Academic literature on the topic 'Vanadium silicate. eng'

The use of redox molecular sieves as heterogeneous catalysts for liquid phase oxidations with H2O2 and alkyl hydroperoxides is reviewed. Emphasis is placed on titanium- and chromium-substituted molecular sieves as examples of catalysts operating via peroxometal and oxometal pathways, respectively. Various titanium-substituted molecular sieves were shown to be stable, heterogeneous catalysts for, e.g., olefin epoxidation, but the remarkable activity of the progenitor of this family of catalysts, titanium-silicalite (TS-1), has not been equalled. The catalytic activity of chromium-substituted molecular sieves was shown to be entirely due to small amounts of homogeneous chromium species leached from the catalyst during reaction. The catalytic activities and stabilities of other materials, including zirconium-substituted hexagonal mesoporous silicas and a vanadium bipyridyl complex encapsulated in zeolite Y, were also tested. They were either unstable (vanadium) towards leaching or showed low activity (zirconium). Attempts to incorporate molybdenum in silicalite were unsuccessful and previously reported activity was shown to be due to the blank reaction. A review with 64 references.

Abstract Vanadium is a multivalent element that can speciate as V2+, V3+, V4+, and V5+ over a range of geologically relevant oxygen fugacities (fO2). The abundance of V in planetary materials can be exploited as a proxy for fO2 when its partitioning behavior is known. The mineral rutile (TiO2) is an important carrier of the high field strength elements Nb and Ta in the solid Earth, but it can also incorporate substantial quantities of vanadium (up to ~2000 ppm; e.g., Zack et al. 2002). However, little work has been done to systematically investigate how the partitioning of V in rutile-bearing systems changes as a function of both fO2 and composition. We measured the partitioning of V and 19 other trace elements (Sc, Cr, Y, Zr, Nb, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu, Hf, and Ta) between rutile and three silicate melt compositions equilibrated at 1 atm pressure, 1300 °C and fO2 values from two log units below the quartz-fayalite-magnetite oxygen buffer (QFM-2) to air (QFM+6.5). Rutile/melt partition coefficients (DVrt/melt) change dynamically over an eight-log unit range of fO2 and are greatest at fO2 = QFM-2 in all compositions. Vanadium solubility in rutile declines continuously as fO2 increases from QFM-2 and approaches unity in air. Trace-element partitioning between rutile and melt is also correlated with melt composition, with the greatest values of Drt/melt measured in the most polymerized melt systems containing the least TiO2. We do not find any circumstances where V becomes incompatible in rutile. Our results indicate that rutile is a considerable sink for V at terrestrial fO2 values and will contribute to the retention of V in refractory slab residues in subduction zones. In agreement with previous work, we find that DTart/melt>DNbrt/melt under all conditions investigated, suggesting that rutile fractionation does not lead to low Nb/Ta ratios in Earth's continental crust.

The aim of this study was to obtain a detailed picture of the origin of the anthropogenic and natural inorganic solutes in the surface waters of the Lake Baikal watershed using limited data on solute sources. To reveal the origin of solutes, the chemical composition of water was considered as a mixture of solutes from different sources such as rocks and anthropogenic wastes. The end-member mixing approach (EMMA), based on the observation that the element ratios in water uncorrelated with one another are those that exhibit differences in values across the different types of rocks and anthropogenic wastes, was used for source apportionment. According to the results of correlation analysis, two tracers of sources of most abundant ions present in riverine waters were selected. The first tracer was the ratio of combined concentration of calcium and magnesium ions to concentration of potassium ion ((Ca2+ + Mg2+)/K+), and the second tracer was the ratio of sulfate and bicarbonate ion concentrations (SO42−/HCO3−). Using these tracers, three sources of main ions in water, such as sulfide-bearing silicate rocks, non-sulfide silicate rocks and carbonate rocks, were apportioned. The results of cluster analysis showed the possibility of using the ratios of strontium, iron, manganese, molybdenum, nickel, and vanadium concentrations (Sr/Fe, Sr/Mn, Ni/V, Mo/V) as tracers of the trace element sources. The use of these tracers and the obtained data on sources of main ions showed the possibility of identifying the natural trace element sources and distinguishing between natural and anthropogenic trace element sources.

Tourmaline, an intermediate member of the oxyschorl–oxydravite–oxymagnesio-foitite-bosiite series with a predominance of the oxy-dravite-bosiite end-member, was studied from late calcite-quartz veins in the eastern zone of the Murtykty gold deposit (Republic of Bashkortostan). Sulfide mineralization in veins includes rare chalcopyrite, pyrite, sphalerite and galena. Accessory minerals are xenotime-(Y), vanadium-containing rutile and fine high-fineness gold. Supergene mineralization resulted from decomposition of carbonates, sulfides and rock-forming silicates includes kaolinite, hydroxides of Mn (chalcophanite, psilomelane) and Fe (goethite and limonite ochers), mainly developed in vein cavities ; chalcopyrite is replaced by cuprite and malachite. The composition of tourmaline is close to metamorphic dravite of orogenic gold deposits and tourmaline of gold-porphyry deposits, transitioning from porphyry to epithermal. Two possible B sources for the formation of tourmaline are considered: sedimentary rocks of the paleoisland-arc complex and granodiorites of the Mansurovo pluton. Figures 9. Table 1. References 36. Key words: tourmaline, boron, gold, xenotime-(Y), Murtykty deposit, Republic of Bashkortostan.

Firing of biomass can lead to rapid deactivation of the vanadia-based NH3-SCR catalyst, which reduces NOx to harmless N2. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly KCl and K2SO4. The main mode of deactivation is neutralization of the catalyst’s acid sites. Four ways of dealing with high potassium contents were identified: (1) potassium removal by adsorption, (2) tail-end placement of the SCR unit, (3) coating SCR monoliths with a protective layer, and (4) intrinsically potassium tolerant catalysts. Addition of alumino silicates, often in the form of coal fly ash, is an industrially proven method of removing K aerosols from flue gases. Tail-end placement of the SCR unit was also reported to result in acceptable catalyst stability; however, flue-gas reheating after the flue gas desulfurization is, at present, unavoidable due to the lack of sulfur and water tolerant low temperature catalysts. Coating the shaped catalysts with thin layers of, e.g., MgO or sepiolite reduces the K uptake by hindering the diffusion of K+ into the catalyst pore system. Intrinsically potassium tolerant catalysts typically contain a high number of acid sites. This can be achieved by, e.g., using zeolites as support, replacing WO3 with heteropoly acids, and by preparing highly loaded, high surface area, very active V2O5/TiO2 catalyst using a special sol-gel method.

Orientador: José Geraldo Nery
Banca: Eleni Gomes
Banca: José Manoel Marconcini
Resumo: Os principais objetivos do presente trabalho de pesquisa são a síntese de novos catalisadores zeolíticos, a avaliação de seus usos como possíveis matrizes para imobilização enzimática, e o uso desse complexo zeólita/enzima como catalisador para produção de biodiesel. Inicialmente foram sintetizadas duas classes de zeólitas: faujasita (FAU) e gismondina (GIS), em suas formas sódicas, e estas zeólitas foram convertidas para as formas Cu2+, Ni2+ e Zn2+ por troca iônica. Na sequência foi avaliado o potencial desses materiais zeolíticos para imobilização e atividade lipolítica da enzima (Lipase de Rhizomucor miehei) na reação de hidrólise do p-nitrofenil palmitato (pNPP) a p-nitrofenol (pNP). Os estudos de imobilização foram feitos variando os parâmetros térmicos do pré-tratamento do suporte zeolítico e o meio catiônico dominante. Os resultados obtidos mostraram que dos 16 suportes avaliados para imobilização enzimática, todos se mostraram capazes de imobilizar a enzima em questão e produzir atividade catalítica, no entanto, o melhor compromisso entre imobilização e atividade enzimática foi obtido pelo complexo LIPASE/GIS/Ni2+ pré-tratada a 200ºC. Este complexo que imobilizou 11,2 ± 0,6% da quantidade de enzima da solução e obteve uma atividade de 13,278 U/mg-suporte. Para as reações de transesterificação foram usados como catalisadores as zeólitas puras (GIS/Ni2+ e GIS/Zn2+), enzimas livres (Lipases de Rhizomucor miehei) e enzimas imobilizadas sobre as zeólitas (LIPASE/GIS/Ni2+ e LIPASE/GIS/Zn2+) para a produção de biodiesel a partir do óleo vegetal (óleo de soja). Os resultados obtidos indicaram que os dois complexos produziram biodiesel, no entanto, o teor de ésteres metílicos de 56,2% produzidos pelo suporte LIPASE/GIS/Ni2+ mostrou que houve... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The main goals of this research work are the syntheses of new zeolitic catalysts and their use as possible solid matrices for enzyme immobilization, and the study this complex zeolite/enzyme as a catalyst for biodiesel production. Initially, two different zeolites were synthesized: faujasite (FAU) and gismondine (GIS). The two zeolites were first prepared in their sodic forms and thereafter they were submitted to an ion exchange process in order to the replace the extra-framework Na+ by Cu2+, Ni2+ and Zn2+. The potential of these zeolitic materials for immobilization and lipolytic activity of the enzyme (Lipase from Rhizomucor miehei) was evaluated through the hydrolysis reaction from p-nitrophenyl palmitate (pNPP) to p-nitrophenol (pNP). Several immobilization studies were performed and two main parameters were singled out for this study: the thermal parameters or thermal stability of the zeolitic support and the main dominant cationic medium. The results showed that all of the 16 prepared zeolitic supports were not only able to immobilize the enzyme, but also they were able to show significant catalytic activity. However, the best compromise between immobilization and enzymatic activity was obtained with the complex LIPASE/GIS/Ni2+ pre-treated at 200°C, since it was able to immobilize 11.2 ± 0.6% of the amount of enzymes in solution and an activity of 13.278 U/mg-support. The transesterification reactions for the production of biodiesel from vegetable oils (soybean oil) were performed with the following catalysts: zeolite pure (GIS/Zn2+ and GIS/Ni2+), free enzymes (Lipases from Rhizomucor miehei) and immobilized enzymes on zeolites (LIPASE/GIS/Zn2+ and LIPASE/GIS/Ni2+). The results indicated that two zeolite/enzyme complexes were able to produce biodiesel, but the content... (Complete abstract click electronic access below)
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