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Adsorption kinetic, thermodynamic and desorption studies of phosphate onto hydrous niobium oxide prepared by reverse microemulsion method

RODRIGUES, Liana Alvares; SILVA, Maria Lucia Caetano Pinto da
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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A type of Nb(2)O(5)center dot 3H(2)O was synthesized and its phosphate removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The phosphate adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model with which the maximum P adsorption capacity was estimated to be 18.36 mg-Pg(-1). The peak appearing at 1050 cm(-1) in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The positive values of both Delta H degrees and Delta S degrees suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. Delta G degrees values obtained were negative indicating a spontaneous adsorption process. A phosphate desorbability of approximately 68% was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive sites on the surface of the adsorbent. The immobilization of phosphate probably occurs by the mechanisms of ion exchange and physicochemical attraction. Due to its high adsorption capacity...

Surfactant-assisted intercalation of high molecular weight poly(ethylene oxide) into vanadyl phosphate di-hydrate

Ferreira, Joao Paulo L.; Oliveira, Herenilton Paulino
Fonte: PERGAMON-ELSEVIER SCIENCE LTD; OXFORD Publicador: PERGAMON-ELSEVIER SCIENCE LTD; OXFORD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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A high molecular weight poly(ethylene oxide)/layered vanadyl phosphate di-hydrate intercalation compound was synthesized via the surfactant-assisted approach. Results confirmed that surfactant molecules were replaced with the polymer, while the lamellar structure of the matrix was retained, and that the material presents high specific surface area. In addition, intercalation produced a more thermally stable polymer as evidenced by thermal analysis. (C) 2011 Elsevier Ltd. All rights reserved.; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq); CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico); FAPESP (Fundacao de Amparo Pesquisa do Estado de So Paulo); FAPESP (Fundacao de Amparo Pesquisa do Estado de So Paulo); CAPES (Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior); Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)

Niobatos lamelares: síntese, caracterização, reatividade e estudo das propriedades luminescentes; Layered Niobates: Synthesis, characterization, reactivity and luminescenece properties study

Bizeto, Marcos Augusto
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 07/07/2003 PT
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O estudo apresentado nesta Tese diz respeito à química dos niobatos lamelares e aborda a síntese, caracterização, avaliação da reatividade intracristalina e das propriedades luminescentes desses materiais. Os niobatos lamelares utilizados foram o hexaniobato K4Nb6O17, o triniobato KNb3O8 e as perovskitas lamelares K1-xLnxCa2-xNb3O10 (Ln = La, Eu e x = 0,02; 0,25; 0,50; 0,75 e 1,00). Esses materiais são constituídos de lamelas que apresentam cargas negativas e a região interlamelar é preenchida por íons de potássio que mantêm a neutralidade dos sistemas. A reatividade intracristalina dos niobatos lamelares foi avaliada frente à intercalação de espécies simples como a butilamina e volumosas como o macrociclo porfirínico, o polioxocátion de alumínio e compostos orgânicos de silício. A alta densidade de carga lamelar dos niobatos lamelares dificulta a intercalação direta de espécies volumosas, o que fez com que novas rotas sintéticas fossem desenvolvidas a fim de permitir a imobilização de tais espécies na região interlamelar. As metodologias sintéticas desenvolvidas foram baseadas, principalmente, no uso de dispersões coloidais dos niobatos esfoliados que, a partir da reestruturação na presença da espécie convidada de interesse...

Voltammetric performance and application of a sensor for sodium ions constructed with layered birnessite-type manganese oxide

Martinez, Murilo T.; Lima, Alex S.; Bocchi, Nerilso; Teixeira, Marcos F. S.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 519-525
ENG
Relevância na Pesquisa
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 05/01296-4; Processo FAPESP: 07/00600-7; The preparation and electrochemical characterization of a carbon paste electrode modified with layered birnessite-type manganese oxide for use as a sodium sensor is described. The effects of powder synthesis process (sol-gel and redox precipitation) for birnessite on the electrochemical activity of the sensor was investigated by cyclic voltammetry. The carbon paste electrode modified with birnessite-type manganese oxide that was synthesized by the sol-gel method showed a best electrochemical for sodium ions. The detection is based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and consequently the sodium ions extraction into the birnessite structure. The best voltammetric response was obtained for an electrode composition of 15% (w/w) birnessite oxide in the paste, aTRIS buffer solution of pH 8.0 and a scan rate of 50 mVs(-1). A sensitive linear voltammetric response for sodium ions was obtained in the concentration range of 7.89 x 10(-5) to 3.49 x 10(-4) mol L(-1) with a slope of 37.5 mu A L mmol(-1) and a detection limit (3 sigma/slope) of 3.43 x 10(-5) mol L(-1) using cyclic voltammetry. Under the working conditions...

Properties of individual YBCO layers in a two-layered design for energy-efficient digital data cables

Yonamine, Anne H.; Dos Santos, Dayse I.; Pan, Alexey V.; Fedoseev, Sergey A.; Oakden, David; Parsons, Bradley; Shcherbakova, Olga V.; Golovchanskiy, Igor A.; Masilamani, Nandhagopal; Webber, Robert J.; Mukhanov, Oleg A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
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We are developing two-layered Yttrium Barium Copper Oxide (YBCO) thin film structures for energy efficient data links for superconducting electronics and present the results of their property measurements. High temperature superconductors (HTS) are advantageous for the implementation of energy-efficient cables interconnecting low temperature superconductor-based circuits and other cryogenic electronics circuits at higher temperature stages. The advantages of the HTS cables come from their low loss and low dispersion properties, allowing ballistic transfer of low power signals with very high bandwidth, low heat conduction and negligible inter-line crosstalk. The microstrip line cable geometry for typical materials is a two-layered film, in which the two superconducting layers are separated by an insulation layer with a minimized permittivity. We have made a proof of concept design of two YBCO films grown by pulsed laser deposition and then assembled into a sandwich with uniform insulating interlayer of tens of micrometers thick. We report on results obtained from such systems assembled in different ways. Structural and electromagnetic properties have been examined on individual films and on the corresponding sandwich composite. © 2013 IEEE.

Chemical modification of niobium layered oxide by tetraalkylammonium intercalation

Shiguihara,Ana L.; Bizeto,Marcos A.; Constantino,Vera R. L.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
Relevância na Pesquisa
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Chemical modification of the layered K4Nb6O17 material was systematically investigated through the reaction of its proton-exchanged form (H2K2Nb6O17) in alkaline solutions containing tetramethylammonium (tma+), tetraethylammonium (tea+) or tetrapropylammonium (tpa+) cations. The intercalated amount reaches 50% (for tma+), 25% (for tea+) and 15% (for tpa+) of the H2K2Nb6O17 negative charge (concerning the exchange at interlayer I) due to the steric hindrance of larger cations. Hexaniobate samples present (020) basal reflections equal to 23.0, 26.3 and 26.5 Å once intercalated respectively with tma+, tea+ and tpa+. When samples are heated above 200-250 ºC, CO2 evolution is observed; Hofmann elimination reaction is also detected for hexaniobate-tpa+ samples. Scanning electron microscopy images show the predominance of plate-like particles; stick-like particles are also observed for samples containing bulky ions. The intercalation reaction is promoted in the order tma+ > tea+ > tpa+, while the formation of a dispersion of colloidal particles is facilitated in the inverse order.

Facile Graphene Oxide Preparation by Microwave-Assisted Acid Method

Viana,Marcelo M.; Lima,Meiriane C. F. S.; Forsythe,Jerimiah C.; Gangoli,Varun S.; Cho,Minjung; Cheng,Yinhong; Silva,Glaura G.; Wong,Michael S.; Caliman,Vinicius
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2015 EN
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Few-layered graphene oxide (GO) was prepared using a fast and energy-saving method by microwave-assisted acid technique. The oxygenated groups existing on the GO surface were determined using UV-Vis, X-ray photoelectron and Fourier-transform infrared spectroscopies. An oxygenated group percentage of 30% in mass for the GO was observed by thermogravimetric analysis. The reduced few-layered graphene oxide (rGO) film annealed at 110 °C deposited onto a silicon/silica wafer showed expanded graphite-like structure with 0.70 nm between the rGO sheets, as determined by X-ray diffraction. This rGO film exhibited a relatively high electrical conductivity value of 7.36 × 102 S m-1 confirming the good restoration of the π-conjugated system. The prepared GO sample exhibited good stability in water from pH 4 to 12, as determined by its zeta potential, and contained 5 to 9 layers, as determined by atomic force microscopy (AFM) and transmission electron microscopy (TEM).

Towards precise defect control in layered oxide structures by using oxide molecular beam epitaxy

Baiutti, Federico; Christiani, Georg; Logvenov, Gennady
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 08/05/2014 EN
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In this paper we present the atomic-layer-by-layer oxide molecular beam epitaxy (ALL-oxide MBE) which has been recently installed in the Max-Planck Institute for Solid State Research and we report on its present status, providing some examples that demonstrate its successful application in the synthesis of different layered oxides, with particular reference to superconducting La2CuO4 and insulator-to-metal La2− xSrxNiO4. We briefly review the ALL-oxide MBE technique and its unique capabilities in the deposition of atomically smooth single-crystal thin films of various complex oxides, artificial compounds and heterostructures, introducing our goal of pursuing a deep investigation of such systems with particular emphasis on structural defects, with the aim of tailoring their functional properties by precise defects control.

Layer-by-layer self-assembly of porphyrin heterogeneous metal-organic thin films on titanium oxide for photocurrent generation

Joyce, Jennifer
Fonte: University of Limerick Publicador: University of Limerick
Tipo: info:eu-repo/semantics/doctoralThesis; all_ul_research; ul_published_reviewed; ul_theses_dissertations
ENG
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peer-reviewed; Dye-sensitized solar cells (DSSCs) are a class of solar cells of the third generation. DSSCs are cheap and simple to fabricate, exhibit flexible properties, and are not limited by the Shockley-Queisser limit of semiconductor junction solar cells. The efficiency of DSSCs has reached a very promising 12% and DSSCs are currently developed for niche applications under low light conditions. Their performances are limited by undesired electron and hole back transfer and quenching of the photoexcited dyes due to dye-dye and dye-substrate interactions. Overcoming these limitations is the subject of a large research activity worldwide. It is our main hypotheses that a self-assembly scheme based on a metal-organic coordination construction is a valid alternative for the preparation of dye films and that the flexibility in achieving heterogeneous assemblies can be exploited to mitigate the various quenching and current hindering factors. This thesis focuses thus on the development of a layer-by-layer self-assembly method for wet deposition of metal-organic coordination thin films of porphyrin-based dyes and HKUST-1 (Honk Kong University of Science and Technology) metal-organic framework (MOF) on flat titanium oxide substrates. The bottom-up growth protocol has been verified on the basis of X-ray photoelectron spectroscopy (XPS) and visible absorption spectroscopy...

Strukturen, thermischer Abbau und mögliche Anwendungen von Oxidnitraten; Structures, thermal decomposition and possible applications of oxide nitrates

Dill, Simone
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
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Die vorliegende Arbeit beschäftigt sich mit der Synthese und Charakterisierung von bekannten und neuen Oxidnitraten, deren Zersetzungsprodukten und der potentiellen Anwendungen der Oxidnitrate als Precursoren und NOx-Speicher. In Kapitel 3 wurde die thermische Zersetzung von Sr(NO3)2 und Ba(NO3)2, welches in NOx-Speicherkatalysatoren in der Automobilindustrie verwendet wird, untersucht. Um eventuell auftretende Zwischenstufen, bei denen es sich auch um Oxidnitrate handeln könnte, zu isolieren, wurden die Nitrate von Barium und Strontium nur kurz über ihren Schmelzpunkt erhitzt und wieder abgekühlt. Beim Abkühlen der jeweiligen Nitratschmelzen an Luft trat eine neue, unbekannte Phase auf. Dabei handelte es sich um die Verbindungen Sr2(OH)3NO3 bzw. Ba2(OH)3NO3. Die Strukturen dieser Verbindungen wurden anhand von Röntgen-Einkristall- und Pulverdaten bestimmt und verfeinert. In den hexagonalen Kristallstrukturen (P6`2m) dieser Hydroxidnitrate sind die Erdalkalimetallionen von den Hydroxidionen in Form von trigonalen Prismen umgeben. Diese Prismen sind über die trigonalen Flächen entlang der c-Richtung und über Kanten in der ab-Ebene verknüpft. Sie bilden sechseckige Röhren, in denen sich die Nitratgruppen befinden. Die Bildung und Zersetzung von Sr2(OH)3NO3 wurde mit Hilfe von DTA/TG-Messungen untersucht...

Phase diagram of the layered oxide SnO: GW and electron-phonon studies

Chen, Peng-Jen; Jeng, Horng-Tay
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 10/11/2015 EN
Relevância na Pesquisa
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First-principles calculations are performed to study the electronic properties and the electron-phonon interactions of the layered oxide semiconductor SnO. In addition to the high hole mobility that makes SnO a promising material in electronics, it has recently been reported that the semimetallic phase under pressure is superconducting. The superconducting Tc curve exhibits a dome-like feature under pressure and reaches the maximum of 1.4 K at p = 9.2 GPa. Both its crystal structure and the dome-like Tc curve are reminiscent of the Fe-based superconductor FeSe. Motivated by this observation, we investigate the electronic, phonon, and their interactions in SnO using first-principles schemes. GW approximation is adopted to correct the underestimated band gaps, including real and continuous band gaps in the semiconducting and semimetallic phases. The phase diagram showing the semiconductor-to-semimetal transition and the Tc curve has been successfully reproduced. Detailed analysis of the electron-phonon interactions demonstrate the importance of the out-of-plane motions of O atoms and the Sn-s lone pairs for the superconductivity to occur. Our method combining GW and e-ph calculations can be further extended to the study of other materials that undergo insulator-to-superconductor phase transition.

Cleaving-temperature dependence of layered-oxide surfaces

Pennec, Y.; Ingle, N. J. C.; Elfimov, I. S; Varene, E.; Damascelli, A.; Barth, J. V.; Maeno, Y.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/07/2008
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The surfaces generated by cleaving non-polar, two-dimensional oxides are often considered to be perfect or ideal. However, single particle spectroscopies on Sr2RuO4, an archetypal non-polar two dimensional oxide, show significant cleavage temperature dependence. We demonstrate that this is not a consequence of the intrinsic characteristics of the surface: lattice parameters and symmetries, step heights, atom positions, or density of states. Instead, we find a marked increase in the density of defects at the mesoscopic scale with increased cleave temperature. The potential generality of these defects to oxide surfaces may have broad consequences to interfacial control and the interpretation of surface sensitive measurements.

Large Thermopower in a Layered Oxide NaCo_2O_4

Terasaki, I.; Sasago, Y.; Uchinokura, K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/03/1999
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A transition-metal oxide NaCo_2O_4 is a layered oxide in which CoO_2 and Na alternately stack along the c axis. Recently we have found that this compound shows unusually large thermopower with low resistivity, which is comparable to those of Bi_2Te_3. The negative transverse magnetoresistance and the strongly temperature-dependent Hall coefficient suggest that electron correlation dominates the conduction mechanism in NaCo_2O_4.; Comment: 3 pages (LaTeX), 4 EPS figures

Nearly free electrons in the layered oxide superconductor Ag5Pb2O6

Sutherland, Mike; Mann, P. D. A.; Bergemann, Christoph; Yonezawa, Shingo; Maeno, Yoshiteru
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/09/2005
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We present first measurements of quantum oscillations in the layered oxide superconductor Ag5Pb2O6. From a detailed angular and temperature dependent study of the dHvA effect we determine the electronic structure and demonstrate that the electron masses are very light, m^* is approximately equalt to 1.2 m_e. The Fermi surface we observe is essentially that expected of nearly-free electrons - establishing Ag5Pb2O6 as the first known example of a monovalent, nearly-free electron superconductor at ambient pressure.; Comment: 4 pages, 3 figures

Interfacial Magnetism in Complex Oxide Heterostructures Probed by Neutrons and X-rays

Liu, Yaohua; Ke, Xianglin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/09/2015
Relevância na Pesquisa
37.18872%
Magnetic complex-oxide heterostructures are of keen interest because a wealth of phenomena at the interface of dissimilar materials can give rise to fundamentally new physics and potentially valuable functionalities. Altered magnetization, novel magnetic coupling and emergent interfacial magnetism at the epitaxial layered-oxide interfaces are under intensive investigation, which shapes our understanding on how to utilize those materials, particularly for spintronics. Neutron and x-ray based techniques have played a decisive role in characterizing interfacial magnetic structures and clarifying the underlying physics in this rapidly developing field. Here we review some recent experimental results, with an emphasis on those studied via polarized neutron reflectometery and polarized x-ray absorption spectroscopy. We conclude with some perspectives.; Comment: 17 pages, 8 figures. A condensed summary with authors' perspectives

Role of van der Waals bonding in layered oxide: Bulk vanadium pentoxide

Londero, Elisa; Schroder, Elsebeth
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/06/2010
Relevância na Pesquisa
47.413647%
Sparse matter is characterized by regions with low electron density and its understanding calls for methods to accurately calculate both the van der Waals (vdW) interactions and other bonding. Here we present a first-principles density functional theory (DFT) study of a layered oxide (V2O5) bulk structure which shows charge voids in between the layers and we highlight the role of the vdW forces in building up material cohesion. The result of previous first-principles studies involving semilocal approximations to the exchange-correlation functional in DFT gave results in good agreement with experiments for the two in-plane lattice parameters of the unit cell but overestimated the parameter for the stacking direction. To recover the third parameter we include the nonlocal (dispersive) vdW interactions through the vdW-DF method [Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] testing also various choices of exchange flavors. We find that the transferable first-principle vdW-DF calculations stabilizes the bulk structure. The vdW-DF method gives results in fairly good agreement with experiments for all three lattice parameters.; Comment: 8 pages, 4 figures, 1 table

Kinetic control of order in the layered perovskite La2Ba2Cu2Ti2O11

Palacín, M. R.; Krumeich, F.; Gómez-Romero, P.
Fonte: Materials Research Society Publicador: Materials Research Society
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
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Definitive evidence on the variable degrees of order/disorder in the layered perovskite La2Ba2Cu2Ti2O11 is presented. This oxide was prepared by the ceramic method with varying reaction times and cooling rates; the average and local structures of the resulting solids were studied by x-ray diffraction, electron diffraction and transmission electron microscopy (low and high resolution). The data clearly show the presence of an ap x ap x 4ap layered perovskite superstructure with a high concentration of defects in samples prepared during 48 h but with increasing degree of order for samples with longer reaction times. For samples reacted during 17 days the order is complete and identical to that found for other related derivatives such as Ln2Ba2Cu2Ti2O11, (Ln=Nd, Eu, Tb). This behavior clearly indicates the existence of a kinetic control of order in this phase.; Peer reviewed

Cationic Substitutions and Doping in the Series of Layered Perovskites Ln2Ba2Cu2Ti2O11 (Ln=La,Nd,Eu,Tb)

Palacín, M. R.; Casañ Pastor, Nieves; Krämer, G.; Jansen, M.; Gómez-Romero, P.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
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Several cationic substitutions have been performed on the series of layered perovskites Ln2Ba2Cu2Ti2O11 (Ln = La, Nd, Eu, Tb). The substitution attempts of the Ln ions that we performed were not successful. On the other hand K could be substituted for Ba and Sc, Al, Co, Zn and Cu for Ti. Nevertheless we found in all case a spontaneous loss of oxygen taking place upon substitution. This oxygen stoichiometry readjustment is such that leaves the oxides effectively undoped. Several attempts at oxidations nder high pressures of oxygen have been made, resulting oxygenation and doping of La2Ba2Cu2.15Ti1.85O11. Nevertheless this oxide does not present signs of superconductivity down to 4 K due most likely to the long Cu---O bond distance in its structure. Some n-type substitutions were also tried.; Financial support for this work was provided by the Spanish Ministry of Education and Science (DGICYT (PB93-0122)) and by the MIDAS Program (93-2331). We also thank the Generalitat de Catalunya for a predoctoral fellowship to M.R.P., and the German and Spanish governments (SGCCT, MAE) for a Joint project (CSIC-Kernforschungszentrum Karlsruhe).; Peer reviewed

Theoretical Chemistry at the Service of the Chemical Defense: Degradation of Nerve Agents in Magnesium Oxide and Hydroxide Surface; A Química Teórica a Serviço da Defesa Química: Degradação de Agentes Neurotóxicos em Superfícies de Óxido e Hidróxido de Magnésio

Raphael S. Alvim; Universidade Federal de Juiz de Fora; Viviane S. Vaiss; Universidade Federal de Juiz de Fora; Alexandre A. Leitão; Universidade Federal de Juiz de Fora; Itamar Borges Júnior; Instituto Militar de Engenharia
Fonte: Revista Virtual de Química Publicador: Revista Virtual de Química
Tipo: ; Formato: binary/octet-stream
Publicado em 24/04/2014 PT
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The Pró-Defesa funding of projects was a joint initiative of CAPES and the Ministry of Defense to fund research in defense. In this article we review the main scientific results obtained in the project “Formação de Pessoal Qualificado em Química Quântica Computacional para Atuação na Área de Defesa Química”, funded by the first edition of Pró-Defesa in 2005, which involved a collaboration between the Departments of Chemistry of the Federal University of Juiz de Fora and of the Military Institute of Engineering. The main goal of this project was to study, using theoretical-computational methods, the potential of magnesium oxide and hydroxide surfaces to degrade organophosphorus (OP) substances used as warfare agents, also known as neurotoxics. These substances inhibit the acetylcholinesterase, enzyme of fundamental role in the central nervous system. The VX (O-ethyl-S-(2-diisopropylethylamino) ethyl methylphosphonothioate) and sarin (isopropyl methylphosphonofluoridate) agents are some of the main neurotoxic agents, thus the search for ways to degrade them is considerably important. In this paper, we present theoretical investigations of two chemical degradation processes of organophosphates: the hydrolysis of a VX-like OP compound (O...

Influence of Vanadium Oxidation States on the Performance of V-Mg-Al Mixed-Oxide Catalysts for the Oxidative Dehydrogenation of Propane

Schacht,Leticia; Navarrete,Juan; Schacht,Persi; Ramírez,Marco A.
Fonte: Sociedad Química de México A.C. Publicador: Sociedad Química de México A.C.
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2010 EN
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V-Mg-Al mixed-oxide catalysts for oxidative dehydrogenation of propane were prepared by thermal decomposition of Mg-Al-layered double hydroxides with vanadium interlayer doping. The obtained catalysts were tested for the oxidative dehydrogenation of propane, obtaining good results in catalytic activity (conversion 16.55 % and selectivity 99.97 %). Results indicated that catalytic performance of these materials depends on how vanadium is integrated in the layered structure, which is determined by the Mg/Al ratio. Vanadium interlayer doping modifies the oxidation state of vanadium and consequently catalytic properties. Surface properties were studied by X-ray photoelectron spectroscopic and diffuse reflectance, UV-visible spectroscopy, and temperature programmed reduction (TPR). The analyses provided information about the oxidation state, before and after the reaction. From these results, it is suggested that selectivity to propylene and catalytic activity depend mainly on vanadium oxidation state.