material for platinum catalyst particles used in polymer electrolyte fuel cells (PEFCs). Carbon possesses qualities needed for a fuel cell catalyst: high surface area and conductivity, but is unacceptable as it is prone to oxidization by carbon dioxide in the fuel cell environment. Molybdenum Carbides is known to have the required conductivity. However, making Mo2C with sufficient surface area and with stabilized platinum remains a materials challenge. In this work a novel approach, a variation on the Aerosol-Through-Plasma (ATP) method was employed for making Mo2C with high surface area and stable supported platinum particles. An ammonium molybdate precursor was processed through different ATP conditions to generate the catalyst. These particles were then characterized using X-ray diffraction and SEM techniques in order to produce a support material with the highest concentration of Mo2C. Using the ideal conditions for the ATP, precursor was loaded with platinum and then processed through the ATP. This sample was then characterized using X-ray and SEM techniques to insure that the material was suitable prior to testing the electrochemical properties under PEFC operating conditions. The results were then compared to other leading support catalysis.
12
Hantzer, Sylvain. "Nouveaux materiaux pour la reaction d'hydrodesulfuration (hds)". Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13120.
Abstract (sommario):
Nouveau modele de phase active obtenu par interpretation des resultats de rmn du **(59)co et de microscopie electronique haute resolution pour des catalyseurs d'hydrotraitement a base de sulfure de molybdene et de cobalt. Application a d'autres systemes : nire, core, rhre et rhmo. Etude de l'empoisonnement par la porphyrine de catalyseur nimo/al::(2)o::(3)
13
Al-Megren, Hamid. "Hydrodenitrogenation of pyridine over bulk and supported molybdenum carbide". Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249636.
14
Naredla, Sai Bhargav. "Electrical Properties of Molybdenum Silicon Carbide Schottky Barrier Diodes". Youngstown State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ysu155901806279725.
15
Martinelli, Antonio Eduardo. "Diffusion bonding of silicon carbide and silicone nitride to molybdenum". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40191.
Abstract (sommario):
This study focuses on various aspects of solid-state diffusion bonding of two ceramic-metal combinations, namely: silicon carbide-molybdenum (SiC-Mo), and silicon nitride-molybdenum (Si$ rm sb3N sb4$-Mo). Single SiC-Mo and $ rm Si sb3N sb4$-Mo joints were produced using hot-uniaxial pressing. The microstructure of the resulting interfaces were characterized by image analysis, scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), and X-ray diffraction (XRD). The mechanical properties of the joints were investigated using shear strength testing, depth sensing nanoindentation, and neutron diffraction for residual stress measurement.SiC was solid-state bonded to Mo at temperatures ranging from 1000$ sp circ$C to 1700$ sp circ$C. Diffusion of Si and C into Mo resulted in a reaction layer containing two main phases: $ rm Mo sb5Si sb3$ and Mo$ sb2$C. At temperatures higher than 1400$ sp circ$C diffusion of C into $ rm Mo sb5Si sb3$ stabilized a ternary phase of composition $ rm Mo sb5Si sb3$C. At 1700$ sp circ$C, the formation of MoC$ rm sb{1-x}$ was observed as a consequence of bulk diffusion of C into Mo$ sb2$C. A maximum average shear strength of 50 MPa was obtained for samples hot-pressed at 1400$ sp circ$C for 1 hour. Higher temperatures and longer times contributed to a reduction in the shear strength of the joints, due to the excessive growth of the interfacial reaction layer. $ rm Si sb3N sb4$ was joined to Mo in vacuum and nitrogen, at temperatures between 1000$ sp circ$C and 1800$ sp circ$C, for times varying from 15 minutes to 4 hours. Dissociation of $ rm Si sb3N sb4$ and diffusion of Si into Mo resulted in the formation of a reaction layer consisting, initially, of $ rm Mo sb3$Si. At 1600$ sp circ$C (in vacuum) Mo$ sb3$Si was partially transformed into $ rm Mo sb5Si sb3$ by diffusion of Si into the original silicide, and at higher temperatures, this transformation progressed extensively within the reaction zone. Residual N$ sb2$ gas, which originated from the decomposition of $ rm Si sb3N sb4,$ dissolved in the Mo, however, most of the gas escaped during bonding or remained trapped at the original $ rm Si sb3N sb4$-Mo interface, resulting in the formation of a porous layer. Joining in N$ sb2$ increased the stability of $ rm Si sb3N sb4,$ affecting the kinetics of the diffusion bonding process. The bonding environment did not affect the composition and morphology of the interfaces for the partial pressures of N$ sb2$ used. A maximum average shear strength of 57 MPa was obtained for samples hot-pressed in vacuum at 1400$ sp circ$C for 1 hour.
16
Oloye, Femi Francis. "Synthesis and characterisation of zirconia supported molybdenum oxide and molybdenum carbide catalysts for hydroconversion of n-heptane". Thesis, University of Aberdeen, 2016. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=230933.
Abstract (sommario):
The current upgrading catalysts are mainly based on the use of expensive noble metals, which are subject to deactivation due to sintering and coking. An alternative would be to introduce a non-noble metal-based catalyst. In this work, supported molybdenum carbide based systems have been assessed for this purpose. These catalysts were formed by impregnation of zirconia (and zirconium hydroxide) and sulfated zirconia (and zirconium hydroxide) with different loadings of MoO3, with an aim of finding a balance between acid sites and metal-like sites (a site capable of performing dehydrogenation and hydrogenation function without necessarily being a metal). The synthesised catalysts were carburised between 823 and 1123 K using a mixture of methane and hydrogen (4:1) in an attempt to obtain β-Mo2C/ZrO2 or β-Mo2C/S ZrO2. Carburisation at 923 K and above resulted in molybdenum carbide with minimal or no oxygen contents. The conversion and specific rate increased with temperature. Conversion was inversely proportional to space velocity. Analysis of the products distribution as a function of conversion implies that the reaction did not simply follow a consecutive reaction pathway, but that other parallel routes were involved. Conversion increased the research octane number (RON) to ca. 66 due to the increased fraction of pentane isomers. Catalyst carburised at 823 K was approximately four times more active compared to those carburised at 923 K and above, but were of similar activity with Pt/sulfated zirconia. The non-noble metal based catalysts were stable at the reaction temperature while the Pt/sulfated zirconia catalyst deactivates.
17
Abou, Hamdan Marwa. "Hydrogenation of succinic acid and carbon dioxide over molybdenum carbide catalysts". Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1065.
Abstract (sommario):
Ce travail de thèse porte sur la synthèse de carbures de molybdène sur support afin de tester leurs performances catalytiques dans des réactions d’hydrogénation. Dans ce but, la conversion d'acide succinique en phase aqueuse dans un réacteur discontinu et du dioxyde de carbone en phase gazeuse dans un réacteur à flux continu, ont été effectuées. Les catalyseurs ont été préparés par la méthode de carburation par réduction en température programmée, pendant laquelle des paramètres ont été modifiés conduisant à différents rapports molybdène/carbone. Les différents catalyseurs testés dans cette réaction étaient actifs pour la conversion de l'acide succinique en gamma-butyrolctone et, plus remarquablement, en acide butyrique, ce dernier n'était pas obtenu en quantités significatives avec des catalyseurs à base de métaux précieux. L’augmentation de la conversion d’acide succinique avec une sélectivité plus élevée en acide butyrique a été faite avec les catalyseurs contenant plus de carbone, préparés en augmentant la vitesse spatiale horaire gazeuse. Les intermédiaires ont été ensuite convertis en tétrahydrofurane, butanol, 1,4-butanediol et butane. La désactivation observée lors de recyclage du catalyseur a été principalement attribuée à une diminution de la quantité de molybdène et de carbone carbidique, démontrée par l'analyse XPS. Des essais préliminaires de ces catalyseurs dans l'hydrogénation du dioxyde de carbone ont montré qu'ils fonctionnaient principalement en tant que catalyseurs pour la réaction du gaz à l’eau inverse, et l'excès de carbone entrave l'activité catalytique d'une manière opposée à la réaction en phase aqueuse. Le support semble jouer un rôle dans la réactivité des catalyseurs, la conversion du dioxyde de carbone ainsi que la sélectivité en méthane et méthanol, qui ont augmenté dans l'ordre suivant: carbure de molybdène sur support DT51 TiO2> P25 TiO2 ˜ ZrO2This work focuses on the synthesis of supported molybdenum carbides and evaluating their catalytic performance in succinic acid hydrogenation reactions in aqueous phase using batch reactor and carbon dioxide hydrogenation in gas phase using continuous flow reactor. The catalysts were prepared by the temperature programmed reduction carburization method, where the parameters were modified leading to different molybdenum to carbon ratios. The different catalysts tested were active in converting succinic acid to gamma butyrolctone and more remarkably butyric acid which is not reported in significant quantities in this reaction with precious metal based catalysts. The catalysts containing more carbon contents that were prepared by increasing the gas hourly space velocity showed higher activity in converting succinic acid and higher selectivity to butyric acid. The intermediates were then converted to tetrahydrofuran, butanol, 1,4-butanediol and butane gas. The deactivation observed while recycling the catalyst was mainly attributed to a decrease in the amounts of carbidic molybdenum and carbidic carbon, as demonstrated by XPS analysis. Preliminary tests for these catalysts in carbon dioxide hydrogenation showed that they functioned mainly as reverse water gas shift catalysts, and the excess of carbon hinders the catalytic activity in an opposite manner of the reaction in aqueous phase. The support seems playing a role in the reactivity of the catalysts, carbon dioxide conversion as well as methane and methanol selectivity increased in the order: molybdenum carbide supported on DT51 TiO2 > P25 TiO2 ˜ ZrO2
18
Björklund, Kajsa. "Microfabrication of Tungsten, Molybdenum and Tungsten Carbide Rods by Laser-Assisted CVD". Doctoral thesis, Uppsala University, Department of Materials Chemistry, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1593.
Abstract (sommario):
Thin films of refractory metals and carbides have been studied extensively over many years because of their wide range of application. The two major techniques used are Chemical Vapour Deposition (CVD) and Physical Vapour Deposition (PVD). These can result in the deposition of two-dimensional blanket or patterned thin films. Laser-assisted Chemical Vapour Deposition (LCVD) can provide a maskless alternative for localised deposition in two and three dimensions. This thesis describes LCVD of micrometer-sized tungsten, molybdenum and tungsten carbide rods. The kinetics, phase composition and microstructure have been studied as a function of in situ measured laser induced deposition temperature.
Tungsten and molybdenum rods were deposited by hydrogen reduction of their corresponding hexafluorides, WF6 and MoF6, respectively. Single crystal and polycrystalline tungsten rods were obtained, depending on the H2/WF6 molar ratio and deposition temperature. The molybdenum rods were either single crystals or dendritic in form depending on experimental conditions. The field emission characteristics of the tungsten single crystals were investigated. The results showed LCVD to be a potential fabrication technique for field emitting cathodes.
Nanocrystalline tungsten carbide rods were deposited from WF6, C2H4 and H2. TEM analysis showed that the carbide rods exhibited a layered structure in terms of phase composition and grain size as a result of the temperature gradient induced by the laser beam. With decreasing WF6/C2H4 molar ratio, the carbon content in the rods increased and the phase composition changed from W/W2C to WC/WC1-x and finally to WC1-x/C.
19
Björklund, Kajsa. "Microfabrication of tungsten, molybdenum and tungsten carbide rods by laser-assisted CVD /". Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5197-7/.
20
St, Clair Todd P. "Characterization and Reactivity of Mo2C". Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/40502.
Abstract (sommario):
Two types of Mo2C have been investigated: polycrystalline beta-Mo2C and single crystal alpha-Mo2C. The beta-Mo2C material was synthesized via a temperature-programmed method, and then characterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), CO chemisorption, and N2 physisorption. The catalytic activity of the beta-Mo2C was tested for cumene hydrogenation under high pressure conditions, and the effect of sulfur and oxygen poisons on cumene hydrogenation was also investigated.
As a complement to the work done on polycrystalline beta-Mo2C, UHV studies of single crystal alpha-Mo2C were undertaken to provide fundamental information about a well-characterized Mo2C surface. The (0001) surface of alpha-Mo2C was investigated using XPS and low energy electron diffraction (LEED). It was found that an ion-bombarded surface could be prepared as either Mo-terminated or C-terminated by choosing either low annealing temperatures (~1000 K) or high annealing temperatures (~1500 K), respectively. CO and O2 adsorption was also studied on alpha-Mo2C (0001) using thermal desorption spectroscopy (TDS), XPS, Auger electron spectroscopy (AES), and LEED. Finally, thiophene adsorption was investigated on alpha-Mo2C (0001).Ph. D.
21
Lucazeau, Emmanuelle. "Contribution à l'étude de la formation du carbure de molybdène sur le diamant". Grenoble INPG, 1997. http://www.theses.fr/1997INPG0110.
Abstract (sommario):
En vue de la realisation de contacts electriques ohmiques sur le diamant compatibles avec les proprietes physiques et chimiques uniques du diamant et qui soient capables de resister aux operations prolongees dans les environnements hostiles pour lesquels ces dispositifs sont destines, nous avons etudie la formation du carbure de molybdene sur le diamant par reaction en phase solide. Ce travail s'articule autour de l'etude de la formation du carbure de molybdene sur les diamants intrinseques ou dopes polycristallins et monocristallins homoepitaxies elabores au laboratoire par pulverisation catholique magnetron de molybdene sur la surface du diamant suivie de recuits sous atmosphere d'argon. La formation du carbure est suivie par diffraction des rayons x, par analyse par retrodiffusion de rutherford ou rbs, ou par spectroscopie de photo-electrons induits par rayons x ou xps. Nous avons mis au point une procedure d'elaboration du carbure de molybdene hexagonal -mo#2c sur le diamant polycristallin conduisant a la formation d'un contact ohmique stable a haute temperature. Sur les films monocristallins homoepitaxies, la formation du -mo#2c se trouve ralentie par une incorporation importante d'oxygene dans la couche metallique durant le depot. La presence de bore ralentit la formation du carbure et sa cristallisation.
22
Darujati, Anna Rini Sekar. "Oxidation stability and activity of bulk, supported and promoted molybdenum carbide catalysts for methane reforming". Online access for everyone, 2005. http://www.dissertations.wsu.edu/Dissertations/Spring2005/A%5FDarujati%5F050405.pdf.
23
Hanif, Ahmad. "Partial oxidation and COâ†2 reforming of methane to valuable products over molybdenum and tunsten carbide". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343512.
24
Лалетіна, К. І., e Б. М. Ярмош. "Кристалічна структура та електрофізичні властивості плівок карбідів молібдену". Thesis, Видавництво СумДУ, 2008. http://essuir.sumdu.edu.ua/handle/123456789/4420.
25
Zhang, Tianyu. "DENSITY FUNCTIONAL THEORY STUDIES ON THE STRUCTURAL EVOLUTION AND CATALYTIC REACTIVITY OF MOLYBDENUM-BASED CATALYSTS FOR METHANE CONVERSION". OpenSIUC, 2019. https://opensiuc.lib.siu.edu/dissertations/1768.
Abstract (sommario):
Methane is an abundant resource existing in the form of natural and shale gas, and molybdenum-based catalysts, including molybdenum oxides and carbides, are the commonly used components in catalysts for converting methane to value-added chemicals. Therefore, understanding the catalytic mechanism underlying the methane conversion over molybdenum-based catalysts is key to designing highly efficient catalysts and optimizing the operating conditions. In this dissertation, I focus on the structural evolution from oxide to carbides and catalytic reactivity of the molybdenum-based catalysts for methane conversion based on the result from density functional theory (DFT) computational studies.First, the surface chemistry and reactivity of α-MoO3 toward C-H bond activation of methane by breaking the first C-H bond on the MoO3 (010) surface were used to evaluate various functionals of the DFT method. Our results indicate that surface reduction of α-MoO3 (010) occurs preferably through releasing the terminal oxygen atoms, generating oxygen vacancies while exposing the reduced Mo centers. These oxygen vacancies tend to be separated from each other at a higher density due to the repulsive interactions. Furthermore, the reduced α-MoO3 (010) surface promotes methane activation kinetically and thermodynamically by reducing the activation barrier for the first C-H bond breaking and stabilizing the product state as compared with those on the stoichiometric surface. There is a synergy between the reduced Mo active site and surface lattice oxygen for C-H bond cleavage. In addition, the performance of different functionals, including the pure-GGA PBE functional with the semi-empirical vdW correction and the meta-GGA SCAN functional, has been investigated. With the meta-GGA functional, we can predict the bulk structure of α-MoO3 more accurately while reproducing the thermal chemistry of MoO3. On the other hand, the reactivity based on the PBE functional is qualitatively consistent with that from the SCAN functional.We then conducted a systematic study of methane activation and conversion over the Mo-terminated surfaces derived from different phases of Mo2C carbides, i.e. the (001) surface of α-Mo2C and the (100) surface of β-Mo2C. The results show that Mo-terminated Mo2C with lower carburization in its subsurface (β-Mo2C) possesses a superior reactivity toward methane activation, resulting in a complete dissociation of methane to carbon adatom on the surface. This carbon adatom causes further carburization of the surface, lowering the reactivity toward methane activation. Moreover, the carburization occurs more easily in the near surface layers of Mo2C than in the bulk. Although carburization lowers the activities for methane activation, it promotes C-C coupling for dimerization of the (CH)ad species, resulting in (C2H2)ad on the Mo-terminated surfaces. On the deep carburized molybdenum carbide (MoC) surfaces, we mapped out the elementary steps of CH4 dissociation and possible mechanisms for forming the C2 species. The results indicate that the Mo-terminated MoC surfaces derived from different bulk phases (α- and δ-) of MoC possess a similar mechanism to that on the noble-metal surfaces for methane dissociation, i.e., CH4 dissociates sequentially to (CH)ad with both kinetic and thermodynamic feasibilities while breaking the last C-H bond in (CH)ad is highly activated. As such, C-C coupling through dimerization of the (CH)ad species occurs more readily, resulting in (C2H2)ad on the Mo-terminated surfaces. Such (C2H2)ad species can dehydrogenate easily to other C2 adsorbates such as (C2H)ad and (C2)ad. Consequently, these C2 species from CH4 dissociation will likely be the precursors for producing long chain hydrocarbons and/or aromatics on molybdenum carbide based catalysts.
26
Kong, Jia Huey. "SINTERING PROPERTIES OF TiC-Ni-Mo CERMET USING NANOSIZED TiC POWDERS". OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/1898.
Abstract (sommario):
The sintering behavior to form TiC-Ni-Mo cermet using a nano-size TiC powders was investigated in flowing Argon gas at 1500°C. Nano-sized titanium carbide powders with high purity, high surface area, and low cost were synthesized from carbon coated Ti containing precursors utilizing a patented process. The sintering studies showed that an increase in theoretical density (TD) with increasing molybdenum content. TiC based cermets were characterized using X-ray diffraction (XRD), Vickers hardness, and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Mechanical properties, electrical conductivity and oxidation resistance results shows potential applications as interconnect for Low/Intermediate Temperature Solid Oxide Fuel Cells (SOFC) and machining tool tips.
27
Okatsu, Hiroko. "New synthetic methods to alter catalytic properties of supported K/MoS₂ catalysts for syngas conversion to higher alcohols". Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/48996.
Abstract (sommario):
The purpose of this study is to develop catalysts for conversion of synthesis gas (H₂ and CO) to higher alcohols, primarily ethanol and propanol. Crude oil is consumed at a rate of more than 20 million barrels a day in the United States, mainly for producing fuels and chemical feedstocks. However, the total amount of crude oil is limited, and alternative ways of producing alcohols as precursors for chemical feedstocks are desirable. In this study, using a known K/MoS₂/metal oxide catalyst as the starting point, two different approaches were explored to improve catalytic properties: 1) Co promotion on K/MoS₂/mixed metal oxide (MMO) catalysts, and 2) Preparation of K/MoS₂/metal oxide catalysts with molybdenum carbide as a precursor, instead of molybdenum oxide. With respect to Co promotion on K/MoS₂/MMO catalysts, the effect of varying the Co content in the K/Mo-Co/MMO catalysts prepared by a co-impregnation method did not produce significant changes in catalytic acitivities or selectivities. It was due to the premature precipitation of cobalt molybdate during synthesis. Cobalt molybdate precipitation can generally be prevented by using water as a solvent, but this approach is not appropriate for this study because of the use of hydrotalcite-derived mixed metal oxide as the support. Co loadings on K/Mo/MMO-Co catalysts did not change selectivities significantly, either. However, they changed catalytic activities, represented by gas hourly space velocity (GHSV) required to obtain 8% conversion while maintaining high selectivities for higher alcohols. As a result, C ₂₊ alcohol productivities reached 0.01g(alcohol)/g(catalyst)/hr with Co loadings higher than 8%. With respect to using Mo2C as the precursor of Mo species instead of MoO3, comparisons between catalysts with different precursors for Mo species and different pretreatments were investigated. In this study, both K/Mo catalysts supported on MgO and α-Al₂O₃ showed similar tendencies of catalytic activities and selectivities. The highest C₂₊ alcohol selectivities and productivities were obtained on presulfided MoO₃ catalysts on both supports. In comparison of K/Mo ₂C catalysts with different pretreatments, higher C₂₊ alcohol selectivities and lower MeOH selectivities were obtained on presulfided catalysts compared to non-pretreated catalysts.
28
Li, Liwei. "Density functional theory study of alcohol synthesis reactions on alkali-promoted Mo2C catalysts". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53456.
Abstract (sommario):
As an important chemical raw material, alcohols can be used as fuels, solvents and chemical feedstocks to produce a variety of downstream products. With limited fossil fuel resources, alcohol synthesis from syngas reactions can be a potential alternative to the traditional petroleum based alcohol synthesis. Among many catalysts active for syngas to alcohol processes, alkali promoted Mo2C has shown promising performance. More interestingly, the alkali promoter was found to play an important role in shifting the reaction selectivity from hydrocarbons to alcohols. However, limited understanding of the mechanism of this alkali promoter effect is available due to the complexity of syngas reaction mechanism and low content of alkali added to the catalysts. In this thesis, we performed a comprehensive investigation of the alkali promoter effect with density functional theory (DFT) calculations as our primary tool. We first examine various Mo2C surfaces to determine a representative surface structure active to alkali adsorption. On this particular surface, we develop a syngas reaction network including relevant reaction mechanisms proposed in previous literature. With energetics derived from DFT calculations and a BEP relation, we predict the syngas reaction selectivity and find it to be in excellent agreement with experimental results. The dominant reaction mechanism and selectivity determining steps are determined from sensitivity analysis. We also propose a formation mechanism of alkali promoters on Mo2C catalysts that shows consistency between experimental IR and DFT computed vibrational frequencies. Finally, the effect of alkali promoters on the selectivity determining steps for syngas reactions are investigated from DFT calculations and charge analysis. We are able to rationalize the role of alkali promoters in shifting the reaction selectivity from hydrocarbons to alcohols on Mo2C catalysts.
29
Holl, Tobias [Verfasser], e Jens [Akademischer Betreuer] Weitkamp. "Competitive hydroconversion of decalin and n-decane on noble-metal catalysts and the evaluation of molybdenum carbide as ring-opening catalyst / Tobias Holl. Betreuer: Jens Weitkamp". Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2014. http://d-nb.info/1049688864/34.
30
Buckley, James. "The manufacture and characterisation of composite nuclear fuel for improved in-reactor performance". Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/the-manufacture-and-characterisation-of-composite-nuclear-fuel-for-improved-inreactor-performance(b5ea0339-7c5b-46d2-a696-743007b9e94b).html.
Abstract (sommario):
Fuel for nuclear reactors with an increased thermal conductivity offers the potential for lower fuel operating temperatures and reduced fission gas release rates. Uranium dioxide (UO2) based composites offer a method of achieving a higher thermal conductivity. Silicon carbide (SiC) and molybdenum (Mo) have been identified as potential candidates for use in a composite fuel material. Uranium dioxide composites were manufactured with the inclusion of whiskers and granules of SiC up to a 30 vol% loading. The manufacturing route used was based on the current process employed to commercially manufacture UO2 fuel, by reductive sintering. Composites containing Mo were manufactured via spark plasma sintering and included loadings of up to 10 vol% Mo. The composites were characterised on their microstructural properties and where appropriate the thermal conductivity was determined by laser flash analysis. The composites containing SiC achieved low densities, 95%TD. The microstructure contained channel like structures of Mo, due to the use of an agglomerated UO2 precursor powder. An increased thermal conductivity was determined for the molybdenum composites. At the maximum measurement temperature of 800°C the increase was found to be 68% in the 10 vol% composites compared to UO2.
31
Strahin, Brandon L. "The Effect of Engineered Surfaces on the Mechanical Properties of Tool Steels Used for Industrial Cutting Tools". University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1506692623324192.
32
Trueman, Anthony Roger. "Characterization and corrosion studies of high carbon tool steel/tungsten carbide metal matrix composites". Thesis, Queensland University of Technology, 1999.
33
Kolb, Veronika [Verfasser], Andreas [Akademischer Betreuer] Jess e Bastian [Gutachter] Etzold. "Synthesis of a Molybdenum Carbide Catalyst for the Application in the Reductive Carbonyl Coupling of trans-Cinnamaldehyde to the all-trans Polyene Diphenyl-hexatriene / Veronika Kolb ; Gutachter: Bastian Etzold ; Betreuer: Andreas Jess". Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2018. http://d-nb.info/1172072450/34.
34
Pasqualeti, Aniélli Martini. "Eletrocatalisadores formados por nitretos, carbetos e óxidos metálicos para o eletrodo de oxigênio". Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-14062017-102848/.
Abstract (sommario):
O desenvolvimento de eletrocatalisadores eletricamente condutores com alta atividade para a reação de redução de oxigênio (ORR - Oxygen Reduction Reaction) e desprendimento de oxigênio (OER - Oxygen Evolution Reaction) é de extrema importância e interesse para dispositivos de eletro-conversão de energia, como as células a combustível e eletrolisadores, que operam tanto em meio alcalino quanto ácido. Em meio alcalino, é possível o uso de metais não nobres e, assim, são viáveis para o uso em larga escala. Em meio ácido, é necessário o uso de materiais estáveis, uma vez que eles são expostos a um ambiente extremamente corrosivo e à altos potenciais, principalmente durante o processo de liga/desliga do dispositivo. Diante disso, este trabalho foi dividido em três linhas de pesquisa: Parte I - estudos de eletrocatalisadores bifuncionais para a ORR e OER em meio alcalino, sendo eles compostos por espinélios de manganês-cobalto em combinação com nanopartículas de ouro (MnCo2O4/Au). Parte II - estudos de eletrocatalisadores alternativos para a ORR em eletrólito ácido, onde foram considerados carbetos e nitretos de molibdênio (Mo2C-MoN) e, oxinitretos de tântalo (Ta-ON). Parte III - estudo de suportes alternativos ao carbono para a ORR em eletrólito ácido, sendo eles compostos por carbonitretos de tântalo e titânio (Ta-CN e Ti-CN). Os resultados da Parte I para MnCo2O4/Au mostraram que houve um aumento significativo na atividade de MnCo2O4 com a adição de ouro para ambas as reações. Foi possível observar que a combinação de nanopartículas condutoras (ouro) com nanopartículas ativas, mas não condutoras (MnCo2O4), é promissora para o desenvolvimento de eletrocatalisadores ativos para uso como eletrodos de oxigênio. Quanto a Parte II, os materiais compostos por Mo2C-MoN foram obtidos por meio da inserção de carbono e nitrogênio com tratamento térmico, na presença de carbono Vulcan e NH3, em alta temperatura. O material nomeado como MoN + Mo2C (molibdato) foi o que apresentou maior atividade catalítica, o que pôde ser atribuído ao menor tamanho de cristalito, maior quantidade da sua fase MoN e ao efeito sinérgico entre MoN e Mo2C, facilitando a ORR em comparação ao nitreto e carbeto de molibdênio puros. Nesta mesma linha de pesquisa, oxinitretos de tântalo foram sintetizados utilizando ureia como fonte de nitrogênio. Foi observado que Ti-Ta-ON apresentou maior atividade catalítica quando comparado aos demais eletrocatalisadores. Já na Parte III, os resultados para carbonitreto de titânio como suporte para a platina (Pt/Ti-CN) mostraram que, além da sua atividade para a ORR ser semelhante à platina suportada em carbono (Pt/C), ele também se mostrou mais estável que Pt/C após a realização de testes de estabilidade.The development of conductive electrocatalysts with high activity for the oxygen reduction and evolution reactions (ORR and OER) is of extremely importance for devices that electroconvert energy, such as fuel cells and electrolizers, which work in alkaline and acid media. A substantial amount of metals can be employed in alkaline electrolytes once the latter do not require the use of noble metals. The acid medium asks for stable materials, since they are exposed to a high oxidative environment and potentials during the start-up/shutdown events of the device. On the base of these facts, this research work has been divided into three parts: Part I - bifunctional electrocatalysts studies for the ORR and OER in alkaline electrolyte, the materials were composed of spinel manganese-cobalt oxide combined with gold nanoparticles (MnCo2O4/Au). Part II - studies of alternative electrocatalysts for the ORR in acid electrolyte, which included molybdenum carbides and nitrides (Mo2C-MoN), and tantalum oxynitrides (Ta-ON). Part III - alternative supports to the carbon for the ORR in acid electrolyte, which included tantalum and titanium carbonitrides (Ta-CN and Ti-CN). The results for MnCo2O4/Au, in Part I, showed that the addition of gold on the surface of the oxide improved the latter activity for both reactions. The combination of conductive nanoparticles (gold) with active, but non-conductive, nanoparticles (MnCo2O4) seems promising for the development of active electrocatalysts for the ORR and OER. In Part II, the materials composed of Mo2C-MoN were synthesized through carbon and nitrogen insertion, in a high temperature heat treatment, in the presence of Vulcan carbon and NH3. Among the gotten materials, the so called MoN + Mo2C (molybdate) showed the better electrocatalytic activity for the ORR, which could be attributed to its smaller crystallite size and the greater amount of its MoN phase, along with the synergistic effect between MoN and Mo2C. In this way, tantalum oxynitrides materials were obtained via a urea synthesis. The catalyst referred to as Ti-Ta-ON showed the better ORR activity among all the others studied oxynitrides materials. In Part III, besides the activity for the ORR of platinum supported on titanium carbonitride (Pt/Ti-CN) was similar to the activity of platinum supported on carbon (Pt/C), Pt/Ti-CN was also more stable than the latter, after the stability tests.
35
Heckman, Elizabeth Pierce. "Functionalizing Ceramic Matrix Composites by the Integration of a Metallic Substructure with Comparable Feature Size". Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1621451032485832.
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Gomes, Kalyanne Keyly Pereira. "S?ntese e caracteriza??o do carbeto de molibd?nio nanoestruturado para fins catal?ticos na rea??o de oxida??o parcial do metano". Universidade Federal do Rio Grande do Norte, 2006. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15789.
Abstract (sommario):
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Previous issue date: 2006-09-12Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
The nanostructures materials are characterized to have particle size smaller than 100 nm and could reach 1 nm. Due to the extremely reduced dimensions of the grains, the properties of these materials are significantly modified relatively when compared with the conventional materials. In the present work was accomplished a study and characterization of the molybdenum carbide, seeking obtain it with particles size in the nanometers order and evaluate its potential as catalyst in the reaction of partial methane oxidation. The method used for obtaining the molybdenum carbide was starting from the precursor ammonium heptamolybdate of that was developed in split into two oven, in reactor of fixed bed, with at a heating rate of 5?C/min, in a flow of methane and hydrogen whose flow was of 15L/h with 5% of methane for all of the samples. The studied temperatures were 350, 500, 600, 650, 660, 675 and 700?C and were conducted for 0, 60, 120 and 180 minutes, and the percent amount and the crystallite size of the intermediate phases were determined by the Rietveld refinement method. The carbide obtained at 660?C for 3 hours of reaction showed the best results, 24 nm. Certain the best synthesis condition, a passivating study was accomplished, in these conditions, to verify the stability of the carbide when exposed to the air. The molybdenum carbide was characterized by SEM, TEM, elemental analysis, ICP-AES, TG in atmosphere of hydrogen and TPR. Through the elemental analysis and ICP-AES the presence carbon load was verified. TG in atmosphere of hydrogen proved that is necessary the passivating of the molybdenum carbide, because occur oxidation in room temperature. The catalytic test was accomplished in the plant of Fischer-Tropsch of CTGAS, that is composed of a reactor of fixed bed. Already the catalytic test showed that the carbide presents activity for partial oxidation, but the operational conditions should be adjusted to improve the conversion
Os materiais nanoestruturados s?o caracterizados por terem um tamanho de cristalito inferior a 100 nm podendo atingir 1 nm. Devido ?s dimens?es extremamente reduzidas dos cristalitos, as propriedades destes materiais s?o significativamente modificadas relativamente ?s dos materiais convencionais. No presente trabalho foi realizado um estudo de s?ntese e caracteriza??o do carbeto de molibd?nio, visando obt?-lo com tamanho de part?culas na ordem de nan?metros e avaliar seu potencial como catalisador na rea??o de oxida??o parcial do metano. O m?todo utilizado para obten??o do carbeto de molibd?nio foi a partir do precursor heptamolibdato de am?nio que foi desenvolvida em forno bipartido, em reator de leito fixo, com uma taxa de aquecimento de 5?C/min, em um fluxo de metano e hidrog?nio cuja vaz?o foi de 15L/h com 5% de metano para todos os ensaios. As temperaturas estudadas foram 350, 500, 600, 650, 660, 675 e 700?C e nos tempos de isoterma de 0, 60, 120 e 180 minutos, sendo que a determina??o das fases presentes, estrutura cristalina e tamanho de cristalitos foram obtidos por refinamento de estrutura pelo m?todo de Rietveld. O carbeto obtido a 660?C e 3 horas de rea??o foi o que apresentou menor tamanho de cristalito 24 nm. Determinada a melhor condi??o de s?ntese foi realizado um estudo de passivac?o, nestas condi??es, para verificar a estabilidade do carbeto ao ser exposto ao ar. O carbeto de molibd?nio foi caracterizado por MEV, MET, an?lise elementar, ICP-AES, TG em atmosfera de hidrog?nio e RTP. Atrav?s da an?lise elementar e ICP-AES foi verificada a presen?a de carbono livre. A TG em atmosfera de hidrog?nio comprovou que ? necess?ria a passivac?o do carbeto de molibd?nio, pois ele ? oxidado em temperatura ambiente. O teste catal?tico foi realizado na planta semipiloto de Fischer-Tropsch do CTGAS, que ? composta de um reator de leito fixo. O teste catal?tico mostrou que o carbeto apresenta atividade para oxida??o parcial, mas as condi??es operacionais devem ser ajustadas para melhorar a convers?o
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Susanto, Laurensius Benny. "Kinetics of carbide dissolution in chromium + molybdenum steels during oxidation /". 2004. http://www.library.unsw.edu.au/~thesis/adt-NUN/public/adt-NUN20040817.151942/index.html.
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Tsai, Chih-yao, e 蔡智堯. "High Silicon Molybdenum Ductile Iron Differential Scanning Calorimetry and Eutectic Carbide M6C Growth Morphology". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/18390124425505149259.
Abstract (sommario):
碩士國立臺灣科技大學
機械工程系
101
Ductile iron, with superior mechanical properties, has been applied in various industrial fields; high silicon ductile iron has a good resistance to high temperature oxidation, but with the adding of molybdenum elements will result in the increasing of high temperature strength. In this paper, using a water-cooled copper mold to achieve unidirectional solidification of high silicon molybdenum ductile iron castings, quality of spheroidal graphite and microstructure of eutectic carbides are presented. Thermal analysis of the casting by using Differential Scanning Calorimetry (DSC) analysis was conducted to calculate value of latent heat of this grade of ductile iron. Electrolytic deep etching technique was used to study the stereo structure of fish-bone M6C structure in the eutectic carbide. The Results shows regardless of the cooling rate is high or low, fish bone-like eutectic carbides appears between grain boundaries, at that vicinity which precipitates with tiny granular carbide; several stereo morphologies of this eutectic carbides were studied and based on that a growth model is proposed in this thesis; DSC analysis of high silicon molybdenum ductile iron in the heating and cooling process latent heat average value with the literature is equivalent.
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Liu, Bo-Liang, e 劉柏良. "Production of Bio-Oil by Hydrocracking of Tung Oil with Molybdenum Carbide Catalyst in Batch System". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/hw6de5.
Abstract (sommario):
碩士國立臺灣大學
環境工程學研究所
105
This study took advantages of using self-manufactured catalysts which were made by adding Mo2C on the surface of γ-Al2O3 particles to conduct the catalytic hydrocracking of tung oil. Tung oil was converted to bio-fuel oil (BFO) as an alternative of aviation fuels or fuel oils. The batch system was designed for the catalytic hydrocracking with a removal packed bed filled with catalyst at a present temperature. By varying experimental conditions, this study was performed to investigate the effects of reaction temperature (T), hydrogen pressure (PH2), holding time (t), types of catalysts, amount of catalyst added (MC), volume of raw tung oil (VLO), and two-stage reaction on the system performances. These include yields of the produced BFOs (YBFO) and their characteristics, such as acid value (AV), iodine value (IV), density (ρLO), heating value (HV), distribution of carbon numbers, and content of (MC1C9), C1~C9 elemental composition. In the same time, products of solid and gas were also analyzed for the related characteristics. The study consists of four parts. The first part was the development of method for preparation of Mo2C based catalysts. The second part was catalytic cracking of tung oil with different reaction temperatures and catalysts (γ-Al2O3 and Mo2C/γ-Al2O3). For the third part, direct cracking of tung oil under different nitrogen pressures was conducted. The forth part was catalytic hydrocracking of raw tung oil with different hydrogen pressures, holding times, volumes of raw tung oil, amounts of catalyst added, and types of processes with one or two stages of reactions. The results showed that tung oil is mainly composed of C16 ~ C22 unsaturated fatty acids. In the catalytic cracking with Mo2C/γ-Al2O3, it achieved MC1C9 = 73 wt%, HV = 47 MJ/kg, and YBFO = 65 vol% at 623 K, 100 psig Ar, 20 min, and MC = 1 wt%. For the direct cracking, the higher the nitrogen pressure, the better the effect of cracking giving higher MC1C9 and HV. At 623 K, 100 psig N2, and 20 min, MC1C9 in BFO was 66 wt% and HV and YBFO of BFO were 58 MJ/kg and 78 vol%, respectively. In the catalytic hydrocracking test, an increasing of catalyst reduced the oxygen content while enhanced the heating value of BFO. At 623 K, 100 psig H2, 40 min, and MC = 5wt%, the oxygen content was 1.5wt%, while MC1C9 = 82 wt%, HV = 38 MJ / kg, and YBFO = 53 vol%. In the stage-wise catalytic hydrocracking , HV and YBFO of BFO of the two-stage reaction were moderate while with high MC1C9. If applying one stage reaction at 623 K, 100 psig H2, 40 min, and MC = 1 wt%, values of MC1C9, HV, and YBFO of BFO were 76 wt%, 34 MJ/kg, and 65 vol%, respectively. For the two-stage reaction, at 623 K, 100 psig N2 (20 min, first stage), 100 psig H2 (40 min, second stage), and MC = 1 wt%, the values of MC1C9, HV, and YBFO were 83 wt%, 30 MJ/kg, and 52 vol%, respectively. For the case with highest overall performance index (PIt) of 0.80 at 623 K, 100 psig H2, 20 min, and MC = 1 wt%, the BFO had MC1C9 = 73 wt%, HV = 54 MJ/kg, and YBFO = 67 vol% with the AV and HV satisfying with the standards of aviation fuel oil. Further, from the results of species analysis, it was found that there were C7 ~ C17 straight chain alkanes in the products. Thus, it is feasible to produce the available BFO via the catalytic hydrocracking used in this study. Therefore, by fractionating the BFO, it can be blended in aviation fuel or gasoline or used directly as fuel oil.
40
Das, Debanjan. "New Avenues to Transition Metal-Based Water Splitting Electrocatalysts". Thesis, 2019. https://etd.iisc.ac.in/handle/2005/4399.
Abstract (sommario):
Solar energy is by far the most abundant renewable resource available to mankind. However, it is diffused and intermittent, and often geographically separated from that of the production results in underwhelming utilization of this resource. Inspired by photosynthesis, various efforts were made to store solar energy in form of chemical bonds than can be used when the sun is not shining. A promising approach is to produce hydrogen, a carbon-neutral energy carrier is via water splitting which requires electrocatalysts to accelerate the two half-cell reactions, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The state-of-art catalysts used for HER is Pt and for OER is IrO2/RuO2 that are prohibitively expensive.
We have developed new synthesis methodologies for various earth-abundant electrocatalysts supported heteroatom-doped carbon nanostructures and exploited for water splitting. An in-situ solid state route was developed to integrate ruthenium nanoparticles with N-doped graphene sheets which exhibited an HER activity rivalling state-of-art Pt/C over a wide pH range. In order to find further cost-effective materials, we sought inspiration from NiFe-hydrogenase (the most efficient catalyst for HER) to develop a general solid state method for bimetallic MFe@ N-doped carbon core-shell nanostructures (M = Ni, Cu, Co, Zn, Mn) as efficient total water splitting catalyst. Thereafter, a new, phosphine-free, solid state method to hybridize Co2P with N, P co-doped CNTs was developed which could also be extended to synthesize Fe2P, Ni2P and Cu3P. Moreover, glucose oxidation was attempted as a possible replacement for the kinetically sluggish OER half-cell reaction, wherein Co2P/N, P-CNTs were demonstrated to be an efficient non-enzymatic glucose sensor for the first time. Thereafter, Co-imidazolate frameworks (ZIF-67) were transformed into hierarchal Co-N-Se nanosheets via a simple selenization method. Investigations were carried out to establish a structure-property correlation between the nanostructures evolved over various interval of time along with their OER activity. Finally, an in-situ strategy was developed to hybridize N-doped graphitic carbon seets with Ni and MoxC (Mo2C and MoC) nanoparticles which exhibited resilient HER activity besides effectively accelerating OER, thereby resulting in overall water splitting that can be attributed to favorable electronic modulation between various strongly coupled components.