Abstract: A series of manganese oxides differing in the structure, composition, average manganese oxidation state and specific surface area have been used in the total oxidation of volatile organic compounds (VOC). Ethanol, ethyl acetate and toluene were chosen as models of VOC. Among the manganese oxides tested, cryptomelane (KMn8O16) was found to be very active in the oxidation of VOC. The performance of cryptomelane was significantly affected by the presence of other phases, namely, Mn2O3 and Mn3O4. Temperature-programmed experiments combined with X-ray photoelectron spectroscopy (XPS) show that the mobility and reactivity of the oxygen species were significantly affected, explaining the catalytic performances of those samples. Mn3O4 improves the catalytic performance due to the increase of the reactivity and mobility of lattice oxygen, while Mn2O3 has the opposite effect. These results show that there is a correlation between the redox properties and the catalytic performance of the manganese oxides. Temperature-programmed surface reactions (TPSR) after adsorption of toluene or ethanol, in addition to reactions performed without oxygen in the feed, show that lattice oxygen is involved in the VOC oxidation mechanism. The conversion level was found to be influenced by the type of VOC, the reactivity into CO2 increasing in the following order: Toluene

Abstract: In situ X-ray photoelectron spectroscopy (XPS) was utilized to identify the chemical state of silver in a range of silver oxide thin films obtained by codeposition of silver and atomic oxygen. A highly oxidized silver species was observed at an unexpectedly low Ag 3d5/2 binding energy (BE) of 366.8 eV with an associated broad satellite at 368.2 eV; this species was assigned as Ag(III). It was found to be highly unstable in vacuum but could be regenerated by further exposure to atomic oxygen. Both BE shifts and intensity changes of the O 1s peak were found to correlate with changes in the silver oxidation state. The theoretical XPS spectrum of high spin Ag(III) was calculated for both an isolated cation and an embedded AgO6 cluster.

Abstract: The catalysts of iron-doped Mn-Ce/TiO2 (Fe-Mn-Ce/TiO2) prepared by sol-gel method were investigated for low temperature selective catalytic reduction (SCR) of NO with NH3. It was found that the NO conversion over Fe-Mn-Ce/TiO2 was obviously improved after iron doping compared with that over Mn-Ce/TiO2. Fe-Mn-Ce/TiO2 with the molar ratio of Fe/Ti = 0.1 exhibited the highest activity. The results showed that 96.8% NO conversion was obtained over Fe(0.1)-Mn-Ce/TiO2 at 180°C at a space velocity of 50,000 hr−1. Fe-Mn-Ce/TiO2 exhibited much higher resistance to H2O and SO2 than that of Mn-Ce/TiO2. The properties of the catalysts were characterized using X-ray diffraction (XRD), N2 adsorption, temperature programmed desorption (NH3-TPD and NOx-TPD), and X-ray photoelectron spectroscopy (XPS) techniques. BET, NH3-TPD and NOx-TPD results showed that the specific surface area and NH3 and NOx adsorption capacity of the catalysts increased with iron doping. It was known from XPS analysis that iron valence state on the surface of the catalysts were in Fe3+ state. The doping of iron enhanced the dispersion and oxidation state of Mn and Ce on the surface of the catalysts. The oxygen concentrations on the surface of the catalysts were found to increase after iron doping. Fe-Mn-Ce/TiO2 represented a promising catalyst for low temperature SCR of NO with NH3 in the presence of H2O and SO2.

Abstract: Structural, optical, and physical properties of glasses prepared by melt reduction in the mixed Sr−Mn metaphosphate system xMnO−(1 − x)SrO−P2O5, 0 ≤ x ≤ 1, have been investigated by vibrational, optical, EPR, and thermal techniques. Mn ions were found mostly in the +2 oxidation state and in sites of octahedral symmetry. Such sites are formed by neighboring Mn−oxygen polyhedra, where the covalent character of Mn−O bonding increases with cation mixing. The phosphate structure was found to consist predominantly of metaphosphate tetrahedral species (Q2) with a minority of pyrophosphate (Q1) and neutral (Q3) phosphate tetrahedra, whose relative abundance changes nonlinearly with MnO content. The symmetric stretching vibration of terminal PO2− units in Q2 species was employed to probe the influence of mixed Sr/Mn environments on phosphate structure, and the results suggested a deviation from the homogeneous distribution of metal cations. This was attributed to the coordination numbers of Sr and Mn ions (i.e., 8...

Abstract: Crystalline tunnel structure cryptomelane type manganese oxides (OMS-2) have been studied as photocatalysts for the selective oxidation of 2-propanol to acetone. The reaction is carried out with visible light irradiation at room temperature. The activities of various K-OMS-2 and metal doped OMS-2 (M-OMS-2) catalysts prepared by different synthesis procedures have been evaluated. K-OMS-2 and M-OMS-2 (M = Fe, Ni) with nanorod morphology were the most active photocatalysts. Conversions obtained for these catalysts ranged from 50 to 15%. K-OMS-2 fibers gave only 5–6% conversion. All reactions gave 100% selectivity to acetone. The reusability of the K-OMS-2 catalyst was also tested. Characterization of K-OMS-2 catalysts was done using several techniques like temperature programmed desorption, UV–vis spectroscopy, average oxidation state analysis, XRD, BET and FE-SEM. As suggested by the photochemical and characterization data, synthesis methodology, morphology, mixed valency and the release of oxygen from the OMS-2 structure are important factors for the design of active OMS-2 photocatalysts. XRD and FTIR were also used to study structural changes in the catalyst after photolysis.

Abstract: Supported gold catalysts prepared by deposition-precipitation with urea were studied in the reaction of oxidation of propene in low concentration in a large excess of oxygen, so as to mimic the conditions of catalytic decomposition of a volatile organic compound of hydrocarbon-type (1200 ppm C3H6, 9% O-2 in He). Several parameters were investigated: the nature of the oxide support (alumina, titania, ceria), the gold loading, the conditions of catalyst activation (oxygen or hydrogen). Titania and alumina alone did not show any conversion in C3H6 oxidation up to 500 degrees C, but when gold was added (1 wt%), active catalysts were obtained with a higher activity for titania than for alumina. Ceria was the only support showing activity, and gold on ceria (1 wt%) led to the most active catalyst. For the Au/CeO2 system, activation under H-2 at 300 degrees C leads to more active catalysts than activation in O-2/He at 500 degrees C, especially for gold loadings lower than 1 wt%. XPS and CO oxidation performed at RT showed that gold on CeO2 was fully reduced to Au-0 after activation under H-2 whatever the gold loading. In contrast after calcination, most of the gold remained under the initial Au-III state for the low loaded samples (<= 1 wt%) whereas art of it was reduced for the 4 wt% Au/CeO2. Thus, ceria seems to be able to stabilise gold as Au-III up to a limited loading. Change in the gold oxidation state was detected for the calcined Au/CeO2 (1 wt%) during C3H6, oxidation performed at increasing temperature, using CO oxidation and DRIFTS combined to CO adsorption. Indeed, gold, initially Au-III, starts reducing at 100 degrees C to form metallic gold Au-0, which was the active species for the reaction. Above 300 degrees C, when 100% conversion was achieved, reoxidation of metallic gold species was observed. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: In this work, we report the synthesis and the electronic properties of the unique highly conjugated molecular wires trans-[Cl-(dppe)(2)Ru=C=C=(Ph)C-CH=(CH(3))C-C[triple bond]C-(X)(2)Ru-C=C-C(CH(3))=CH-C(Ph)=C=C=Ru(dppe)(2)Cl](n+) (n = 2, X = dppe ([3a](OTf)(2)) and dppm ([3b](OTf)(2)) with three similar metal centers spanned by two odd-numbered unsaturated C(7) chains providing a 28 A long conjugated path and displaying five well-separated redox states (n = 0-4). Successive one-electron transfer steps were studied by means of cyclic voltammetry, EPR and UV-vis-NIR-IR spectroelectrochemistry. The electronic and physical properties of the different states were further rationalized with the help of DFT-based calculations. Upon one-electron reduction (n = 1), the single electron is delocalized over the two carbon chains through the central metal atom to an extent driven by the rotations within and between the chains. The second reduction (n = 0) involves the whole carbon-rich conjugated path of the molecule in a spin polarized scheme: one electron is delocalized over each chain, and the two electrons are antiferromagnetically coupled with a coupling on the order of kT. Interestingly, oxidation processes strongly involve both the metal atoms and the bridging ligands. The combined investigations reveal that the mono-oxidized system (n = 3) presents a spin density uniformly distributed between the metal atoms and the carbon atoms of the chains, whereas in the second oxidation state (n = 4) the compounds show a strong antiferromagnetic coupling on the order of 4 kT between the two single electrons localized in two distinct delocalized spin orbitals implying all the carbon atoms of the bridges and the three metal atoms. Thus, for the first time, electronic communication was fully evidenced and tuned in homonuclear trimetallic oligomeric carbon-rich systems in either an oxidation or a reduction process.

Abstract: Solutions of allyl indium reagents formed in the reactions of indium with allyl bromide and allyl iodide, respectively, in N,N-dimethylformamide, tetrahydrofuran, and water were analyzed by a combi...

Abstract: The electronic structures of bulk and (001) surfaces of λ-MnO2 and LiMn2O4 have been studied with density functional theory. In λ-MnO2, the Mn oxidation state is +4 both in the bulk and at the (001) surface. In LiMn2O4, however, Mn atoms exhibit mixed Mn3+/Mn4+ oxidation states in the bulk, while only Mn3+ at the (001) surface, due to lower coordination with O atoms. The technically undesired Mn3+ ions form at LixMn2O4 (001) even for very small Li concentrations. Upon covering the LiMn2O4 (001) surface with Al2O3, the oxidation state of surface Mn atoms changes from +3 to +4, which explains the improved performance of coated LiMn2O4 cathodes in Li-ion batteries.

Abstract: Alkaline earth metals (Ae) are regarded as redox-inactive, and their chemistry is dominated by the oxidation state +2. Nevertheless, in recent years several compound classes with alkaline earth metals in low oxidation states were investigated. Various concepts proved to be valid for the stabilization of such compounds and are discussed in this review. In the solid state, subvalency can be achieved by offering a matrix that takes over the excess electrons as, for example, in subnitrides. This fact leads to normal-valent alkaline earth metals with electrons free to move between alkaline-earth-metal-containing cages with or without a metal matrix. Another concept focuses on the synthesis of [Ae 2 ] 2+ cations with adequate substituents. The homodinuclear Ae-Ae bonds exhibit binding energies that should allow the synthesis of molecules such as R-Ae-Ae-R. The synthesis of magnesium derivatives succeeded by use of extremely bulky bidentate ligands with a delocalized anionic charge. The heavier alkaline earth metal derivatives are investigated by quantum chemical methods. Another possibility takes advantage of the fact that the first and second ionization potentials of the alkaline earth metals are clearly separated. Therefore, an arene with an extended π-system having an energy level between the two ionization potentials should be able to overtake only one electron, which leads to Ae + cations. Sophisticated procedures allowed the synthesis of a calcium(I) derivative, [(thf) 3 Ca(μ-η 6 ,η 6 -C 6 H 3 -1,3,5-Ph 3 )Ca(thf) 3 ], and such structures are investigated by quantum chemical methods also for the other alkaline earth metals.

Abstract: A computational study with the B3LYP density functional theory was carried out to study the reaction mechanism for the cycloisomerization of allenes catalyzed by Au(I) and Au(III) complexes. The catalytic performance of Au complexes in different oxidation states as well as the effects of the counterion on the catalytic activities has been studied in detail. Our calculations show that the catalytic reaction is initiated by coordination of the Au(I) or Au(III) catalyst to the distal double bond of allene and activation of allene toward facile nucleophilic attack, then 3-pyrroline obtained via two-step proton shift, followed by demetalation. On the basis of our calculations, H shifts are key steps of the catalytic cycle, which are significantly affected by the gold oxidation state, counterion, ligands, and assistant catalyst. AuCl is found to be more reactive than AuCl3; however, the Au(III)-catalyzed path does not involve an oxidation state change from Au(III) to Au(I). Our calculated results rationalize th...

Abstract: Systems and methods for the formation of carbon-based nanostructures are generally described. In some embodiments, the nanostructures may be formed on a nanopositor. The nanopositor can comprise, in some embodiments, at least one of metal atoms in a non-zero oxidation state and metalloid atoms in a non-zero oxidation state. For example, the nanopositor may comprise a metal oxide, a metalloid oxide, a metal chalcogenide, a metalloid chalcogenide, and the like. The carbon-based nanostructures may be grown by exposing the nanopositor, in the presence or absence of a growth substrate, to a set of conditions selected to cause formation of carbon-based nanostructures on the nanopositor. In some embodiments, metal or metalloid atoms in a non-zero oxidation state are not reduced to a zero oxidation state during the formation of the carbon-based nanostructures. In some cases, metal or metalloid atoms in a non-zero oxidation state do not form a carbide during the formation of the carbon-based nanostructures.

Abstract: Crystal structures of TiO(OH)2 and Li2TiO3 have been studied in detail and refined using X-ray powder diffraction data. Both compounds possess a high concentration of defects in the structure. The crystal structure of the Li2TiO3 salt obtained at 700 °C reveals stacking faults of LiTi2 metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3112. The possibility to stabilise this imperfect state increases the mobility of the Li+ ions in the structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)2. The crystal structure of TiO(OH)2 belongs to the layered double hydroxide structure type with the 3R1 sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)2OTi2O(OH)2]. TiO(OH)2 is the first layered double hydroxide structure formed by a cation with oxidation state +4 only.

Abstract: Selective oxidation of alcohols to carbonyl compounds with molecular oxygen was carried out over ruthenium supported on a CaO–ZrO 2 solid solution prepared by the co-precipitation method. In the oxidation of benzyl alcohol, the Ru/CaO–ZrO 2 catalyst gave benzaldehyde in a yield higher than 98% at 90 °C, and the turnover frequency reached 224 h −1 . The Ru/CaO–ZrO 2 catalyst also exhibited high catalytic activities and selectivities to carbonyl compounds in the oxidation of aromatic ring-substituted benzylic, allylic, and aliphatic alcohols. Moreover, this catalyst exhibited high activities in the oxidation of alcohols at a low temperature (40 °C). The catalytic activity and oxidation state of ruthenium depended on the Ca/Zr molar ratio of the support, and the highest catalytic activity was obtained with Ca/Zr = 0.125. DRIFT and XPS analyses revealed that Ru n + –OH ( n = 3, 4) on the surface of CaO–ZrO 2 were likely the active species in the oxidation of alcohols.

Abstract: In view of the importance of the thermodynamic behavior of chromium in the slag phase as well as the serious discrepancies in the earlier reports on the valence state of chromium in slag melts, the oxidation state of chromium oxides in CaO-SiO2-CrOx and CaO-MgO-(FeO-) Al2O3-SiO2-CrOx were investigated experimentally in the present study using two different experimental techniques. The gas–slag equilibrium technique was adopted to study the CaO-SiO2-CrOx system between 1823 K (1550 °C) and 1923 K (1650 °C) and equilibrated with mixtures of CO-CO2-Ar gases corresponding to three different oxygen partial pressures (between 10−4 and 10−5 Pa). After equilibrating, the samples were quenched and subjected to analysis using the X-ray absorption near edge structure method to determine the distribution ratio of Cr2+/Cr3+ in the slags. The second technique examined the applicability of the high-temperature mass spectrometric method combined with the Knuden effusion cell for quantifying the valence states of Cr in the multicomponent system CaO-MgO-(FeO-) Al2O3-SiO2-CrOx up to a maximum temperature of 2000 K (1727 °C). The results showed that the Knudsen cell-mass spectrometric method could be used successfully to estimate the valence ratio for Cr in silicate melts. According to the present study, the Cr2+/Cr3+ ratio increased with increasing temperature and a decreasing slag basicity as well as the oxygen partial pressure prevailing in the system. A mathematical correlation of X CrO/X CrO1.5 as a function of temperature, oxygen partial pressure, and basicity was developed in the present work based on the present results as well as on those assessed from earlier data.

Abstract: The computer simulation studies employing both static lattice and molecular dynamics (MD) methods, were used to identify anion migration pathways, relevant energetic parameters and effects of the transition metal cation dopants on oxygen ion transport in La 2 Ni(M)O 4+ δ (M = Fe, Co, Cu) solid solutions, a family of promising oxide materials for fuel cell electrodes and dense ceramic membranes for oxygen separation. The factors related to different oxygen sublattices in the K 2 NiF 4 -type structure of La 2 Ni(M)O 4+ δ were appraised analyzing the MD data. The results show, in particular, that the incorporation of dopants having 3+ oxidation state leads to higher ionic charge-carrier concentration affecting the overall anion diffusivity, which is essentially determined by cooperative mechanisms involving oxygen interstitials and anions occupying regular apical sites in the layered lattices. However, these dopants tend to decrease anion mobility, both in the rock-salt and perovskite-like layers of the K 2 NiF 4 -type structure. The likely microscopic mechanisms of anion diffusion in oxygen-hyperstoichiometric La 2 Ni(M)O 4+ δ are determined.

Abstract: The use of phenyl-2-pyridyl ketone oxime and di-2-pyridyl ketone oxime in Mn chemistry has led to hexanuclear clusters with unprecedented (MnII4MnIIIMnIV) or extremely rare (MnIIMnIII5 and MnII3MnIII3) metal oxidation-state combinations and uncommon structural motifs.

Abstract: The octahedral site in iron oxides has been shown to undergo changes in its occupation when iron oxides form in the presence of single and multiple foreign metals in controlled laboratory settings as well as the natural environment. X-ray absorption spectroscopy coupled with the increased precision of synchrotron-based X-ray diffraction (SXRD) have shed new light on important basic mechanisms controlling the fate of foreign metals during the precipitation of iron oxides and their transformation into crystalline products. For example, total manganese incorporation into goethite is circa 47 mol.%; however, actual Mn-for-Fe substitution is limited to circa 13 mol.% as shown by extended X-ray absorption fine structure spectroscopy. Vanadium-for-Fe substitution in goethite is controlled by the ability of V to maintain its octahedral coordination environment as it oxidizes from 3+ to 5+ oxidation state. In conjunction with other spectroscopies—for example, FTIR—Ni speciation in hematite has been shown to occur in the octahedral site usually occupied by Fe 3+ , with the charge discrepancy being compensated by the protonation of O 2− moieties in the structure. In the presence of multiple metal cations, metals that assume a near-perfect octahedral symmetry appear to substitute for Fe 3+ more readily and as a result also enhance the substitution of other metals. With much of the work on this subject matter having been conducted on synthetic laboratory samples, the increased availability of synchrotron X-ray microprobes and future X-ray nanoprobes offers the possibility of focusing research onto naturally occurring iron oxides occurring in size from a few nano- to several micrometers from a wide range of environmental conditions.