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Previous issue date: 2010-11-26 / One of the main applications of methane is in the production of syngas, a
mixture of hydrogen and carbon monoxide. Procedures used in this process are
steam reforming, CO2 reforming, partial oxidation and autothermal reforming. The
present study evaluated and compared the behavior of nickel catalysts supported on
mixed oxides of cerium and manganese in the partial oxidation of methane with that
of nickel catalysts supported on mixed oxides of cerium and zirconium. Mixed oxides
of cerium and zirconium or cerium and manganese were synthesized using two
different preparation methods, the polymeric precursor based on Pechini method and
combustion reaction using a microwave. This was followed by impregnation with
nickel content of 15 %. Samples were calcined at 300, 800 and 900 ?C and
characterized by specific surface area (SSA), X-ray fluorescence (XRF), X-ray
diffraction (XRD), scanning electron microscopy (SEM), temperature programmed
reduction (TPR) and the reaction of partial oxidation of methane. The specific areas
of samples decrease with the rise in calcination temperature and after nickel
impregnation. Metal-cerium solid solution was formed and the presence of other
manganese species outside the solid solution structure was confirmed in the
compound with the highest amounts of manganese oxides showed. With regard to
scanning electron microscopy, supports based on cerium and zirconium prepared by
Pechini method exhibited agglomerated particles without uniform geometry or visible
pores on the surface. However, compounds containing manganese presented empty
spaces in its structure. Through synthesis by combustion reaction, morphology
acquired independently of the proposed composition demonstrated greater porosity
in relation to Pechini synthesis. Although catalysts were prepared using different
synthesis methods, the insertion of nickel showed very similar reduction profiles
(TPR). In relation to nickel catalysts supported on mixed oxide of cerium and
zirconium, there is an initial reduction of NiO species that present certain interaction
with the support. This is followed by the reduction of Ce4+ in Ce3+ surface, with
subsequent bulk reduction. For catalysts containing manganese, a reduction of nickel
oxide species occurs, followed by two stages of reduction for species Mn2O3 in
Mn3O4 and Mn3O4 in MnO, with subsequent reduction of bulk. With respect to partial
oxidation reactions, the nickel catalyst supported on mixed oxide of cerium and
zirconium, prepared using the Pechini method, exhibited CH4 conversion of
approximately 80 %, with conversion of 81 % when prepared by combustion. This
behavior continued for 10 hours of reaction. Manganese content was also found to
directly influence catalytic activity of materials; the greater the manganese oxide
content, the faster deactivation and destabilization occurred in the catalyst. In both
synthesis methods, the nickel catalyst supported on mixed oxide of cerium and
zirconium maintained an H2/CO ratio very close to 2 during the 10 hours of partial
oxidation reaction. Samples containing manganese displayed smaller H2/CO ratios
and lower performance in partial oxidation. / Uma das principais aplica??es do metano ? a produ??o de g?s de s?ntese,
mistura de hidrog?nio e mon?xido de carbono. Os processos utilizados na produ??o
de g?s de s?ntese a partir do metano s?o: reforma a vapor, reforma com CO2,
oxida??o parcial e reforma autot?rmica. Neste trabalho, o comportamento de
catalisadores de n?quel suportados em ?xidos mistos de c?rio e mangan?s na
rea??o de oxida??o parcial do metano foi avaliado e comparado com o catalisador
de n?quel suportados no ?xido misto de c?rio e zirc?nio. Os ?xidos mistos de c?rio e
zirc?nio ou c?rio e mangan?s foram sintetizadas usando dois diferentes m?todos de
prepara??o; o de precursores polim?ricos baseado no processo Pechini e por rea??o
de combust?o usando um micro-ondas, seguido da impregna??o de n?quel com teor
de 15 %. As amostras foram calcinadas a 300, 800 e 900 ?C e caracterizados por
?rea espec?fica (ASE), fluoresc?ncia de raios X (FRX), difra??o de raios X (DRX),
microscopia eletr?nica de varredura (MEV), redu??o ? temperatura programada
(RTP) e a rea??o de oxida??o parcial do metano. As ?reas espec?ficas das amostras
diminuem com o aumento da temperatura de calcina??o e ap?s a impregna??o com
n?quel. A solu??o s?lida c?rio-metal foi formada e nos composto com as maiores
quantidades de ?xidos de mangan?s verificou-se a presen?a de outras esp?cies de
mangan?s fora da estrutura da solu??o s?lida. Quanto ? microscopia eletr?nica de
varredura os suportes a base de c?rio e zirc?nio preparados via Pechini exibem
part?culas aglomeradas, sem geometria uniforme e sem a visualiza??o de poros na
superf?cie, enquanto os compostos contendo mangan?s apresentaram alguns vazios
na sua estrutura. Atrav?s da s?ntese por rea??o de combust?o a morfologia
adquirida independente da composi??o proposta apresentou uma maior porosidade
em rela??o ? s?ntese Pechini. Mesmo sendo os catalisadores preparados por
diferentes m?todos de s?ntese, a inser??o de n?quel deixou seus perfis de redu??o
(RTP) muito semelhantes. Para os catalisadores de n?quel suportados no ?xido
misto de c?rio e zirc?nio, h? em primeiro lugar redu??o de esp?cies NiO que
apresentam certa intera??o com o suporte, seguido da redu??o de Ce4+ em Ce3+
superficiais, com posterior redu??o do bulk. Para os catalisadores contendo
mangan?s h? a redu??o das esp?cies de ?xido de n?quel, seguido de duas etapas
de redu??o para as esp?cies Mn2O3 em Mn3O4 e Mn3O4 em MnO, com posterior
redu??o do bulk. Quanto ?s rea??es de oxida??o parcial, o catalisador de n?quel
suportados no ?xido misto de c?rio e zirc?nio preparado via m?todo Pechini,
apresentou uma convers?o de CH4 de cerca de 80 %, sendo 81 % a convers?o
quando preparado via combust?o. Esse comportamento manteve-se durante 10
horas de rea??o. Observou-se tamb?m que o teor de mangan?s influencia
diretamente na atividade catal?tica dos materiais, quanto maior o teor de ?xido de
mangan?s mais r?pido o catalisador apresentava desativa??o e desestabiliza??o.
Para ambos os m?todos de s?ntese o catalisador de n?quel suportados no ?xido
misto de c?rio e zirc?nio manteve a raz?o H2/CO bem pr?xima de 2 durante as 10
horas em que ocorre a rea??o de oxida??o parcial. As amostras contendo mangan?s
apresentaram menores raz?es de H2/CO e menor desempenho na oxida??o parcial.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/17740 |
| Date | 26 November 2010 |
| Creators | Silveira, Valdelice Rodrigues da |
| Contributors | CPF:06117988320, http://lattes.cnpq.br/3318871716111536, Pedrosa, Anne Michelle Garrido, CPF:81357443404, http://lattes.cnpq.br/5052401160158651, Barros, Br?ulio Silva, CPF:00735018405, Vitor Sobrinho, Eledir, CPF:64656969915, http://lattes.cnpq.br/8488499388852606, Souza, Marcelo Jos? Barros de, CPF:02276845406, http://lattes.cnpq.br/9197899107763639, Ruiz, Juan Alberto Chavez, Melo, Dulce Maria de Ara?jo |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Qu?mica, UFRN, BR, F?sico-Qu?mica; Qu?mica |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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