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Preparação e caracterização de catalisadores baseados em hidrotalcitas oligovanadatos pilarizadas; Preparation and characterization of catalysts based on pillared oligovanadate hydrotalcite

Cipolli, Flávia de Almeida
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 04/05/2012 PT
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Óxidos mistos são potencialmente utilizados como catalisadores por apresentarem áreas superficiais específicas elevadas, estabilidade térmica e uma distribuição homogênea dos cátions inseridos na estrutura. Nas últimas décadas tem sido investigado o uso de óxidos metálicos de transição como catalisadores para a oxidação seletiva de alcanos de baixo peso molecular. Atualmente a investigação vem sendo explorada com o uso de vanádio como metal ativo em catalisadores para a produção de parafinas leves. O objetivo deste trabalho foi preparar e caracterizar óxidos mistos V-Mg-Al. Para a obtenção dos óxidos, foram preparados, como precursores, compostos tipo hidrotalcita (hidróxidos duplos lamelares, LDHs) de Mg-Al intercalados com V2O7 4-, HV2O7 3- e VO3 -. Os precursores tipo hidrotalcitas oligovanadatos pilarizadas foram sintetizados por dois métodos diferentes, dos quais o primeiro consiste em uma reação de coprecipitação sob pH variável, a partir da mistura das soluções de nitrato de magnésio, nitrato de alumínio e metavanadato de sódio. Por este método foram preparados os compostos LDH-MgAl(V2O7)c, LDHMgAl(HV2O7)c e LDH-MgAl(VO3)c. O segundo método foi o de troca aniônica, pelo qual os íons vanadatos substituem os íons interlamelares de um precursor previamente preparado. O precursor foi sintetizado através da mistura das soluções de nitratos de sódio...

Desenvolvimento de materiais catalíticos à base de óxidos mistos para a decomposição do monopropelente peróxido de hidrogênio; Development of catalytic materials based on mixed oxides for the decomposition of hydrogen peroxide materials monopropellant

Pereira, Luís Gustavo Ferroni
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/04/2014 PT
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Este trabalho teve como objetivo o desenvolvimento de materiais catalíticos à base de óxidos mistos, de baixo custo, para serem empregados como catalisadores mássicos, na decomposição do peróxido de hidrogênio 90%, em massa, possibilitando múltiplas partidas a frio em um micropropulsor de satélites a monopropelente. Foram utilizados diferentes métodos de síntese de óxidos mistos com altos teores de manganês e cobalto. Os materiais foram avaliados, preliminarmente, na decomposição espontânea do peróxido de hidrogênio em bancada (teste da gota). Em seguida, os catalisadores com melhores desempenhos foram selecionados e testados em um micropropulsor de 2N, onde foram monitorados o empuxo, a pressão e a temperatura da câmara do propulsor. Todos os catalisadores foram caracterizados por Adsorção de Nitrogênio, Termogravimetria, Espectroscopia Fotoeletrônica de Raios-X, Difratometria de Raios-X e Resistência Mecânica à Compressão Radial, visando correlacionar suas propriedades físico-químicas com suas atividades na decomposição catalítica do peróxido de hidrogênio concentrado. Os catalisadores denominados MnAl2 e Co4MnAl, sintetizados pelo método da co-precipitação em solução aquosa, foram aqueles que apresentaram os melhores resultados...

Análise térmica aplicada à síntese e caraterização de óxidos mistos de níquel e terras raras; Thermal analysis applied to the synthesis and characterization of mixed oxides of nickel and rare earth

Silva, Adélia Maria Lima da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 15/01/1999 PT
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Este trabalho apresenta um estudo sistemático sobre síntese, caracterização e análise térmica aplicada a óxidos mistos dos tipos TR2NiO4 [TR = La, Eu e Y (III)] e TRNiO3 [TR = Pr, Nd e Sm (III)]. Os primeiros óxidos foram obtidos a partir da decomposição térmica de acetatos de terras raras e níquel utilizando-se três métodos distintos: (1) mistura mecânica; (2) evaporação do solvente e (3) cristalização com acetona. Os acetatos simples e binários foram caracterizados por análise elementar, espectroscopia de absorção na região do infravermelho, difração de raios X, TG/DTG, DSC e DTA. Os resultados revelaram a formação de sais binários quando utilizaram-se os métodos 2 e/ou 3. Os produtos da decomposição térmica foram basicamente os óxidos individuais e após tratamento térmico obteveram-se os óxidos desejados. Os óxidos TRNiO3 foram preparados através de três métodos diferentes: (1) mistura de óxidos; (2) precipitação simultânea de hidróxidos e (3) processo sol-gel. Estas amostras foram sinterizadas em temperaturas 650 ≤ T ≤ 1000°C e sob pressões de até 70 atm de O2, caracterizadas por difração de raios X, resistividade elétrica, microscopia eletrônica de varredura e calorimetria exploratória diferencial. Os resultados indicaram que o método sol-gel produziu óxidos monofásicos. Os outros dois métodos...

Mesoporous zirconia-based mixed oxides as versatile acid catalystsfor producing bio-additives from furfuryl alcohol and glycerol

Castanheiro, J; Neves, P; Russo, P; Fernandes, A; Antunes, M; Farinha, J; Pillinger, M; Ribeiro, M; Valente, A
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
POR
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Mesostructured zirconium-based mixed oxides (MZM) are versatile solid acid catalysts for the chemicalvalorisation of biomass, within sugar and fatty acid platforms of biorefineries. MZM catalysts contain-ing tungsten and/or aluminium were prepared via a templating route that allows the texture and acidproperties to be improved. Their catalytic potential was explored for synthesising different types ofinteresting oxygenated fuel bio-additives, specifically levulinate esters, furfuryl alkyl ethers and glyc-erol acetals of the type 1,3-dioxolane and 1,3-dioxane. Levulinate esters are synthesised from furfurylalcohol (FA), which is produced industrially from lignocelluloses; the acetals are obtained from glycerol,which is a coproduct of the industrial production of biodiesel. The performances of the MZM catalystshave been compared with those of zirconium–(tungsten and/or aluminium) mixed oxides synthesisedvia conventional co-precipitation (without a template). Structure–activity relationships were establishedwhich reveal advantages of the templating route used for the synthesis of the MZM catalysts. The MZMcatalysts were more active and led to higher total yields of bio-additives (e.g. up to 86% yield at 100% FAconversion, 140◦C...

Dielectric properties of Al-Nb amorphous mixed oxides

Di Franco, F.; Santamaria, M.; Di Quarto, F.; La Mantia, F.; Sá, A. I. Correia de; Rangel, C. M.
Fonte: The Electrochemical Society Publicador: The Electrochemical Society
Tipo: Artigo de Revista Científica
Publicado em //2013 ENG
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An impedance study of amorphous thin oxide films grown on sputtered Al-Nb alloys is presented. The characterization of the electronic properties of mixed amorphous oxide on the basis of the theory of amorphous semiconductor Schottky barrier has been carried out for anodic film on Al-92at.%Nb in a very detailed manner. The semiconductor to insulator transition of formed oxides as a function of the alloy composition at fixed final voltage has been supported by differential admittance study. A possible rationale for this transition has been suggested taking into account the changes of solid state properties, optical bandgap and electronic structure of the films, derived from the fitting of the differential admittance curves at different frequencies.

Influence of basic properties of Mg,Al-mixed oxides on their catalytic activity in knoevenagel condensation between benzaldehyde and phenylsulfonylacetonitrile

Pérez,Caridad Noda; Monteiro,José Luiz Fontes; López Nieto,Jose Manoel; Henriques,Cristiane Assumpção
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 EN
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The catalytic performance of Mg,Al-mixed oxides (MO20, MO25 and MO33) derived from hydrotalcites was evaluated in the Knoevenagel reaction between benzaldehyde and phenylsulfonylacetonitrile at 373 and 383 K. The best results were obtained for the sample MO20 that presented the highest basic sites density and external area and the smallest crystallite sizes. The relative amount of basic sites with weak to intermediate strength also played an important role on catalytic performance. By increasing the catalyst content from 1 to 5 wt.% at 383 K, a complete conversion of the reactants is attained, producing α-phenylsulfonylcinnamonitrile with a selectivity of 100%.

Influence of thermal treatments on the basic and catalytic properties of Mg,Al-mixed oxides derived from hydrotalcites

Bastiani,R.; Zonno,I. V.; Santos,I. A. V.; Henriques,C. A.; Monteiro,J. L. F.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2004 EN
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This work studied the influence of calcination conditions on basic properties and catalytic performance of Mg,Al-mixed oxides derived from a hydrotalcite sample (Al/(Al+Mg)=0.20). Various heating rates, calcination atmospheres and lengths of calcination at 723K were evaluated. TPD of CO2 and retroaldolization of diacetone alcohol (DAA) were used to determine the basic properties of the mixed oxides. The basic site density determined by TPD of CO2 showed a better correlation with catalytic activity for acetone/citral aldol condensation than the relative basicity obtained from retroaldolization of DAA. Calcination atmosphere was the parameter that influenced most the basic and the catalytic properties of the Mg,Al-mixed oxides, with calcination under dry air being the best choice.

Vanadium oxides supported on hydrotalcite-type precursors: the effect of acid-base properties on the oxidation of isopropanol

Meira,D. M.; Cortez,G. G.; Monteiro,W. R.; Rodrigues,J. A. J.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2006 EN
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Vanadium oxide supported on hydrotalcite-type precursors was studied in the oxidation of isopropanol. Hydrotalcites with different y = Mg/Al ratios were synthesized by the method of coprecipitation nitrates of Mg and Al cations with K2CO3 as precipitant. The decomposition of these hydrotalcite precursors at 450°C yielded homogeneous MgyAlOx mixed oxides that contain the Al+3 cations totally incorporated into the MgO framework. The materials were characterized by chemical analysis, BET superficial area, X-ray diffraction, temperature-programmed reduction (TPR) and the reaction of isopropanol, a probe molecule used to evaluate the acid-base properties. The results of TPR showed that the reducibility of V+5 decreased with the increase in magnesium loading in catalysts. The X-ray diffraction patterns of Al-rich hydrotalcite precursors showed the presence of crystalline phases of brucite and gibbsite. It was shown that chemical composition, texture, acid-base properties of the active sites and also Mg/Al ratio strongly affect the formation of the products in the oxidation of isopropanol. The Al-rich catalysts were much more active than the Mg-rich ones, converting isopropanol mainly to propylene.

Photocatalytic discoloration of reactive blue 5g dye in the presence of mixed oxides and with the addition of iron and silver

Souza,M. C. P; Lenzi,G. G; Colpini,L. M. S; Jorge,L. M. M; Santos,O. A. A
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2011 EN
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This work reports the use of cerium - titania - alumina - based systems modified with Ag and Fe by the wetness impregnation method for the discoloration of blue 5G dye. The techniques employed to characterize the photocatalysts were: temperature - programmed reduction (TPR), X - ray diffraction (XRD), specific surface area, average pore volume, and average pore diameter. The characterization results indicated that the photocatalysts had different crystalline structures and textural properties. Discoloration with the mixed oxide photocatalyst CeO2 - TiO2 - Al2O3 gave a result similar to that of TiO2. On the other hand, the addition of Ag and Fe to the mixed oxide increased the discoloration and reaction rates of reactive blue 5G dyes.

Synthesis and characterization of novel ZrO2-SiO2 mixed oxides

Santos,Milena Araújo Ferreira e; Lôbo,Ivon Pinheiro; Cruz,Rosenira Serpa da
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 EN
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In this study the mixed oxides ZrO2-SiO2, were synthesized by the sol-gel method with a molar ratio of 95:5 (Si/metal) and characterized by X-ray diffraction, absorption-desorption of N2, Fourier transform infrared spectroscopy, thermal gravimetric analysis, temperature-programmed desorption of ammonia, and acidity test by titration. The synthesized materials, which are amorphous to X-rays, are composed of a mixture of micro- and mesopores. They show a higher acid strength than the separate oxides, indicating that the ZrO2 is highly dispersed in the silica matrix.

Nanoporous composites prepared by a combination of SBA-15 with Mg–Al mixed oxides. Water vapor sorption properties

Pérez-Verdejo, Amaury; Sampieri, Alvaro; Pfeiffer, Heriberto; Ruiz-Reyes, Mayra; Santamaría, Juana-Deisy; Fetter, Geolar
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 07/08/2014 EN
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This work presents two easy ways for preparing nanostructured mesoporous composites by interconnecting and combining SBA-15 with mixed oxides derived from a calcined Mg–Al hydrotalcite. Two different Mg–Al hydrotalcite addition procedures were implemented, either after or during the SBA-15 synthesis (in situ method). The first procedure, i.e., the post-synthesis method, produces a composite material with Mg–Al mixed oxides homogeneously dispersed on the SBA-15 nanoporous surface. The resulting composites present textural properties similar to the SBA-15. On the other hand, with the second procedure (in situ method), Mg and Al mixed oxides occur on the porous composite, which displays a cauliflower morphology. This is an important microporosity contribution and micro and mesoporous surfaces coexist in almost the same proportion. Furthermore, the nanostructured mesoporous composites present an extraordinary water vapor sorption capacity. Such composites might be utilized as as acid-base catalysts, adsorbents, sensors or storage nanomaterials.

Síntese e Caracterização de Titanatos de Cobalto e Níquel, dopados com Praseodímio, obtidos a partir da decomposição de Nitrilotriacetatos

Fonseca, Saulo Gregory Carneiro
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Química; Físico-Química; Química Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Química; Físico-Química; Química
Tipo: Dissertação Formato: application/pdf
POR
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In recent years, studies about the physicochemical properties of mixed oxides, call attention of the scientific community, properties like as piezoelectricity, photoluminescence, or applications as catalysts, arise in these compounds, when their chemical compositions are modified, in this context some routes are employed in the synthesis of these materials, among which can be cited these methods: ceramic, combustion, co-precipitation, Pechini or polymeric precursor method, hydrothermal, sol-gel; these routes are divided into traditional routes or chemical routes. In this work were synthesized oxides with variable composition, from the thermal decomposition of titanium, cobalt, nickel and praseodymium nitrilotriacetates. The nitrilotriacetates were characterized by IR Spectroscopy (FTIR), Thermogravimetric (TG/ DTG) and Differential Scanning Calorimetry (DSC), while oxides have been characterized by X-ray diffraction (XRD), Spectrofluorimetry and IR Spectroscopy (FTIR). From FTIR data, it was demonstrated that the displacement of the band corresponding to the carboxylate group (νCOOH) at 1712 cm-1, present in nitrilotriacetic acid (H3NTA), for 1680-1545 cm-1, these stretches are characteristics of coordinated nitrilotriacetates...

Thermal Diffusivity and Conductivity of Thorium - Plutonium Mixed Oxides

COZZO Cedric; STAICU Dragos; SOMERS Joseph; FERNANDEZ A.; KONINGS Rudy
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Articles in Journals Formato: Printed
ENG
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The thermal diffusivity of (Th,Pu)O2 (with 3, 8 and 30 wt.% PuO2) mixed oxides and of the single oxides PuO2 and ThO2 was measured using the laser flash technique. In several samples, a further degradation in the thermal diffusivity due to auto-irradiation damage was noted, and a recovery could be achieved by thermal treatment. The ThO2 and (Th,Pu)O2 samples with 3 and 8 wt.% PuO2 were found to be semitransparent and had to be coated with C for the thermal diffusivity measurement. The experimental thermal conductivity of the fuels was calculated and analysed. The introduction of PuO2 in the ThO2 was found to have an effect similar to that observed in (U,Pu)O2 mixed oxides: small decrease in the range 3-8 wt.% PuO2 and higher decrease at 30 wt.% PuO2 content. Using the classical phonon transport model in crystal structures, a new correlation for the thermal conductivity of (Th,Pu)O2 mixed oxides is proposed and is comparedto the results of another correlation built after the Klemens-Callaway theory. Keywords: thermal diffusivity, thermal conductivity, Th-MOX, laser-flash.; JRC.E.3-Materials research

Heat capacity, thermal conductivity and thermal diffusivity of uranium-americium mixed oxides

VALU SORIN; STAICU Dragos; BENES ONDREJ; KONINGS Rudy; LAJARGE Patrick
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Articles in Journals Formato: Printed
ENG
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The enthalpy increments of ðU1y; AmyÞO2x mixed oxides with y = 0.0877 and 0.1895 and x = 0.01–0.03 were measured using drop calorimetry in the temperature range 425–1790 K and the heat capacity was obtained as differential of the obtained enthalpy increments with respect to temperature. The thermal diffusivity was measured using the laser flash technique from 500 to 1550 K. The thermal conductivity was calculated from the measured thermal diffusivity, density and heat capacity. Measured enthalpy increments of the ðU1y; AmyÞO2x solid solutions are very close to the end members, indicating no excess contribution. The derived heat capacities for the two intermediate compositions are slightly higher than that of UO2 and in a good agreement with literature data of AmO2 up to 1100 K. For the thermal conductivity of (U, Am)O2x mixed oxides a correlation using the classical phonon transport model in crystal structures is proposed.; JRC.E.3-Materials research

Surface Reduction of Neptunium Dioxide and Uranium Mixed Oxides with Plutonium and Thorium by Photocatalytic Reaction with Ice

CAKIR PELIN; ELOIRDI Rachel; HUBER Frank; KONINGS Rudy; GOUDER Thomas
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Tipo: Articles in periodicals and books Formato: Online
ENG
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The surface reductions of neptunium dioxide (NpO2) and two mixed oxides of uranium (U−Pu−O2 and U−Th−O2) with adsorbed water ice were studied by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively). The oxides were produced as thin films by reactive sputter deposition. Water was condensed as a thick ice overlayer on the surface at low temperature. Subsequent warming led to desorption of the ice. When warmed up under ultraviolet light (UV light, HeI and HeII radiation), the surface was reduced. NpO2 was reduced to surface neptunium sesquioxide (Np2O3). In the uranium−plutonium mixed oxide (U−Pu MOX), plutonium was reduced from plutonium dioxide (PuO2) to plutonium sesquioxide (Pu2O3). In uranium−thorium mixed oxide (U−Th MOX), the uranium was reduced from hyperstoichiometric uranium dioxide (UO2+x) to stoichiometric UO2 but not to lower oxides: the lowest thermodynamically stable oxides are formed. In the mixed oxides, uranium reduction seems to be activated for oxides with both thorium and plutonium. Surface reduction is explained as a photocatalytic reaction of the surface, triggered by the excitation of electrons from the valence (or impurity) band into the conduction band. The enhancement of reactivity of the mixed oxides compared to pure uranium is explained by the higher band gap of thorium dioxide (ThO2) and plutonium dioxide (PuO2) compared to uranium dioxide (UO2).; JRC.E.6-Actinide research

Construção de sensores eletroquímicos utilizando como matriz materiais cerâmicos SI 'O IND. 2'/ 'M IND. X' 'O IND. Y', e materiais cerâmicos eletricamento condutores SI 'O IND. 2'/ C/'M IND. X' 'O IND. Y', preparados pelo processo sol-gel; Construction of electrochemical sensors using ceramic materials SI 'O IND. 2'/ 'M IND. X' 'O IND. Y' and electrically conducting ceramic materials SI 'O IND. 2'/C/ 'M IND. X' 'O IND. Y' as matrix, prepared for the sol-gel process

Thiago da Cruz Canevari
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/04/2012 PT
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Este trabalho tem como objetivo sintetizar e caracterizar três materiais diferentes obtidos pelo processo sol-gel: SiO2/SnO2, SiO2/SnO2/Sb2O5 e o filme de Nb2O5 formado sobre a superfície do material cerâmico SiO2/C e utilizá-los como matriz no desenvolvimento de sensores eletroquímicos. O óxido misto, SiO2/SnO2, foi sintetizado utilizando como fonte de SnO2, SnCl4.5H2O, utilizando diferentes catalisadores ácidos HCl e HF (F-). As diferenças estruturais e morfológicas apresentadas pelos óxidos mistos, SiO2/SnO2, em virtude do uso de diferentes catalisadores ácidos, foram investigadas por meio das isotermas de adsorção/dessorção de N2, espectroscopia de fluorescência de raios X, difração de raios X, espectroscopia na região do infravermelho, microscopia eletrônica de transmissão, espectroscopia fotoeletrônica de raios X (XPS), medidas de condutividade elétrica e medidas eletroquímicas visando a utilização destes óxidos mistos como matriz suporte para desenvolvimento de sensores eletroquímicos. O material, SiO2/SnO2/Sb2O5, foi obtido por meio da incorporação do Sb2O5 sobre a superfície do óxido misto, SiO2/SnO2, previamente sintetizado utilizando como fonte de SnO2, o dibutildiacetato de estanho. Este recobrimento foi realizado utilizando...

Spectroscopic characterization of Mn-Co-Ce mixed oxides, active catalysts for COPROX reaction

Gómez, Leticia Ester; Miro, Eduardo Ernesto; Boix, Alicia Viviana
Fonte: Pergamon-elsevier Science Ltd Publicador: Pergamon-elsevier Science Ltd
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
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Mn-Co-Ce mixed oxides are active and selective catalysts for the CO preferential oxidation (COPROX), which is a promising process for the purification of hydrogen streams. In this work, we report a careful spectroscopic characterization of the said system, with the aim of relating its physical chemistry properties to the catalytic behavior. In all the Co-Mn-Ce samples, we detected the formation of partially developed (Mn,Co)3O4 mixed spinels. The presence of these species, which can be reduced during the TPR experiments at an intermediate temperature range (300-600°C), was also suggested by XRD and LRS. XPS results show that in all cases the catalytic surface is enriched in Mn, while the opposite occurs for Co. As regards the catalytic activity, we observed that the best formulations were those containing intermediate Mn/Co ratios (1/4 and 1/1), which can be ascribed to the promoting effect of Mn in improving the redox properties of Co active sites and provoking an increase in surface area. The best catalyst, which has a Mn/Co ratio of 1/4, was very stable after 75 h of time-on-stream with CO2 included in the feed.; Fil: Gómez, Leticia Ester. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET -Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica; Argentina;; Fil: Miro...

Films delgados mesoporosos de óxidos metálicos, mixtos e híbridos. Hacia un diseño racional de nanomateriales funcionales; Mesoporus metallic, mixed and hybrid oxide thin films. Towards a rational design of functional nanomaterials

Angelomé, Paula C.
Fonte: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires Publicador: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
Tipo: info:eu-repo/semantics/doctoralThesis; tesis doctoral; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2008 SPA
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Los óxidos mesoporosos son materiales que presentan poros monodispersos (de tamaños de entre 2 y 50 nm) altamente ordenados, de elevada área específica (100 - 1000 m2/g). Se sintetizan mediante la combinación de dos procesos: reacciones sol gel, que dan lugar al material inorgánico o híbrido, y autoensamblado de moléculas anfifílicas, que actúan como molde de los poros. Entre las aplicaciones de estos materiales se encuentran: (foto)catálisis, sorción, sensores y otros dispositivos, etc. En este trabajo se realizó un estudio de la síntesis de films delgados mesoporosos de óxidos metálicos, mixtos e híbridos orgánico-inorgánicos. Estos films delgados se obtuvieron mediante dip coating a través del proceso conocido como Autoensamblado Inducido por Evaporación, y fueron caracterizados mediante una gran variedad de técnicas de microscopía, espectroscopia y difracción, de manera de conocer cabalmente la estructura a nivel micro, meso y macroscópico. En una primera parte, se presenta la síntesis de films delgados mesoporosos de TiO2, ZrO2 y óxidos mixtos Ti-Si, Zr-Si. En todos los casos, se estudió la relación existente entre la estructura del material obtenido y las condiciones de síntesis (composición del sol...

Discussing the use of modified ceria as support for Pt catalysts on water-gas shift reaction.

Fraga, Marco André; Farias, Andréa Maria Duarte de; Nguyen-Thanh, Danh
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
EN
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CeO2 was doped with 25 wt.% of MeOx (Me = Zr, Sm, or La) and Ce75Me25 mixed oxides were obtained. Pt (1 wt.%) was then deposited on these oxides and CeO2. The resulting catalysts were tested for the water–gas shift (WGS) reaction in amixture whose composition was 5.49% CO, 4.10% CO2, 9.71% H2, 30.75% H2O. Subsequently, CeO2 was loaded with various levels of ZrO2 (y wt.%), which gave another set of Ce100 yZry (y = 25, 40, 50, and 75) supports and the respective catalysts were also tested for the WGS. While XRD analysis showed that all the mixed oxides had retained the cubic structure of CeO2, Raman analysis suggested that the doped ceria supports contain more oxygen vacancies resulting in higher oxygen mobility than CeO2, which were corroborated by the TPR analyses of all modified catalysts

Effect of the acid-base properties of Mg-Al mixed oxides on the catalysts deactivation during aldol condensation reactions

Díez,V.K.; Apesteguía,C.R.; Di Cosimo,J.I.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2003 EN
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The effect of chemical composition of Mg-Al mixed oxides on both the acid-base properties and the deactivation process during the gas phase self-condensation of acetone was studied. The activity and selectivity for acetone oligomerization depended on the catalyst acid-base properties. Mg-rich catalysts selectively yielded mesityl oxides whereas Al-rich Mg yAlOx oxides produced mainly isophorone. The initial deactivation rate, increased linearly with the density of surface basic sites, thereby suggesting that although Mg yAlOx oxides promote the self-condensation of acetone by both acid- and base-catalyzed mechanisms, the deactivation rate would be closely related to the surface basic properties. The Mg yAlOx activity declines in the acetone oligomerization reaction due to a blockage of both base and acid active sites by a carbonaceous residue formed by secondary reactions. The amount and the nature of the carbon deposits were characterized by temperature-programmed oxidation technique. Mg yAlOx and Al2O3 formed more and heavier coke than pure MgO but the latter deactivates faster. The deactivation rate and coke composition are defined by the nature of the active site involved in the coke-forming reactions at different catalyst compositions rather than by the carbon amount or polymerization degree.