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Oxidation and oxidative dehyrogenation of n-octane using V₂O₅ supported on hydroxyapatites.Dasireddy, Venkata D. B. C. January 2012 (has links)
Vanadium pentoxide with loadings varying from 2.5-15 wt% was supported on hydroxyapatite
(HAp) by the wet impregnation technique. The materials were characterized by techniques such
as X-ray powder diffraction (XRD), Inductively coupled plasma-optical emission spectroscopy
(ICP-OES), Brunauer Emmett Teller (BET) surface area measurement, Fourier Transformation-
Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron
Microscopy (TEM), Temperature Programmed Desorption (TPD) and Temperature Programmed
Reduction (TPR). From XRD and IR analyses, vanadium is found in the vanadium pentoxide
phase for the lower loadings, whereas for weight loadings in excess of 10%, an additional
pyrovanadate phase exists. Electron microscopy provides evidence of a homogenous distribution
of the vanadium species on the hydroxyapatite.
Oxidative dehydrogenation reactions carried out in a continuous flow fixed bed reactor showed
that selectivity towards desired products was dependent on the vanadium concentration and the
phase composition of the catalyst. Good selectivity towards octenes was achieved using the 2.5
wt% V₂O₅ on HAp loaded catalyst. There was a marked decrease in octene selectivity and a
significant increase in the formation of C8 aromatics when higher loadings of vanadium were
used. At a conversion of 24% at 450 ˚C, the 15 wt% V₂O₅ on HAp showed a selectivity of 72%
towards octenes. A maximum selectivity of 10 % for C8 aromatics was obtained using the 15
wt% V₂O₅ on HAp catalyst at a conversion of 36 % at 550 ˚C.
Vanadium pentoxide with 2.5 wt% and 10 wt% loading supported on Ca-HAp, Sr-HAp, Mg-
HAp, Ba-HAp was tested at different temperatures with varying n-octane to oxygen ratios. The selectivity towards products depended on the hydroxyapatite support. Ca-HAp showed
preference towards octenes, Sr-HAp towards aromatics, Mg-HAp towards oxygenates and Ba-
HAp towards aromatics and oxygenates.
In the development of a more detailed mechanistic study for the oxidative dehydrogenation noctane,
the role of the intermediates such as 1-octene, 2-octene, 3-octene, 4-octene and 1, 7-
octadiene was investigated. The influence of hydrocarbon to oxygen ratios was also considered.
Ethyl benzene and styrene were produced with high selectivities using 1-octene and 1, 7-
octadiene as feeds, whereas o-xylene was the main product when 2-octene, 3-octene and 4-
octene were used as feedstocks. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.
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Magnetic Exchange in Oxovanadium(IV) Complexes with N-Salicylideneamino AcidsHu, James Hung-Jen 01 1900 (has links)
Copper(II) and oxovanadium(IV) ions resemble one another magnetically in having one unpaired electron in their complexes irrespective of their geometrical structures and bond types involved. Copper(II) complexes with antiferromagnetic exchange are well known. On the contrary, antiferromagnetic exchange in oxovanadium(IV) complexes is rather new and not well established. Very few oxovanadium(IV) complexes have been reported to have this anomalous magnetic property. In the investigation of the magnetic properties of oxovanadium(IV) complexes, we have successfully prepared two series of new oxovanadium(IV) complexes with N-salicylideneamino acids.
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Electrical and optical properties of vanadium tellurite glassesFlynn, Brian William January 1977 (has links)
Glasses in the system v₂o₅-Te0₂ were prepared at intervals throughout the glass-forming composition range. The vanadium valence state was varied for each composition by the addition of elemental tellurium to reduce the melt. A chemical analysis method was devised to determine the v⁴⁺:vtotal ratio. Conductivity and thermopower measurements were made as functions of composition, valence ratio and temperature. The conductivity was found to increase as the total vanadium content increased and to be 21/2 to 3 orders of magnitude greater than that of a v₂0₅-P₂0₅ glass of similar v₂o₅ content. A maximum in conductivity was observed as the vanadium valence ratio was varied. This maximum was shifted to values around v⁴⁺:vtotal = 0.2 from the theoretically predicted value of 0.5. At temperatures above 250 K the conductivity varied exponentially with temperature with activation energies in the range 0.25 to 0.40 eV. Below this temperature there was a continuous decrease in slope of the conductivity down to the lowest temperature at which measurements were made. Thermopower was found to be negative and temperature independent above 250 K, while below this temperature it decreased in an activated manner with an activation energy of 0.02 eV. As a function of valence ratio the thermopower followed the behaviour predicted by Heikes and Ure, with the exception that the change of sign occurred at v⁴⁺:vtot ratios of around 0.2, instead of the theoretically predicted value of 0.5. (iii) Measurements were made of the optical absorption coefficient as functions of photon energy, composition, valence ratio and temperature. Temperature and composition did not affect the absorption spectrum significantly except that an absorption band appeared below the fundamental absorption edge as the glasses were reduced. The high electric field and a.c. properties of the glasses were also measured. These are consistent with hopping conduction of carriers between v⁴⁺ and v⁵⁺ sites. This data gives indirect indications of an inhomogeneous glass structure.
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The chemistry of para-tolylimidovanadium V trichloride: synthesis and characterization of dialkyldithiocarbamate and related derivatives and of bis(organophosphine)vanadium IV complexesWheeler, Dale E. January 1986 (has links)
Call number: LD2668 .T4 1986 W43 / Master of Science / Chemistry
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COMPARISON OF ALUMINIUM GRAIN REFINED AND VANADIUM GRAIN REFINED SPRING STEELS FOR THE MANUFACTURE OF HIGHLY STRESSED AUTOMOTIVE COIL SPRINGSLimalia, Firoz 31 October 2006 (has links)
Student Number: 9400670E
School of Chemical and Metallurgical Engineering
Faculty of Engineering and Built Environment / The selection of a particular steel grade for an application is extremely
important to ensure that the final components have a long serviceable life. The
chemical compositions of the steels are critical, and minor changes in
chemistry can make substantial differences. Aluminium and vanadium are
used in heat treatable steels as grain refining agents. These elements affect the
properties of the steels.
Two steels with identical chemical composition except for the aluminium and
vanadium additions were comparatively tested to determine the better steel for
a particular automotive coil spring. The tests included mechanical testing and
on site fatigue testing. Fatigue resistance is extremely important especially for
automotive coil springs. The mechanical properties revealed superior tensile
strength in the vanadium grain refined spring steel while the aluminium grain
refined spring steel had superior ductility and fatigue resistance.
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Complexos de vanádio como miméticos de peroxidases e catalisadores de oxidação: síntese e caracterização espectroscópica / Vanadium complexes mimetics as peroxidases and oxidation catalysts: synthesis and spectroscopic characterizationSouza, Joelson de 25 September 2006 (has links)
Quatro novos complexos mononucleares e um dinuclear de vanádio(IV) contendo ligantes do tipo imínico e carboxilato foram sintetizados e caracterizados através de diferentes técnicas espectroscópicas, UVNis, FT/IR e EPR, além de análise elementar, medidas de condutividade molar e, para alguns deles, análise termogravimétrica. Alguns deles foram obtidos como espécies neutras e outros, contendo grupos carboxilatos, foram isolados como espécies aniônicas, com contra-íons Na+ ou NH4+. Os complexos clássicos da literatura, largamente estudados e caracterizados, [VIVO(acac)2] e [VIvO(salen)], também foram sintetizados e caracterizados, a fim de comparar suas propriedades com aquelas dos novos complexos de vanádio(IV) sintetizados. Através das técnicas espectroscópicas, as principais bandas de transição e os principais grupos funcionais existentes nos complexos puderam ser verificados, bem como a simetria da estrutura geométrica e a confirmação do estado de oxidação do metal nos complexos. Além disso, através de medidas de condutividade molar e análise térmica foram confirmadas as razões estequiométricas ligante: metal em cada complexo, verificando-se, por exemplo, a natureza dimérica proposta para o complexo [VIVO(dbhab)] 2. / Some new vanadyl complexes, including four mononuclear and one dimeric species, were isolated and characterized by different spectroscopic techniques (UV/Vis, IR and EPR), in addition to elemental analysis, molar conductivity and, for a few ones, thermal analysis. Two of them were obtained as neutral compounds, and the others, withearboxylate ligands, as anionic species with sodium or ammonium as counter-ions. Additionally, the classical examples of vanadium complexes, [VIVO(acac)2] e [VIVO(salen)], already extensively studied in the literature, were prepared for comparison purposes. The main absorption bands in the UVNis and the characteristic ones at the IR spectra permitted the identification of the various complexes, while EPR spectroscopic data allowed to verify the oxidation state and the geometrical arrangements of the ligands around the metal center. Molar conductivity measurements and thermal analysis curves helped to determine the stoichiometric ratio ligand to metal, specially for the [VIVO(dbhab)]2 complex.
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[en] STUDY OF THE ELECTROCHEMICAL BEHAVIOR OF SAME CALIXARENES IN THE PRESENT OF IONS METALS / [pt] ESTUDO DO COMPORTAMENTO ELETROQUÍMICO DE ALGUNS CALIXARENOS EM PRESENÇA DE ÍONS METÁLICOSMARISTELA DE CASTRO REZENDE 27 October 2005 (has links)
[pt] O comportamento eletroquímico de eletrodos de pasta de
carbono
quimicamente modificados com os seguintes calixarenos: 4-
sulfcalix[4]areno e 4-terc-butilcalix[4,6,8]areno foi investigado na
presença de
alguns cátions (Sb 3+, Se4+, Mn2+, Cd2+, Zn2+, Cu2+, Pb2+,
V4+ e V5+) através
das técnicas de voltametria de pulso diferencial, onda
quadrada e
voltametria cíclica. Estes estudos foram realizados para
demonstrar a
utilização dos calixarenos como moléculas hospedeiras de
íons metálicos
ou metalóides bem como a formação de complexos. No estudo
eletroquímico dos calixarenos foram feitos sucessivos
voltamogramas no
modo pulso diferencial e em varredura linear (cíclica) sob
diferentes
velocidades de varredura, utilizando como eletrodo de
trabalho de
carbono vítreo e de platina sendo observado que na
oxidação do 4-sulfcalix[4]areno e do 4-terc-butilcalix[4,6,8]areno ocorre a
passivação ou acumulação na superfície do eletrodo. No estudo do processo
eletroquímico observado na presença dos oito cátions (Sb
3+, Se4+, Mn2+, Cd2+, Zn2+, Cu2+, Pb2+ ,V4+ e V5+) utilizaram-se os
seguintes eletrodos de trabalho: eletrodo de pasta de carbono quimicamente
modificado com 4-terc-butilcalix[4]areno, eletrodo carbono e eletrodo de
pasta de carbono não modificado. Maior atenção foi dedicada ao estudo do
comportamento do 4-sulf-calix[4]areno na presença de V4+ e V5+
utilizando como eletrodo de trabalho, o eletrodo de carbono vítreo e os de pasta de
carbono modificada e não modificada. Observou-se que, na presença deste íon
metálico, o aparecimento no voltamograma de novos picos
relacionados à formação de complexos. Uma corrente voltamétrica
analiticamente útil foi obtida para oxidação do(s) complexo
(s) (vanádio / calixareno). Sendo estimada a constante de formação dos complexos formados
com vanádio. A interferência de alguns cátions (Sb 3+, Se4+, Mn2+,
Cd2+, Zn2+, Cu2+, Pb2+) na análise de V4+ na presença de 4-sulf-calix[4]
areno foi estudada, onde somente o íon Cu2+ não interferiu na análise. Curvas
de calibração de V4+ foram construídas com eletrodo de pasta de carbono,
eletrodo de pasta de carbono quimicamente modificado com 4-terc-
butilcalix[4]areno e com eletrodo de carbono na presença de 4-sulf-calix[4]
areno. / [en] The study of the electrochemical behavior of electrodes of
carbon paste
chemically modified with the following calixarenes: 4-sulf-
calix[4]arene and 4-terc-butilcalix[4,6,8]arene was investigated in the
present of cations (Sb3+, Se4+, Mn2+, Cd2+, Zn2+, Cu2+, Pb2+, V4+ and V5+)
using differential pulse , square wave and cyclical voltammetry. Other
electrochemical studies for each cited calixarene was investigated.
Successive voltammograms in the way had been made differential pulse
voltammetric and sweepings linear (cyclic) under different scan rates
and observed that in the oxidation of the 4-sulf-calix[4]arene and 4-terc-
butilcalix[4,8]arene passivation and accumulation in the surface of exactly. In
the study of the electrochemical process observed in the presence of eight
cations (Sb3+, Se4+, Mn2+, Cd2+, Zn2+, Cu2+, Pb2+, V4+ and V5+) the
following electrodes of work was used: carbon paste modified with 4-terc-butilcalix
[4]arene, electrode carbon and unmodified carbon paste electrode.
Considerable attention was dedicated to the study of the behavior of
the 4-sulfcalix[4]arene in the present of V4+ and V5+ using as work
electrode the carbon and carbon paste modified with 4-terc-butil-calix[4]
areno and unmodified. It was observed, in presence of this ion
metallic, the appearance in the voltammogram of new peaks related to the
formation of complexes. An analytical useful voltammetric current was
gotten for oxidation of complex (calixarene / vanadium). The
interference of some cations (Sb3+, Se4+, Mn2+, Cd2+, Zn2+, Cu2+, Pb2+) in the
V4+ analysis in presence of 4-sulf-calix[4]areno was studied. Calibration
curve gotten in presence of V4+ had been constructed with
carbon paste modified with 4-terc-butilcalix[4]arene, unmodified carbon paste electrode
and carbon electrode in the presence of 4-sulfcalix[4]areno.
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Síntese, caracterização e estudos das propriedades catalíticas de compostos formados por óxido de tungstênio e pentóxido de vanádio / Synthesis, Characterization and Study of Catalytic Properties of Compounds Formed by Tungsten Oxide and Vanadium Oxide.Bolsoni, Aline Turini 11 November 2011 (has links)
Métodos de síntese que viabilizam a obtenção de compósitos contendo xerogéis de óxido de tungstênio e de pentóxido de vanádio pelo método sol-gel foram investigados, bem como a caracterização e propriedades catalíticas nas reações de epoxidação destes materiais. Brometo de cetiltrimetilamina e hexadecilamina foram intercalados nos xerogéis de óxidos vanádio e de tungstênio formando compostos híbridos orgânico-inorgânico ternários. Estas moléculas foram usadas com o objetivo de aumentar a distância interlamelar e conferir caráter hidrofóbico nos compostos híbridos para que facilitasse o acesso dos substratos orgânicos quando utilizados como catalisadores nas reações de epoxidação. Os parâmetros de difração de raios X comprovam a intercalação, com aumento da distância interplanar. Observa-se uma variação na posição da banda M=O para maiores valores de energia devido à interação eletrostática entre as cargas positivas das espécies convidadas com densidade de carga negativa das ligações M=O. O xerogel de óxido de tungstênio e o compósito com xerogel de óxido de vanádio com óxido tungstênio foram dispersos em matrizes de óxido hidróxido de alumínio e de xerogel de óxido de silício. Foi observado que os modos vibracionais no infravermelho não sofreram variações significativas, indicando que pequenas distorções ocorrem quando os xerogéis dos óxidos estão dispersos, ou seja, há interações fracas entre os componentes, corroborando com os padrões de difração de raios X que mostram a manutenção da estrutura inicial dos óxidos. No caso dos compósitos contendo óxido de vanádio em sílica empregando metiltrietóxissilano, houve a formação de partículas esféricas de sílica recobertas por filmes de óxido de vanádio. No entanto, ao utilizar o tetraelilortossilicato como precursor, houve a manutenção da estrutura lamelar dos óxidos, mas não se observou a formação das partículas esféricas de sílica. As propriedades catalíticas destes materiais foram testadas em reações de oxidação do cis-cicloocteno, estireno e ciclo-hexano usando peróxido de hidrogênio (H2O2), terc-butil hidroperóxido (t-BOOH) e ácido meta-cloroperbenzóico (m-CPBA) como agentes oxidantes. De modo geral, os resultados obtidos são satisfatórios e estão de acordo com os resultados apresentados na literatura para sistemas similares, sugerindo uma aplicação potencial destes materiais como catalisadores em reações de epoxidação e oxidação. / Synthetic procedures based on sol-gel process were developed aiming produce xerogel composites of mixed oxides such as tungsten oxide and vanadium oxide, as well as their characterization and catalytic properties in epoxidation reactions. Cetyltrimetylamine bromide and hexadecylamine were intercalated into vanadium oxide and tungsten oxide xerogels resulting in ternary hybrid inorganic-organic compounds. These molecules were used in order to increase the interlamelar distance and confer hydrophobic character facilitating the substrate access in catalyzes epoxidation reactions. X ray diffraction patterns demonstrate the intercalation. It was verified the shift of the M=O vibrational mode towards higher energy region due to electrostatic interaction between positive charges of guest species with negative character of M-O bonding. Tungsten oxide and vanadium and tungsten mixed oxide xerogels were dispersed in oxohydroxiy aluminum and silicon oxide matrices. No significant changes in the infrared vibrational modes were observed, suggesting that few distortions occur when xerogel materials are dispersed, due to weak interactions corroborating previous results. In the case of composites containing vanadium oxide and silica (methyltriethoxysilane as precursor), the final material is formed by sphere particles of silica covered with vanadium oxide film. However, when tetraethylorthosilicate was used as silica precursor, the lamelar structure of metal oxide is retained instead of spherical morphology. The catalytic properties of these materials were verified in oxidation of cis-cyclooctene, styrene, and cyclohexane using hydrogen peroxide (H2O2), terc-butyl hydroperoxide (t-BOOH), and cloroperoxybenzoic acid (m-CPBA) as oxygen donors. From a general point of view, the results are satisfactory and close with those found for similar systems, enabling them as catalysts for epoxidation and oxidation.
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Biossorção de vanádio pela macroalga marinha Sargassum filipendula / Vanadium biosorption by seaweeds Sargassum filipendulaMarcelo de Souza Oliveira 25 February 2011 (has links)
Muitos biossorventes naturais têm sido pesquisados por possuírem baixo custo e apresentarem propriedades ligantes, como é o caso da macroalga marinha Sargassum filipendula (S. filipendula) que vem sendo utilizada como material biossorvente no processo de biossorção de metais pesados. No presente trabalho a alga marrom foi utilizada para estudos realizados em batelada, onde se determinou o pH ideal de biossorção de vanádio, a relação sólido/líquido ideal e a importância da velocidade de agitação. O estudo cinético e de equilíbrio dos íons metálicos também foram realizados em bateladas nas seguintes condições de ensaio: (1) 0,10 g de biomassa, 25,0 mL de solução de vanádio igual a 18,0 mg L-1, temperatura 25,0 C e 150 rpm de agitação; (2) 0,10 g de biomassa, 25,0 mL de solução de vanádio igual a 36,0 mg L-1, temperatura 25,0 C e 150 rpm de agitação. A melhor condição para biossorção de vanádio foi encontrada para 36,0 mg L-1 e pH= 2,0. O estudo cinético de biossorção de vanádio mostrou que o modelo de segunda ordem descreve melhor os dados experimentais em 36,0 mg L-1 (R2= 0,9825). O estudo de equilíbrio mostrou um perfil crescente de remoção de vanádio. A melhor eficiência de captação dos íons de vanádio foi de 61,0 % para Co= 40,0 mg L-1 em pH= 2,0. Os dados experimentais da isoterma de vanádio mostraram-se mais adequados ao modelo de Langmuir para pH= 2,0, Os parâmetros de equilíbrio calculados a partir do modelo de Langmuir (b, qmax ) 0,009 e 43,3 mg/g, respectivamente, corroboram melhor para a interpretação dos resultados quando comparados com o modelo de Freundlich (kF, n) 1,56 e 2,41, visto que o coeficiente de correlação é maior para Langmuir / Many natural biosorbents have been investigated for having low cost and submit binding properties, as is the case of marine marcoalgae Sargassum filipendula (S. filipendula) that has been used biosorbent material in the processes of biosorption of heavy metals. In the present study the brown seaweed has been used to study conducted in bach mode, where it was determined the optimum pH for biosorption of vanadium, the solid/liquid ratio ideal and the importance of speed of agitation. The kinetic and equilibrium study of metal ions were also performed in batches in the following test conditions: (1) 0.10 g of biomass, 25.0 mL of vanadium solution equal to 18.0 mg L-1, temperature 303 K and 150 rpm agitation. (2) 0.10 g of biomass, 25.0 mL of vanadium solution equal to 36.0 mg L-1, temperature 303 K and 150 rpm agitation. The optimum conditions for biosorption of vanadium was found to 36.0 mg L-1, pH 2,0. The kinetic study of vanadium biosorption showed that the second order model best describes the experimental data 36.0 mg L-1, (R2 = 0.9825). The balance study showed an increased uptake profile of vanadium. The best collection efficiency of vanadium ion was 46.0 % for Co = 36.0 mg L-1 at pH 2.0. The experimental isotherm data of vanadium were more suitable for the Langmuir model at pH 2.0. The equilibrium parameters calculated from the Langmuir model (b, qmax ) were 0.009 e 43.3 mg/g respectively, to better corroboration to interpretation of results when compared with the Freundlich model (kF, n) 1,56 e 2,41, whereas the correlation coefficient is higher for Langmuir
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Complexos de vanádio como miméticos de peroxidases e catalisadores de oxidação: síntese e caracterização espectroscópica / Vanadium complexes mimetics as peroxidases and oxidation catalysts: synthesis and spectroscopic characterizationJoelson de Souza 25 September 2006 (has links)
Quatro novos complexos mononucleares e um dinuclear de vanádio(IV) contendo ligantes do tipo imínico e carboxilato foram sintetizados e caracterizados através de diferentes técnicas espectroscópicas, UVNis, FT/IR e EPR, além de análise elementar, medidas de condutividade molar e, para alguns deles, análise termogravimétrica. Alguns deles foram obtidos como espécies neutras e outros, contendo grupos carboxilatos, foram isolados como espécies aniônicas, com contra-íons Na+ ou NH4+. Os complexos clássicos da literatura, largamente estudados e caracterizados, [VIVO(acac)2] e [VIvO(salen)], também foram sintetizados e caracterizados, a fim de comparar suas propriedades com aquelas dos novos complexos de vanádio(IV) sintetizados. Através das técnicas espectroscópicas, as principais bandas de transição e os principais grupos funcionais existentes nos complexos puderam ser verificados, bem como a simetria da estrutura geométrica e a confirmação do estado de oxidação do metal nos complexos. Além disso, através de medidas de condutividade molar e análise térmica foram confirmadas as razões estequiométricas ligante: metal em cada complexo, verificando-se, por exemplo, a natureza dimérica proposta para o complexo [VIVO(dbhab)] 2. / Some new vanadyl complexes, including four mononuclear and one dimeric species, were isolated and characterized by different spectroscopic techniques (UV/Vis, IR and EPR), in addition to elemental analysis, molar conductivity and, for a few ones, thermal analysis. Two of them were obtained as neutral compounds, and the others, withearboxylate ligands, as anionic species with sodium or ammonium as counter-ions. Additionally, the classical examples of vanadium complexes, [VIVO(acac)2] e [VIVO(salen)], already extensively studied in the literature, were prepared for comparison purposes. The main absorption bands in the UVNis and the characteristic ones at the IR spectra permitted the identification of the various complexes, while EPR spectroscopic data allowed to verify the oxidation state and the geometrical arrangements of the ligands around the metal center. Molar conductivity measurements and thermal analysis curves helped to determine the stoichiometric ratio ligand to metal, specially for the [VIVO(dbhab)]2 complex.
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