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End date: 2023 × Start date: 2010 × Has files: Yes × Type: Text × Subject: Raman spectroscopy × WGL Institute: LIKAT ×

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Now showing 1 - 3 of 3
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    Chemical Imaging of Mixed Metal Oxide Catalysts for Propylene Oxidation: From Model Binary Systems to Complex Multicomponent Systems
    (Weinheim : Wiley-VCH, 2021) Sprenger, Paul; Stehle, Matthias; Gaur, Abhijeet; Weiß, Jana; Brueckner, Dennis; Zhang, Yi; Garrevoet, Jan; Suuronen, Jussi‐Petteri; Thomann, Michael; Fischer, Achim; Grunwaldt, Jan‐Dierk; Sheppard, Thomas L.
    Industrially-applied mixed metal oxide catalysts often possess an ensemble of structural components with complementary functions. Characterisation of these hierarchical systems is challenging, particularly moving from binary to quaternary systems. Here a quaternary Bi−Mo−Co−Fe oxide catalyst showing significantly greater activity than binary Bi−Mo oxides for selective propylene oxidation to acrolein was studied with chemical imaging techniques from the microscale to nanoscale. Conventional techniques like XRD and Raman spectroscopy could only distinguish a small number of components. Spatially-resolved characterisation provided a clearer picture of metal oxide phase composition, starting from elemental distribution by SEM-EDX and spatially-resolved mapping of metal oxide components by 2D Raman spectroscopy. This was extended to 3D using multiscale hard X-ray tomography with fluorescence, phase, and diffraction contrast. The identification and co-localisation of phases in 2D and 3D can assist in rationalising catalytic performance during propylene oxidation, based on studies of model, binary, or ternary catalyst systems in literature. This approach is generally applicable and attractive for characterisation of complex mixed metal oxide systems. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH
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    Probing Oxide Reduction and Phase Transformations at the Au-TiO2 Interface by Vibrational Spectroscopy
    (Bussum : Baltzer, 2017-8-17) Pougin, Anna; Lüken, Alexander; Klinkhammer, Christina; Hiltrop, Dennis; Kauer, Max; Tölle, Katharina; Havenith-Newen, Martina; Morgenstern, Karina; Grünert, Wolfgang; Muhler, Martin; Strunk, Jennifer
    By a combination of FT-NIR Raman spectroscopy, infrared spectroscopy of CO adsorption under ultrahigh vacuum conditions (UHV-IR) and Raman spectroscopy in the line scanning mode the formation of a reduced titania phase in a commercial Au/TiO2 catalyst and in freshly prepared Au/anatase catalysts was detected. The reduced phase, formed at the Au-TiO2 interface, can serve as nucleation point for the formation of stoichiometric rutile. TinO2n−1 Magnéli phases, structurally resembling the rutile phase, might be involved in this process. The formation of the reduced phase and the rutilization process is clearly linked to the presence of gold nanoparticles and it does not proceed under similar conditions with the pure titania sample. Phase transformations might be both thermally or light induced, however, the colloidal deposition synthesis of the Au/TiO2 catalysts is clearly ruled out as cause for the formation of the reduced phase.
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    Hydrogen bonding in ionic liquids probed by linear and nonlinear vibrational spectroscopy
    (Bristol : IOP, 2012) Roth, C.; Chatzipapadopoulos, S.; Kerlé, D.; Friedriszik, F.; Lütgens, M.; Lochbrunner, S.; Kühn, O.; Ludwig, R.
    Three imidazolium-based ionic liquids of the type [Cnmim] [NTf2] with different alkyl chain lengths (n = 1, 2 and 8) at the first position of the imidazolium ring were studied applying infrared, linear Raman and multiplex coherent anti-Stokes Raman scattering spectroscopy. The focus has been on the CH-stretching region of the imidazolium ring, which is supposed to carry information about a possible hydrogen bonding network in the ionic liquid. The measurements are compared with calculations of the corresponding anharmonic vibrational spectra for a cluster of [C 2mim][NTf2] consisting of four ion pairs. The results support the hypothesis of weak hydrogen bonding involving the C(4)-H and C(5)-H groups and somewhat stronger hydrogen bonds of the C(2)-H groups.