72 research outputs found

    Ga and In Modified Ceria as a Support for Cobalt Fischer-Tropsch Synthesis

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    Ceria modified by the addition of gallium or indium (20 mol%) was used as a support for cobalt Fischer-Tropsch synthesis. The addition of gallium to ceria improved the CO conversion for cobalt, whereas indium tended to decrease it. A similar trend was observed with the Ag-promoted cobalt/ceria catalysts that were doped with Ga or In. For Ag promoted catalysts, doping with Ga or In decreased methane and increased the product selectivities of olefins and alcohols. The sum of olefins and alcohols in terms of product selectivity for the Ag-promoted catalysts decreased in the following order: Ag-Co/Ce-Ga \u3e Ag-Co/Ce-In \u3e Ag-Co/Ce. The H2-TPR-XANES data shown that addition of gallium or indium to ceria increased the fraction of surface Ce3+ for both unpromoted and Ag promoted catalysts. This partially reduced ceria plays an important role in the product selectivity of cobalt for FT synthesis

    Nonresonant valence-to-core x-ray emission spectroscopy of niobium

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    The valence-to-core (V2C) portion of x-ray emission spectroscopy (XES) measures the electron states close to the Fermi level. These states are involved in bonding, thus providing a measure of the chemistry of the material. In this article, we show the V2C XES spectra for several niobium compounds. The K β ′′ peak in the V2C XES results from the transition of a ligand 2 s electron into the 1 s core-hole of the niobium, a transition allowed by hybridization with the niobium 4 p . This location in energy of this weak peak shows a strong ligand dependence, thus providing a sensitive probe of the ligand environment about the niobium

    Atomically dispersed single iron sites for promoting Pt and Pt3Co fuel cell catalysts: performance and durability improvements

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    Significantly reducing platinum group metal (PGM) loading while improving catalytic performance and durability is critical to accelerating proton-exchange membrane fuel cells (PEMFCs) for transportation. Here we report an effective strategy to boost PGM catalysts through integrating PGM-free atomically-dispersed single metal active sites in the carbon support toward the cathode oxygen reduction reaction (ORR). We achieved uniform and fine Pt nanoparticle (NP) (∼2 nm) dispersion on an already highly ORR-active FeN4 site-rich carbon (FeN4–C). Furthermore, we developed an effective approach to preparing a well-dispersed and highly ordered L12 Pt3Co intermetallic nanoparticle catalyst on the FeN4–C support. DFT calculations predicted a synergistic interaction between Pt clusters and surrounding FeN4 sites through weakening O2 adsorption by 0.15 eV on Pt sites and reducing activation energy to break O–O bonds, thereby enhancing the intrinsic activity of Pt. Experimentally, we verified the synergistic effect between Pt or Pt3Co NPs and FeN4 sites, leading to significantly enhanced ORR activity and stability. Especially in a membrane electrode assembly (MEA) with a low cathode Pt loading (0.1 mgPt cm−2), the Pt/FeN4–C catalyst achieved a mass activity of 0.451 A mgPt−1 and retained 80% of the initial values after 30 000 voltage cycles (0.60 to 0.95 V), exceeding DOE 2020 targets. Furthermore, the Pt3Co/FeN4 catalyst achieved significantly enhanced performance and durability concerning initial mass activity (0.72 A mgPt−1), power density (824 mW cm−2 at 0.67 V), and stability (23 mV loss at 1.0 A cm−2). The approach to exploring the synergy between PGM and PGM-free Fe–N–C catalysts provides a new direction to design advanced catalysts for hydrogen fuel cells and various electrocatalysis processes

    Behavioral Corporate Finance: An Updated Survey

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    Microsoft Word - LM CWFColloidPaperr3b.DOC

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    ABSTRACT In glass-bonded sodalite, which is the ceramic waste form (CWF) to immobilize radioactive electrorefiner salt from spent metallic reactor fuel, uranium and plutonium are found as 20-50 nm (U,Pu)O 2 particles encapsulated in glass near glass-sodalite phase boundaries. In order to determine whether the (U,Pu)O 2 affects the durability of the CWF, and to determine release behavior of uranium and plutonium during CWF corrosion, tests were conducted to measure the release of matrix and radioactive elements from crushed CWF samples into water and the properties of released plutonium. Released colloids have been characterized by sequential filtration of test solutions followed by elemental analysis, dynamic light scattering, transmission electron microscopy (TEM), and X-ray absorption spectroscopy. This paper reports the composition, size, and agglomeration of these colloids. Significant amounts of colloidal, amorphous aluminosilicates and smaller amounts of colloidal crystalline (U,Pu)O 2 were identified in test solutions. The normalized releases of uranium and plutonium were significantly less than the normalized releases of matrix elements

    Isotope effect in formaldehyde steam reforming on Pt/m-ZrO2: Insight into chemical promotion by alkalis

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    Infrared spectroscopy, temperature programmed reaction mass spectrometry (TP-reaction/MS), and catalyst testing were used to investigate alkali promotion of dehydrogenation selectivity during formaldehyde steam reforming (FSR) on Pt/m-ZrO2. In a preferred pathway, formaldehyde reacts with water forming hydrogen and formate, followed by forward formate decomposition to CO2 and H2. Alkali-doping of 2 wt% Pt/m-ZrO2 increases catalyst basicity, which weakens the formate CH bond promoting formate dehydrogenation / decarboxylation. Promotion by alkali in FSR was observed through a formate ν(CH) band shift to lower wavenumbers in infrared spectroscopy, and through a decrease in the normal isotope effect in switching from H- to D-labeled formaldehyde in TP-reaction/MS

    An X-ray absorption spectroscopy study of an oxide dispersion strengthened steel

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    Oxide dispersion strengthened (ODS) steels are being investigated as possible structural material for components of future nuclear power plants. The dispersoids in the matrix (yttria particles) serve as pinning points for moving dislocations, and thereby improve the creep behavior of the material. Depending on the product, the dimension of the particles is in the range from a few nm up to 100 nm. The material properties depend on the size distribution. It is also expected that other parameters of the dispersoids may influence the materials behavior. An extended X-ray absorption fine structure (EXAFS) study has been conducted on PM2000 (ferritic ODS steel) samples, in order to determine the structure of the yttria inclusions. A PM2000 sample, which had been irradiated with He ions of 1.5 MeV up to a matrix-damage of not, vert, similar1 displacement per atom (dpa) in a surface layer of 2.7 μm in depth was measured. A multi angle implantation was performed, in order to avoid damage peaks as function of depth. A direct comparison of the EXAFS spectra and of the Fourier transformations shows no major difference between the irradiated samples and the non-irradiated one. Therefore any potential radiation induced damage or phase transformation of the dispersoids must be minor, which indicates good radiation stability under the given circumstances
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