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Estudo do desempenho de catalisadores tipo Ni/CexM1-xO2 (M = Zr ou Mn) na rea??o de oxida??o parcial do metanoSilveira, Valdelice Rodrigues da 26 November 2010 (has links)
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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.
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Obten??o de ?xidos a base de n?quel e cobalto para rea??o de oxida??o parcial do metanoPeres, Ana Paula da Silva 07 January 2011 (has links)
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Previous issue date: 2011-01-07 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Nickel-based catalysts supported on alumina have been widely used in various
reactions to obtain synthesis gas or hydrogen. Usually, higher conversion levels are
obtained by these catalysts, however, the deactivation by coke formation and sintering
of metal particles are still problems to be solved. Several approaches have been
employed in order to minimize these problems, among which stands out in recent
years the use of additives such as oxides of alkali metals and rare earths. Similarly, the
use of methodologies for the synthesis faster, easier, applicable on an industrial scale
and to allow control of the microstructural characteristics of these catalysts, can
together provide the solution to this problem. In this work, oxides with spinel type
structure AB2O4, where A represents divalent cation and B represents trivalent cations
are an important class of ceramic materials investigated worldwide in different fields
of applications. The nickel cobaltite (NiCo2O4) was oxides of spinel type which has
attracted considerable interest due to its applicability in several areas, such as
chemical sensors, flat panel displays, optical limiters, electrode materials, pigments,
electrocatalysis, electronic ceramics, among others. The catalyst precursor NiCo2O4
was prepared by a new chemical synthesis route using gelatine as directing agent. The
polymer resin obtained was calcined at 350?C. The samples were calcined at different
temperatures (550, 750 and 950?C) and characterized by X ray diffraction,
measurements of specific surface area, temperature programmed reduction and
scanning electron microscopy. The materials heat treated at 550 and 750?C were
tested in the partial oxidation of methane. The set of techniques revealed, for solid
preparations, the presence of the phase of spinel-type structure with the NiCo2O4
NixCo1-xO solid solution. This solid solution was identified by Rietveld refinement at all
temperatures of heat treatment. The catalyst precursors calcined at 550 and 750?C
showed conversion levels around 25 and 75%, respectively. The reason H2/CO was
around 2 to the precursor treated at 750?C, proposed reason for the reaction of partial
oxidation of methane, one can conclude that this material can be shown to produce
synthesis gas suitable for use in the synthesis Fischer-Tropsch process / Catalisadores a base de n?quel suportados em alumina, t?m sido amplamente
empregados nas diversas rea??es para obten??o de g?s de s?ntese ou hidrog?nio.
Normalmente, altos n?veis de convers?o s?o obtidos por estes catalisadores,
entretanto, a desativa??o por forma??o de coque e sinteriza??o das part?culas
met?licas s?o ainda problemas a serem solucionados. Diversas abordagens t?m sido
empregadas com a finalidade de minimizar estes problemas, dentre as quais tem se
destacado nos ?ltimos anos a utiliza??o de aditivos como ?xidos de metais alcalinos e
metais terras raras. 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. Neste trabalho, ?xidos com estrutura tipo espin?lio AB2O4, onde A
representa c?tions divalentes e B representa c?tions trivalentes, s?o uma classe
importante de materiais cer?micos mundialmente investigados em diferentes campos
de aplica??es. As cobaltitas de n?quel (NiCo2O4) s?o ?xidos do tipo espin?lio que tem
atra?do consider?vel interesse devido a sua aplicabilidade em diversas ?reas, como em
sensores qu?micos, monitores de tela plana, limitadores ?pticos, materiais para
eletrodos, pigmentos, eletrocat?lise, cer?micas eletr?nicas, entre outras. O precursor
catal?tico NiCo2O4 foi preparado por uma nova rota de s?ntese qu?mica usando a
gelatina como agente direcionador. A resina polim?rica obtida foi tratada
termicamente a 350?C. As amostras foram calcinadas em diferentes temperaturas 550,
750 e 950?C e caracterizadas por difra??o de raios X, medidas de ?rea superficial
espec?fica, redu??o a temperatura programada e microscopia eletr?nica de varredura.
Os materiais tratados termicamente a 550 e 750?C foram testados na oxida??o parcial
do metano. O conjunto de t?cnicas revelaram, nos s?lidos preparados, a presen?a da
fase de estrutura espin?lio do tipo NiCo2O4 juntamente com a solu??o s?lida NixCo1-xO.
Esta solu??o s?lida foi identificada atrav?s do refinamento Rietveld em todas as
temperaturas de tratamento t?rmico. Os precursores catal?ticos calcinados a 550 e
750?C apresentaram n?veis de convers?o em torno de 25 e 75%, respectivamente. A
raz?o H2/CO foi em torno de 2 para o precursor tratado a 750?C, raz?o proposta pela
rea??o de oxida??o parcial do metano, pode-se concluir que este material pode ser
indicado para produzir g?s de s?ntese adequado para ser utilizado na s?ntese de
Fischer-Tropsch
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S?ntese de catalisadores do tipo LaNixFe1-xO3 como precursores catal?ticos para rea??o oxida??o parcial do metanoMartinelli, Daniele de Macedo Henrique 21 February 2011 (has links)
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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
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