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Träfflista för sökning "L773:1864 5631 OR L773:1864 564X ;pers:(Kärkäs Markus D.)"

Search: L773:1864 5631 OR L773:1864 564X > Kärkäs Markus D.

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1.
  • Abdel-Magied, Ahmed F., et al. (author)
  • Chemical and Photochemical Water Oxidation Mediated by an Efficient Single-Site Ruthenium Catalyst
  • 2016
  • In: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 9:24, s. 3448-3456
  • Journal article (peer-reviewed)abstract
    • Water oxidation is a fundamental step in artificial photosynthesis for solar fuels production. In this study, we report a single-site Ru-based water oxidation catalyst, housing a dicarboxylate-benzimidazole ligand, that mediates both chemical and light-driven oxidation of water efficiently under neutral conditions. The importance of the incorporation of the negatively charged ligand framework is manifested in the low redox potentials of the developed complex, which allows water oxidation to be driven by the mild one-electron oxidant [Ru(bpy)(3)](3+) (bpy = 2,2'-bipyridine). Furthermore, combined experimental and DFT studies provide insight into the mechanistic details of the catalytic cycle.
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2.
  • Kärkäs, Markus D. (author)
  • Lignin Hydrogenolysis: Improving Lignin Disassembly through Formaldehyde Stabilization
  • 2017
  • In: ChemSusChem. - : Wiley-VCH Verlagsgesellschaft. - 1864-5631 .- 1864-564X. ; 10:10, s. 2111-2115
  • Research review (peer-reviewed)abstract
    • Lignocellulosic biomass is available in large quantities and constitutes an attractive feedstock for the sustainable production of bulk and fine chemicals. Although methods have been established for the conversion of its cellulosic fractions, valorization of lignin has proven to be challenging. The difficulty in disassembling lignin originates from its heterogeneous structure and its propensity to undergo skeletal rearrangements and condensation reactions during biorefinery fractionation or biomass pretreatment processes. A strategy for hindering the generation of these resistive interunit linkages during biomass pretreatment has now been devised using formaldehyde as a stabilizing agent. The developed method when combined with Ru/C‐catalyzed hydrogenolysis allows for efficient disassembly of all three biomass fractions: (cellulose, hemicellulose, and lignin) and suggests that lignin upgrading can be integrated into prevailing biorefinery schemes.
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3.
  • Shatskiy, Andrey, et al. (author)
  • Electrochemically Driven Water Oxidation by a Highly Active Ruthenium-Based Catalyst
  • 2019
  • In: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 12:10, s. 2251-2262
  • Journal article (peer-reviewed)abstract
    • The highly active ruthenium-based water oxidation catalyst [Ru-X(mcbp)(OHn)(py)(2)] [mcbp(2-)=2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine; n=2, 1, and 0 for X=II, III, and IV, respectively], can be generated in a mixture of Ru-III and Ru-IV states from either [Ru-II(mcbp)(py)(2)] or [Ru-III(Hmcbp)(py)(2)](2+) precursors. The precursor complexes are isolated and characterized by single-crystal X-ray analysis, NMR, UV/Vis, EPR, and FTIR spectroscopy, ESI-HRMS, and elemental analysis, and their redox properties are studied in detail by electrochemical and spectroscopic methods. Unlike the parent catalyst [Ru(tda) (py)(2)] (tda(2-)=[2,2:6,2-terpyridine]-6,6-dicarboxylate), for which full transformation into the catalytically active species [Ru-IV(tda)(O)(py)(2)] could not be carried out, stoichiometric generation of the catalytically active Ru-aqua complex [Ru-X(mcbp)(OHn)(py)(2)] from the Ru-II precursor was achieved under mild conditions (pH7.0) and short reaction times. The redox properties of the catalyst were studied and its activity for electrocatalytic water oxidation was evaluated, reaching a maximum turnover frequency (TOFmax) of around 40000s(-1) at pH9.0 (from foot-of-the-wave analysis), which is comparable to the activity of the state-of-the-art catalyst [Ru-IV(tda)(O)(py)(2)].
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