Showing papers on "Oxidation state published in 2004"
TL;DR: The charge storage mechanism in MnO2 electrode, used in aqueous electrolyte, was investigated by cyclic voltammetry and X-ray photoelectron spectroscopy as discussed by the authors.
Abstract: The charge storage mechanism in MnO2 electrode, used in aqueous electrolyte, was investigated by cyclic voltammetry and X-ray photoelectron spectroscopy. Thin MnO2 films deposited on a platinum substrate and thick MnO2 composite electrodes were used. First, the cyclic voltammetry data established that only a thin layer of MnO2 is involved in the redox process and electrochemically active. Second, the X-ray photoelectron spectroscopy data revealed that the manganese oxidation state was varying from III to IV for the reduced and oxidized forms of thin film electrodes, respectively, during the charge/discharge process. The X-ray photoelectron spectroscopy data also show that Na+ cations from the electrolyte were involved in the charge storage process of MnO2 thin film electrodes. However, the Na/Mn ratio for the reduced electrode was much lower than what was anticipated for charge compensation dominated by Na+, thus suggesting the involvement of protons in the pseudofaradaic mechanism. An important finding o...
2,659 citations
TL;DR: In this paper, the binding energy of the V2p3/2 core level for each vanadium oxidation state is fixed relative to the O1s level, and satellite peaks are added to the fit especially for the lower vanadium oxides.
1,656 citations
TL;DR: Kinetic measurements for the catalytic oxidation of carbon monoxide show that the gold bilayer structure is significantly more active than the monolayer, thus eliminating particle shape and direct support effects.
Abstract: The high catalytic activity of gold clusters on oxides has been attributed to structural effects (including particle thickness and shape and metal oxidation state), as well as to support effects. We have created well-ordered gold mono-layers and bilayers that completely wet (cover) the oxide support, thus eliminating particle shape and direct support effects. High-resolution electron energy loss spectroscopy and carbon monoxide adsorption confirm that the gold atoms are bonded to titanium atoms. Kinetic measurements for the catalytic oxidation of carbon monoxide show that the gold bilayer structure is significantly more active (by more than an order of magnitude) than the monolayer.
1,643 citations
TL;DR: Decamethyldizincocene, Zn2(η5-C5Me5)2, an organometallic compound of Zn(I) formally derived from the dimetallic [Zn–Zn]2+ unit, has been isolated from the low-temperature (–10°C) reaction
Abstract: Unlike mercury, which has an extensive +1 oxidation state chemistry, zinc usually adopts the +2 oxidation state. Decamethyldizincocene, Zn2(eta5-C5Me5)2, an organometallic compound of Zn(I) formally derived from the dimetallic [Zn-Zn]2+ unit, has been isolated from the low-temperature (-10 degrees C) reaction of Zn(C5Me5)2 and Zn(C2H5)2 in diethyl ether. X-ray studies show that it contains two eclipsed Zn(eta5-C5Me5) fragments with a Zn-Zn distance (+/- standard deviation) of 2.305(+/-3) angstroms, indicative of a metal-metal bonding interaction.
508 citations
TL;DR: In this paper, the characterization of manganese-lanthanum oxides modified with silver has been performed in order to identify factors responsible for the variation of their activity in the oxidation of methane.
378 citations
TL;DR: In this article, the mixed transition metal layered compound, LiNi0.4Mn 0.4Co0.2O2, with the α-NaFeO2 layer structure has been synthesized and characterized.
Abstract: The mixed transition metal layered compound, LiNi0.4Mn0.4Co0.2O2, with the α-NaFeO2 layer structure has been synthesized and characterized. The optimum temperature of synthesis was found to be 800–900 °C. Rietveld refinement showed that cobalt suppresses transition metal ion migration into the Li sites whereas nickel promotes the migration. XPS analysis shows that the Co and about 20% of the Ni and Mn are in the 3+ oxidation state, while 80% of the Ni and Mn are in the 2+ and 4+ oxidation states, respectively. LiNi0.4Mn0.4Co0.2O2 shows Curie–Weiss paramagnetic behavior above 150 K, and the value of the Curie constant is consistent with the above oxidation states. In lithium electrochemical cells the composition LiNi0.4Mn0.4Co0.2O2 gave the highest reversible capacity among the studied compositions. It shows excellent rate capability, giving reversible capacities ranging from 180 to 155 mA h g−1 at current densities from 0.1 to 2.0 mA cm−2.
283 citations
TL;DR: The kinetic results indicated that the rates of manganese and iron oxidation were several orders of magnitude greater than the respective for abiotic oxidation.
278 citations
TL;DR: In this paper, the pre-edge X-ray absorption near edge structure (XANES) and Mossbauer spectra were collected on synthetic glasses of basaltic composition and of glasses on the sodium oxide-silica binary to establish a relation between the preedge of the XANES at the K-edge and the Fe oxidation state of depolymerised glasses.
220 citations
TL;DR: In this article, gold nanoparticles of 2-5 nm supported on woven fabrics of activated carbon fibers (ACF) were used to obtain a high metal dispersion during CO oxidation at room temperature, and the concentration and nature of surface functional groups were controlled using HNO3 pretreatment followed by either calcination in He (300-1273 K) or by iron oxide deposition.
213 citations
TL;DR: In this paper, the X-ray absorption near-edge structure (XANES) spectra were recorded for silicate glasses of various compositions in the system CaO + MgO + Al2O3 + SiO2 ± TiO2, quenched from melts equilibrated as a function of oxygen fugacity ( f O2) at 1400°C.
Abstract: Cr K -edge X-ray absorption near-edge structure (XANES) spectra were recorded for silicate glasses of various compositions in the system CaO + MgO + Al2O3 + SiO2 ± TiO2, quenched from melts equilibrated as a function of oxygen fugacity ( f O2) at 1400°C. The spectra vary systematically with f O2 (log f O2 ~0 to −16) indicating changes in the Cr oxidation state. The intensity of a shoulder on the absorption edge (attributed to the 1 s → 4 s transition) was quantified using the corresponding peak in the XANES derivative spectrum and used to determine Cr2+/∑Cr. The resulting Cr2+/∑Cr values are in agreement with the theoretical dependence on log f O2 suggesting that the 1s → 4s feature is diagnostic of Cr2+ in a silicate glass and σ(Cr2+/∑Cr) = ± 0.015. The Cr2+/∑Cr ratio for a given log f O2 changes with the glass composition which may reflect the ability of the melt to accommodate the Jahn-Teller distorted coordination geometry which stabilizes Cr2+. Cr2+/∑Cr varies between ~0.3 and 0.8 over the log f O2 range bounded by the Ni/NiO and Fe/FeO f O2 buffers, suggesting that Cr2+ may be important in natural melts even though this oxidation state has never been identified in a terrestrial material. The development of a methodology for determining Cr2+/∑Cr from XANES spectra of quenched glasses is an essential precursor to in situ experiments on Fe-bearing silicate melts at high temperature.
159 citations
TL;DR: Changes in aqueous- and solid-phase Pu oxidation state were monitored over time in magnetite (Fe3O4) suspensions containing 239Pu(V)-amended 0.01 M NaCl to find the Pu(IV) solid- phase species became more stable over time.
Abstract: Changes in aqueous- and solid-phase Pu oxidation state were monitored over time in magnetite (Fe3O4) suspensions containing 239Pu(V)-amended 0.01 M NaCl. Oxidation state distribution was determined by leaching of Pu into an aqueous phase followed by an ultrafiltration/solvent extraction technique. The capability of the technique to measure Pu oxidation state distribution was verified using 230Th(IV), 237Np(V), and 233U(VI) as oxidation state analogues. Reduction of Pu(V) was observed at all pH values (pH 3 to 8) and magnetite concentrations (10 to 100 m2 L-1). In the pH range 5 to 8, adsorption was a rate-limiting step, and reduction was mediated by the solid phase; at pH 3 reduction occurred in the aqueous phase. The overall reaction (describing both adsorption and reduction of Pu(V)) was found to be approximately first order with respect to the magnetite concentration and of order −0.34 ± 0.02 with respect to the hydrogen ion concentration. Assuming first order dependence with respect to Pu, the overall...
TL;DR: In this article, vanadium-containing mesoporous molecular sieves synthesized by direct hydrothermal (V-MCM-41), grafting, and immobilization methods were studied in the one-step liquid-phase oxidation of naphthalene using aqueous H2O2 and TBHP as oxidants.
TL;DR: In this article, a layer-structured LiMn0.5-xCo2xNi 0.5.5 O2 was prepared as cathode material for lithium-ion batteries and the structures of the layered materials and the oxidation states of the elements in the compounds were characterized by X-ray diffraction and Xray photoelectron spectroscopy.
Abstract: Layer-structured LiMn0.5-xCo2xNi0.5-xO2 was prepared as cathode material for lithium-ion batteries. The structures of the layered materials and the oxidation states of the elements in the compounds were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. Adsorbed oxygen was detected on the surface of material. With the increase of Co content in LiMn0.5-xCo2xNi0.5-xO2, the oxidation state of Ni, Mn, Co, and O became higher gradually while the amount of oxygen adsorbed on the surface of LiMn0.5-xCo2xNi0.5-xO2 grains reduced obviously. Electrochemical evaluation showed that addition of Co in LiMn0.5-xCo2xNi0.5-xO2 is beneficial to its rate performance. The variations of the electronic structure of Ni, Mn, and O may be responsible for the improvement of the rate capability in LiMn0.5-xCo2xNi0.5-xO2 with addition of Co. (C) 2004 The Electrochemical Society.
TL;DR: Ionically dispersed Rh over CeO2 in Rh/CeO2 catalysts prepared by a single step solution combustion method is shown to improve the redox property and catalytic activity.
Abstract: Ionically dispersed Rh over CeO2 in Rh/CeO2 catalysts prepared by a single step solution combustion method is shown to improve the redox property and catalytic activity. The H2/Rh ratio obtained from hydrogen uptake measurement was 5.4, 2.4, and 2.1, respectively in 0.5, 1, and 2% Rh/CeO2, indicating a significant contribution from the reduction of CeO2 in the presence of Rh. In 1% Rh/CeO2, the light-off temperature for CO oxidation is about 80 °C lower compared to Rh metal and 190 °C lower than that of Rh2O3. The enhanced redox property and CO oxidation activity of the catalyst has been correlated with the structure. The X-ray diffraction (XRD) pattern could be refined to the fluorite structure with Rh substituting in the Ce site. Transmission electron microscopy (TEM) images show only CeO2 crystallites of about 50 nm and no evidence of any metal particles up to 1 atom % Rh. X-ray photoelectron spectroscopy (XPS) studies demonstrate that Rh is dispersed in the +3 oxidation state on CeO2 with enhanced Rh ...
TL;DR: The surface of mackinawite, the first-formed iron sulfide phase in anoxic conditions, can promote redox changes so a series of laboratory experiments were carried out to explore the interactions of Tc, U and Np with this mineral.
Patent•
15 Apr 2004TL;DR: An uncycled electrode for a non-aqueous lithium electrochemical cell including a lithium metal oxide having the formula Li(2+2x) M'2x/(2+x)M(2-2x)/(2 +x)O2-δ, in which 0≤x<1 and δ is less than 0.2, was disclosed in this article.
Abstract: An uncycled electrode for a non-aqueous lithium electrochemical cell including a lithium metal oxide having the formula Li(2+2x)/(2+x) M’2x/(2+x)M(2-2x)/(2+x)O2-δ, in which 0≤x<1 and δ is less than 0.2, and in which M is a non-lithium metal ion with an average trivalent oxidation state selected from two or more of the first row transition metals or lighter metal elements in the periodic table, and M’ is one or more ions with an average tetravalent oxidation state selected from the first and second row transition metal elements and Sn. Methods of preconditioning the electrodes are disclosed as are electrochemical cells and batteries containing the electrodes. It is also disclosed an electrode for a non-aqueous lithium cell, comprising a lithium metal oxide having the formula xLi2M’O3•(1-x)LiMO2, in which 0≤x<1, and in which M is a non-lithium metal ion with an average trivalent oxidation state selected from two or more first-row transition metals or lighter metal elements in the periodic table, and M’ is one or more ions with an average tetravalent oxidation state selected from the first- and second row transition metal elements and Sn, the electrodes being preconditioned in a proton-containing medium with a pH<7.0 to yield xLi2-yHyO• xM’O2•(1-x)Li1-2H2MO2 compounds in which 0
TL;DR: An amine-templated iron(II) sulfate of the composition [H3N(CH2)6NH3] [FeII1.5F3(SO4)]·0.5H2O, I, representing an example of a Kagome lattice with Fe in the +2 state, has been synthesized under solvothermal conditions as mentioned in this paper.
Abstract: An amine-templated iron(II) sulfate of the composition [H3N(CH2)6NH3] [FeII1.5F3(SO4)]·0.5H2O, I, representing an example of a Kagome lattice with Fe in the +2 state, has been synthesized under solvothermal conditions. Having determined the structure by single-crystal X-ray diffraction, the oxidation state of iron was established by Mossbauer spectroscopy. The magnetic properties of the Fe(II) Kagome compound are rather unusual in that it undergoes ferrimagnetic ordering below 19 K and does not exhibit spin-glass freezing.
TL;DR: In this article, the structures of three 1:1 composite compounds were characterized by IR, UV, and ESR spectroscopy, single-crystal X-ray structural analysis, and by a study of their thermal properties.
Abstract: The structures of three 1:1 composite compounds prepared with the polyoxometalate (POM) [PMo12O40]3− and the cations [Ln(NMP)6]3+ [Ln = La (1), Ce (3), Pr (2); NMP = N-methyl-2-pyrrolidone] exhibit two types of zig-zag chains with alternating cations and anions through Mo−Ot−Ln−Ot−Mo links in the crystal. The compounds were characterized by IR, UV, and ESR spectroscopy, single-crystal X-ray structural analysis, and by a study of their thermal properties. In all the compounds, the La3+, Pr3+, and Ce3+ centers are eight-coordinate with the oxygen atoms in bicapped trigonal-prismatic geometries. The variation of the average Ln−O separations along the La, Ce, and Pr series is consistent with the effects of the lanthanide contraction. The results of the single-crystal X-ray diffraction analyses and the IR spectroscopic studies are in agreement and both show the metal cation units are coordinatively bonded to the Keggin clusters. The UV spectra of the title compounds suggest that their structures are entirely disrupted in dilute solution. Low-temperature ESR spectra indicate that thermal electron delocalization occurs among the Mo atoms in the three compounds. The results of cyclic voltammetry (CV) show that compounds 1, 2, and 3 all undergo five two-electron reversible reductions and that the [PMo12O40]3− anions are the active centers for electrochemical redox reactions in solution, while the corresponding cations have only a small effect on the electrochemical properties. Studies of magnetic properties show that 1 is diamagnetic, while 2and 3 exhibit antiferromagnetic Pr−Pr or Ce−Ce exchange interactions. In addition to the results of CV, the average bond lengths and the magnetic properties of compound 3 indicate that the oxidation state of cerium is III in the compound of formula [{Ce(NMP)6}(PMo12O40)]n. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
TL;DR: In this article, the authors used temperature-programmed desorption (TPD), micro-calorimetry, and X-ray photoelectron spectroscopy (XPS) to study the mechanism of methanol oxidation on supported vanadia.
TL;DR: In this article, it was shown that the oxidation of gallium upon cooling of reduced samples to room temperature in hydrogen can be attributed to an oxidative addition of H2 resulting in the formation of Gallium dihydrides.
TL;DR: In this paper, a study on the influence of calcination temperature on the catalytic behavior of the Au/iron oxide systems in the water-gas shift reaction has been conducted.
Abstract: This paper reports a study on the influence of calcination temperature on the catalytic behavior of the Au/iron oxide systems in the water–gas shift reaction. The catalytic activity has been found to be strongly dependent on the catalyst pretreatment, decreasing on increasing the calcination temperature. Detailed characterization of the uncalcined and the calcined sample at different temperatures, employing BET analysis, XRD, H 2 -TPR, HRTEM and XPS, has shown that the catalytic behavior is related to the gold state and/or the particle size and the properties and structure of iron oxide support. Both the oxidation state and dispersion of gold and the phase transition and its crystallinity and reductive property of the support exert great influence on the catalytic performance of the gold/metal oxide. The wave of the activity within the middle reaction temperature range (i.e. 523–623 K) could be attributed to the difference of the operating temperatures belonging to the gold species and the active magnetite phase.
TL;DR: In this paper, five manganese complexes in an N 4O 2 donor environment have been prepared and the relative stabilities of the Mn +2 and Mn +3 oxidation states were analyzed using the structural data and MO calculations.
TL;DR: In this article, cyclic voltammetry (CV), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to characterize methanol oxidization.
Abstract: PtRu is a promising catalyst for methanol oxidation in direct methanol fuel cells. However, the most active Pt:Ru ratio and oxidation state of the Ru component are still under investigation. PtRu black was obtained from Johnson Matthey, and the as-received catalyst was treated with either hydrogen or oxygen at elevated temperatures to alter the oxidation state. The samples were characterized by cyclic voltammetry (CV), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and X-ray diffraction (XRD) to confirm their redox states and for correlation with their methanol oxidation activity. All of the characterization techniques support successful oxidation and reduction of the PtRu catalyst. The methanol oxidation activity was measured, and the sequence at 25 °C was found to be reduced > as-received > oxidized ≫ strongly oxidized. The effect of the drying regime and the dispersing agent for the catalysts was also investigated, and it was found that samples supported using acetic acid wer...
TL;DR: In this article, the reactivities of vanadium and niobium oxide cations and methanol were investigated using a guided ion beam mass spectrometer coupled to a laser vaporization source.
Abstract: As part of an ongoing study in our laboratory to elucidate the reactivities of the group V metal oxide clusters, reactions between vanadium and niobium oxide cations and methanol were conducted using a guided ion beam mass spectrometer coupled to a laser vaporization source. Size-specific cluster reactions were identified, with some indicated products being the same as those formed in methanol reactions over condensed phase niobia and vanadia catalysts, namely, H2CO and C2H6O. The effects of the properties of the clusters, among them size, stoichiometry, oxidation state, and composition on their reactivity toward methanol, are discussed.
TL;DR: In this paper, the M1 phase was shown to be active and selective for propane oxidation to oxygenates and ammoxidation to acrylonitrile in the presence of water vapor in the feed.
Abstract: The model Mo–V–Te–O catalysts containing the orthorhombic (M1) and hexagonal (M2) phases with well-defined crystal morphologies and promising for the selective oxidation of propane to oxygenates were obtained hydrothermally over a wide range of synthesis compositions (Mo 0.70–0.30 V 0.60–0.20 Te 0.15–0.05 ). The bulk (ICP), local (EDS) elemental and structural (XRD) analyses of this compositionally simple model system indicated that the M1 phase with the bulk Mo/V ratio of ∼2 was dominant in the Mo–V–Te–O catalysts. This phase has been proposed as active and selective for propane oxidation to oxygenates and ammoxidation to acrylonitrile. The model catalysts displayed high selectivity to acrylic acid in the presence of water vapor in the feed, which is believed to enhance the apparent rates of formation of oxygenates as well as maintain the catalytic surface in a partially reduced oxidation state. The selectivity to acrylic acid over these model catalysts correlated with the extent of exposure of the surface ab planes of the M1 phase proposed to contain the active and selective surface sites. Therefore, the Mo–V–Te–O catalysts represent a well-defined and highly promising model system for elucidating the surface molecular structure–activity/selectivity relationships in propane oxidation to acrylic acid over multicomponent Mo–V–Te–Nb–O catalysts.
TL;DR: Donor-acceptor bonding between group 13 elements seems counter-intuitive because one normally thinks of e.g. boron and aluminium compounds as classical Lewis acids, but it turns out that in the +1 oxidation state these species are excellent donors--hence the formation of these unprecedented donor- acceptor bonds.
TL;DR: In this paper, a five weight percentage of Pd/γ-Al2O3 catalysts were used for the oxidation of n-hexane, and it was shown that the catalysts whose initial activities at lower temperatures were higher than the oxidized catalysts showed a gradual deactivation.
TL;DR: In this article, the authors conducted a catalytic study of low oxidation state transition metal (carbonyl) clusters in ionic liquids and found that the activity of certain carbonyl clusters to hydrogenate alkene substrates, when they were immobilised in the ionic liquid, was up to 3.6-fold faster than that observed in organic solvents.
Abstract: Many low oxidation state transition metal (carbonyl) clusters are salts and are highly soluble in ionic liquids. Since many are also effective catalysts/precatalysts for hydrogenation reactions, we have conducted a catalytic study of these compounds in ionic liquids and found that the activity of certain clusters to hydrogenate alkene substrates, when immobilised in ionic liquids, is up to 3.6-fold faster than that observed in organic solvents. Using high-pressure NMR it has been possible to trace the improvements in activity to the increased stability of the cluster species in the ionic liquid. The ionic liquid also gives rise to higher regioselectivity in the hydrogenation of cyclic dienes to monoenes compared to that observed in organic solvents.
TL;DR: In this article, a combined experimental and theoretical investigation of met-myoglobin (Fe III ) with H 2 O 2 gives rise to ferryl myoglobin, which is closely related to compound II in peroxidases.
TL;DR: All important points of the potential energy surface (PES) are reported, and the complete catalytic cycle for the oxidative cleavage of olefins by ruthenium tetraoxide is presented.
Abstract: Quantum chemical calculations using gradient-corrected (B3LYP) density functional theory have been carried out to investigate the mechanism of the oxidative cleavage of alkenes by ruthenium tetraoxide. The initial reaction of the tetraoxide with the olefin occurs via a [3+2] cycloaddition as in the case of osmium tetraoxide. The results clearly show that the bond cleavage does not take place at the primary adduct, but much later in the reaction path. After the formation of the ruthenium(VI)dioxo-2,5-dioxolane, the reaction proceeds with the addition of a second olefin to yield ruthenium(IV)-bis(2,5-dioxolane), which in turn becomes oxidized first to rutheniumoxo(VI)-bis(2,5-dioxolane) 6(Ru) and then to ruthenium(VIII)-dioxo-bis(2,5-dioxolane) 7(Ru). Only in complexes containing the metal center in the formal oxidation state +VIII are low activation barriers for C-C bond cleavage and exothermic formation of carbonyl compounds as products calculated. The lowest activation barrier, DeltaH(++) = 2.5 kcal/mol, is calculated for the C-C bond breaking reaction of 7(Ru) which is predicted as the pivotal intermediate of the oxidation reaction. The calculations of the oxidation reaction with OsO(4) show that those reactions where the oxidation state of the metal increases have larger activation barriers for M = Ru than for M = Os, while reactions which reduce the oxidation state have a lower activation barrier for ruthenium compounds. Also, reactions which increase the oxidation state of the metal are in the case of M = Os more exothermic than for M = Ru. In this work, all important points of the potential energy surface (PES) are reported, and the complete catalytic cycle for the oxidative cleavage of olefins by ruthenium tetraoxide is presented.