Abstract: Catalytic oxidation of n-hexane, benzene and 2-propanol was investigated on Au/CeO2/Al2O3 and Au/Al2O3 catalysts prepared from the deposition–precipitation method and characterised by XRD, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–VIS and X-ray photoelectron spectroscopy (XPS) techniques. It is shown that ceria enhances the fixation and final dispersion of gold particles, leading to stabilise them in lower crystallite sizes. Catalytic results show that ceria improves the activity of gold particles in the oxidation of the tested volatile organic compounds (VOCs), probably by increasing the mobility of the lattice oxygen and controlling and maintaining the adequate oxidation state of the active gold particles.

Abstract: The oxidation state and local geometry of tellurium in MoVTeNbO catalysts used in the ammoxidation or oxidation of propane were characterized by X-ray absorption, Mossbauer, and X-ray photoelectron (XPS) spectroscopies. The results obtained by Mossbauer, and XPS spectroscopies showed that the catalysts contained Te(IV) in the bulk and mainly Te(VI) at the surface. X-ray absorption fine structure (EXAFS) measurements allowed to determine that the tellurite entities corresponded to TeO4E trigonal bipyramid in the hexagonal phase and to TeO3E somewhat distorted trigonal pyramid in the orthorombic one. The completely determined environment appeared to correspond in both phases to crystallographic sites in hexagonal channels. These results allowed to determine the stoichiometries of the two phases which are TeM3O10 for the hexagonal phase and Te2M20O57 for the orthorombic phase (M=Mo, V, Nb). 125Te Mossbauer isomer shift and pre-peak surface of the X-ray absorption spectra of the Te LIII-edge have been correlated and contributions of the Te(5s) and Te(2p3/2) to the structure have been analyzed.

Abstract: We have investigated the electronic and atomic structure of a manganese-chromium-based layered oxide material Li@Li0.2Cr0.4Mn0.4#O2 during electrochemical cycling using in situ X-ray absorption spectroscopy. Our results indicate that charge compensation in the cathode material is achieved by the oxidation/reduction of octahedral Cr~III! ions to tetrahedral Cr~VI! ions during delithiation/lithiation. Manganese ions are present predominantly in the Mn~IV! oxidation state and do not appear to actively participate in the charge compensation process. To accommodate the large changes in coordination symmetry of the Cr~III! and Cr~VI! ions, the chromium ions have to move between the regular octahedral sites in the R3 m-like lattice to interstitial tetrahedral sites during the charge/discharge process. The highly reversible ~at least after the first charge! three-electron oxidation/ reductions and the easy mobility of the chromium between octahedral and tetrahedral sites are very unusual and interesting. Equally interesting is the fact that chromium is the active metal undergoing oxidation/reduction rather than manganese. Our results also suggest that in the local scale manganese and chromium ions are not evenly distributed in the as-prepared material, but are present in separate domains of Mn and Cr-rich regions.

Abstract: The molecule Ni3(dpa)4Cl2 (1) can be oxidized by AgPF6 to give crystalline Ni3(dpa)4(PF6)3 (2) (dpa is the anion of di(2-pyridyl)amine). This reversible oxidation occurs at a potential of 0.908 V vs Ag/AgCl electrochemically. The X-ray structure of 2 shows that the oxidation causes a major structural change (even though it is reversible), namely, a contraction of the Ni−Ni distances from ca. 2.43 A to 2.284[1] A. In addition, the electronic structure changes so that from four unpaired electrons in 1 there is only one in 2. From these remarkable results, it is inferred that while 1, and all higher homologues with 5, 7, 9, ..., nickel atoms are poor electronic conductors, the cations obtainable from them may be much better ones. This in turn means that by controlling the oxidation state electrochemically, these molecules may be able to function as nanoscale diodes.

Abstract: The synthesis of MoVNbTe(Sb)Ox composite oxide catalysts based on the self-organization of polyoxometalates (POMs) was investigated. The catalysts which were synthesized via reduction of POMs by using reducing agents under mild conditions and/followed by calcination in an O2-excluded atmosphere which superior performance for propane (amm)oxidation. It was suggested that the metastable phase formed at an elevated temperature with a specific oxidation state corresponds to the catalytic activity.

Abstract: The crystal and molecular structure of the layered weak-ferromagnet Fe[CH3PO3]·H2O has been solved by X-ray single-crystal diffraction techniques. Crystal data for Fe[CH3PO3]·H2O are the following: orthorhombic space group Pna21; a =17.538(2), b = 4.814(1), c = 5.719(1) A. The structure is lamellar, and it consists of alternating organic and inorganic layers along the a direction of the unit cell. The inorganic layers are made of Fe(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one from oxygen of the water molecule. Each phosphonate group coordinates four metal ions, through chelation and bridging, making in this way a cross-linked Fe−O network. The resultant layers are then separated by bilayers of the methyl groups, with van der Waals contacts between them. The compound is air stable, and it dehydrates under inert atmosphere at temperatures above 120 °C. The oxidation state of the metal ion is +2, and the electronic configuration is d6 high spin (S = 2), as determined from dc m...

Abstract: The oxidation of a variety of substrates (thioethers, hydrocarbons, alkenes, benyzl alcohol and benzaldehyde) by t BuOOH catalyzed by Mn 4 O 4 (O 2 PPh 2 ) 6 ( 1 ) and Mn 4 O 4 (O 2 P( p -MePh) 2 ) 6 ( 2 ) is reported. These reactions illustrate the first examples of oxidative catalysis using a manganese-oxo complex with a Mn 4 O 4 cubane core. These uncharged complexes contain Mn ions in a mixed valence oxidation state, formally Mn 4 (2III, 2IV), and are bridged by bulky diphenylphosphinate chelates across each of the six faces of the cube. Using this system, methyl phenyl sulfide is selectively mono-oxygenated to methyl phenyl sulfoxide with high catalytic efficiency, and no evidence for further oxidation to the thermodynamically preferred sulfone. Toluene is oxidized to a mixture of benzyl alcohol, benzaldehyde, and benzoic acid with high catalytic efficiencies. Lower catalytic efficiencies are observed in the oxidation of styrene to a mixture of styrene oxide and benzaldehyde, of cyclohexene to a mixture of cyclohexene oxide, 2-cyclohexen-1-ol, and 2-cyclohexen-1-one, and of cyclohexane to a mixture of cyclohexanol and cyclohexanone. The observed product distribution from the oxidation of hydrocarbons has the characteristics of a free radical-based oxidation mechanism. However, the sulfoxidation and epoxidation activity of the 1 / t BuOOH system, as well as the observed steric preferences for less congested substrates, suggest that a metal-oxo centered oxidation mechanism is active in the reactions studied here. An intermediate species, characterized by a UV–VIS band centered at 610 nm is observed in all reaction mixtures, and forms upon reaction of 1 or 2 with t BuOOH . Preliminary evidence suggests this reactive intermediate may correspond to a Mn(V)O species. Kinetic studies suggest two pathways for oxidation: one involving an oxygen atom transfer (two-electron branch), and the other involving a hydrogen atom abstraction (one-electron branch).

Abstract: Recent experiments on the dehydrogenation−aromatization of methane (DHAM) to form benzene using a MoO3/HZSM-5 catalyst stimulated us to examine methane activation by the transition-metal oxide molecules, MOx (M = Cr, Mo, W; x = 1, 2, 3). The present studies use hybrid density functional theory (B3LYP). The reactivity trend is rationalized in terms of changes in the electrophilicity of MOx, the strength of the M−O π bond, and the bonding properties of MOx to methyl or hydrogen as M and x are varied. It is found that σ-bond metathesis to the metal hydride product (H−MOx-1−OCH3) occurs preferentially over the high oxidation state form (MO3) of the heavier metals, as well as all chromium oxides (CrOx). Instead, oxidative addition of MOx leading to methyl metal hydride (H−M(Ox)−CH3) is more favorable over the low oxidation state of MOx (M = Mo, W, x = 2, 1). In particular, it is found that WO2 can undergo oxidative addition with negligible activation barrier and is predicted to be the most reactive compound of...

Abstract: Various Au/Fe2O3 catalysts were prepared by the coprecipitation method, and CO oxidation was studied at ambient temperature and in the presence of water vapor in the feed. It was found that the precipitation method and the calcination temperatures have a significant effect on the catalytic performance of CO oxidation. The stability is related to the particle size of metallic gold and α-Fe2O3 and the oxidation state of gold and the iron crystalline phase. The sintering of the gold particles, the reduction of oxide gold to metallic gold, the accumulation of carbonate, and a decrease in the specific surface area were observed during the reaction, which may contribute to the deactivation of Au/Fe2O3 catalysts.

Abstract: The relationship between the structure and ion intercalation in electrodeposited nickel hexacyanoferrate thin films is investigated using energy-dispersive X-ray (EDS) and Raman spectroscopies combined with electrochemical control of the iron centers' oxidation states. Nickel hexacyanoferrate thin films are prepared by cathodic deposition on a platinum substrate. Potential cycling in the range −100 to +900 mV vs saturated calomel electrode is used to reversibly intercalate and deintercalate K+ from the matrix. Raman spectroscopy is used to determine the oxidation state of the iron centers, and EDS quantifies K+ intercalation. Potential step changes are made between −100 and +900 mV, with spectroscopic analysis following each step change. A number of structural analogues to “soluble” and “insoluble” Prussian Blue are tested against the experimental results. The relationship between the amount of intercalated alkali cations and the oxidation state of the iron centers suggests that this material is nickel-ri...

Abstract: The behavior of V=O band over V2O5 crystallite during NH3 adsorption and SCR reaction was characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and the results are correlated with the reactivity in NH3 oxidation and SCR reaction. It is found that the decrease of V=O band intensity is due either to the reduction of V2O5 surface and/or to the adsorption of ammonia. The 70% intensity of original V=O band is preserved up to 573 K under the conditions of SCR reaction. The vanadium oxidation state is about +4.4. When the temperature reached 673 K, almost all the V=O band was recovered. From these results, it can be suggested that the decrease of the apparent SCR activity due to the increase of NO amount through NH3 oxidation above 673 K he attributed to the increase of two neighboring V=O sites, which favor the NO formation in ammonia oxidation. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: The reaction between CO 2 and ZSM-5- and SiO 2 -supported Mo 2 C catalysts, found to be active in the aromatization of methane, has been studied in a flow and static system by measuring changes in the gas composition. The reaction was also followed with X-ray photoelectron spectroscopy. The decomposition of CO 2 occurred above 823 K to give CO and O atoms. Using 1 3 CO 2 it was possible to establish that a fraction of O atoms oxidized the carbon of Mo 2 C into CO, the other part reacted with Mo to give MoO x species. The ratio of 1 3 CO/ 1 2 CO varied between 5 and 6.0. XPS study confirmed the oxidation of Mo resulting in the formation of Mo ions of various oxidation states. Although the dominant oxidation state is Mo 6 + at every temperature, Mo 4 + and Mo 5 + were present in the sample even after the reaction at 1073 K. The reaction proceeded at a faster rate on MO 2 C/ZSM-5 than on MO 2 C/SiO 2 .

Abstract: X-ray photoelectron spectroscopy analysis of Cu 2p peaks is able to discriminate between Cu(II) and Cu(I). This is particularly useful when copper is supported in a zeolite matrix, as in heterogeneous catalysts. The preparation route, the Si/Al ratio and the kind of zeolite all contribute to determine the final oxidation state of copper. In turn, the oxidation state determines the effectiveness of the catalyst. Samples prepared via the gas phase and solution are considered in this work after calcination. Both H-zeolite and Na-zeolite are found in different copper final states when considered just after preparation, depending on ion-exchange or impregnation routes. Copyright © 2002 John Wiley & Sons, Ltd.

Abstract: This invention relates to electrode active materials, electrodes, and batteries. In particular, this invention relates to active materials comprising lithium or other alkali metals, transition metals, +3 oxidation state non-transition elements, and phosphates or similar moieties.

Abstract: Metal ions in unusual oxidation states can be introduced into water clusters using a standard laser vaporization source. Such nanosolutions of a single ion in typically 50 water molecules are comparable to a 1 M bulk solution, and their chemistry can be studied in the ion trap of a Fourier transform ion cyclotron resonance mass spectrometer. We find that a strong acid like hydrogen chloride oxidizes the early transition metal vanadium to the more common +III state, while later first row transition metals retain their unusual +I oxidation state, and the binary metal chlorides M(I)Cl precipitate.

Abstract: We examined the oxidation reaction of n-C6H14 and SO2 over two types of Pt/ZrO2 catalysts with low (8 m2/g) and high (75 m2/g) surface areas of the ZrO2 supports (referred to as ZrO2-8 and ZrO2-75, respectively). The catalytic activity was evaluated under simulated diesel exhaust gas which simultaneously contained n-C6H14 and SO2. The Pt/ZrO2-75 exhibited a desirably higher selectivity for the complete oxidation of n-C6H14 than that of SO2, as compared with the Pt/ZrO2-8. In order to clarify the cause of this selective oxidation, we investigated the Arrhenius parameter for these oxidation reactions and characterized these catalysts using X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), Transmission electron micrograph (TEM), IR and CO2 temperature-programmed desorption (CO2-TPD) methods. The amount of Pt0 (metal) in the Pt/ZrO2-75 was significantly lower than that in Pt/ZrO2-8, because the high basicity of the ZrO2-75 support stabilized the high oxidation state of Pt such as Pt2+ and Pt4+. It was concluded that the difference in the number of Pt0 sites as catalytic active sites causes the apparent selectivity to change due to the much slower reaction rate for the SO2 oxidation than that for the n-C6H14 oxidation.

Abstract: “Nanodroplets” consisting of a central ion surrounded by a solvation shell of water molecules provide an interesting medium for studies of aqueous transition-metal chemistry in the unusual oxidation state (I). While VI undergoes efficient, solvent shell dependent redox reactions to VII and VIII, the absence of any similar reactivity in aqueous CrI, MnI, FeI, CoI, NiI, and CuI clusters is explained by a rapid precipitation of the corresponding single monochloride molecules from the nanosolutions.

Abstract: We investigated the gas phase reaction mechanisms in the ZrO2-deposition plasma using zirconium tert-butoxide (ZTB) as a metalorganic precursor, Ar as a carrier of the ZTB vapor, and O2 as an oxidant using quadrupole mass spectrometry (QMS). Zirconium containing ions including Zr+, ZrO+, ZrO2H+, ZrO3H3+, and ZrO4H5+ were clearly observed in the plasma, and ions of higher zirconium oxidation states become progressively favored at higher O2-to-ZTB carrying Ar flow rate ratio (O2/Ar), increased chamber pressure, and decreased microwave power. The average oxidation state calculated from the partition of ZrOxHy+ varied from 0.5 to 2.1 in the process range covering O2/Ar of 0 to 4, pressure of 5 to 40 mTorr, and power of 150 to 700 W. Based on the QMS analyses, we proposed two main opposing reaction paths responsible for the complex gas phase reactions, i.e., serial dissociations and serial oxidations. The increase in the electron temperature and density resulted in the shift of ZrOxHy+ to lower oxidation state...