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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Structural and compositional analysis of cobalt palladium model catalyst surfaces

Murdoch, Alexander January 2012 (has links)
To date there has been much work carried out in the field of surface science to gain a better understanding of the fundamentals of a wide range of catalytic systems and reactions. The central theme of this thesis relates to cobalt based Fischer-Tropsch synthesis (FTS) with particular focus on the structure, composition and surface chemistry of CoPd bimetallic systems and on the interaction of Co with oxide support materials. In the work described in this thesis MEIS and STM are used to examine the growth of Co on Pd{111} and to characterise the structure of CoPd alloys created by thermal treatment of thin Co films. MEIS investigations indicate that Co grows initially as an fcc overlayer, but beyond a few layers, a stacking fault exists resulting in hcp growth. On annealing between 550 and 700 K, a previously unreported ordered surface alloy is observed giving rise to a p(2 x 1) structure which is concluded to be the surface termination of an ordered CoPd bulk alloy. At higher annealing temperatures, long range Moiré structure is observed by STM which MEIS reveals to correspond to a Pd-rich alloy. MEIS is used to investigate adsorbate induced segregation effects at CoPd surfaces on Pd{111}. The adsorption of O2, CO, H2 and CO/H2 mixtures (syngas) were all examined on a range of bimetallic surfaces. Oxygen adsorption on CoPd alloys strongly segregates cobalt to the surface as a result of the facile oxidation reaction. The behaviour of the components of syngas was more complex with the most noticeable effects being observed on surfaces which were more defect rich. The growth, annealing behaviour and adsorption properties of Co particles on oxide and mixed oxide surfaces are examined using MEIS and TPD.
12

Computer Simulation of a Plug Flow Reactor for Cobalt Catalyzed Fischer Tropsch Synthesis Using a Microkinetic Model

Jing, Yin January 2012 (has links)
No description available.
13

Desenvolvimento dos catalisadores Co/SBA-15 e Ru/Co/SBA-15 a partir das fontes de sílica. / Development of Co / SBA-15 and Ru / Co / SBA-15 catalysts from silica sources.

RODRIGUES, Jocielys Jovelino. 23 March 2018 (has links)
Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-03-23T19:48:20Z No. of bitstreams: 1 JOCIELYS JOVELINO RODRIGUES - TESE PPGEQ 2015..pdf: 2539318 bytes, checksum: 88878182929175962ca411ac34f42556 (MD5) / Made available in DSpace on 2018-03-23T19:48:20Z (GMT). No. of bitstreams: 1 JOCIELYS JOVELINO RODRIGUES - TESE PPGEQ 2015..pdf: 2539318 bytes, checksum: 88878182929175962ca411ac34f42556 (MD5) Previous issue date: 2015 / Capes / Este trabalho teve como objetivo, desenvolver peneiras moleculares utilizando fontes de sílica convencional (TEOS) e alternativa (cinza da casca de arroz), utilizá-las como suportes para catalisadores de Cobalto destinados à síntese de FischerTropsch, e também, investigar o efeito da introdução de rutênio como promotor na reação acima mencionada. Preparou-se a SBA-15 a partir de um gel com composição molar: 1.0 FONTE DE SÍLICA: 0.017 P123: 5.7 HCl: 193 H2O. Os catalisadores foram preparados pelo processo de impregnação úmida utilizando solução de 0,1 M de (Co(NO3)2.6H2O). Na sequência, foi incorporado o promotor rutênio usando solução aquosa de 0,1M de Cloreto de Rutênio (RuCl3xH2O). As amostras foram caracterizadas por DRX, EDX, TG/ATD, MEV, MET, RTP e adsorção física de N2. A reação de Fischer-Tropsch foi conduzida em reator leito de lama durante 6 horas de reação a 240oC e pressão de 20 bar, utilizando uma relação molar H2/CO = 1. A obtenção da SBA-15 utilizando fontes de sílica convencional e alternativa pôde ser confirmada pelos difratogramas, com destaque para a SBA-15 obtida com a fonte alternativa cinzas da casca de arroz, resíduo agrícola produzido em longa escala e que praticamente não tem aplicação comercial. Os difratogramas dos catalisadores na faixa angular de 0-8º mostraram que após a impregnação dos metais e calcinação, não ocorreram modificações na estrutura hexagonal dos materiais mesoporosos, observando-se os picos principais da fase do SBA-15. As análises de adsorção física de N2 das peneiras moleculares SBA-15 (CCA) e SBA15 (TEOS), mostram isotermas com perfil do tipo IV e histerese H1, características de materiais mesoporosos. As análises térmicas das peneiras moleculares SBA-15 (TEOS) e SBA-15 (CCA) indicaram a eliminação do direcionador (Pluronic) no processo de calcinação. As áreas superficiais específicas dos catalisadores diminuem e o volume de poro varia, devido ao bloqueio parcial dos poros pelo cobalto e pelo promotor rutênio, mas a estrutura da peneira molecular SBA-15 não é alterada. Os perfis de RTP dos catalisadores das séries Co/SBA-15 e Ru/Co/SBA-15 permitiram verificar a presença de picos distintos que pode ser causado pela redução dos óxidos de cobalto. A MET mostrou espécies de cobalto na forma esférica com tamanho de 20 nm, e após a co-impregnação com rutênio, houve uma melhor dispersão dessas espécies de cobalto resultando em partículas menores com tamanho médio de 10 nm. Os resultados obtidos a partir da síntese de FischerTropsch pelos catalisadores, apresentaram altas seletividades a hidrocarbonetos C5+ de alto valor agregado, bem como, verificou-se que a co-impregnação do promotor rutênio no catalisador Co/SBA-15, favoreceu o aumento da seletividade para hidrocarbonetos C5+ e diminuiu a seletividade para metano, com destaque para o desempenho do catalisador 20%Co/0,5%Ru/SBA-15 preparado com as cinzas da casca de arroz. / The aim of this work was to prepare the mesoporous molecular sieve SBA-15 using conventional silica sources (TEOS) and alternative (Ash rice husk) and uses them as support for cobalt catalysts for the Fischer-Tropsch process. And investigate the introduction of ruthenium as a promoter. It was prepared SBA- 15 from a gel of molar composition : 1.0 silica source : 0.017 P123 : 5.7 HCl : 193 H2O. The catalysts were prepared by wet impregnation process using 0.1 M solution (Co(NO3)2.6H2O) (Vetec). Following ruthenium promoter was incorporated using 0.1 M aqueous solution of ruthenium chloride (RuCl3xH2O). The samples were characterized by XRD, EDX , TG/DTA, SEM, TEM, TPR and adsorption of N2. The Fischer-Tropsch reaction is conducted at 240 °C , pressure of 20 bar using a molar ratio H2/CO = 1, on a slurry reactor for a reaction time of 8 h. Obtaining the SBA -15 silica using conventional sources and alternative could be confirmed by X ray diffraction , with emphasis on the SBA -15 obtained with the alternative source of rice husk ash , a residue of agriculture abundant and cheap that is usually discarded. The XRD patterns of the catalysts in the angular range 0-8º showed that after impregnation and calcination of the metal changes did not occur in the hexagonal structure of mesoporous materials , observing the main peaks of the phase of SBA -15. The physical adsorption of N2 analysis of SBA -15 molecular sieves (CCA) and SBA -15 (TEOS) show with type IV isotherm profile and H1 hysteresis characteristics of mesoporous material. The thermal analysis of SBA -15 molecular sieves (TEOS) and SBA -15 (CCA) indicated the elimination of the template (Pluronic) in the calcination process. The specific surface areas of the catalysts decreases , and the pore volume changes due to partial blockage of the pores by cobalt and ruthenium promoter, but the structure of SBA -15 molecular sieve is not changed. TPR profiles of the catalysts of the series Co /SBA- 15 and Ru /Co /SBA -15 evidenced the presence of distinctive peaks that can be caused by the reduction of cobalt oxides. TEM showed cobalt species on spherical 20 nm in size, and after co- impregnation with ruthenium was a better dispersion of these cobalt species resulting in particles with average size smaller than 10 nm. The results obtained from the Fischer- Tropsch the catalysts showed high selectivity to hydrocarbons C5+ of high value, and it was found that co- impregnation of the ruthenium promoter in the Co catalyst /SBA -15 promoted the increase of selectivity to C5+ hydrocarbons and decreased the selectivity to methane, highlighting the performance of the catalyst 20 % Co/0.5 % Ru/SBA-15 prepared with the ashes of the rice husk .
14

Fischer-Tropsch Cobalt Catalyst Improvements with the Presence of TiO2, La2O3, and ZrO2 on an Alumina Support

Klettlinger, Jennifer Lindsey Suder 17 May 2012 (has links)
No description available.
15

[en] CATALYSTS SUPPORTED IN MICRO AND MESOPOROUS MOLECULAR SIEVES FOR THE FISCHER- TROPSCH SYNTHESIS / [pt] CATALISADORES SUPORTADOS EM PENEIRAS MOLECULARES MICRO E MESOPOROSAS PARA A SÍNTESE DE FISCHER-TROPSCH

JAQUELINE FARIAS DA SILVA 06 April 2005 (has links)
[pt] A síntese de Fischer-Tropsch converte o gás de síntese (H2 + CO), em uma variedade complexa de hidrocarbonetos na presença de um catalisador (principalmente Co/Al2O3). Neste trabalho foram estudados catalisadores de Co e o Fe (1 e 5% em massa), incorporados aos suportes: zeólitas KL, HL 0,1M e HL 1,0 M, além da peneira molecular mesoporosa MCM- 41, pelo método de impregnação úmida incipiente, para a reação de Fischer- Tropsch. As amostras preparadas foram analisadas pelas técnicas de: Espectometria de Emissão Atômica de Plasma Acoplado Induzido, Adsorção Física de N2 pelo método BET, Difração de Raios-X, Redução com Temperatura Programada, Microscopia Eletrônica de Transmissão (MET), Quimissorção de Hidrogênio e Espectroscopia no Infravermelho de piridina adsorvida. Além disso, as amostras foram avaliadas em um reator de leito fixo na reação de Fischer-Tropsch. Para as amostras de ferro, com mesmo teor e suportes diferentes, pode-se observar que a amostra suportada na MCM-41 apresentou um grau de redução menor. Entre as amostras de ferro suportadas na KL, a 5% Fe/KL apresentou maior grau de redução e foi observado por microscopia eletrônica de transmissão (MET) que as partículas de ferro apresentaram diâmetro em torno de 6 nm. Para as amostras de cobalto foi observado que a temperatura de redução da amostra suportada na MCM-41 foi mais alta. A amostra 5% Co/KL apresentou um maior grau de redução. Foi possível observar por MET que as partículas de cobalto apresentaram diâmetro variando entre 8 e 20 nm. Verificou-se que o catalisador com maior teor de ferro proporcionou uma maior conversão de CO, tendo sido a distribuição de produtos deslocada para as frações mais leves. Comparando os catalisadores de ferro suportados na zeólita KL e na MCM-41 pode-se concluir que as conversões são da mesma ordem de grandeza. Foi observado que o ferro foi mais ativo que o cobalto em termos de conversão do CO, sendo que o cobalto promoveu a formação de uma maior quantidade de produtos na faixa de diesel, assim como uma menor quantidade de leves. / [en] The Fischer- Tropsch synthesis converts the synthesis gas (H2 + CO), in a complex variety of hydrocarbons, using a catalyst (Co/Al2O3 normally) were introduced to the used supports by the wetness incipient impregnation. The samples were analyzed by several techniques such as: plasma- emission spectrometry (ICP- EAS), N2 physical adsorption by BET method, X-ray diffraction (XRD), temperature programmed reduction (TPR), transmission electronic microscopy (TEM), hydrogen chemisorption and Infrared Spectroscopy of adsorbed pyridine. The catalysts were evaluated using a fixed bed reactor in the Fischer-Tropsch synthesis. For the iron samples, with the same metal content and different supports, it was observed that the MCM-41 sample presented the lowest reduction level. Among the iron samples supported in KL zeolite, the 5% Fe/KL sample presented the largest reduction level. It was observed by transmission electronic microscopy that the iron particles diameter measured around 6 nm. For the cobalt samples, it was observed that the reduction temperature of the MCM-41 supported was the highest one. The 5% Co/KL sample presented the largest reduction level. It was observed by TEM that the cobalt particles presented diameters in the range from 8 to 20 nm. It was verified that the catalyst with the largest iron percentage promoved the highest CO conversion. The products distribuition was shifted to light fractions. It was observed similar conversions to iron catalysts supported in the KL zeolite and in the MCM- 41 mesoporous molecular sieve. The iron catalysts were more active than the cobalt ones in the CO conversion, but tha cobalt catalysts promoted a higher content of diesel fraction and lesser light fractions.
16

Utilização de catalisadores de cobre e cobalto suportados em CeO2, TiO2 e matrizes de CeO2-TiO2, para redução de NO com CO na ausência ou presença de O2 / Copper and cobalt catalysts supported on CeO2, TiO2 and CeO2-TiO2 to reduction NO by CO

Conte, Carlos Henrique 30 November 2007 (has links)
A redução da emissão de compostos nitrogenados tem sido um dos grandes desafios da área de proteção ambiental e o tratamento catalítico pode reduzir significativamente tal emissão. Neste caminho, têm sido testadas várias categorias de catalisadores. Considerando-se o potencial de utilização de catalisadores de cobre e de cobalto nos processos de abatimento de compostos nitrogenados, bem como a necessidade de exploração dos efeitos gerados pelos suportes de óxido de cério e óxido de titânio, este trabalho teve como objetivos a preparação e a caracterização dos sistemas catalíticos CuO e Co3 O4 suportados em TiO2 , CeO2 e CeO2 -TiO3 (1%, 10%, 20% e 50% de CeO2 ), para aplicação no processo de redução de NO com CO na presença e ausência de O2 . Os catalisadores foram obtidos a partir do método de impregnação. Na caracterização das amostras foram utilizadas as técnicas de difração de raios X (DRX), redução à temperatura programada com H2 (RTP-H2 ), espectroscopia Raman, espectroscopia por energia dispersiva de raios X (EDX), fisissorção de nitrogênio e espectroscopia UV-visível próxima a região do infra-vermelho (UV-VIS-NIR). Os resultados da caracterização mostraram que os catalisadores apresentam fases de CuO altamente dispersas, bem como formando cristalitos com os suportes. Mostraram, também, que o cobalto está sobre a forma oxida Co3 O4 . As reações de redução de NO com CO mostraram que os catalisadores de cobre são mais ativos para estas reações e a adição do suporte CeO2 em TiO2 aumenta significativamente esta atividade. A adição de O2 na reação diminuiu a atividade frente à reação de redução de NO, isso porque o oxigênio é adsorvido sobre a superfície do catalisador, diminuindo sua atividade. / The reduction of the nitrogen composites emissions has been one of the great challenges of the ambient protection area and the catalytic treatment can reduce significantly such emissions. In this way, it has been tested some categories of catalysts. Considering the potential of use of copper and cobalt catalysts in the processes of nitrogen composites discouragement, as well as the necessity of exploration of the effect generated for CeO2 and TiO2 supported , this work had as objective the preparation and the characterization of the catalytic systems supported CuO and Co3O4 in TiO2, CeO2 and CeO2-TiO2 (1%, 10%, 20% and 50% of CeO2), for application in the reduction process of NO with CO in presence and absence of O2. The catalysts had been gotten from the impregnation method. In the characterization of the samples the techniques that had been used was: X-ray diffraction had been used, temperature programmed reduction, Raman spectroscopy, energy dispersive X-ray spectroscopy, nitrogen physsisorption and UV-visible spectroscopy next the region to the infra-red ray (UV-VIS-NIR). The results of the characterization had shown that the catalysts present highly dispersed phases of CuO, as well as cristalitts. And, that cobalto meets under the form Co3O4. The reactions of reduction of NO with CO had shown that the copper catalysts are more active than the cobalto and the addition of the CeO2 support in TiO2 increases significantly this activity. The addition of O2 in the reaction diminished the activity front to the reaction of reduction of NO, just because the oxygen is adsorbed on the surface of the catalysts, diminishing its activity
17

Utilização de catalisadores de cobre e cobalto suportados em CeO2, TiO2 e matrizes de CeO2-TiO2, para redução de NO com CO na ausência ou presença de O2 / Copper and cobalt catalysts supported on CeO2, TiO2 and CeO2-TiO2 to reduction NO by CO

Carlos Henrique Conte 30 November 2007 (has links)
A redução da emissão de compostos nitrogenados tem sido um dos grandes desafios da área de proteção ambiental e o tratamento catalítico pode reduzir significativamente tal emissão. Neste caminho, têm sido testadas várias categorias de catalisadores. Considerando-se o potencial de utilização de catalisadores de cobre e de cobalto nos processos de abatimento de compostos nitrogenados, bem como a necessidade de exploração dos efeitos gerados pelos suportes de óxido de cério e óxido de titânio, este trabalho teve como objetivos a preparação e a caracterização dos sistemas catalíticos CuO e Co3 O4 suportados em TiO2 , CeO2 e CeO2 -TiO3 (1%, 10%, 20% e 50% de CeO2 ), para aplicação no processo de redução de NO com CO na presença e ausência de O2 . Os catalisadores foram obtidos a partir do método de impregnação. Na caracterização das amostras foram utilizadas as técnicas de difração de raios X (DRX), redução à temperatura programada com H2 (RTP-H2 ), espectroscopia Raman, espectroscopia por energia dispersiva de raios X (EDX), fisissorção de nitrogênio e espectroscopia UV-visível próxima a região do infra-vermelho (UV-VIS-NIR). Os resultados da caracterização mostraram que os catalisadores apresentam fases de CuO altamente dispersas, bem como formando cristalitos com os suportes. Mostraram, também, que o cobalto está sobre a forma oxida Co3 O4 . As reações de redução de NO com CO mostraram que os catalisadores de cobre são mais ativos para estas reações e a adição do suporte CeO2 em TiO2 aumenta significativamente esta atividade. A adição de O2 na reação diminuiu a atividade frente à reação de redução de NO, isso porque o oxigênio é adsorvido sobre a superfície do catalisador, diminuindo sua atividade. / The reduction of the nitrogen composites emissions has been one of the great challenges of the ambient protection area and the catalytic treatment can reduce significantly such emissions. In this way, it has been tested some categories of catalysts. Considering the potential of use of copper and cobalt catalysts in the processes of nitrogen composites discouragement, as well as the necessity of exploration of the effect generated for CeO2 and TiO2 supported , this work had as objective the preparation and the characterization of the catalytic systems supported CuO and Co3O4 in TiO2, CeO2 and CeO2-TiO2 (1%, 10%, 20% and 50% of CeO2), for application in the reduction process of NO with CO in presence and absence of O2. The catalysts had been gotten from the impregnation method. In the characterization of the samples the techniques that had been used was: X-ray diffraction had been used, temperature programmed reduction, Raman spectroscopy, energy dispersive X-ray spectroscopy, nitrogen physsisorption and UV-visible spectroscopy next the region to the infra-red ray (UV-VIS-NIR). The results of the characterization had shown that the catalysts present highly dispersed phases of CuO, as well as cristalitts. And, that cobalto meets under the form Co3O4. The reactions of reduction of NO with CO had shown that the copper catalysts are more active than the cobalto and the addition of the CeO2 support in TiO2 increases significantly this activity. The addition of O2 in the reaction diminished the activity front to the reaction of reduction of NO, just because the oxygen is adsorbed on the surface of the catalysts, diminishing its activity
18

Surface composition of cobalt catalysts for steam reforming of ethanol / Étude de la composition de la surface des catalyseurs à base de cobalt pour le reformage des vapeurs d'éthanol

Turczyniak, Sylwia 28 September 2016 (has links)
L’objectif de cette thèse de doctorat a consisté à déterminer l’influence des conditions réactionnelles du vaporeformage de l’éthanol (ESR), de la dispersion du catalyseur et de la promotion par le potassium sur l’état de la surface. Ce travail a aussi aidé à comprendre l’influence de ces facteurs sur les propriétés catalytiques. Nous avons utilisé les catalyseurs à base de cobalt (promus et non promus par le potassium) supportés à l’oxyde de cérium et à l’oxyde de zirconium à faible et à forte dispersion. Les changements de l’état de la surface des catalyseurs pendant la réaction d’ERS ont été étudiés à travers la spectrométrie photoélectronique X (XPS), alors que les changements des produits ont été analisés en utilisant la spectrométrie de masse et la chromatographie en phase gazeuse. Le catalyseur supporté sur oxyde de cérium à forte dispersion a été caractérisé sous une basse pression (0.2-20 mbar) avec le rapport molaire eau/éthanol de 3/1 (420ºC). Les autres tests ont été faits sur tous les catalyseurs sous une pression totale de 1 atm avec les rapports molaires de 3/1, 9/1, 12/1 (420ºC). Nous avons utilisé un mélange eau/éthanol dans un rapport molaire de 12/1 pour étudier les changements de l’état de la surface de tous les catalyseurs dans le temps. Il a été démontré que la sélectivité d’ESR des catalyseurs pour produire des gaz et pour déposer le carbone est réglée par la concentration des groupes hydroxyles sur la surface. Quant aux catalyseurs promus, elle dépend aussi de la concentration Kδ+–Osurfδ-. / The aim of the thesis was determination the influence of the ethanol steam reforming (ESR) reaction conditions, catalyst’s dispersion and potassium promotion on a surface’s composition and understanding the influence of these changes on catalysts’ performance. Cobalt-based catalysts (unpromoted and promoted with potassium) with low- and high-dispersed ceria and zirconia supports were used. The changes of the surface state of catalysts during the ESR were studied by means of X-ray photoelectron spectroscopy, whereas the reaction products evolution was followed by mass spectrometer or gas chromatograph. Highly-dispersed ceria-supported catalyst was characterized under low pressure conditions (0.2–20 mbar) with the water/ethanol molar ratio equal to 3/1 (at 420ºC). The other tests were carried out over all catalysts under total pressure of 1 atm with 3/1, 9/1 and 12/1 molar ratios (at 420ºC). The water/ethanol ratio of 12/1 was chosen for studies of the surface state of all catalysts with time-on-stream. It was found that the ESR selectivity to gaseous products and carbon deposition is governed mainly by surface hydroxyl species concentration; in the promoted catalysts together with Kδ+–Osurfδ- surface sites.
19

Kinetic and mechanistic studies of CO hydrogenation over cobalt-based catalysts

Schweicher, Julien 25 November 2010 (has links)
During this PhD thesis, cobalt (Co) catalysts have been prepared, characterized and studied in the carbon monoxide hydrogenation (CO+H2) reaction (also known as “Fischer-Tropsch” (FT) reaction). In industry, the FT synthesis aims at producing long chain hydrocarbons such as gasoline or diesel fuels. The interest is that the reactants (CO and H2) are obtained from other carbonaceous sources than crude oil: natural gas, coal, biomass or even petroleum residues. As it is well known that the worldwide crude oil reserves will be depleted in a few decades, the FT reaction represents an attractive alternative for the production of various fuels. Moreover, this reaction can also be used to produce high value specialty chemicals (long chain alcohols, light olefins…).<p>Two different types of catalysts have been investigated during this thesis: cobalt with magnesia used as support or dispersant (Co/MgO) and cobalt with silica used as support (Co/SiO2). Each catalyst from the first class is prepared by precipitation of a mixed Co/Mg oxalate in acetone. This coprecipitation is followed by a thermal decomposition under reductive atmosphere leading to a mixed Co/MgO catalyst. On the other hand, Co/SiO2 catalysts are prepared by impregnation of a commercial silica support with a chloroform solution containing Co nanoparticles. This impregnation is then followed by a thermal activation under reductive atmosphere.<p>The mixed Co/Mg oxalates and the resulting Co/MgO catalysts have been extensively characterized in order to gain a better understanding of the composition, the structure and the morphology of these materials: thermal treatments under reductive and inert atmospheres (followed by MS, DRIFTS, TGA and DTA), BET surface area measurements, XRD and electron microscopy studies have been performed. Moreover, an original in situ technique for measuring the H2 chemisorption surface area of catalysts has been developed and used over our catalysts.<p>The performances of the Co/MgO and Co/SiO2 catalysts have then been evaluated in the CO+H2 reaction at atmospheric pressure. Chemical Transient Kinetics (CTK) experiments have been carried out in order to obtain information about the reaction kinetics and mechanism and the nature of the catalyst active surface under reaction conditions. The influence of several experimental parameters (temperature, H2 and CO partial pressures, total volumetric flow rate) and the effect of passivation are also discussed with regard to the catalyst behavior.<p>Our results indicate that the FT active surface of Co/MgO 10/1 (molar ratio) is entirely covered by carbon, oxygen and hydrogen atoms, most probably associated as surface complexes (possibly formate species). Thus, this active surface does not present the properties of a metallic Co surface (this has been proved by performing original experiments consisting in switching from the CO+H2 reaction to the propane hydrogenolysis reaction (C3H8+H2) which is sensitive to the metallic nature of the catalyst). CTK experiments have also shown that gaseous CO is the monomer responsible for chain lengthening in the FT reaction (and not any CHx surface intermediates as commonly believed). Moreover, CO chemisorption has been found to be irreversible under reaction conditions.<p>The CTK results obtained over Co/SiO2 are quite different and do not permit to draw sharp conclusions concerning the FT reaction mechanism. More detailed studies would have to be carried out over these samples.<p>Finally, Co/MgO catalysts have also been studied on a combined DRIFTS/MS experimental set-up in Belfast. CTK and Steady-State Isotopic Transient Kinetic Analysis (SSITKA) experiments have been carried out. While formate and methylene (CH2) groups have been detected by DRIFTS during the FT reaction, the results indicate that these species play no role as active intermediates. These formates are most probably located on MgO or at the Co/MgO interface, while methylene groups stand for skeleton CH2 in either hydrocarbon or carboxylate. Unfortunately, formate/methylene species have not been detected by DRIFTS over pure Co catalyst without MgO, because of the full signal absorption.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

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