Robert Schlögl

Fritz Haber Institute of the Max Planck Society, Berlín, Berlin, Germany

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Publications (755)2037.52 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In situ Raman spectroscopy is applied to investigate the speciation of molybdates under hydrothermal conditions in 0.2 M aqueous solution of (NH4)6Mo7O24 (autoclave, 20—200 °C, pH 1—7).
    ChemInform 01/2015; 46(2).
  • Sylvia Reiche, Natalia Kowalew, Robert Schlögl
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    ABSTRACT: A specific control of the morphology and chemical structure of hydrothermal carbon (HTC) is of crucial importance for its application, both in catalyst supports or electrochemical devices. Here we show how the morphology, that is, particles size and homogeneity, and the distribution of functional groups can be controlled by the control of the synthesis pH of the hydrothermal carbonization. A complementary analysis of liquid byproducts by HPLC provides useful information on the nature of the polymeric species produced during the poly-condensation in the hydrothermal process and reveals the potential implementation of the process into the biorefinery concept. The acidic byproducts levulinic acid and formic acid determine the hydrothermal carbonization autocatalytically by additional supply of protons to the reaction medium. Thus, for a starting pH>3, only minor structural differences can be detected for HTC. The use of oxidizing acids favors higher yields of HTC and improves carbonization towards higher condensed carbon domains. Scaling up the process in a stirred 2 L batch reactor favors carbonization leading to higher condensed carbonaceous products. The relative trends of pH variation are maintained.
    ChemPhysChem 12/2014; · 3.35 Impact Factor
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    ABSTRACT: Hydrogen peroxide (H2O2) functionalized carbon nanotubes exhibited better catalytic performance than their nitric acid oxidized counterparts in the reduction of nitrobenzene. One important reason may be attributed to the notably less negative oxygenated groups on the surface of the former one.
    Physical chemistry chemical physics : PCCP. 12/2014;
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    ABSTRACT: In situ Raman spectroscopy was applied to investigate the speciation of molybdates under hydrothermal conditions in 0.2 M aqueous solution in the temperature range between 20 °C and 200 °C and at pH values between 7 and 1. The nature and abundance of molecular and supra-molecular species differs significantly compared to the distribution of species under ambient conditions at the same pH. Whereas heptamolybdate Mo7O246– dominates under ambient pressure at 25 °C in the pH range between 6 and 5, at 170–190 °C, chain-like or molecular structures of dimolybdates Mo2O72– and trimolybdates Mo3O102– are preferentially formed. In acidic solutions (pH < 2), supramolecular species, like Mo36O1128–, which generally predominate at 25 °C, do not occur at T > 100 °C. Instead, β-Mo8O264– is the final molecular precursor of precipitation reactions that was detectable by Raman spectroscopy. The structural type of the solid phase formed through addition of vanadyl sulfate under hydrothermal conditions is sensitively controlled by the nature of the molecular precursor, which is adjusted by the pH. In acidic medium, hexagonal MoO3 (ICSD 80290) is formed, while at pH = 5.8 nano-crystalline M1 (ICSD 55096) was obtained.
    Zeitschrift für anorganische Chemie 10/2014; · 1.16 Impact Factor
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    ABSTRACT: Intercalation of oxygen at the interface of graphene grown by chemical vapour deposition and its polycrystalline copper catalyst can have a strong impact on the electronic, chemical and structural properties of both, the graphene and the Cu. This can affect the oxidation resistance of the metal as well as a subsequent graphene transfer. Here, we show, using near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), X-ray absorption near edge spectroscopy (XANES), energy dispersive X-ray spectroscopy (EDX) and (environmental) scanning electron microscopy (ESEM) that both the oxygen intercalation and de-intercalation are kinetically driven and can be clearly distinguished from carbon etching. The obtained results reveal that a charge transfer between as grown graphene and Cu can be annulled by intercalating oxygen creating quasi-free-standing graphene. This effect is found to be reversible on vacuum annealing proceeding via graphene grain boundaries and defects within the graphene but not without loss of graphene by oxidative etching for repeated (de-)intercalation cycles.
    Physical Chemistry Chemical Physics 10/2014; · 4.20 Impact Factor
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    ABSTRACT: Polycrystalline MoVTeNb oxide composed of the M1 phase was studied in the transformation of propene at reaction temperatures between 323 and 573 K in the absence of oxygen and water. Surprisingly, the catalyst showed considerable activity in propene metathesis to ethene and 2-butenes, which was attributed to partial reduction of the catalyst surface under the reaction conditions. The multifunctionality of the M1 phase, which is known as a selective catalyst for the direct oxidation of propane to acrylic acid, was furthermore reflected in the formation of 1-butene and isobutene owing to C4 isomerization. This study demonstrates the diversity of the M1 phase as a catalyst, which is based on surface dynamics and structural stability, and further improves the understanding of the complex reaction network of short-chain hydrocarbons over MoVTeNbO M1 catalysts.
    ChemCatChem 10/2014; · 5.18 Impact Factor
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    ABSTRACT: The dynamics of the graphene-catalyst interaction during chemical vapor deposition are investigated using in situ, time- and depth-resolved X-ray Photoelectron Spectroscopy and complementary grand canonical Monte Carlo simulations coupled to a tight-binding model. We thereby reveal the interdependency of the distribution of carbon close to the catalyst surface and the strength of the graphene-catalyst interaction. The strong interaction of epitaxial graphene with Ni(111) causes a depletion of dissolved carbon close to the catalyst surface, which prevents additional layer formation leading to a self-limiting graphene growth behavior for low exposure pressures (10-6-10-3 mbar). A further hydrocarbon pressure increase (to ~10-1 mbar) leads to weakening of the graphene-Ni(111) interaction accompanied by additional graphene layer formation, mediated by an increased concentration of near-surface dissolved carbon. We show that growth of more weakly adhered, rotated graphene on Ni(111) is linked to an initially higher level of near-surface carbon compared to the case of epitaxial graphene growth. The key implications of these results for graphene growth control and their relevance to carbon nanotube growth are highlighted in the context of existing literature.
    Journal of the American Chemical Society 09/2014; · 10.68 Impact Factor
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    ABSTRACT: Coking dynamics of Ni-based and Ni-free catalysts were studied in a magnetic suspension thermobalance under methane dry reforming conditions. Ni-rich catalysts undergo strong coking featured with a surface saturation point where the coking rate is drastically reduced. Catalyst resistance towards coking may be enhanced by using noble-metal-based Ni-free precursors or decreasing the Ni content in the catalytic system. The post reaction performed temperature-programmed oxidation experiment of the coked catalyst is diffusion-limited due to large amounts of formed carbon.
    09/2014; 86(2):1916.
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    ABSTRACT: The reduction of nitrobenzene could proceed in the presence of carbon. The activity mainly originated from carbonyl groups on the carbon surface instead of metal impurities which were embedded in the carbon.
    Catal. Sci. Technol. 08/2014;
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    ABSTRACT: We report the application of an optimised synthesis protocol of a Cu/ZnO:Al catalyst. The different stages of synthesis are all well-characterised by using various methods with regard to the (micro-)structural, textural, solid-state kinetic, defect and surface properties. The low amount of the Al promoter (3 %) influences but does not generally change the phase evolution known for binary Cu/ZnO catalysts. Its main function seems to be the introduction of defect sites in ZnO by doping. These sites as well as the large Cu surface area are responsible for the large N2O chemisorption capacity. Under reducing conditions, the Al promoter, just as Zn, is found enriched at the surface suggesting an active role in the strong metal–support interaction between Cu and ZnO:Al. The different stages of the synthesis are comprehensively analysed and found to be highly reproducible in the 100 g scale. The resulting catalyst is characterised by a uniform elemental distribution, small Cu particles (8 nm), a porous texture (pore size of approximately 25 nm), high specific surface area (approximately 120 m2 g−1), a high amount of defects in the Cu phase and synergetic Cu–ZnO interaction. A high and stable performance was found in methanol synthesis. We wish to establish this complex but well-studied material as a benchmark system for Cu-based catalysts.
    ChemCatChem 08/2014; · 5.18 Impact Factor
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    ABSTRACT: The fundamental problem of the symmetry breaking in the resonant inelastic X-ray scattering (RIXS) of the CO2 gas molecule is studied. The measurements were performed under catalytically relevant conditions within an in-house constructed reaction cell. The experimental RIXS plane is constructed from a sequence of resonances, covering the near-edge X-ray absorption fine structure (NEXAFS) spectrum up to 539 eV. The spectra show significant sensitivity with respect to the excitation frequency. The NEXAFS absorption spectrum, as well as the corresponding RIXS spectra, is interpreted with the aid of multireference configuration interaction (MRCI) theory. In this framework, the configuration interaction space spans the space of the intermediate and final states with single and single−double excitations. The dynamic character of the RIXS spectra is investigated by considering the electronic−nuclear vibrational coupling with the bending and antisymmetric stretching vibrations in the important intermediate excited states. In addition, the vibronic coupling mechanism involving the Renner−Teller effect and the core−hole localization pseudo-Jahn−Teller effect of the intermediate states is fully considered. The physical origin of the observed spectral features is discussed qualitatively and quantitatively in terms of individual core-to-valence excitations and valence-to-core decays, respectively. The computational protocol presented here, based on multireference wave function ab initio theory, serves as an important reference for future theoretical and experimental applications of RIXS spectroscopy.
    The Journal of Physical Chemistry C 08/2014; · 4.84 Impact Factor
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    ABSTRACT: Die mittels Dichtefunktionaltheorie berechneten Energiebarrieren für die H-Abstraktion durch Sauerstoffradikale in Li-dotiertem MgO sind viel kleiner (12±6 kJ mol−1) als die Barrieren, die man bei unterschiedlichen Methanaktivierungsexperimenten findet (80–160 kJ mol−1). Das nährt weitere Zweifel an Lunsfords Hypothese, dass Li+O.−-Paare die aktiven Zentren sind. Temperaturprogrammierte oxidative Kupplungsreaktionen von Methan (OCM) zeigen, dass bei reinem und Li-dotiertem MgO die gleichen Zentren für die Reaktion verantwortlich sind. MgO-Katalysatoren, die durch Sol-Gel-Synthese hergestellt wurden, zeigen große Unterschiede zwischen anfänglicher Aktivität und der Aktivität im stationären Zustand. Transmissionselektronenmikroskopie zeigt, dass damit substanzielle morphologische Veränderungen und Restrukturierungen der Oberfläche einhergehen. Berechnungen an (MgO)9-Clustermodellen ergeben, dass CH4 heterolytisch an Mg2+O2−-Paaren chemisorbiert wird, die sich an Stufen oder Ecken befinden. Die homolytische Freisetzung von Methylradikalen erfordert jedoch die Anwesenheit von O2 auf der Oberfläche.
    Angewandte Chemie 08/2014; 126(33).
  • Journal of Catalysis 08/2014; 317:220–228. · 5.79 Impact Factor
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    ABSTRACT: A versatile flow-reactor design is presented that permits multi-species profile measurements under industrially relevant temperatures and pressures. The reactor combines a capillary sampling technique with a novel fiber-optic Laser-Induced Fluorescence (LIF) method. The gas sampling provides quantitative analysis of stable species by means of gas chromatography (i.e. CH4CH4, O2,CO,CO2O2,CO,CO2, H2O,H2H2O,H2, C2C2H6H6, C2C2H4H4), and the fiber-optic probe enables in situ detection of transient LIF-active species, demonstrated here for CH2H2O. A thorough analysis of the LIF correction terms for the temperature-dependent Boltzmann fraction and collisional quenching are presented. The laminar flow reactor is modeled by solving the two-dimensional Navier–Stokes equations in conjunction with a detailed kinetic mechanism. Experimental and simulated profiles are compared. The experimental profiles provide much needed data for the continued validation of the kinetic mechanism with respect to C1C1 and C2C2 chemistry; additionally, the results provide mechanistic insight into the reaction network of fuel-rich gas-phase methane oxidation, thus allowing optimization of the industrial process.
    Combustion and Flame 07/2014; · 3.60 Impact Factor
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    Dataset: SI
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    Dataset: SI
  • Marc Armbrüster, Robert Schlögl, Yuri Grin
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    ABSTRACT: The application of intermetallic compounds for understanding in heterogeneous catalysis developed in an excellent way during the last decade. This review provides an overview of concepts and developments revealing the potential of intermetallic compounds in fundamental as well as applied catalysis research. Intermetallic compounds may be considered as platform materials to address current and future catalytic challenges, e.g. in respect to the energy transition.
    Science and Technology of Advanced Materials 06/2014; 15(3):034803. · 3.75 Impact Factor
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    ABSTRACT: The stability of the surface termination of intermetallic Pd2Ga nanoparticles and its effect on the hydrogenation of acetylene was investigated. For this purpose, a precursor synthesis approach was applied to synthesize supported intermetallic Pd2Ga nanoparticles. A series of Pd-substituted MgGa-hydrotalcite (HT)-like compounds with different Pd loading was prepared by coprecipitation and studied in terms of loading, phase formation, stability and catalytic performance in the selective hydrogenation of acetylene. Higher Pd loadings than 1 mol % revealed an incomplete incorporation of Pd into the HT lattice, as evidenced by XANES and TPR measurements. Upon thermal reduction in hydrogen, Pd2Ga nanoparticles were obtained with particle sizes varying with the Pd loading, from 2 nm to 6 nm. The formation of intermetallic Pd2Ga nanoparticles led to a change of the CO adsorption properties as was evidenced by IR spectroscopy. Dynamic changes of the surface were noticed at longer exposure times to CO and higher coverage at room temperature as a first indication of surface instability. These were ascribed to the decomposition into a Ga-depleted Pd phase and Ga2O3, which is a process that was suppressed at liquid nitrogen temperature. The reduction of the Pd precursor at 473 K is not sufficient to form the Pd2Ga phase and yielded a poorly selective catalyst (26% selectivity to ethylene) in the semihydrogenation of acetylene. In accordance with the well-known selectivity-promoting effect of a second metal, the selectivity was increased to 80% after reduction at 773 K due to a change from the elemental to the intermetallic state of palladium in our catalysts. Interestingly, if air contact was avoided after reduction, the conversion slowly rose from initially 22% to 94% with time on stream. This effect is interpreted in the light of chemical response of Pd and Pd2Ga to the chemical potential of the reactive atmosphere. Conversely to previous interpretations, we attribute the initial low active state to the clean intermetallic surface, while the increase in conversion is related to the surface decomposition of the Pd2Ga particles.
    ACS Catalysis 05/2014; 4(6):2048–2059. · 5.27 Impact Factor
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    ABSTRACT: Different surface sites of solid catalysts are usually quantified by dedicated chemisorption techniques from the adsorption capacity of probe molecules, assuming they specifically react with unique sites. In case of methanol synthesis catalysts, the Cu surface area is one of the crucial parameters in catalyst design and was for over 25 years commonly determined using diluted N2O. To disentangle the influence of the catalyst components, different model catalysts were prepared and characterized using N2O, temperature programmed desorption of H2, and kinetic experiments. The presence of ZnO dramatically influences the N2O measurements. This effect can be explained by the presence of oxygen defect sites that are generated at the Cu-ZnO interface and can be used to easily quantify the intensity of Cu-Zn interaction. N2O in fact probes the Cu surface plus the oxygen vacancies, whereas the exposed Cu surface area can be accurately determined by H2.
    Angewandte Chemie 05/2014;

Publication Stats

3k Citations
2,037.52 Total Impact Points

Institutions

  • 1994–2014
    • Fritz Haber Institute of the Max Planck Society
      • Department of Inorganic Chemistry
      Berlín, Berlin, Germany
  • 1990–2014
    • Max Planck Society
      München, Bavaria, Germany
  • 2013
    • Max Planck Institute for Chemical Energy Conversion
      Mülheim-on-Ruhr, North Rhine-Westphalia, Germany
  • 2011–2012
    • University of Cambridge
      • Department of Engineering
      Cambridge, ENG, United Kingdom
    • University of Strasbourg
      Strasburg, Alsace, France
  • 2006–2012
    • University of Innsbruck
      • Institut für Physikalische Chemie
      Innsbruck, Tyrol, Austria
    • N. D. Zelinsky Institute of Organic Chemistry
      Moskva, Moscow, Russia
    • Cardiff University
      • School of Chemistry
      Cardiff, WLS, United Kingdom
  • 2005–2012
    • Max Planck Institute of Colloids and Interfaces
      • Department of Colloid Chemistry
      Potsdam, Brandenburg, Germany
  • 2010
    • University of Sydney
      • School of Physics
      Sydney, New South Wales, Australia
    • Max Planck Institute for Chemical Physics of Solids
      Dresden, Saxony, Germany
    • Vienna University of Technology
      • Institute of Materials Chemistry
      Vienna, Vienna, Austria
  • 2001–2010
    • MPG Ranch
      Lolo, Montana, United States
  • 2008
    • Max Planck Institute for Solid State Research
      Stuttgart, Baden-Württemberg, Germany
    • University of Rostock
      • Leibniz-Institut für Organische Katalyse
      Rostock, Mecklenburg-Vorpommern, Germany
  • 2007
    • Lawrence Berkeley National Laboratory
      • Materials Sciences Division
      Berkeley, CA, United States
    • Technical University Darmstadt
      • Ernst-Berl-Institut für Technische Chemie und Makromolekulare Chemie
      Darmstadt, Hesse, Germany
    • Università degli Studi di Messina
      • Dipartimento di Ingegneria Elettronica, Chimica e Ingegneria Industriale (DIECII)
      Messina, Sicily, Italy
  • 2001–2006
    • Boreskov Institute of Catalysis
      Novo-Nikolaevsk, Novosibirsk, Russia
  • 2004
    • Northeast Institute of Geography and Agroecology
      • State Key Laboratory of Catalysis
      Beijing, Beijing Shi, China
  • 2000
    • Ruhr-Universität Bochum
      • Industrial Chemistry
      Bochum, North Rhine-Westphalia, Germany
  • 1995
    • Hungarian Academy of Sciences
      Budapeŝto, Budapest, Hungary
  • 1993
    • Goethe-Universität Frankfurt am Main
      Frankfurt, Hesse, Germany