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  • 1
    Language: English
    In: Analytical chemistry, 03 November 2015, Vol.87(21), pp.10815-21
    Description: Grazing emission X-ray fluorescence (GEXRF) is well suited for nondestructive elemental-sensitive depth-profiling measurements on samples with nanometer-sized features. By varying the grazing emission angle under which the X-ray fluorescence signal is detected, the probed depth range can be tuned from a few to several hundred nanometers. The dependence of the XRF intensity on the grazing emission angle can be assessed in a sequence of measurements or in a scanning-free approach using a position-sensitive area detector. Hereafter, we will show that the combination of scanning-free GEXRF and fluorescence detected X-ray absorption spectroscopy (XAS) allows for depth-resolved chemical speciation measurements with nanometer-scale accuracy. While the conventional grazing emission geometry is advantageous to minimize self-absorption effects, the use of a scanning-free setup makes the sequential scanning of the grazing emission angles obsolete and paves the way toward time-resolved depth-sensitive XAS measurements. The presented experimental approach was applied to study the surface oxidation of an Fe layer on the top of bulk Si and of a Ge bulk sample. Thanks to the penetrating properties and the insensitivity toward the electric conduction properties of the incident and emitted X-rays, the presented experimental approach is well suited for in situ sample surface studies in the nanometer regime.
    Keywords: X-Rays ; Absorption Spectroscopy ; Bulk Sampling ; X-Ray Fluorescence ; Grazing ; Emission Spectroscopy ; Nanostructure ; Angles (Geometry) ; Analysis (MD) ; Chemical Analysis (Ep) ; Chemical Analysis (Ed) ; Chemical Analysis (EC);
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 2
    Language: English
    In: Analytical Chemistry, Nov 3, 2015, Vol.87(21), p.10815(7)
    Description: The article shows that the combination of scanning-free Grazing emission X-ray fluorescence (GEXRF) and fluorescence detected X-ray absorption spectroscopy (XAS) allows for depth-resolved chemical speciation measurements with nanometer-scale accuracy. The presented experimental approach is applied to study the surface oxidation of Fe layer on the top of bulk Si and of a Ge bulk sample. The insensitivity toward the electric conduction properties of the incident and emitted X-rays, the presented experimental approach is well suited for in situ sample surface studies in the nanometer regime.
    Keywords: Absorption Spectroscopy – Usage ; Fluorescence – Analysis ; Iron Compounds – Chemical Properties ; Iron Compounds – Spectra
    ISSN: 0003-2700
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Journal of the American Chemical Society, 26 December 2013, Vol.135(51), pp.19071-4
    Description: We report an in situ time-resolved high-energy resolution off-resonant spectroscopy study with subsecond resolution providing insight into the oxidation and reduction steps of a Pt catalyst during CO oxidation. The study shows that the slow oxidation step is composed of two characteristic stages, namely, dissociative adsorption of oxygen followed by partial oxidation of Pt subsurface. By comparing the experimental spectra with theoretical calculations, we found that the intermediate chemisorbed O on Pt is adsorbed on atop position, which suggests surface poisoning by CO or surface reconstruction.
    Keywords: Natural Sciences ; Chemical Sciences ; Physical Chemistry ; Naturvetenskap ; Kemi ; Fysikalisk Kemi;
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 4
    Language: English
    In: Science of the Total Environment, 10 December 2018, Vol.644, pp.287-297
    Description: Herein, it is presented a catalytic system for gas-phase hydrodechlorination of tetrachloromethane at low temperature and atmospheric pressure, using iridium supported on silica as parent catalyst. Iridium electronic configuration is suitable to catalyse the hydrodechlorination reactions, however, it has been rarely used in this reaction to date. The catalytic abilities were significantly improved when a second transition metal was added. Catalysts' stability and selectivity to the desired products (i.e. C -C hydrocarbons) improved compared to conventional activation in hydrogen when catalysts were activated shortly with microwave irradiation. Microwave irradiation of catalysts favourably influences the homogeneity of the metallic active phase, both in terms of the size of metal crystals and the homogeneity of bimetallic systems. Addition of platinum to the ‘parent’ iridium catalyst improved its catalytic properties and decreased deactivation. Fresh and spent catalysts were comprehensively characterized using several techniques (BET, CO-chemisorption, XRD, XPS, electron microscopy and mass spectrometry) to determine structure-activity relationships and potential causes for catalyst deactivation. No significant changes in crystalline size or bimetallic phase composition were observed for spent catalysts (with the exception of Ir-Pd catalysts which underwent bulk carbide during the reaction).
    Keywords: Hydrodechlorination of Tetrachloromethane ; Iridium Nanoparticles ; Bimetallic Catalysts ; Selectivity for Hydrocarbons ; High Stability ; Microwave Irradiation ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 5
    In: Recyclable Catalysis, 01/17/2015, Vol.2(1)
    Description: We report an in situ time-resolved high-energy resolution off-resonant spectroscopy (HEROS) study with unprecedented 100 ms time resolution revealing the unoccupied electronic states of platinum during regenerative oxidation and reduction cycles. The study depicted a slowed oxidation step in comparison with reduction. The oxidation cycle is composed of two characteristic stages, namely adsorption of dissociated oxygen followed by partial oxidation of Pt subsurface. Besides improved temporal resolution of the experiment, the detected reduction process of platinum showed no intermediate features and was completed in a single step within a few seconds.
    Keywords: Platinum-Catalysts ; Oxidation-Reaction ; Partial-Oxidation ; Reduction-Process ; Platinum ; Temporal-Resolution ; Oxygen ; Spectrometry ; Electronic-Structure ; High-Energy ; Platinkatalysator ; Oxidation ; Partielle Oxidation ; Reduktionsverfahren ; Platin ; Zeitauflösung ; Sauerstoff ; Spektroskopie ; Elektronische Struktur ; Hochenergie ; Chemistry;
    ISSN: Recyclable Catalysis
    E-ISSN: 2084-7629
    Source: Walter de Gruyter (via CrossRef)
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  • 6
    Language: English
    In: Catalysis Today, 01 June 2013, Vol.208, pp.1-1
    Keywords: Engineering ; Chemistry
    ISSN: 0920-5861
    E-ISSN: 1873-4308
    Source: ScienceDirect Journals (Elsevier)
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  • 7
    Language: English
    In: Chemical Communications, 2018, Vol. 54, pp. 7770-7773
    Description: The molecular water oxidation catalyst [Ru(bda)(L)(2)] has been incorporated into pyridine-decorated MIL-101(Cr) metal-organic frameworks. The resulting MIL-101@Ru materials exhibit turnover frequencies (TOFs) up to ten times higher compared to the homogenous reference. An unusual dependence of the formal TOFs on oxidant concentration is observed that ultimately arises from differing amounts of catalysts in the MOF crystals being active.
    Keywords: Natural Sciences ; Chemical Sciences ; Inorganic Chemistry ; Naturvetenskap ; Kemi ; Oorganisk Kemi ; Natural Sciences ; Chemical Sciences ; Materials Chemistry ; Naturvetenskap ; Kemi ; Materialkemi
    ISSN: 1359-7345
    E-ISSN: 1364548X
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  • 8
    Language: English
    In: Chemical Physics Letters, 2016, Vol.664, pp.73-76
    Description: Resonant X-ray emission spectroscopy (RXES) was applied to probe the electronic states above Fermi level for Cr-doped anatase TiO2. The results reveal doping-induced electronic band on low energy side of unoccupied electronic states. The experimental RXES data in combination with theoretical simulations...
    Keywords: Natural Sciences ; Chemical Sciences ; Naturvetenskap ; Kemi
    ISSN: 0009-2614
    E-ISSN: 18734448
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  • 9
    Language: Swedish
    In: Recycl. Catal., 2015, Vol.2, pp.23-26
    Description: We report an in situ time-resolved high-energy resolution off-resonant spectroscopy (HEROS) study with unprecedented 100 ms time resolution revealing the unoccupied electronic states of platinum during regenerative oxidation and reduction cycles. The study depicted a slowed oxidation step in comparison...
    Keywords: Natural Sciences ; Chemical Sciences ; Physical Chemistry ; Naturvetenskap ; Kemi ; Fysikalisk Kemi ; Chemistry With Specialization In Physical Chemistry ; Kemi Med Inriktning Mot Fysikalisk Kemi
    Source: SwePub (National Library of Sweden)
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  • 10
    Language: English
    In: Chemical communications (Cambridge, England), 11 July 2015, Vol.51(54), pp.10914-6
    Description: Understanding electron mobility on TiO2 is crucial because of its applications in photocatalysis and solar cells. This work shows that shallow traps believed to be involved in electron migration in TiO2 conduction band are formed upon band gap excitation, i.e., are not pre-existing states. The shallow traps in TiO2 results from large polarons and are not restricted to surface.
    Keywords: Conduction Band ; Titanium Dioxide ; Solar Cells ; Anatase ; Polarons ; Hunting ; Electron Mobility ; Migration ; Miscellaneous Sciences (So) ; Chemical and Electrochemical Properties (MD) ; Chemical and Electrochemical Properties (Ep) ; Chemical and Electrochemical Properties (Ed) ; Chemical and Electrochemical Properties (EC);
    ISSN: 13597345
    E-ISSN: 1364-548X
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