Abstract: The oxidation state of alumina- and titania-supported Ru catalysts has been investigated as a function of reduction temperature, as well as by following the interaction with a methane−oxygen mixture at 773 and 973 K, employing XPS and FTIR techniques. It is found that the chemical behavior of Ru depends strongly on the material on which it is supported. Over Al2O3, ruthenium is incompletely reduced by treatment with hydrogen at 573 and 823 K, while oxidized Ru species are also detected following exposure of the catalyst to a methane−oxygen mixture at 773 and 973 K. In contrast, over TiO2, ruthenium is more easily reduced and is stabilized in its reduced state following hydrogen treatment at 823 K. During treatment with the methane−oxygen mixture, no reoxidation of Ru occurs. The interaction between Ru and TiO2, which inhibits the oxidation of ruthenium under conditions of partial oxidation of methane, is related to the unique ability of the Ru/TiO2 catalyst to promote the direct route of synthesis gas for...

Abstract: The dissolution of metal sulfides is controlled by their solubility product and thus the [H + ] concentration of the solution and further enhanced by several chemical mechanisms which lead to a disruption of sulfide chemical bonds. They include extraction of electrons and bond breaking by [Fe 3+ ] extraction of sulfur by polysulfide and iron complexes forming reactants [Y + ] and electrochemical dissolution by polarization of the sulfide [high Fe 3+ concentration]. All these mechanisms have been exploited by sulfide and iron oxidizing bacteria. Basically, the bacterial action is a catalytic one during which [H + ], [Fe 3+ ] and [Y + ] are breaking chemical bonds and are recycled by the bacterial metabolism. While the cyclic bacterial oxidative action via [H + ] and [Fe 3+ ] can be called indirect, bacteria had difficulties harvesting chemical energy from an abundant sulfide such as FeS 2 , the electron exchange properties of which are governed by coordination chemical mechanisms (extraction of electrons does not lead to a disruption of chemical bonds but to an increase of the oxidation state of interfacial iron). Here bacteria have evolved alternative strategies which require an extra cellular polymeric layer for appropriately conditioned contact with the sulfide. Thiobacillus ferrooxidans cycles [Y + ] across such a layer to disrupt FeS2 and Leptospyrillum ferrooxidans accumulates [Fe 3+ ] in it to depolarize FeS 2 to a potential where electrochemical oxidation to sulfate occurs. Corrosion pits and high resolution electron microscopy leave no doubt that these mechanisms are strictly localized and depend on specific conditions which bacteria create. Nevertheless they can not be called ‘direct because the definition would require an enzymatic interaction between the bacterial membrane and the cell. Therefore, the term 'contact' leaching is proposed for this situation. In practice, multiple patterns of bacterial leaching coexist, including indirect leaching, contact leaching and a recently discovered cooperative (symbiotic) leaching where ‘contact leaching bacteria are feeding so wastefully that soluble and particulate sulfide species are supplied to bacteria in the surrounding electrolyte.

Abstract: Specimens of titania with platinum in various oxidation states deposited by a photocatalytic method, as well as mixture of PtO2 + TiO2, and PtO2 have been studied by means of XPS, TEM and UV-VIS diffuse reflectance spectroscopy. Activities of the specimens in thermal and photocatalytic complete oxidation of gaseous acetone and CO by atmospheric oxygen at 40°C have been evaluated using a flow-circulating reactor. Photocatalytic activity increases with lowering of Pt oxidation state. Possible reasons of this behavior are discussed.

Abstract: CeO2 and Cu/CeO2 are effective catalysts/sorbents for the removal or destruction of SO2. Synchrotron‐based high‐resolution photoemission, X‐ray absorption near‐edge spectroscopy (XANES), and temperature‐programmed desorption (TPD) have been employed to study the reaction of SO2 with pure and reduced CeO2 powders, ceria films (CeO2, CeO2−x, Ce2O3+x) and model Cu/CeO2 catalysts. The results of XANES and photoemission provide evidence that SO4 was formed upon the adsorption of SO2 on pure powders or films of CeO2 at 300 K. The sulfate decomposed in the 390–670 K temperature range with mainly SO2 and some SO3 evolving into gas phase. At 670 K, there was still a significant amount of SO4 present on the CeO2 substrates. The introduction of O vacancies in the CeO2 powders or films favored the formation of SO3 instead of SO4. Ceria was able to fully dissociate SO2 to atomic S only if Ce atoms with a low oxidation state were available in the system. When Cu atoms were added to CeO2 new active sites for the destruction of SO2 were created improving the catalytic activity of the system. The surface chemistry of SO2 on the Cu‐promoted CeO2 was much richer than on pure CeO2. The behavior of ceria in several catalytic processes (oxidation of SO2 by O2, reduction of SO2 by CO, automobile exhaust converters) is discussed in light of these results.

Abstract: The dominant oxidation state of rhenium in high-temperature, chloride-bearing hydrothermal solutions at geologically reasonable oxygen fugacities has been experimentally determined to be q4, although a small percentage of dissolved . rhenium F 10% may be present in the q5 or higher valence state. This conclusion is based on a series of solubility experiments in 1.0 molal KCl solutions at 5008C using ReO , the K-feldspar-muscovite-quartz assemblage as a pH buffer, 2 and Co-CoO, Ni-NiO, Re-ReO , MnO-Mn O , and MoO -MoO pairs as oxygen fugacity buffers. Experiments were 23

Abstract: The synthesis and atomic structure of [Mn4O4L6]+(CF3SO3-), 1+OTf- (L = diphenylphosphinate), is reported. This new model for the photosynthetic water oxidizing complex extends the known [Mn4O4]n+ cubane core type to the Mn4(III,3IV) oxidation state. Synthesis of this cluster is achieved by one-electron oxidation of Mn4O4L6 (1) by molecular oxygen in a series of steps initiated by the protonation or silylation of one oxide bridge in 1.

Abstract: The interaction of SO2 with highly oriented ceria films is studied as a function of coverage, temperature, and degree of oxidation of the ceria. Soft X-ray photoemission (SXPS) is used to analyze the oxidation state of the ceria and the evolution of the SO2-derived species, while thermal desorption spectroscopy is used to analyze the desorption products. The principle interaction is chemisorption of SO2 at oxygen anions, which reversibly desorbs as SO2 over a broad temperature range from 200 to 600 K. This interaction is characterized as a Lewis acid−base interaction and occurs with approximately equal facility if the surface is hydroxylated or sulfided. On reduced ceria the adsorption is more heterogeneous, suggesting a variety of local bonding environments, including a small, distinguishable amount of adsorption at Ce3+ sites. A significant portion of the chemisorbed SO2 converts to sulfide above 300 K, and the resulting sulfide then equilibrates between bulk and surface sites above 600 K. Adsorption at...

Abstract: Differential SHG signals from chiral surfaces are recorded using right and left circularly polarized incident light. We show that chiral information from the surface is conveyed through this SHG process. This study focuses on the model protein system, cytochrome c, adsorbed on various self-assembled mono- and bi-layers at the solid/liquid interface. SHG-CD signals are shown to be related to the oxidation state of the protein and are utilized to observe changes in this feature of the protein in situ at surfaces of varying chemical properties.

Abstract: New amorphous MnV2O6+δ·nH2O (0 < δ < 1) compounds have been prepared by a soft chemistry route including the precipitation of a crystallized precursor, MnV2O6·4H2O, and its ozonation at temperatures below 100 °C. A combination of techniques (TGA, magnetic measurements, IR, XANES, EXAFS, XPS, and EELS) was used for their characterization. At low voltage, very large amounts of Li (e.g., Li12MnV2O6.96) are stored into anhydrous MnV2O6+δ compounds. After the first Li uptake, subsequent charge/discharge cycles correspond to fully reversible Li uptake between the two compositions: LiαMnV2O6+δ (α ≥ 2) and Li12MnV2O6+δ (from 600 to 900 mAh/g). The Li derivatives were characterized at various steps of the discharge/charge process. During the first discharge the VOn polyhedron changes from VO5 to VO6, and reversibly from VO6 to VO4 during subsequent cycles. Meanwhile, the V oxidation state varies reversibly between +3 and +5, respectively. Upon the first discharge Mn4+ cations are reduced to Mn2+. During the subse...

Abstract: We have investigated the oxidation state and size effects on the electronic structure of 10 and 20 nm CoO nanoparticles by means of surface spectroscopies. It has been concluded that the surface of...

Abstract: An understanding of the catalytic mechanism of NOx reduction is critical for the development of next-generation high-fuel efficiency, low-emission vehicles. This paper compiles our investigations in recent years on the mechanism of NO selective catalytic reduction (SCR) by hydrocarbon over Cu-ZSM-5. The studies were focused on the oxidation state and coordination chemistry of the exchanged Cu as the active site during the catalytic reaction using X-ray absorption spectroscopic (XAS) techniques, mainly XANES and EXAFS. Our experiment demonstrated the existence of a redox mechanism which involves cyclic switching of the oxidation states between Cu(II) and Cu(I) in an oxygen-rich gas mixture under elevated temperature. We also observed the coordination structural change of copper ion in ZSM-5 accompanying the change of oxidation state. A correlation between cuprous ion concentration and catalytic activity was found in NO SCR by propene. The impact of another two hydrocarbons, propane and methane, on the copp...

Abstract: should be chemicallystable during the photocatalytic oxidation reaction or storagein atmospheric condition. If the loaded metals are oxidized,conductivity of metal will be decreased down and theirenergy level may be altered from its metallic state. Then, thephotocatalytic activity will be degenerated, since they can-not trap or transfer the photoexcited electron efficiently. In this work, we investigate the effect of oxidation state ofloaded Cu on the photocatalytic oxidation reaction. Cu isone of extraordinary metals, which exist stably as metallicform as well as metal oxides in atmospheric condition. Inaddition, it is expected that the loaded Cu may improve pho-tocatalytic activity of TiO