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Previous issue date: 2011-02-21 / Nickel-bases catalysts have been used in several reform reactions, such as in the
partial oxidation of methane to obtain H2 or syngas (H2 + CO). High levels of
conversion are usually obtained using this family of catalysts, however, their
deactivation resulting from carbon deposition still remains a challenge. Different
approaches have been tested aiming at minimizing this difficulty, including the
production of perovskites and related structures using modern synthesis methods
capable of producing low cost materials with controlled microstructural characteristics
at industrial scale. To establish grounds for comparison, in the present study
LaNixFe1-xO3 (x=0, 0.3 or 0.7) perovskites were prepared following the Pechini
method and by microwave assisted self-combustion. All samples were sub sequently
calcined at 900 ?C to obtain the target phase. The resulting ceramic powders were
characterized by thermogravimetric analysis, infrared spectroscopy, X ray diffraction,
specific area and temperature programmed reduction tests. Calcined samples were
also used in the partial oxidation reaction of methane to evaluate the level of
conversion, selectivity and carbon deposition. The results showed that the calcined
samples were crystalline and the target phase was formed regardless of the
synthesis method. According to results obtained by Rietveld refinement, we observed
the formation of 70.0% of LaNi0.3Fe0.7O3 and 30.0% of La2O3 for samples LN3F7-900-
P, LN3F7-900-M and 41,6% of LaNi0.7Fe0.3O3, 30.7% of La2NiO4 and 27.7% of La2O3
for samples LN7F3-900-P and LN7F3-900-M.Temperature-programmed profiles of
the LaNiO3 sample revealed the presence of a peak around 510 ?C, whereas the
LaFeO3 sample depicted a peak above 1000?C. The highest l evel of methane
conversion was obtained for LaNiO3 synthesized by the Pechini method. Overall,
catalysts prepared by the Pechini method depicted better conversion levels
compared to those produced by microwave assisted self-combustion / Catalisadores a base de n?quel t?m sido empregados em diversos tipos de rea??es
de reforma, inclusive na oxida??o parcial do metano para obten??o de H2 ou g?s de
s?ntese (H2 + CO). Normalmente, altos n?veis de convers?o s?o obtidos por estes
catalisadores, entretanto, a desativa??o por deposi??o de carbono ainda ? um
problema a ser solucionado. Diversas abordagens t?m sido empregadas no intuito
de minimizar este problema, dentre as quais tem se destacado nos ?ltimos anos a
utiliza??o de ?xidos com estrutura perovisquita e/ou estruturas relacionadas.
Paralelamente, o uso de metodologias de s?nteses mais r?pidas, f?ceis, aplic?veis
em escala industrial e que permitam o controle das caracter?sticas microestruturais
destes catalisadores, pode em conjunto, prover a solu??o para este problema.
A n?vel de compara??o perovisquitas do tipo LaNixFe1-xO3 (x=0, x=0,3 e x=0,7) foram
preparados por dois m?todos: precursores polim?ricos (pechini) e autocombust?o
assistida por microondas. Todas as amostras foram calcinadas a 900 ?C/4h para
obten??o das fases desejadas. Os p?s-obtidos foram caracterizados por an?lise
termogravim?trica, espectroscopia na regi?o do infravermelho, difra??o de raios-X,
medidas de ?rea superficial especifica, redu??o ? temperatura programada.
As amostras calcinadas foram testadas na rea??o de oxida??o parcial do metano,
sendo avaliados os respectivos n?veis de convers?o, seletividade e a resist?ncia ?
deposi??o de carbono. Ap?s calcina??o a fase desejada foi obtida para todas as
amostras independente do m?todo de s?ntese, sugerindo claramente a forma??o de
p?s cristalinos. De acordo com o resultados obtidos pelo refinamento Rietveld,
observou-se a forma??o de 70,0% de LaNi0,3Fe0,7O3 e 30,0 % de La2O3 para as
amostras LN3F7-900-P e LN3F7-900-M e 41,6% de LaNi0.7Fe0.3O3; 30,7% de
La2NiO4 e 27,7 % de La2O3 para as amostras LN7F3-900-P e LN7F3-900-M. Os
perfis de redu??o ? temperatura programada da amostra LaNiO3 apresentou pico de
redu??o em torno de 510 ?C, j? a amostra LaFeO 3 apresentou pico de redu??o
acima de 1000?C. Dentre os catalisadores estudados o que apresentou maior n?vel
de convers?o de metano foi LaNiO3 obtido pelo m?todo pechini, de uma maneira
geral os catalisadores obtidos pelo m?todo pechini apresentaram melhores
resultados de convers?o que os catalisadores obtidos pela autocombust?o assistida
por microondas
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/12769 |
| Date | 21 February 2011 |
| Creators | Martinelli, Daniele de Macedo Henrique |
| Contributors | CPF:06117988320, http://lattes.cnpq.br/3318871716111536, Melo, Marcus Ant?nio de Freitas, CPF:04514998320, http://lattes.cnpq.br/5840621182000517, Pedrosa, Anne Michelle Garrido, CPF:81357443404, http://lattes.cnpq.br/5052401160158651, Barros, Br?ulio Silva, CPF:00735018405, Ruiz, Juan Alberto Chavez, CPF:00744293456, http://lattes.cnpq.br/5051286289341242, Melo, Dulce Maria de Ara?jo |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Ci?ncia e Engenharia de Materiais, UFRN, BR, Processamento de Materiais a partir do P?; Pol?meros e Comp?sitos; Processamento de Materiais a part |
| 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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