Abstract: Mn–Ce–O composite catalysts have been widely used in sub- and supercritical catalytic wet oxidation of toxic organics contained in aqueous streams. In order to investigate their composition–activity relationship, 11 samples with Ce/(Mn+Ce) atomic bulk ratios ranging from 0 to 100% were prepared by co-precipitation. Phenol was selected as a model pollutant and the catalytic oxidation was carried out in a batch slurry reactor using oxygen as the oxidizing agent under mild reaction conditions. The results showed that the catalytic activity was greatly influenced by the catalyst composition. The catalyst with Mn/Ce ratio=6/4 was found to be the most active in reducing both phenol concentration and total organic carbon (TOC). All catalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), temperature programmed reduction (TPR) and nitrogen adsorption techniques. Systematic shifts in binding energy, diffraction angle, and reduction temperature were observed in the XPS, XRD and TPR spectra, respectively. XPS and XRD data revealed the occurrence of significant interactions between Mn and Ce oxides, resulting in the evolution of textural, structural and oxidation state with composition. TPR analysis showed that the interaction between Mn and Ce greatly improved the oxygen storage capacity of manganese and cerium oxides as well as oxygen mobility on the surface of catalyst. Catalytic active sites have been ascribed to manganese oxide species exhibiting higher oxidation state. Furthermore, XPS revealed that the most active catalyst, i.e. Mn/Ce 6/4, exhibits an electron-rich surface which may be very important in the activation of adsorbed oxygen.

Abstract: This paper reports a study on the influence of calcination pretreatments on the catalytic behaviour of the Au/iron oxide system towards the combustion of some representative volatile organic compounds (2-propanol, ethanol, methanol, acetone and toluene). The catalytic activity of Au/Fe 2 O 3 samples towards the total oxidation to CO 2 has been found to be strongly dependent on the catalyst pretreatment, decreasing on increasing the calcination temperature. On the basis of characterisation data (XPS, FT-IR, XRD, BET surface area) it has been proposed that the catalytic behaviour is related to the gold state and/or the iron oxide phase. It appears plausible to suggest that the gold oxidation state and/or the particle size play a key role in the catalytic combustion of volatile organic compounds.

Abstract: At room temperature CO is adsorbed strongly on Cu+ sites (band at 2131 cm−1) whereas NO is preferably adsorbed on Cu2+ sites (band at 1882 cm−1). Coadsorption of CO and NO allows simultaneous and selective detection of both kinds of cations. This observation is used to follow the changes on the sample surface occurring in the presence of oxygen. Addition of small amounts of O2 to the CO–NO–Cu/SiO2 system first leads to the oxidation of the Cu+ sites to Cu2+. This process is followed by formation of surface nitrates which block the Cu2+ sites for NO adsorption. Adsorption of CO at 85 K allows detection of Cu2+ cations (ca. 2200 cm−1) in addition to the Cu+, CO is replaced by NO from these sites. Cu0 sites form carbonyls which, when copper is highly dispersed, can absorb at the same frequency at which Cu+–CO carbonyls are detected. In this case both kinds of species could be distinguished by their stability: the Cu0–CO species are easily destroyed during evacuation.

Abstract: Two structurally homologous Mn compounds in different oxidation states were studied to investigate the relative influence of oxidation state and ligand environment on Mn K-edge X-ray absorption near-edge structure (XANES) and Mn Kβ X-ray emission spectroscopy (Kβ XES). The two manganese compounds are the di-μ-oxo compound [L‘2MnIIIO2MnIVL‘2](ClO4)3, where L‘ is 1,10-phenanthroline (Cooper, S. R.; Calvin, M. J. Am. Chem. Soc. 1977, 99, 6623−6630) and the linear mono-μ-oxo compound [LMnIIIOMnIIIL](ClO4)2, where L- is the monoanionic N,N-bis(2-pyridylmethyl)-N‘-salicylidene-1,2-diaminoethane ligand (Horner, O.; Anxolabehere-Mallart, E.; Charlot, M. F.; Tchertanov, L.; Guilhem, J.; Mattioli, T. A.; Boussac, A.; Girerd, J.-J. Inorg. Chem. 1999, 38, 1222−1232). Preparative bulk electrolysis in acetonitrile was used to obtain higher oxidation states of the compounds: the MnIVMnIV species for the di-μ-oxo compound and the MnIIIMnIV and MnIVMnIV species for the mono-μ-oxo compound. IR, UV/vis, EPR, and EXAFS spec...

Abstract: The compounds Cp*Fe(dppe)X ([Fe]X) and the corresponding cation radicals [Fe*]X*+ are available for the series X = F, Cl, Br, I, H, CH3. This has allowed for a detailed investigation of the dependence of the nature of Fe-X bonding on the identity of X and the oxidation state (charge) of the complex. Cyclic voltammetry demonstrates that the electrode potentials for the [Fe]X0/+ couples decrease in the order I > Br > Cl > H > F > CH3. An "inverse halide order" is seen, in which the most electronegative X leads to the most easily oxidized complex. This suggests that F is the best donor among the halides. The halide trend is also reflected in NMR spectroscopic data. Mossbauer spectroscopy data also suggest that the F ligand is a strong donor (relative to H and CH3) in [Fe*]X*+. DFT calculations on CpFe(dpe)X ([Fe]X) model complexes nicely reproduce the trend in the electrode potentials for the [Fe*]X0/+ couples. Analysis of the theoretical data within the halogen series indicates that the energy of the [Fe]X HOMO does not correlate with the extent of its Fe(d(pi))-X(p(pi)) antibonding character, which varies in the order I > Br > Cl > F, but rather depends on the destabilizing electrostatic effect caused by X. This effect varies in the order F > Cl > Br > I. A thermochemical cycle that incorporates the [Fe*]X0/+ and [Fe*]0/+ electrode potentials was used to investigate the effect of the oxidation state of the complex on the homolytic bond dissociation energy (BDEhom), defined for the processes Fe-X --> Fe* + X* and Fe-X*+ --> Fe*+ + X*. For all X, it was found that a one-electron oxidation leads to a weakening of the Fe-X bond. This trend was reproduced by the DFT calculations. On the other hand, IR nu(Fe-X) spectroscopy data showed an increase in the stretching frequencies for X = H and Cl upon oxidation. X-ray crystallographic data showed a shortening of the Fe-Cl bond upon oxidation. The trends in IR and Fe-Cl bond distances were reproduced in the DFT calculations. The combined data therefore suggest that oxidation leads to weaker, but shorter, Fe-X bonds. A second thermochemical cycle was applied to investigate the effect of the one-electron oxidation on the heterolytic bond dissociation energies (BDEhet), defined for the processes Fe-X --> Fe+ + X- and Fe-X*+ --> Fe2+ + X-. In this case, the oxidation led to bond strengthening in all cases. The computed BDE values have been analyzed within Ziegler's transition state methodology and decomposed into two components, one electrostatic and one covalent, describing the interaction between the unrelaxed fragments. In all the computed BDEhom and BDEhet values of the [Fe]X models the electrostatic component is important. This helps to understand their respective variations upon oxidation.

Abstract: The electrospray ionization mass spectrometry (ESI-MS) behavior of seven Cu(II) complexes with tetradentate ligands has been studied. An unexpected reduction process, in positive ion mode, of the Cu oxidation state was observed, and shown to be due to charge transfer between the metal complex and the solvent molecules in the gas phase. Ion trap collision-induced dissociation experiments and deuterated solvents were used to support the proposed mechanism that is not a common electrochemical redox reaction at the ESI tip, but a gas-phase process. A series of solvents (acetonitrile, methanol, ethanol, propanol and iso-butanol) were tested, and a correlation between ionization energy (IE) and the amount of Cu(I) produced in ESI has been demonstrated for the alcohols, although some other solvent properties should also be taken into account. The electrochemical reduction potential of the complexes in solution is also an important parameter, since complexes more easily reduced in solution are also easier to reduce in the gas phase. Copyright © 2001 John Wiley & Sons, Ltd.

Abstract: The geochemical behavior of sulfur in magmas depends strongly on the oxidation state of sulfur, but this is not easily determined by standard analytical methods. We have measured XANES absorption spectra at the sulfur K-edge and have found that such measurements are useful to characterize the oxidation state and speciation of sulfur in silicate glasses of geological rel evance. Measured spectra of a set of reference minerals show the effects of different oxidation states and coordination numbers of sulfur; there is a large shift in energy (~10‐12 eV) of the sulfur K-edge between S 2‐ and S 6+ . This large and easily detectable difference makes possible the measurement of the valence of sulfur in unknown samples by measuring the shift in energy of the absorption edge. This approach is applicable to both crystalline and glassy materials, and useful results have been obtained on samples with as little as 450 ppm S. We have used XANES measurements to characterize oxidation state and speciation of sulfur in a set of natural and synthetic sulfur-bearing glasses. The samples cover a range of composition from basaltic to almost rhyo litic, and some were synthesized over a range of pressure, temperature and oxygen fugacity; glass S content varies between 450 and 3000 ppm. XANES analyses, carried out in fluorescence mode at LURE, allowed determination of the sulfur oxidation state in all of the samples and clearly show that some samples contain a mixture of S 2‐ and S 6+ ; no other sulfur species were observed. Quantitative determination of the abundance of sulfide and sulfate shows good agreement with independent measurements based on electron-microprobe determination of the wavelength shift of sulfur K X-rays.

Abstract: The nature of the vanadium species present on V2O5/Al2O3 catalysts was investigated by using solid state 51V NMR, diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD) and temperature programmed reduction (TPR). 51V NMR and DRS analyses indicated the presence of V5+ in tetrahedral symmetry at low vanadium loading. A surface polymeric vanadium species and/or the bulk crystalline V2O5 were mainly observed at high vanadium loading as also detected by XRD. The positions of the absorption edges determined through the UV–VIS spectra allowed distinguishing between various tetrahedral symmetries. After TPR, the average oxidation state of vanadium depended on the vanadium content. The nature of vanadium species was related to the catalyst behavior on the benzene oxidation reaction. The catalysts containing high vanadium content were more active suggesting that a high amount of V4+ is responsible for the higher activity.

Abstract: A method and system of removing arsenic from aqueous solutions is provided. Specifically, the aqueous solution includes arsenic, said arsenic being present in the +3 oxidation state. Arsenic can also be present in the +5 oxidation state. The pH of the aqueous solution is first adjusted to a pH in the range of about 3 to 5. Iron salts , such as ferric or an ferrous salts, are introduced into the aqueous solution. Hydrogen peroxide is added to the aqueous solution wherein the arsenic present in the +3 oxidation state is oxidized to the +5 oxidation state. Next, the pH of the aqueous solution is adjusted to a value in the range of about 5 to 8 to form an insoluble ferric hydroxide compound including arsenic in the +5 oxidation state adsorbed onto the compound which is then removed from the aqueous solution.

Abstract: Voltammetric activities are compared for the designated compounds in 0.50 M H 2 SO 4 at the specified film electrodes configured as rotated disks. The effective number of electrons (n eff equiv mol -1 1 ) calculated from the Koutecky-Levich plot is 3.1 ± ± 0.2 for toluene oxidation at the Fe-PbO 2 electrode, compared to 2.0 0 ± 0.05 and 4.1 ± 0.3 at the Bi-PbO 2 and PbO 2 electrodes, respectively. Gas chromatography--mass spectrometry data confirm that the primary product of toluene oxidation is benzyl alcohol (2 equiv mol -1 ) at the Fe-PbO 2 electrode with production of small amounts of henzaldehyde (4 equiv mol 1 ) and benzoic acid (6 equiv mol -1 ). X-ray photoelectron spectroscopy data indicate the ratio of Fe:Pb is ca. 1: 100 (atom:atom) in the Fe-PbO 2 films. By comparison, a Bi:Pb ratio of 33:100 (atom:atom) is easily attained in Bi-PbO 2 films. Nevertheless, the apparent heterogeneous rate constant (k app , cm s -1 ) for toluene oxidation is larger at the Fe-PbO 2 electrode (6.5 ± 0.06 × 10 -3 ) compared to the Bi-PbO 2 electrode (2.0 ± 0.05 × 10 -3 ). X-ray absorption near-edge structure data confirm speculation that iron exists in the 3+ oxidation state with octahedral coordination by O atoms in Fe-PbO 2 films. The large activity of the Fe-PbO 2 electrode is attributed to the benefit of adsorption of aromatic molecules at Fe(III) sites.

Abstract: X-ray Absorption Near Edge Spectroscopy (XANES) shows that Pt in Pt nitrate solutions has +4 oxidation state. Extended X-ray absorption fine structure (EXAFS) reveals each Pt is coordinated to an average of 5.4(±0.5) oxygen atoms with a PtO bond distance of 1.99(5) A. Each Pt center has an average of 2.9 neighboring Pt atoms with a Pt···Pt non-bonding distance of 3.08(3) A. A Pt[μ-O(H)]2Pt ring with two Pt atoms linked by two O or OH ligands is proposed to be the primary structure moiety and building blocks for more complex oligomeric structures. Pt(IV) nitrate solution is prone to hydrolysis upon dilution forming an amorphous reddish-brown precipitate PtO2·xH2O. Pt nitrate has more complete adsorption on alumina than H2PtCl6 with no significant change of Pt coordination and oxidation state observed upon adsorption. Upon calcination to 500°C, Pt complexes undergo structural changes but remain as Pt(IV). H2 TPR of Pt nitrate on alumina is consistent with Pt(IV) to Pt metal reduction. The rapid and strong adsorption of Pt nitrate results in Pt depositing only at the outer surface of catalyst washcoats, in sharp contrast to uniform distribution from H2PtCl6. Pt/Rh three-way catalysts made from Pt nitrate/Rh nitrate have equivalent light-off but better hydrocarbon, CO and NOx conversions than those made from H2PtCl6/RhCl3 solutions.

Abstract: The synthesis and full characterization of [(tmc)MnCl]·X (where tmc is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X is BPh4- or BF4-) are reported. The complex is of type I geometry. The manganese ion is pentacoordinated by the four tertiary nitrogen atoms of the macrocycle and one axial chloride. Variable-temperature magnetic susceptibility data indicate that the oxidation state of the manganese ion is +II with S = 5/2. The EPR spectrum exhibits unusual signals, with the main derivative line at g = 3.7 and transitions at more than 900 mT. The cyclic voltammogram of this derivative consists of two reversible systems at +1.14 and +1.36 V vs SCE related by a chemical equilibrium attributed to an isomerization process.

Abstract: Partial oxidation of the tetraalkyltetraindium(I) compound In4[C(SiMe3)3]4] 1 with halogen donors such as 1,2-dibromoethane and hexachloroethane or with mixtures of bromine and aluminum tribromide afforded novel alkylindium halides in which the indium atoms still possess unusually low oxidation states. Indium-indium single bonds between bivalent indium atoms were found in the compounds In2X2R2 (R = C(SiMe3)3, X = Cl (2) or Br (4)), which gave dimers in the solid state with all four halogen atoms in a bridging position. The tetrahedral arrangement of four indium atoms in a cluster was retained in the compound In4Br2R4 (3), in which one bromine atom occupied a mu3-bridging position above one triangular face of the In4 tetrahedron. One edge of that triangle was bridged by the second bromine atom. Mixed-valent indium atoms resulted with an average oxidation state of + 1.5.