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Reaction kinetics of direct gas-phase propylene epoxidation on Au/TS-1 catalystsJeremy Arvay (12401182) 26 April 2022 (has links)
<p> Propylene oxide (PO), is a key intermediate in the production of value-added products, such as polyurethanes and propylene glycol. Current industrially practiced methods of propylene epoxidation, including hydrochlorination, epoxidation by organic peroxides, and the Hydrogen Peroxide to Propylene Oxide (HPPO) process either produce PO unselectively, necessitating energy intensive separation processes, produce environmentally damaging byproducts, or require several sequential reaction vessels. A potential solution for these issues exists in the form of a single-step, highly selective gas phase reaction to produce PO. Industrial adoption of a process utilizing this technology has not occurred due to the failure of state-of-the-art Au/TS-1 catalysts, consisting of gold supported on titanium MFI, to meet economic targets for hydrogen use efficiency, selectivity to PO, and PO rate-permass, improvement on all of which has been hindered by a lack of understanding of how Au-TS-1 catalysts fundamentally operate. Therefore, the goal of this work has been to understand the active site requirements and reaction kinetics with the aim of lowering barriers to commercialization of this more environmentally benign process. Once we had developed a general understanding of product inhibition, we applied this knowledge to the kinetics of propylene epoxidation over Au/TS-1 catalysts. We measured gas phase kinetics in a continuous stirred tank reactor (CSTR) free from temperature and concentration gradients. Apparent reaction orders measured at 473 K for H2, O2, and propylene for a series of Au-DP/TS-1 with varied Au and Ti contents were consistent with those reported previously. Co-feeding propylene oxide enabled measurement of the apparent reaction order in propylene oxide and the determination that relevant pressures of propylene oxide reversibly inhibit propylene epoxidation over Au-DP/TS-1, while co-feeding carbon dioxide and water had no effect on the propylene epoxidation rate. The measured reaction orders for propylene epoxidation, after corrected to account for propylene oxide inhibition, are consistent with a ‘simultaneous’ mechanism requiring two distinct, but adjacent, types of sites. H2 oxidation rates are not inhibited by propylene oxide, implying that the sites required for hydrogen oxidation are distinct from those required for propylene epoxidation. 26 We then shifted focus to elucidate structural details of gold active sites and their interaction with Ti active sites. To determine whether the roles of extracrystalline and intracrystalline gold nanoparticles supported on titanosilicate-1 on direct propylene epoxidation are intrinsically different, the kinetics of direct propylene epoxidation were measured in a gas-phase continuous stirred tank reactor (CSTR) over PVP-coated gold nanoparticles (Au-PVP/TS-1) deposited on TS-1 supports. The PVP-coated gold nanoparticles were too large to fit into the micropores of TS-1, even after ligands were removed in situ by a series of pretreatments, as confirmed by both TEM and TGA-DSC. The activation energy and reaction orders for H2, O2, propylene, propylene oxide, carbon dioxide, and water for propylene epoxidation measured on Au-PVP/TS-1 catalysts were consistent with those reported for Au/TS-1 prepared via deposition-precipitation (Au-DP/TS-1). However, while the reaction orders for hydrogen oxidation on Au-PVP/TS-1 were similar to those measured on AuDP/TS-1, a decrease in activation energy from approximately 30 kJ mol−1 for Au-DP/TS-1 to 4-5 kJ mol−1 for Au-PVP/TS-1 suggests there is a change in mechanism, rate-limiting step, and/or active site for hydrogen oxidation. Additionally, an active site model was developed which determines the number of Ti within an interaction range of the perimeter of extracrystalline Au nanoparticles (i.e., the number of Au-Ti active site pairs). Turnover frequencies estimated for this active site model for a dataset containing both Au-DP/TS-1 and Au-PVP/TS-1 were ∼20x higher than any previous report ( 80 s−1 vs. 1-5 s−1 at 473 K) for catalytic oxidation on noble metals, suggesting that the simultaneous mechanism occurring over proximal Au-Ti sites alone is incapable of explaining the observed rate of propylene epoxidation and that short-range migration of hydrogen peroxide is necessary to account for the catalytic rate. The agreement of reaction orders, activation energy, and active site model for propylene epoxidation on both Au-DP/TS-1 and Au-PVP/TS-1 suggests a common mechanism for propylene epoxidation on both catalysts containing small intraporous gold clusters and catalysts with exclusively larger extracrystalline nanoparticles. Rates of hydrogen oxidation were found to vary proportionally to the amount of surface gold atoms. This is also consistent with the hypothesis that the observed decrease in hydrogen efficiency and PO site-time-yield per gold mass with increasing gold loading are driven primarily by the gold dispersion in Au/TS-1 catalysts. </p>
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IN SITU INFRARED STUDY OF ADSORBED SPECIES DURING CATALYTIC OXIDATION AND CARBON DIOXIDE ADSORPTIONKhatri, Rajesh A. 23 September 2005 (has links)
No description available.
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Ionic Conducting Ceramic Membrane Reactor for Partial Oxidation of Light HydrocarbonsAkin, Figen Tulin 21 May 2002 (has links)
No description available.
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Sulphur dioxide capture under fluidized bed combustion conditions / Tholakele Prisca NgelekaNgeleka, Tholakele Prisca January 2005 (has links)
An investigation was undertaken to determine the feasibility of increasing the hydrogen
production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process
(HyS). This investigation also involved the technical and economical analysis of the water gas
shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical
analysis of the water gas shift reaction was determined under the operating conditions selected
on the basis of some information available in the literature. The high temperature system (HTS)
and low temperature system (LTS) reactors were assumed to be operated at temperatures of
350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30
atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was
242T/D, which is approximately two times the amount produced by the HyS process alone. The
PSA was used for the purification process leading to a hydrogen product with a purity of
99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2
is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2
and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with
PSA is about US$50 million. The production cost is highly dependent on the cost of all of the
required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2
based on the input cost of synthesis gas as produced by the POX process. In this case the
production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen
was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the
corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.
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Gazéification non catalytique des huiles de pyrolyse de bois sous vapeur d'eau / Non catalytic steam gasification of wood bio-oilChhiti, Younes 05 September 2011 (has links)
La production d'énergie à partir de biomasse ligno-cellulosique via la technologie de gazéification est une option intéressante dans le contexte énergétique actuel. La combinaison d‘une pyrolyse rapide décentralisée de la biomasse pour produire les bio-huiles, suivie par le transport et le vaporeformage dans des bio-raffineries, est apparue comme l'une des méthodes économiquement les plus viables pour la production de gaz de synthèse (H2+CO). L‘objectif de ce travail est de combler le manque de connaissances concernant les processus de transformation physicochimique de l‘huile de pyrolyse en gaz de synthèse utilisant la gazéification non catalytique dans des réacteurs à flux entrainé. Il s‘agit d‘un processus complexe, mettant en oeuvre la vaporisation, les réactions de craquage thermique avec formation de gaz, de tars et de deux résidus solides : le char et les suies, qui sont des produits indésirables. Ceci est suivi par le reformage des gaz et des tars, ainsi que la conversion du char et des suies. Pour mieux comprendre le processus, la première étape de la gazéification (la pyrolyse), et par la suite l'ensemble du processus (pyrolyse + gazéification) ont été étudiés. L‘étude de la pyrolyse est focalisée sur l‘influence de la vitesse de chauffe, de la température ainsi que de la teneur en cendres dans la bio-huile, sur les rendements en char, tars et gaz. A très grande vitesse de chauffe le rendement en char est inferieur à 1%. Les cendres semblent favoriser les réactions de polymérisation et provoquent la diminution du rendement en gaz. Concernant la gazéification, l'effet de la température sur le rendement et la composition du gaz de synthèse a été étudié. Une augmentation de la température de réaction implique une augmentation du rendement en hydrogène et une conversion très élevée du carbone solide. Un calcul d'équilibre thermodynamique a montré que l'équilibre a été atteint à 1400°C. Finalement les mécanismes de formation et d‘oxydation des suies ont été étudiés expérimentalement sous différentes atmosphères : inerte (pyrolyse), riche en vapeur d‘eau (gazéification) et en présence d‘oxygène (oxydation partielle). Un modèle semi empirique est proposé et validé. Il est fondé sur la chimie détaillée pour décrire les réactions en phase gaz, une seule réaction basée sur la concentration de C2H2 pour décrire la formation des suies et principalement une réaction hétérogène pour décrire l‘oxydation des suies. / Energy production from ligno-cellulosic biomass via gasification technology appears as an attractive option in the current energy context. The combination of decentralized fast pyrolysis of biomass to produce bio-oil, followed by transportation and gasification of bio-oil in bio-refinery has appeared as one of the most economically viable methods for syngas (H2+CO) production. The objective of this work is to bridge the lack of knowledge concerning the physicochemical transformation of bio-oil into syngas using non catalytic steam gasification in entrained flow reactors. This complex process involves vaporization, thermal cracking reactions with formation of gas, tars and two solid residues - char and soot - that are considered as undesirable products. This is followed by steam reforming of gas and tars, together with char and soot conversion. To better understand the process, the first step of gasification (pyrolysis) and thereafter the whole process (pyrolysis + gasification) were studied. The pyrolysis study focused on the influence of the heating rate, the final pyrolysis temperature and the ash content of bio-oil on char, tars and gas yields. At the higher heating rate char yield is smaller than 1%. In addition, ash seems to promote polymerization reactions and causes a decrease of gas yield. Concerning gasification, the effect of temperature on syngas yield and composition was studied. An increase in the reaction temperature implies higher hydrogen yield and higher solid carbon conversion. A thermodynamic equilibrium calculation showed that equilibrium was reached at 1400°C. Finally, the soot formation and oxidation mechanisms were investigated through experiments in three different atmospheres: inert (pyrolysis), rich in steam (gasification) and in the presence of oxygen (partial oxidation). A semi-empirical model was proposed and validated. It is based on detailed chemistry to describe gas phase reactions, a single reaction using C2H2 concentration to describe soot formation and one main heterogeneous reaction to describe soot oxidation.
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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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Sulphur dioxide capture under fluidized bed combustion conditions / Tholakele Prisca NgelekaNgeleka, Tholakele Prisca January 2005 (has links)
An investigation was undertaken to determine the feasibility of increasing the hydrogen
production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process
(HyS). This investigation also involved the technical and economical analysis of the water gas
shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical
analysis of the water gas shift reaction was determined under the operating conditions selected
on the basis of some information available in the literature. The high temperature system (HTS)
and low temperature system (LTS) reactors were assumed to be operated at temperatures of
350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30
atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was
242T/D, which is approximately two times the amount produced by the HyS process alone. The
PSA was used for the purification process leading to a hydrogen product with a purity of
99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2
is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2
and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with
PSA is about US$50 million. The production cost is highly dependent on the cost of all of the
required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2
based on the input cost of synthesis gas as produced by the POX process. In this case the
production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen
was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the
corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.
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An investigation into the feasibility of applying the watergas shift process to increase hydrogen production rate of the hybrid sulphur process / T.P. NgelekaNgeleka, Tholakele Prisca January 2008 (has links)
An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350°C and 200°C, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with C02 and traces of CH4, CO, and saturated H20. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.
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An investigation into the feasibility of applying the watergas shift process to increase hydrogen production rate of the hybrid sulphur process / T.P. NgelekaNgeleka, Tholakele Prisca January 2008 (has links)
An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350°C and 200°C, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with C02 and traces of CH4, CO, and saturated H20. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.
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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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