First-Principles Study of Pressure-Induced Phase Transitions and Electronic Properties of Ag2MoO4

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Development of a Yellow Pigment Based on Bismuth and Molybdenum-Doped TiO2 for Coloring Polymers

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Electrochemical behavior and corrosion resistance of Ti-15Mo alloy in naturally-aerated solutions, containing chloride and fluoride ions

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Third-order nonlinearities and other properties of molybdenum lead-pyrophosphate glass

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Nanopartículas de Pd suportadas em compósitos óxido-carbono: influência das interações metal-suporte na oxidação de etanol em meio básico

Fuel cells powered directly with ethanol (Direct Ethanol Fuel Cell-DEFC) are very attractive for the possibility of using a renewable fuel in the generation of clean energy. However, it is still necessary to deepen the understanding of catalytic processes and their dependence on the catalytic properties. This work proposes to study the catalytic activity of ethanol oxidation in an alkaline medium of Pd nanoparticles supported in carbon oxide hybrids using various transition metal oxides (MoO3, TiO2, WO3 and ZrO2). The materials prepared were characterized by techniques such as X-ray diffraction, transmission electron microscopy (TEM) and X-ray dispersive spectroscopy (EDX) to verify the structure, the distribution of particles in the supports and the presence of Pd on particles oxide. Experiments of X-rays absorption spectroscopy were carried out using soft X-rays (SXS) to evaluate the changes in the electronic properties of the Pd particles caused by interactions with different oxides. Measurements of cyclic voltammetry and potential sweeps of adsorbed CO oxidation allowed evaluating general aspects of the catalysts' electrochemical behavior and determining the electrochemically active area thereof. The catalytic performances of ethanol oxidation in alkaline medium were evaluated by electrochemical techniques (potential scan and chronoamperometry), and showed an improvement in activity with the addition of oxides in material containing only carbon, which was most pronounced for the catalyst containing TiO2. This improvement was predominantly associated with the electronic effects caused by the interaction of Pd on the support, causing a vacancy in the 4d band of Pd which, in turn, produces variations in adsorption energies of the species...

Nanopartículas de Pd suportadas em compósitos óxido-carbono: influência das interações metal-suporte na oxidação de etanol em meio básico

Fuel cells powered directly with ethanol (Direct Ethanol Fuel Cell-DEFC) are very attractive for the possibility of using a renewable fuel in the generation of clean energy. However, it is still necessary to deepen the understanding of catalytic processes and their dependence on the catalytic properties. This work proposes to study the catalytic activity of ethanol oxidation in an alkaline medium of Pd nanoparticles supported in carbon oxide hybrids using various transition metal oxides (MoO3, TiO2, WO3 and ZrO2). The materials prepared were characterized by techniques such as X-ray diffraction, transmission electron microscopy (TEM) and X-ray dispersive spectroscopy (EDX) to verify the structure, the distribution of particles in the supports and the presence of Pd on particles oxide. Experiments of X-rays absorption spectroscopy were carried out using soft X-rays (SXS) to evaluate the changes in the electronic properties of the Pd particles caused by interactions with different oxides. Measurements of cyclic voltammetry and potential sweeps of adsorbed CO oxidation allowed evaluating general aspects of the catalysts' electrochemical behavior and determining the electrochemically active area thereof. The catalytic performances of ethanol oxidation in alkaline medium were evaluated by electrochemical techniques (potential scan and chronoamperometry), and showed an improvement in activity with the addition of oxides in material containing only carbon, which was most pronounced for the catalyst containing TiO2. This improvement was predominantly associated with the electronic effects caused by the interaction of Pd on the support, causing a vacancy in the 4d band of Pd which, in turn, produces variations in adsorption energies of the species...

Unprecedented Trapping of Difluorooctamolybdate Anions within an α-Polonium Type Coordination Network

New fluorinated hybrid solids [Mo2F2O5(tr2pr)] (1), [Co3(tr2pr)2(MoO4)2F2]·7H2O (2), and [Co3(H2O)2(tr2pr)3(Mo8O26F2)]·3H2O (3) (tr2pr = 1,3-bis(1,2,4-triazol-4-yl)propane) were prepared from the reaction systems consisting of Co(OAc)2/CoF2 and MoO3/(NH4)6Mo7O24, as CoII and MoVI sources, in water (2) or in aqueous HF (1, 3) employing mild hydrothermal conditions. The tr2pr ligand serves as a conformationally flexible tetradentate donor. In complex 1, the octahedrally coordinated Mo atoms are linked in the discrete corner-sharing {Mo2(μ2-O)F2O4N4} unit in which a pair of tr-heterocycles (tr = 1,2,4-triazole) is arranged in cis-positions opposite to “molybdenyl” oxygen atoms. The anti−anti conformation type of tr2pr facilitates the tight zigzag chain packing motif. The crystal structure of the mixed-anion complex salt 2 consists of trinuclear [Co3(μ3-MoO4)2(μ2-F)2] units self-assembling in CoII-undulating chains (Co···Co 3.0709(15) and 3.3596(7) Å), which are cross-linked by tr2pr in layers. In 3, containing condensed oxyfluoromolybdate species, linear centrosymmetric [Co3(μ2-tr)6]6+ SBUs are organized at distances of 10.72−12.45 Å in an α-Po-like network using bitopic tr-linkers. The octahedral {N6} and {N3O3} environments of the central and peripheral cobalt atoms, respectively, are filled by triazole N atoms, water molecules, and coordinating [Mo8O26F2]6− anions. Acting as a tetradentate O-donor, each difluorooctamolybdate anion anchors four [Co3(μ2-tr)6]6+ units through their peripheral Co-sites, which consequently leads to a novel type of a two-nodal 4,10-c net with the Schläfli symbol {32.43.5}{34.420.516.65}. The 2D and 3D coordination networks of 2 and 3, respectively, are characterized by significant overall antiferromagnetic exchange interactions (J/k) between the CoII spin centers on the order of −8 and −4 K. The [Mo8O26F2]6− anion is investigated in detail by quantum chemical calculations.

Synthesis and Structural Elucidation of Triazolylmolybdenum(VI) Oxide Hybrids and Their Behavior as Oxidation Catalysts

A large family of bifunctional 1,2,4-triazole molecular tectons (tr) has been explored for engineering molybdenum(VI) oxide hybrid solids. Specifically, tr ligands bearing auxiliary basic or acidic groups were of the type amine, pyrazole, 1H-tetrazole, and 1,2,4-triazole. The organically templated molybdenum(VI) oxide solids with the general compositions [MoO3(tr)], [Mo2O6(tr)], and [Mo2O6(tr)(H2O)2] were prepared under mild hydrothermal conditions or by refluxing in water. Their crystal structures consist of zigzag chains, ribbons, or helixes of alternating cis-{MoO4N2} or {MoO5N} polyhedra stapled by short [N–N]-tr bridges that for bitriazole ligands convert the motifs into 2D or 3D frameworks. The high thermal (235–350 °C) and chemical stability observed for the materials makes them promising for catalytic applications. The molybdenum(VI) oxide hybrids were successfully explored as versatile oxidation catalysts with tert-butyl hydroperoxide (TBHP) or aqueous H2O2 as an oxygen source, at 70 °C. Catalytic performances were influenced by the different acidic–basic properties and steric hindrances of coordinating organic ligands as well as the structural dimensionality of the hybrid.

Geochemistry of manganese nodules from a British Columbia fjord

Concretions of iron and manganese oxides and hydrous oxidesóobjects commonly called manganese nodulesóare widely distributed not only on the deep-sea floor but also in shallow marine environments1. Such concretions were not known to occur north of Cape Mendocino in the shallow water zones bordering the North-East Pacific Ocean until the summer of 1966 when they were recovered by one of us (J. W. M.) in dredge samples from Jervis Inlet, a fjord approximately 50 miles north-west of Vancouver, British Columbia.

Analysis of Mn-nodules from the Indian Ocean

This report studies the principal paramters governing the distribution of iron-manganese concretions on the sea floor of the Indian Ocean, as well as their petrography and mineralogy. The results are mainly based on the recoveries made during voyages 31, 33 and 35 of the "Vityaz"' (1959-1962) and partly during voyages 36 and 41 (1964-1966). During these voyages samples of Mn concretions and Mn crust were collected (by bottom grabs, cores, trawlings, and dredgings) at 39 stations. The following account is devoted to the problems concerning the geochemistry of these concretions.

Description and chemical composition of manganese nodules sampled during the R/V "Vityaz" Expedition Vityaz-35

This paper presents data on the chemical composition of iron-manganese nodules and associated sediments collected during the 35th voyage of the R/V "Vityaz" in 1962. The samples were made available to the author by Prof, P. L. Bezrukov. Data on the general distribution of manganese nodules at the bottom of the Indian Ocean were already given by P. L. Bezrukov (1962, 1963). Here the author analyzed the geochemistry of nodules samples from seven stations and four samples from the associated sediments. The analysis separates the outer layer of nodules from their apparent internal core.

Chemistry on manganese nodules from the Pacific Ocean

Three manganese nodules from the Pacific Ocean have been analysed for 35 elements by using mainly spectrophotometric and spectrographic methods. Cu, Co, Ni, Zn, and Pb were found in amounts approaching 1 %, which far exceeds their average concentrations in igneous rocks. On the other hand, elements having readily hydrolysable ions, such as Ga, Sc, Zr, Y, La and Ti, are present only in amounts comparable with their concentrations in igneous rocks. Sb, Bit Be, and Cr were not detected. The hydrochloric acid-insoluble fraction of nodules is practically free of the heavy metals that are characteristic of the acid-soluble fraction; it consists principally of clay minerals, together with lesser amounts of quartz, apatite, biotite and sodium and potassium felspars.

A catalytic reactor for the trapping of free radicals from gas phase oxidation reactions

A catalytic reactor for the trapping of free radicals originating from gas phase catalytic reactions is described and discussed. Radical trapping and identification were initially carried out using a known radical generator such as dicumyl peroxide. The trapping of radicals was further demonstrated by investigating genuine radical oxidation processes, e.g., benzaldehyde oxidation over manganese and cobalt salts. The efficiency of the reactor was finally proven by the partial oxidation of cyclohexane over MoO3, Cr2O3, and WO3, which allowed the identification of all the radical intermediates responsible for the formation of the products cyclohexanol and cyclohexanone. Assignment of the trapped radicals was carried out using spin trapping technique and X -band electron paramagnetic resonance spectroscopy. © 2010 American Institute of Physics.

Obtenção de Mo2C com adição de Co por reação gás-sólido em reator de leito fixo

Sulfur compounds emissions have been, on the late years, subject to more severe environmental laws due to its impact on the environment (causing the acid rain phenomena) and on human health. It has also been object of much attention from the refiners worldwide due to its relationship with equipment’s life, which is decreased by corrosion, and also with products’ quality, as the later may have its color, smell and stability altered by the presence of such compounds. Sulfur removal can be carried out by hydrotreating (HDT) which is a catalytic process. Catalysts for HDS are traditionally based on Co(Ni)-Mo(W)/Al2O3. However, in face of the increased contaminants’ content on crude oil, and stricter legislation on emissions, the development of new, more active and efficient catalysts is pressing. Carbides of refractory material have been identified as potential materials for this use. The addition of a second metal to carbides may enhance catalytic activities by increasing the density of active sites. In the present thesis Mo2C with Co addition was produced in a fixed bed reactor via gas-solid reaction of CH4 (5%) and H2(95%) with a precursor made of a mix of ammonium heptamolybdate [(NH4)6[Mo7O24].4H2O] and cobalt nitrate[Co(NO3)2.6H2O] at stoichiometric amounts. Precursors’ where analyzed by XRF, XRD, SEM and TG/DTA. Carboreduction reactions were carried out at 700 and 750°C with two cobalt compositions (2,5 and 5%). Reaction’s products were characterized by XRF, XRD, SEM, TOC, BET and laser granulometry. It was possible to obtain Mo2C with 2,5 and 5% cobalt addition as a single phase at 750°C with nanoscale crystallite sizes. At 700°C, however, both MoO2 and Mo2C phases were found by XRD. No Co containing phases were found by XRD. XRF, however, confirmed the intended Co content added. SEM images confirmed XRD data. The increase on Co content promoted a more severe agglomeration of the produced powder. The same effect was noted when the reaction temperature was increased. The powder synthesized at 750°C with 2,5% Co addition TOC analysis indicated the complete conversion from oxide material to carbide, with a 8,9% free carbon production. The powder produced at this temperature with 5% Co addition was only partially converted (86%)

Single-crystal micro/nanostructures and thin films of lamellar molybdenum oxide by solid-state pyrolysis of organometallic derivatives of a cyclotriphosphazene

The solid-state pyrolysis of organometallic derivatives of a cyclotriphosphazene is demonstrated to be a new, simple and versatile solid-state templating method for obtaining single-crystal micro- and nanocrystals of transition and valve metal oxides. The technique, when applied to Mo-containing organometallics N3P3[OC6H4CH2CN·Mo(CO)5]6 and N3P3[OC6H4CH2CN·Mo(CO)4 py]6, results in stand-alone and surface-deposited lamellar MoO3 single crystals, as determined by electron and atomic force microscopies and X-ray diffraction. The size and morphology of the resulting crystals can be tuned by the composition of the precursor. X-ray photoelectron and infrared spectroscopies indicate that the deposition of highly lamellar MoO3 directly on an oxidized (400 nm SiO2) surface or (100) single-crystal silicon surfaces yields a layered uniphasic single-crystal film formed by cluster diffusion on the surface during pyrolysis of the metal-carbonyl derivatives. For MoO3 in its layered form, this provides a new route to an important intercalation material for high energy density battery materials.