Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol
Autor(a) principal: | |
---|---|
Data de Publicação: | 2012 |
Tipo de documento: | Tese |
Idioma: | por |
Título da fonte: | Repositório Institucional da UFSCAR |
Texto Completo: | https://repositorio.ufscar.br/handle/ufscar/3915 |
Resumo: | Cobalt-based catalysts supported on γ-alumina and magnesium aluminate modified with lanthanum and cerium have been applied to various conditions of reforming of ethanol. The initial challenge was to control the rate of carbon accumulation, a major cause of deactivation of catalysts under steam reforming of ethanol. In situ X-ray absorption spectroscopy analyses showed that the rate of carbon accumulation is inversely proportional to the amount of Co2+ species and directly proportional to the amount of Co0 species. X-ray photoelectron spectroscopy analyses showed that, after reducing the catalysts in hydrogen, the oxidized fraction of the particles is mainly on their surface. Both the oxidized and reduced fractions of cobalt crystallites have face-centered cubic structure. The concentration of superficial oxygen under reforming conditions is determined by the curvature of the surface of the particles, the nature of the supports and the presence of promoters such as platinum and copper. The concentration of superficial oxygen is also highly sensitive to reaction conditions such as the composition and amount of oxidizing agents, such as oxygen and water, and reaction temperature. The rate of accumulation of carbon could be controlled with co-feeding oxygen to the reactor, process called oxy-reforming of ethanol, and using ceria as support. However, stability tests showed that catalyst deactivation may also occur by oxidation of metal sites. The ignition of the reforming process takes place in a microregion at the entrance of the catalyst bed where ethanol is fully oxidized, releasing energy and increasing the local temperature. Spatial-resolved X-ray absorption spectroscopy analyses showed that the ratio Co2+/Co0 is much greater than one inside this microregion. The high local temperature and the presence of oxidized species in the entrance of the bed produce the appropriate conditions which lead the Co2+ ions to diffuse into the defect spinel structure of γ-alumina, leading to loss of potentially active sites for reforming of ethanol. This phenomenon is unleashed as a wave that propagates from the entrance of the bed downstream to the regions where Co2+ species exist. However, one can prevent the diffusion of Co2+ species to the structure of γ- alumina using aluminates as supports. |
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Ávila Neto, Cícero Naves deBueno, José Maria Corrêahttp://lattes.cnpq.br/0157452280626031http://lattes.cnpq.br/5876235459236551eae42f7f-f242-4d3d-baf4-29fce5177e222016-06-02T19:55:32Z2012-10-022016-06-02T19:55:32Z2012-06-11ÁVILA NETO, Cícero Naves de. Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol. 2012. 170 f. Tese (Doutorado em Ciências Exatas e da Terra) - Universidade Federal de São Carlos, São Carlos, 2012.https://repositorio.ufscar.br/handle/ufscar/3915Cobalt-based catalysts supported on γ-alumina and magnesium aluminate modified with lanthanum and cerium have been applied to various conditions of reforming of ethanol. The initial challenge was to control the rate of carbon accumulation, a major cause of deactivation of catalysts under steam reforming of ethanol. In situ X-ray absorption spectroscopy analyses showed that the rate of carbon accumulation is inversely proportional to the amount of Co2+ species and directly proportional to the amount of Co0 species. X-ray photoelectron spectroscopy analyses showed that, after reducing the catalysts in hydrogen, the oxidized fraction of the particles is mainly on their surface. Both the oxidized and reduced fractions of cobalt crystallites have face-centered cubic structure. The concentration of superficial oxygen under reforming conditions is determined by the curvature of the surface of the particles, the nature of the supports and the presence of promoters such as platinum and copper. The concentration of superficial oxygen is also highly sensitive to reaction conditions such as the composition and amount of oxidizing agents, such as oxygen and water, and reaction temperature. The rate of accumulation of carbon could be controlled with co-feeding oxygen to the reactor, process called oxy-reforming of ethanol, and using ceria as support. However, stability tests showed that catalyst deactivation may also occur by oxidation of metal sites. The ignition of the reforming process takes place in a microregion at the entrance of the catalyst bed where ethanol is fully oxidized, releasing energy and increasing the local temperature. Spatial-resolved X-ray absorption spectroscopy analyses showed that the ratio Co2+/Co0 is much greater than one inside this microregion. The high local temperature and the presence of oxidized species in the entrance of the bed produce the appropriate conditions which lead the Co2+ ions to diffuse into the defect spinel structure of γ-alumina, leading to loss of potentially active sites for reforming of ethanol. This phenomenon is unleashed as a wave that propagates from the entrance of the bed downstream to the regions where Co2+ species exist. However, one can prevent the diffusion of Co2+ species to the structure of γ- alumina using aluminates as supports.Catalisadores de cobalto suportados em γ-alumina e aluminato de magnésio modificados com lantânio e cério foram aplicados a diferentes condições de reforma do etanol. O desafio inicial foi tentar controlar a taxa de acúmulo de carbono, um dos principais fatores de desativação de catalisadores em condições de reforma a vapor do etanol. Análises de espectroscopia de absorção de raios X in situ comprovaram que a diminuição da taxa de acúmulo de carbono está ligada ao aumento da quantidade de espécies Co2+ em relação à quantidade de espécies Co0 nas partículas de cobalto. Análises de espectroscopia de fotoelétrons excitados por raios X demonstraram que, após redução em hidrogênio, a fração oxidada das partículas encontra-se majoritariamente na superfície das mesmas. Ambas as frações oxidadas e reduzidas das partículas de cobalto apresentam estrutura cúbica de face centrada. A concentração de oxigênio superficial em condições de reforma do etanol é determinada pela curvatura da superfície das partículas, pela natureza dos suportes e pela presença de promotores tais como platina e cobre. A concentração de oxigênio superficial é também fortemente sensível às condições de reação, tais como a composição e quantidade de agentes oxidantes, como a água e o oxigênio, e a temperatura de reação. O acúmulo de carbono pôde ser controlado com a coalimentação de oxigênio ao reator, processo denominado reforma a vapor com coalimentação de oxigênio, e utilizando-se céria como suporte. Entretanto, testes de estabilidade demonstraram que a desativação do catalisador pode também ocorrer por oxidação dos sítios metálicos. A ignição da reforma ocorre em uma microrregião na entrada do leito catalítico onde o etanol é completamente oxidado, liberando energia e aumentando a temperatura local. Análises de espectroscopia de absorção de raios X in situ resolvidas no espaço demonstraram que, nesta microrregião, a razão Co2+/Co0 é muito maior que um. O aumento da temperatura local e a presença de espécies oxidadas na entrada do leito produzem as condições adequadas para que íons Co2+ se difundam na estrutura espinela defeituosa da γ- alumina, levando a perdas de sítios potencialmente ativos para a reforma do etanol. Este fenômeno se deflagra como uma onda de desativação que se propaga da entrada do leito em direção às regiões à jusante onde existem espécies Co2+. Por outro lado, pode-se evitar a difusão de espécies Co2+ na estrutura da γ-alumina utilizando-se aluminatos como suporte.Financiadora de Estudos e Projetosapplication/pdfporUniversidade Federal de São CarlosPrograma de Pós-Graduação em Engenharia Química - PPGEQUFSCarBRCatáliseProdução de hidrogênioReforma do etanoCatalisadores de cobaltoMecanismos de desativaçãoXAS in situEstabilidadeHydrogen productionEthanol reformingCobalt-supported catalystsStabilityDeactivation mechanismsIn situ XAFSENGENHARIAS::ENGENHARIA QUIMICASobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanolinfo:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/doctoralThesis-1-13b275236-acc5-4218-a33b-8f802e7f5a18info:eu-repo/semantics/openAccessreponame:Repositório Institucional da UFSCARinstname:Universidade Federal de São Carlos (UFSCAR)instacron:UFSCARORIGINAL4549.pdfapplication/pdf10506362https://repositorio.ufscar.br/bitstream/ufscar/3915/1/4549.pdf622f533bcc042279d1b10154620ecb35MD51THUMBNAIL4549.pdf.jpg4549.pdf.jpgIM Thumbnailimage/jpeg6973https://repositorio.ufscar.br/bitstream/ufscar/3915/2/4549.pdf.jpgb3e5bbe9d553d3d498118e8f5db8da16MD52ufscar/39152023-09-18 18:31:17.894oai:repositorio.ufscar.br:ufscar/3915Repositório InstitucionalPUBhttps://repositorio.ufscar.br/oai/requestopendoar:43222023-09-18T18:31:17Repositório Institucional da UFSCAR - Universidade Federal de São Carlos (UFSCAR)false |
dc.title.por.fl_str_mv |
Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol |
title |
Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol |
spellingShingle |
Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol Ávila Neto, Cícero Naves de Catálise Produção de hidrogênio Reforma do etano Catalisadores de cobalto Mecanismos de desativação XAS in situ Estabilidade Hydrogen production Ethanol reforming Cobalt-supported catalysts Stability Deactivation mechanisms In situ XAFS ENGENHARIAS::ENGENHARIA QUIMICA |
title_short |
Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol |
title_full |
Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol |
title_fullStr |
Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol |
title_full_unstemmed |
Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol |
title_sort |
Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol |
author |
Ávila Neto, Cícero Naves de |
author_facet |
Ávila Neto, Cícero Naves de |
author_role |
author |
dc.contributor.authorlattes.por.fl_str_mv |
http://lattes.cnpq.br/5876235459236551 |
dc.contributor.author.fl_str_mv |
Ávila Neto, Cícero Naves de |
dc.contributor.advisor1.fl_str_mv |
Bueno, José Maria Corrêa |
dc.contributor.advisor1Lattes.fl_str_mv |
http://lattes.cnpq.br/0157452280626031 |
dc.contributor.authorID.fl_str_mv |
eae42f7f-f242-4d3d-baf4-29fce5177e22 |
contributor_str_mv |
Bueno, José Maria Corrêa |
dc.subject.por.fl_str_mv |
Catálise Produção de hidrogênio Reforma do etano Catalisadores de cobalto Mecanismos de desativação XAS in situ Estabilidade |
topic |
Catálise Produção de hidrogênio Reforma do etano Catalisadores de cobalto Mecanismos de desativação XAS in situ Estabilidade Hydrogen production Ethanol reforming Cobalt-supported catalysts Stability Deactivation mechanisms In situ XAFS ENGENHARIAS::ENGENHARIA QUIMICA |
dc.subject.eng.fl_str_mv |
Hydrogen production Ethanol reforming Cobalt-supported catalysts Stability Deactivation mechanisms In situ XAFS |
dc.subject.cnpq.fl_str_mv |
ENGENHARIAS::ENGENHARIA QUIMICA |
description |
Cobalt-based catalysts supported on γ-alumina and magnesium aluminate modified with lanthanum and cerium have been applied to various conditions of reforming of ethanol. The initial challenge was to control the rate of carbon accumulation, a major cause of deactivation of catalysts under steam reforming of ethanol. In situ X-ray absorption spectroscopy analyses showed that the rate of carbon accumulation is inversely proportional to the amount of Co2+ species and directly proportional to the amount of Co0 species. X-ray photoelectron spectroscopy analyses showed that, after reducing the catalysts in hydrogen, the oxidized fraction of the particles is mainly on their surface. Both the oxidized and reduced fractions of cobalt crystallites have face-centered cubic structure. The concentration of superficial oxygen under reforming conditions is determined by the curvature of the surface of the particles, the nature of the supports and the presence of promoters such as platinum and copper. The concentration of superficial oxygen is also highly sensitive to reaction conditions such as the composition and amount of oxidizing agents, such as oxygen and water, and reaction temperature. The rate of accumulation of carbon could be controlled with co-feeding oxygen to the reactor, process called oxy-reforming of ethanol, and using ceria as support. However, stability tests showed that catalyst deactivation may also occur by oxidation of metal sites. The ignition of the reforming process takes place in a microregion at the entrance of the catalyst bed where ethanol is fully oxidized, releasing energy and increasing the local temperature. Spatial-resolved X-ray absorption spectroscopy analyses showed that the ratio Co2+/Co0 is much greater than one inside this microregion. The high local temperature and the presence of oxidized species in the entrance of the bed produce the appropriate conditions which lead the Co2+ ions to diffuse into the defect spinel structure of γ-alumina, leading to loss of potentially active sites for reforming of ethanol. This phenomenon is unleashed as a wave that propagates from the entrance of the bed downstream to the regions where Co2+ species exist. However, one can prevent the diffusion of Co2+ species to the structure of γ- alumina using aluminates as supports. |
publishDate |
2012 |
dc.date.available.fl_str_mv |
2012-10-02 2016-06-02T19:55:32Z |
dc.date.issued.fl_str_mv |
2012-06-11 |
dc.date.accessioned.fl_str_mv |
2016-06-02T19:55:32Z |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
dc.type.driver.fl_str_mv |
info:eu-repo/semantics/doctoralThesis |
format |
doctoralThesis |
status_str |
publishedVersion |
dc.identifier.citation.fl_str_mv |
ÁVILA NETO, Cícero Naves de. Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol. 2012. 170 f. Tese (Doutorado em Ciências Exatas e da Terra) - Universidade Federal de São Carlos, São Carlos, 2012. |
dc.identifier.uri.fl_str_mv |
https://repositorio.ufscar.br/handle/ufscar/3915 |
identifier_str_mv |
ÁVILA NETO, Cícero Naves de. Sobre a estabilidade de catalisadores de cobalto suportados durante a reforma do etanol. 2012. 170 f. Tese (Doutorado em Ciências Exatas e da Terra) - Universidade Federal de São Carlos, São Carlos, 2012. |
url |
https://repositorio.ufscar.br/handle/ufscar/3915 |
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por |
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por |
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-1 -1 |
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3b275236-acc5-4218-a33b-8f802e7f5a18 |
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info:eu-repo/semantics/openAccess |
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openAccess |
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Universidade Federal de São Carlos |
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Programa de Pós-Graduação em Engenharia Química - PPGEQ |
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UFSCar |
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BR |
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Universidade Federal de São Carlos |
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