This thesis addressed the development of new porous carbides and carbide-derived carbons; in particular materials based on silicon-, boron-, tungsten-, and titanium carbide. Therefore, different hard- and soft-templating approaches were applied and the materials were additionally functionalized with catalytic active components and shaped into nm- and mm-sized spherical particles.

This thesis addressed the development of new porous carbides and carbide-derived carbons; in particular materials based on silicon-, boron-, tungsten-, and titanium carbide. Therefore, different hard- and soft-templating approaches were applied and the materials were additionally functionalized with catalytic active components and shaped into nm- and mm-sized spherical particles.

SILVA, Antônio Neves da. Caracterização de Óxidos Nanoestruturados através de Espectroscopia Raman em condições de pressões elevadas. 2015. 115 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2015. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-06-11T18:16:10Z No. of bitstreams: 1 2015_tese_ansilva.pdf: 10244378 bytes, checksum: f5574341b39d6d68105f6205b730556d (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-06-11T18:25:13Z (GMT) No. of bitstreams: 1 2015_tese_ansilva.pdf: 10244378 bytes, checksum: f5574341b39d6d68105f6205b730556d (MD5) / Made available in DSpace on 2015-06-11T18:25:13Z (GMT). No. of bitstreams: 1 2015_tese_ansilva.pdf: 10244378 bytes, checksum: f5574341b39d6d68105f6205b730556d (MD5) Previous issue date: 2015 / Raman spectroscopy studies has been used to investigate the structural properties of nanocasted oxides, CeO2 (Ce), ZrO2 (Zr), TiO2 (Ti), SnO2 (Sn), MnOx (Mn), CeO2−Al2O3 (CeAl), CeO2−MnO2 (CeMn) and NiO−Al2O3 (NiAl), obtained from nanocasting technique. The studies were collaborated by Transmission Electron Microscopy (TEM) and Infrared Spectroscopy with Fourier transform (FT-IR) techniques. The results suggested that Ce, Sn and Mn monoxides have structural defects (vacancies) derived from the preparation method of the solids. This result is indeed not common for ordinary oxides. At room pressure Ti anatase is tetragonal belonging to D4h19 (I41/amd) space group and changes for the monoclinic phase at pressures around 14 GPa. With pressure release Ti changes to orthorhombic phase. The sample Mn showed a phase transition at about 17,5 GPa, whose phase is still unknown. For all samples the spectra appear strongly influenced by the particle size, shape and structure of the material, especially in the position value of pression for phase transition. The Ce, Zr and Sn remained stable up to the maximum pressure achieved and Ti and Mn showed phase transition. TEM analysis estimated the average nanoparticle size of 9 nm (Ce), 34 nm (Sn), 54 nm (Mn), 10 nm (CeMn) and 8 nm (CeAl); and distance between crystallographic planes of d111 = 0,3 nm (Ce), d110 = 0,33 nm (Sn), d111 = 0,36 nm (Mn), d111 = 0,32 nm (CeMn) e d111 = 0,3 nm (CeAl). The nanoparticles sizes for Ce, CeMn and CeAl, obtained from Raman spectroscopy data were 7, 8 and 3 nm, respectively, wich agree well with the results of TEM. The images suggest that all the nanoparticles were distributed over the remaining silica surface. All nanoparticles were agglomerated in some regions, due to the fact that in the silica-based nanocomposites, calcination leads to migration to nucleation sites. The FT-IR spectra indicated the presence of modes related to vibrations of OH bonds in na- nostructures; and the vibrations of Ce-O, Sn-O and Mn-O bonds of Ce, Sn and Mn oxides, respectively. The spectra of sample CeMn showed that the interaction between Mn and Ce can break the structure of the fluorite type and form oxygen vacancies in the Ce structure whereas the CeMn and NiAl high pressure results showed line broadening, decreasing in modes intensity and remained stable until the maximum pressure value reached, 14 and 18 GPa respectively. The stability of CeAl was maintained up to 36 GPa, in contrast with that observed for Ce monoxide, in which a phase transition occurs at about 35 GPa to a structure of PbCl2 orthorhombic (space group D2h16). The introduction of oxide Al2O3 in the structure of CeO2 increases the stability of this structure. The effect of varying laser power incident in nanostructured oxides showed an increase in intensity in all nano oxides spectra with the increasing laser power. Mn oxide, in particular, presented an increase in the modes related to defects due to vacancies generated by OH removing. / Neste trabalho caracteriza-se os óxidos de Cério (Ce), Zircônio (Zr), Titânio (Ti), Estanho (Sn), Manganês (Mn), CeO2−Al2O3 (CeAl), CeO2−MnO2 (CeMn) e NiO−Al2O3 (NiAl), sintetizados a partir do método da nanomoldagem, por espectroscopia Raman a altas pressões, Microscopia Eletrônica de Transmissão (TEM) e Espectroscopia na região do Infravermelho com transformada de Fourier FT-IR. Os resultados sugerem que os monóxidos Ce, Sn e Mn possuem defeitos estruturais (vacâncias) derivados do método de preparação dos sólidos. Na pressão ambiente Ti anatase é tetragonal pertencendo ao grupo espacial D4h19 (I41/amd) e muda para a fase monoclínica, em pressões em torno de 14 GPa. Ao se realizar a descompressão Ti muda para a fase ortorrômbica. A amostra Mn mostrou uma transição de fase em cerca de 17,5 GPa, cuja fase ainda é desconhecida. Através da análise de TEM, estimou-se o tamanho médio das nanopartículas de 9 nm (Ce), 34 nm (Sn), 54 nm (Mn), 10 nm (CeMn) e 8 nm (CeAl); e distância entre planos cristalográficos de d111 = 0,3 nm (Ce), d110 = 0,33 nm (Sn), d111 = 0,36 nm (Mn), d111 = 0, 32 nm (CeMn) e d111 = 0,3 nm (CeAl). Os tamanhos médios estimados para o Ce, CeMn e CeAl, através dos dados de espectroscopia Raman foram de 7, 8 e 3 nm respectivamente, em concordância com os resultados de TEM. As micrografias sugerem que todas as nanopartículas estavam distribuídas sobre a superfície da sílica remanescente e todas apresentaram-se aglomeradas em algumas regiões, devido ao fato de que em nanocompostos à base de sílica, a calcinação conduz à migração para sítios de nucleação. Os modos identificados nos espectros FT-IR foram relacionados às vibrações das ligações O-H nas nanoestruturas e às vibrações das ligações Ce-O, Sn-O e Mn-O dos óxidos Ce, Sn e Mn, respectivamente. Os experimentos sob condições de altas pressões do CeMn mostram que a interação entre Mn e Ce pode deformar a estrutura do tipo fluorita e formar vacâncias de oxigênio na rede de Ce. Os óxidos CeMn e NiAl apresentaram alargamento de linha, diminuição na intensidade dos modos e permaneceram estáveis até o valor máximo de pressão alcançado, 14 e 18 GPa respectivamente. Para o sólido CeAl, a estabilidade da fase cúbica é mantida até 36 GPa, fato oposto àquele observado para o monóxido Ce, no qual ocorre uma transição de fase em cerca de 35 GPa para uma estrutura do tipo PbCl2 ortorrômbica (grupo espacial D2h16). Conclui-se que a introdução do óxido Al2O3 na estrutura do CeO2 aumenta a estabilidade dessa estrutura. Os experimentos com a variação da potência mostraram que o aumento na potência está relacionado a um aumento na intensidade dos modos em todos os óxidos. O óxido Mn, em particular, apresentou um aumento nos modos de defeitos devido às vacâncias geradas pela eliminação da água presente, evidenciado pelos modos do grupo OH.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / Neste trabalho caracteriza-se os Ãxidos de CÃrio (Ce), ZircÃnio (Zr), TitÃnio (Ti), Estanho (Sn), ManganÃs (Mn), CeO2−Al2O3 (CeAl), CeO2−MnO2 (CeMn) e NiO−Al2O3 (NiAl), sintetizados a partir do mÃtodo da nanomoldagem, por espectroscopia Raman a altas pressÃes, Microscopia EletrÃnica de TransmissÃo (TEM) e Espectroscopia na regiÃo do Infravermelho com transformada de Fourier FT-IR. Os resultados sugerem que os monÃxidos Ce, Sn e Mn possuem defeitos estruturais (vacÃncias) derivados do mÃtodo de preparaÃÃo dos sÃlidos. Na pressÃo ambiente Ti anatase à tetragonal pertencendo ao grupo espacial D4h19 (I41/amd) e muda para a fase monoclÃnica, em pressÃes em torno de 14 GPa. Ao se realizar a descompressÃo Ti muda para a fase ortorrÃmbica. A amostra Mn mostrou uma transiÃÃo de fase em cerca de 17,5 GPa, cuja fase ainda à desconhecida. AtravÃs da anÃlise de TEM, estimou-se o tamanho mÃdio das nanopartÃculas de 9 nm (Ce), 34 nm (Sn), 54 nm (Mn), 10 nm (CeMn) e 8 nm (CeAl); e distÃncia entre planos cristalogrÃficos de d111 = 0,3 nm (Ce), d110 = 0,33 nm (Sn), d111 = 0,36 nm (Mn), d111 = 0, 32 nm (CeMn) e d111 = 0,3 nm (CeAl). Os tamanhos mÃdios estimados para o Ce, CeMn e CeAl, atravÃs dos dados de espectroscopia Raman foram de 7, 8 e 3 nm respectivamente, em concordÃncia com os resultados de TEM. As micrografias sugerem que todas as nanopartÃculas estavam distribuÃdas sobre a superfÃcie da sÃlica remanescente e todas apresentaram-se aglomeradas em algumas regiÃes, devido ao fato de que em nanocompostos à base de sÃlica, a calcinaÃÃo conduz à migraÃÃo para sÃtios de nucleaÃÃo. Os modos identificados nos espectros FT-IR foram relacionados Ãs vibraÃÃes das ligaÃÃes O-H nas nanoestruturas e Ãs vibraÃÃes das ligaÃÃes Ce-O, Sn-O e Mn-O dos Ãxidos Ce, Sn e Mn, respectivamente. Os experimentos sob condiÃÃes de altas pressÃes do CeMn mostram que a interaÃÃo entre Mn e Ce pode deformar a estrutura do tipo fluorita e formar vacÃncias de oxigÃnio na rede de Ce. Os Ãxidos CeMn e NiAl apresentaram alargamento de linha, diminuiÃÃo na intensidade dos modos e permaneceram estÃveis atà o valor mÃximo de pressÃo alcanÃado, 14 e 18 GPa respectivamente. Para o sÃlido CeAl, a estabilidade da fase cÃbica à mantida atà 36 GPa, fato oposto Ãquele observado para o monÃxido Ce, no qual ocorre uma transiÃÃo de fase em cerca de 35 GPa para uma estrutura do tipo PbCl2 ortorrÃmbica (grupo espacial D2h16). Conclui-se que a introduÃÃo do Ãxido Al2O3 na estrutura do CeO2 aumenta a estabilidade dessa estrutura. Os experimentos com a variaÃÃo da potÃncia mostraram que o aumento na potÃncia està relacionado a um aumento na intensidade dos modos em todos os Ãxidos. O Ãxido Mn, em particular, apresentou um aumento nos modos de defeitos devido Ãs vacÃncias geradas pela eliminaÃÃo da Ãgua presente, evidenciado pelos modos do grupo OH. / Raman spectroscopy studies has been used to investigate the structural properties of nanocasted oxides, CeO2 (Ce), ZrO2 (Zr), TiO2 (Ti), SnO2 (Sn), MnOx (Mn), CeO2−Al2O3 (CeAl), CeO2−MnO2 (CeMn) and NiO−Al2O3 (NiAl), obtained from nanocasting technique. The studies were collaborated by Transmission Electron Microscopy (TEM) and Infrared Spectroscopy with Fourier transform (FT-IR) techniques. The results suggested that Ce, Sn and Mn monoxides have structural defects (vacancies) derived from the preparation method of the solids. This result is indeed not common for ordinary oxides. At room pressure Ti anatase is tetragonal belonging to D4h19 (I41/amd) space group and changes for the monoclinic phase at pressures around 14 GPa. With pressure release Ti changes to orthorhombic phase. The sample Mn showed a phase transition at about 17,5 GPa, whose phase is still unknown. For all samples the spectra appear strongly influenced by the particle size, shape and structure of the material, especially in the position value of pression for phase transition. The Ce, Zr and Sn remained stable up to the maximum pressure achieved and Ti and Mn showed phase transition. TEM analysis estimated the average nanoparticle size of 9 nm (Ce), 34 nm (Sn), 54 nm (Mn), 10 nm (CeMn) and 8 nm (CeAl); and distance between crystallographic planes of d111 = 0,3 nm (Ce), d110 = 0,33 nm (Sn), d111 = 0,36 nm (Mn), d111 = 0,32 nm (CeMn) e d111 = 0,3 nm (CeAl). The nanoparticles sizes for Ce, CeMn and CeAl, obtained from Raman spectroscopy data were 7, 8 and 3 nm, respectively, wich agree well with the results of TEM. The images suggest that all the nanoparticles were distributed over the remaining silica surface. All nanoparticles were agglomerated in some regions, due to the fact that in the silica-based nanocomposites, calcination leads to migration to nucleation sites. The FT-IR spectra indicated the presence of modes related to vibrations of OH bonds in na- nostructures; and the vibrations of Ce-O, Sn-O and Mn-O bonds of Ce, Sn and Mn oxides, respectively. The spectra of sample CeMn showed that the interaction between Mn and Ce can break the structure of the fluorite type and form oxygen vacancies in the Ce structure whereas the CeMn and NiAl high pressure results showed line broadening, decreasing in modes intensity and remained stable until the maximum pressure value reached, 14 and 18 GPa respectively. The stability of CeAl was maintained up to 36 GPa, in contrast with that observed for Ce monoxide, in which a phase transition occurs at about 35 GPa to a structure of PbCl2 orthorhombic (space group D2h16). The introduction of oxide Al2O3 in the structure of CeO2 increases the stability of this structure. The effect of varying laser power incident in nanostructured oxides showed an increase in intensity in all nano oxides spectra with the increasing laser power. Mn oxide, in particular, presented an increase in the modes related to defects due to vacancies generated by OH removing.

No description available.

Des nanoparticules d’or dispersées dans un carbone mésoporeux CMK-n (n = 1,3 et 8) ont été obtenues par une méthode originale qui consiste à répliquer des silices mésoporeuses dans lesquelles les particules d’or ont été préalablement formées. La taille des particules d’or est plus petite lorsque la surface de la silice est fonctionnalisée par un thiol (MPTMS) (dAu ~ 2 nm) que par un ammonium (TPTAC) (dAu ~ 6 nm). La taille des particules d’or dans les répliques peut être contrôlée à la fois par la température de calcination du moule et par la température de pyrolyse de la source de carbone. Bien que les répliques carbonées soient beaucoup mieux dispersées dans le milieu réactionnel apolaire que les moules siliciques correspondants, elles sont moins actives dans les oxydations aérobies du cyclohexène et du trans-stilbène en phase liquide. Les meilleures performances dans l'oxydation de ces deux molécules ont été obtenues sur les répliques pyrolysées à 750°C et contenant des particules d’or de taille moyenne d'environ 2 nm. Les très petites particules sont moins actives, probablement parce qu'elles sont complètement enrobées par du carbone, donc inaccessibles. Les performances catalytiques de nos répliques ont été comparées avec celles d'un catalyseur Au/CMK-3 préparé par dépôt colloïdal sur un carbone mésoporeux pré-formé. Les résultats montrent que nos catalyseurs sont beaucoup moins actifs que celui préparé par dépôt colloïdal, car la majorité des particules dans nos répliques sont recouvertes par du carbone. L'inaccessibilité des particules aux gaz a été confirmée par une mesure de chimisorption d’hydrogène sur un catalyseur Pt/CMK-3 préparé par une méthode identique. / Highly dispersed gold nanoparticles in ordered mesoporous carbons CMK-3 have been obtained by an original method which consists in replicating mesoporous SBA-15 silicas containing gold nanoparticles. The gold particle size is smaller when the silica surface is functionalized with a thiol (mercaptopropyl graft, MPTMS) (dAu ~ 2 nm) than with an ammonium (TPTAC) (dAu ~ 6 nm). The gold particle size in replicas can be controlled by both the calcination temperature of the silica template and the pyrolysis temperature of the carbon source. Although the carbon replicas are much better dispersed in non polar solvents than the corresponding silica templates, they are less active in the aerobic oxidations of cyclohexene and trans-stilbene in the liquid phase. The best performances in the oxidation of these two molecules have been obtained on replicas pyrolysed at 750°C and containing gold particles with an average size of about 2 nm. The very small particles are unexpectedly less active probably because they are completely coated by carbon, and thus inaccessible. The catalytic performances of our replicas have been compared with those of a Au/CMK-3 catalyst prepared by colloidal deposition onto a preformed mesoporous carbon replica. The results show that our catalysts are much less active than that prepared by colloidal deposition because the majority of particles in our replicas are covered by carbon. The inaccessibility of particles to gases has been confirmed by hydrogen chemisorption on a Pt/CMK-3 catalyst prepared by an identical method.

Des nanoparticules d'or dispersées dans un carbone mésoporeux CMK-n (n = 1,3 et 8) ont été obtenues par une méthode originale qui consiste à répliquer des silices mésoporeuses dans lesquelles les particules d'or ont été préalablement formées. La taille des particules d'or est plus petite lorsque la surface de la silice est fonctionnalisée par un thiol (MPTMS) (dAu ~ 2 nm) que par un ammonium (TPTAC) (dAu ~ 6 nm). La taille des particules d'or dans les répliques peut être contrôlée à la fois par la température de calcination du moule et par la température de pyrolyse de la source de carbone. Bien que les répliques carbonées soient beaucoup mieux dispersées dans le milieu réactionnel apolaire que les moules siliciques correspondants, elles sont moins actives dans les oxydations aérobies du cyclohexène et du trans-stilbène en phase liquide. Les meilleures performances dans l'oxydation de ces deux molécules ont été obtenues sur les répliques pyrolysées à 750°C et contenant des particules d'or de taille moyenne d'environ 2 nm. Les très petites particules sont moins actives, probablement parce qu'elles sont complètement enrobées par du carbone, donc inaccessibles. Les performances catalytiques de nos répliques ont été comparées avec celles d'un catalyseur Au/CMK-3 préparé par dépôt colloïdal sur un carbone mésoporeux pré-formé. Les résultats montrent que nos catalyseurs sont beaucoup moins actifs que celui préparé par dépôt colloïdal, car la majorité des particules dans nos répliques sont recouvertes par du carbone. L'inaccessibilité des particules aux gaz a été confirmée par une mesure de chimisorption d'hydrogène sur un catalyseur Pt/CMK-3 préparé par une méthode identique.

L'objectif de ce travail est de développer de nouveaux matériaux carbonés dont la structure poreuse est contrôlée en taille et en morphologie dès l'étape de synthèse. Nous nous sommes tout d'abord intéressés à la technique de nanomoulage. Nous avons, tout d'abord, cherché à optimiser les conditions de synthèse de la réplique carbonée de la zéolithe EMC-2 (EMT) qui a l'avantage de conduire à un diagramme de diffraction bien résolu. Ensuite, différentes zéolithes ont été utilisées comme moule en s'appuyant sur les conditions optimales définies par la première étude. Dans un troisième temps, nous avons étudié la capacité d'adsorption et de séparation de gaz à température ambiante de la réplique carbonée de la zéolithe Y (FAU). L'inconvénient de cette technique est qu'elle est multi-étapes et de grandes quantités ne peuvent être obtenues. Aussi, nous avons cherché à développer d'autres méthodes d'obtention de carbones poreux. Nous nous sommes alors intéressés à la synthèse basée sur l'auto-assemblage entre un tensioactif structurant et un polymère précurseur de carbone. Nous avons cherché à comprendre le mécanisme de formation de ces matériaux et l'influence des différents paramètres de synthèse. Ce type de synthèse permet également l'obtention de composites silice/carbone mésoporeux lorsqu'un précurseur silicique est ajouté au milieu de synthèse. En outre, nous avons étudié la synthèse et la caractérisation de composites obtenus par « tapissage » des pores d'un matériau silicique par une couche de carbone. Les matériaux obtenus présenteraient alors des pores de plus petits diamètres dont la surface aurait des caractéristiques proches de celles de matériaux carbonés. / The aim of this work is to develop new carbon materials with controlled pore structure and to control the size and the morphology of pore structure during the synthesis step. First we interested to the nanocasting technique and to optimise the synthesis conditions in order to obtain the carbon replica of zeolite EMC-2 (EMT). The use of this zeolite allow to obtain well resolved X-ray diffraction pattern. Then carbon replicas have been obtained by using various zeolites as mould and the optimal conditions defined during the first study. The adsorption and separation capacities of carbon replica of zeolite Y (FAU) have been studied. But this technique is multi-step and it is not possible to obtain large quantities. Also other methods in order to obtain porous carbons have been developped. We interested to the synthesis by self-assembly between surfactant as structuring agent and polymer as carbon precursor. We tried to understand the formation mechanism and the inflence of synthesis parameters. Theses types of synthesis allows to obtain mesoporous silica/carbon composite if silicic precursor is added. Moreover, we studied the synthesis and the characterization of carbon-coated porous silica. The obtained materials have pores with smaller diameters but their surfaces have the same characterics than carbon materials.

Grâce à ses excellentes propriétés de résistance et de conductivité thermique ainsi qu'à sa stabilité mécanique et chimique à température ambiante et à haute température, le carbure de silicium (SiC) est un matériau de choix pour le gainage du combustible nucléaire ou les supports de catalyseurs. Cependant, une grande surface spécifique est souvent requise pour ce type d'applications. Cette étude propose deux approches de synthèse :(1) L'approche « Soft Templating ». La porosité et la structure des matériaux finaux sont définies par l'auto-assemblage supramoléculaire d'un agent de structure (SDA) dans un précurseur moléculaire de SiC. Des organogélateurs à faible masse moléculaire et un copolymère tri-bloc commercial sont considérés pour la synthèse de SiC méso-poreux.(2) L'approche « Hard Templating ». Des céramiques SiC sont synthétisées par nanomoulage de silices méso-poreuses par des polymères précéramiques. Ce procédé conserve la nanostructure du template solide et conduit à des SiC méso-poreux à forte surface spécifique.L'approche hard templating permet une bonne réplication du template solide mais la difficulté de cette méthode provient de l'étape d'élimination de ce même template. L'approche soft templating ne présente pas ce désavantage et peut, suivant le SDA utilisé, mener à des céramiques poreuses possédant des structures beaucoup plus variées. La complexité de cette approche réside dans l'étape de réplication du template. / Due to its excellent thermal resistance, mechanical and chemical stability both at room and elevated temperature, silicon carbide (SiC) is an attractive material for nuclear fuel cladding or catalyst substrates. Pore size control and high porosity are the key factors for such applications. Two approaches are studied during this PhD thesis:(1) The Soft Templating Approach. The porosity and the structure of the final materials are defined by the supramolecular self-assembly of a structure directing agent (SDA) into a molecular SiC precursor. Low molecular-mass organic gelators and a commercial tri-block copolymer are considered as SDA for the synthesis of mesoporous SiC materials.(2) The Hard Templating Approach. SiC materials are synthesized by preceramic polymer nanocasting into mesoporous silica. This process preserves the nanoscale structure of the solid template and leads to mesostructured SiC materials with a high specific surface area.The hard templating approach allows a good replication of the solid template but the difficulty of this method lies in the elimination step of this template. Meanwhile, soft templating approach does not have this drawback and may lead to porous ceramics with more varied structures depending on the SDA used. The complexity of this approach is the template replication step.

Made available in DSpace on 2016-06-02T19:55:24Z (GMT). No. of bitstreams: 1 2075.pdf: 4577723 bytes, checksum: 80abdc876165c000f61328875ff2a061 (MD5) Previous issue date: 2008-10-20 / Financiadora de Estudos e Projetos / Mixed oxides with perovskite structure have high potential as catalysts in gas depollution processes and particularly in the abatement of nitrogen oxides (NOx). Such solids could be considered as a promising alternative for the replacement of noble metals based catalysts, whose use is predominant. Great flexibility of composition, easy synthesis, low cost and high thermal stability justify the special interest in these materials. However, the low specific surface areas (<10 m2/g) of these solids, when prepared by conventional methods, limit your use in catalytic processes. Some efforts have been made in order to overcome that disadvantage. Nevertheless, the preparation of high surface area ternary or multinary oxides is not easy once their synthesis is associated with solid state reactions carried out at high temperatures. Considering the discussed context, perovskites were obtained in this work by means of a conventional method or via sequencial nanocasting. In the first case, perovskites with LaFe1-xCoxO3 (x = 0, 0.2, 0.3, 0.4, 0.5 and 1) nominal compositions were prepared using the citrate method and nitrate salts as inorganic precursors. In the second case, LaFeO3 and LaFe0.6Co0.4O3 perovskites were obtained by nanocasting using Fluka 05120 activated carbon, Black Pearls 2000 black carbon (Cabot Corporation), and porous carbons nanocasted in Aerosil 200 pyrogenic silica and sílica-SBA-15 mesoporous molecular sieve. X-ray diffraction (XRD), N2 sorption measurements, X-ray fluorescence (XRF), hydrogen temperature programmed reduction (H2-TPR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry (TG) were used to characterize the studied solids. The catalytic activity of the prepared perovskites was evaluated in the reduction of NO to N2 with CO and in the oxidation of the latter compound to CO2. According to the obtained results, it was evident that in comparison with the conventional route, the nanocasting technique using carbons as hard template was efficient to obtain the pure perovskite phase with specific surface areas substantially higher (25 a 49 m2/g). The prepared perovskites were highly active and selective in the reduction of NO to N2 with CO, as well as in the oxidation of the latter compound to CO2. The most active samples were those whose B sites contain up to about 30 % Co. However, the activity of these catalysts decreases strongly with the presence of O2 or water steam. The La-Fe nanocasted binary perovskites showed, in the studied reactions, remarkable higher catalytic activity than the perovskite with the same composition prepared using the conventional method. The higher activity of these materials was related with the increase of their specific surface area. The nanocasted ternary perovskites with LaFe0.6Co0.4O3 composition, despite of the significant increase in their specific surface area, did not show a considerable increase in their activity. This result is in agreement with the behaviour of La-Fe-Co ternary perovskites, in which Co occupies a proportion of B sites greater than 30 %. / Óxidos mistos com estrutura perovskita apresentam alto potencial como catalisadores em processos de despoluição de gases e particularmente no abatimento de óxidos de nitrogênio (NOx). Tais sólidos são uma alternativa promissora para substituição de catalisadores à base de metais nobres, cujo uso é predominante. Vantagens como grande flexibilidade de composição, fácil síntese, baixo custo e elevada estabilidade térmica justificam o especial interesse por esses materiais. Contudo, as baixas áreas superficiais específicas desses sólidos (< 10 m2/g), quando sintetizados por métodos convencionais, limitam o seu uso em processos catalíticos. Algumas tentativas têm sido feitas no sentido de contornar essa desvantagem. No entanto, a obtenção de óxidos ternários ou multinários de alta área superficial específica é especialmente difícil, uma vez que sua síntese está associada a reações no estado sólido realizadas em temperaturas elevadas. Considerando o contexto discutido, neste trabalho foram obtidas perovskitas através de método convencional ou via nanomoldagem seqüencial. No primeiro caso, perovskitas com composição nominal LaFe1-xCoxO3 (x = 0; 0,2; 0,3; 0,4; 0,5 e 1) foram preparadas utilizando o método do citrato e sais de nitratos como precursores inorgânicos. No segundo caso, perovskitas LaFeO3 e LaFe0,6Co0,4O3 foram obtidas por nanomoldagem utilizando carbono ativado Fluka 05120, negro de fumo Black Pearls 2000 (Cabot Corporation), e carbonos porosos nanomoldados em sílica pirogênica Aerosil 200 e peneira molecular mesoporosa sílica-SBA-15. Difração de raios X (DRX), medidas de adsorção/dessorção de N2, fluorescência de raios X (FRX), redução com hidrogênio a temperatura programada (RTP-H2), microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET), espectroscopia no infravermelho por transformada de Fourier (IV) e termogravimetria (TG) foram utilizadas para caracterizar os sólidos estudados. A atividade catalítica das perovskitas preparadas foi avaliada na redução de NO a N2 com CO e na oxidação desse último composto a CO2. De acordo com os resultados obtidos, ficou evidente que em comparação com a rota convencional, a técnica de nanomoldagem utilizando moldes de carbono foi eficiente na obtenção da fase perovskita pura com área superficial específica substancialmente maior (25 a 49 m2/g). As perovskitas preparadas foram altamente ativas e seletivas na redução de NO a N2 com CO, bem como na oxidação desse último composto a CO2, sendo mais ativas aquelas cujos sítios B contêm até cerca de 30 % de Co. A presença de O2 ou vapor de água, entretanto, reduz fortemente a atividade desses catalisadores. As perovskitas binárias La-Fe nanomoldadas apresentaram, nas reações estudadas, atividade catalítica consideravelmente superior a da perovskita com a mesma composição preparada pelo método convencional. A maior atividade desses materiais foi relacionada com o aumento da sua área superficial específica. As perovskitas nanomoldadas ternárias com composição LaFe0,6Co0,4O3, apesar do significativo aumento na sua área superficial específica, não apresentaram um aumento considerável na atividade, fato esse condizente com o comportamento de perovskitas ternárias La-Fe-Co, nas quais o Co ocupa uma proporção de sítios B superior a 30 %.