Misaki Katayama

Combined adsorption and oxidation mechanisms of hydrogen sulfide on granulated coal ash

Hydrogen sulfide is highly toxic to benthic organisms and may cause blue tide with depletion of dissolved oxygen in water column due to its oxidation. The purpose of this study is to reveal the combined adsorption and oxidation mechanisms of hydrogen sulfide on granulated coal ash that is a byproduct from coal electric power stations to apply the material as an adsorbent for hydrogen sulfide in natural fields. Sulfur species were identified in both liquid and solid phases to discuss removal mechanisms of the hydrogen sulfide with the granulated coal ash. Batch experiments revealed that hydrogen sulfide decreased significantly by addition of the granulated coal ash and simultaneously the sulfate ion concentration increased. X-ray absorption fine structure analyses showed hydrogen sulfide was adsorbed onto the granulated coal ash and successively oxidized by manganese oxide (III) contained in the material. The oxidation reaction of hydrogen sulfide was coupling with reduction of manganese oxide. On the other hand, iron containing in the granulated coal ash was not involved in hydrogen sulfide oxidation, because the major species of iron in the granulated coal ash was ferrous iron that is not easily reduced by hydrogen sulfide.

Ionic Conduction in Lithium Ion Battery Composite Electrode Governs Cross-sectional Reaction Distribution

Composite electrodes containing active materials, carbon and binder are widely used in lithium-ion batteries. Since the electrode reaction occurs preferentially in regions with lower resistance, reaction distribution can be happened within composite electrodes. We investigate the relationship between the reaction distribution with depth direction and electronic/ionic conductivity in composite electrodes with changing electrode porosities. Two dimensional X-ray absorption spectroscopy shows that the reaction distribution is happened in lower porosity electrodes. Our developed 6-probe method can measure electronic/ionic conductivity in composite electrodes. The ionic conductivity is decreased for lower porosity electrodes, which governs the reaction distribution of composite electrodes and their performances.

Mechanisms of hydrogen sulfide removal with steel making slag.

In the present study, we experimentally investigated the removal of hydrogen sulfide using steel-making slag (SMS) and clarified the mechanism of hydrogen sulfide removal with the SMS. The results proved that SMS is able to remove hydrogen sulfide dissolved in water, and the maximum removal amount of hydrogen sulfide per unit weight of the SMS for 8 days was estimated to be 37.5 mg S/g. The removal processes of hydrogen sulfide were not only adsorption onto the SMS, but oxidation and precipitation as sulfur. The chemical forms of sulfide adsorbed onto the SMS were estimated to be sulfur and manganese sulfide in the ratio of 81% and 19%, respectively. It is demonstrated here that the SMS is a promising material to remediate organically enriched coastal sediments in terms of removal of hydrogen sulfide. Furthermore, using SMS is expected to contribute to development of a recycling-oriented society.

Development of a two-dimensional imaging system of X-ray absorption fine structure

A two-dimensional imaging system of X-ray absorption fine structure (XAFS) has been developed at beamline BL-4 of the Synchrotron Radiation Center of Ritsumeikan University. The system mainly consists of an ionization chamber for I(0) measurement, a sample stage, and a two-dimensional complementary metal oxide semiconductor (CMOS) image sensor for measuring the transmitted X-ray intensity. The X-ray energy shift in the vertical direction, which originates from the vertical divergence of the X-ray beam on the monochromator surface, is corrected by considering the geometrical configuration of the monochromator. This energy correction improves the energy resolution of the XAFS spectrum because each pixel in the CMOS detector has a very small vertical acceptance of ∼0.5 µrad. A data analysis system has also been developed to automatically determine the energy of the absorption edge. This allows the chemical species to be mapped based on the XANES feature over a wide area of 4.8 mm (H) × 3.6 mm (V) with a resolution of 10 µm × 10 µm. The system has been applied to the chemical state mapping of the Mn species in a LiMn(2)O(4) cathode. The heterogeneous distribution of the Mn oxidation state is demonstrated and is considered to relate to the slow delocalization of Li(+)-defect sites in the spinel crystal structure. The two-dimensional-imaging XAFS system is expected to be a powerful tool for analyzing the spatial distributions of chemical species in many heterogeneous materials such as battery electrodes.

The liquid structure of various nitriles and N, N-dimethylformamide studied by the X-ray diffraction method using a CCD detector

Abstract The liquid structure of acetonitrile (AN), propionitrile (PN), acrylonitrile (ACN), and benzonitrile (BN) was investigated by the transmission mode X-ray diffraction method with a newly developed CCD detector at room temperature and one atmospheric pressure. The nitriles were shielded in a thin wall glass tube. The reduced intensities, si(s), extracted from the measured intensities were compared with those obtained by the X-ray diffraction measurements with the θ–θ type reflection mode for benzonitrile and N,N-dimethylformamide (DMF) as the reference. In all the nitriles it was found that molecules are arrayed in the zigzag form as found in previous studies for AN. The non-bonding N···C (nitrile carbon) distance between the anti-parallel adjacent molecules was 340 pm for all nitriles. The intermolecular C···C distance between next neighbour molecules was 420 pm for CH2···CH2 in AN, 430 pm for CH3···CH3 in PN, 425 pm for CH···CH in ACN, and 390 pm for C6H5···C6H5 in BN. The short C6H5···C6H5 distance was explained in terms of the π–π stacking interactions of the aromatic rings. DMF molecules interact each other through dipole–dipole interactions, and the O···C distance of 320 pm at the O···H–CO– interaction through the formyl proton may partly contribute to the intermolecular interactions. The distance between parallel DMF molecules in a plane was estimated to be 743 pm. The diffraction data were well explained in terms of a weak layered structure of DMF, and the layers were separated by about 365 pm.

Oxidation property of SiO2-supported small nickel particle prepared by the sol-gel method

The oxidation property of SiO2-supported small Ni particle has been studied by means of the in-situ XAFS method. The Ni particle with the average diameter of 4 nm supported on SiO2 was prepared by the sol-gel method. The XANES spectrum of the small metallic Ni particle was clearly different from that of bulk Ni. The exposure of diluted O2 gas at room temperature promoted the surface oxidation of Ni(0) particle. During the temperature programmed oxidation process, the supported Ni(0) particle was quantitatively oxidized to NiO, and the oxidation temperature was lower by ca. 200 °C than that of the SiO2-supported Ni particle with the larger particle radius of 17 nm prepared by the impregnation method.

Liquid structure of benzene and its derivatives as studied by means of X-ray scattering

The liquid structures of benzene, toluene, aniline, benzaldehyde and nitrobenzene were investigated by the X-ray scattering method. The X-ray scattering data were analysed by a method without constructing any structure models. The obtained liquid structure of benzene is different from the previous X-ray scattering results which were derived from the quasi-lattice structure for the liquid based on the crystal structure of benzene. This is because a molecular arrangement which is not found in the crystal structure is left out of consideration. In liquid toluene, benzaldehyde and nitrobenzene, two molecules are associated with the dipole–dipole interaction in the antiparallel fashion. Two aniline molecules are hydrogen-bonded in liquid aniline. The third molecule weakly interacts with the other two in liquid toluene, aniline and benzaldehyde. In liquid nitrobenzene, the parallel dipole–dipole interaction of the third molecule with another one is present in the coplanar form. The substituent effect on the liquid structures is discussed.

Evidence of valence state change of Ce 3+ and Cr 3+ during UV charging process in Y 3 Al 2 Ga 3 O 12 persistent phosphors

To elucidate the persistent luminescence mechanism of the Ce3+-Cr3+-codoped Y3Al2Ga3O12 garnet (YAGG), the valence states of Ce and Cr ions before and during UV charging were investigated by X-ray absorption near edge structure (XANES) spectroscopy. In the XANES spectra for Ce LIII and Cr K edges of YAGG:Ce3+-Cr3+ under UV illumination, the valence states of Ce4+ and Cr2+ were detected, but not in the XANES spectra of YAGG:Ce3+ and YAGG:Cr3+. We conclude that the combination of Ce3+ and Cr3+ causes the valence state change into Ce4+ and Cr2+ by UV illumination, which is the mechanism of persistent luminescence.

Reduction Kinetics of Nickel Species Supported on Silica

The reaction mechanism of reduction processes of NiO supported on silica has been clarified by means of the time-resolved dispersive XAFS (DXAFS) technique. The reduction of NiO shows two-phase changes. The first reaction corresponds to the reduction of NiO to the metallic Ni particle, and the sintering of the formed Ni particles occurs in the second step. The reduction process is composed of the surface reduction of the NiO particle and the successive oxygen diffusion from the particle core to the surface. The first-order kinetics suggests that the latter is the rate-determining step. The conditional rate constants indicate that the diffusion of oxygen atoms is relatively faster for the lower Ni loading.

Kinetic Study of Reduction Reaction for Supported PdO Species by Means of Dispersive XAFS Method

Time-resolved dispersive XAFS experiments have been performed to study the reduction reaction of supported PdO species on γ-Al2O3. It has been clarified that the reduction of PdO by H2 proceeds with an unique kinetic behavior, i.e., the initial part of the reduction is expressed by the first-order kinetics on Pd and the reaction order is changed to be zero as the progress of the reduction. The observation is different from that for the other supported metal oxides, for which the reduction is first order through the reaction. The reduction process of PdO is divided into the surface reduction to form the surface Pd(0) species and the succeeding oxygen exchange between inner PdO and surface Pd(0). When the latter step is faster than the former, the reduction rate of PdO is explained in terms of the zero-order kinetics. The pressure dependences of the conditional first- and zero-order rate constants suggest that the Langmuir-type molecular adsorption of H2 precedes the surface reduction of PdO particles.