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  • Chemistry  (10)
  • XPS  (2)
  • frontal chromatography  (2)
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Topics in catalysis 11-12 (2000), S. 263-270 
    ISSN: 1572-9028
    Schlagwort(e): nitric oxide ; selective catalytic reduction ; supported ruthenium catalysts ; frontal chromatography ; temperature-programmed surface reaction ; reaction mechanism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Steady-state and transient kinetic experiments were performed in a versatile microreactor flow set-up with magnesia- and alumina-supported ruthenium catalysts in order to elucidate the mechanism of the selective catalytic reduction (SCR) of nitric oxide with hydrogen. Both Ru/MgO and Ru/γ-Al2O3 were found to be highly active catalysts converting NO and H2 into N2 and H2O with selectivities close to 100% at full conversion, although Ru-based catalysts are known to be active in the synthesis of NH3 from N2 and H2. Frontal chromatography experiments with NO at room temperature revealed that NO and its dissociation products displace adsorbed atomic hydrogen (H−*) almost completely from hydrogen-precovered Ru surfaces. Obviously, NO and H2 compete for the same adsorption sites, H−* being the weaker bound adsorbate. Temperature-programmed surface reaction (TPSR) experiments in H2 subsequent to NO exposure demonstrated that higher heating rates and lower partial pressures of H2 shift the selectivity from NH3 to N2. Therefore, the coverage of H−* is concluded to govern the branching ratio between the rate of associative desorption of N2 (2N−*→N2 + 2*) and the rate of hydrogenation of N−* (N−* + 3H–* →NH3 + 4*). Finally, the steady-state coverages of N- and O-containing adsorbates were derived by interrupting the SCR reaction and hydrogenating the adsorbates off as NH3 and H2O. By solving the site balance, the Ru surfaces were found to be essentially N2 is attributed to the very low coverage of H−* due to site blocking by a N + O coadsorbate layer, favouring the recombination of N−* instead of its hydrogenation to NH3.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Catalysis letters 11 (1991), S. 19-31 
    ISSN: 1572-879X
    Schlagwort(e): Ammonia synthesis ; iron catalyst ; surface characterization ; promoter effects ; nitrides ; ion scattering spectroscopy ; XPS ; HRTEM
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Industrial doubly-promoted iron catalysts and model systems of singly-promoted K- and Al-iron catalysts were characterised by their catalytic performance at 1 bar pressure. The relevance of bulk nitrogen for catalytic performance is shown. The catalysts were also activated in an in-situ reaction chamber of a He-ion scattering spectrometer (ISS) and their top atomic layer elemental composition was determined after they had reached similar performance as in the microreactor tests. The bulk microstructure of these samples was investigated by high resolution transmission electron microscopy (TEM) and microdiffraction. All evidence indicates that small highly crystalline α-Fe platelets act as active phase. Their surfaces are covered to a large extent by promotor compounds which are partly present as poorly crystalline aggregates with iron oxide leaving only a small fraction of elemental iron directly exposed to the gas phase. The intimate contact between iron crystals and promoters particles prevents recrystallisation and is the key to the understanding of the structural stability of the catalyst system.
    Materialart: Digitale Medien
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  • 3
    ISSN: 1572-879X
    Schlagwort(e): Ammonia synthesis ; supported ruthenium catalyst ; dispersed ruthenium ; instationary kinetics ; lifetime effects ; ruthenium oxidation ; surface analysis ; XPS
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Reaction of Ru(NH3)6Cl3 with Na-A and K-A zeolites yielded oligomeric amino-oxo-complexes supported on the zeolite. Controlled thermal activation under hydrogen converted the precursor in a two-step reaction into an active catalyst with good long-term stability and resistance against small doses of oxygen poison. Several nanometers sized Ru metal particles are chemically bonded to the zeolite surface which provides in the K form an alkali promoter at the metal-zeolite interface. Extensive oxidation breaks the metal-support anchoring and re-reduction produces Ru metal particles sintering rapidly into large metal crystals with only small residual catalytic activity.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Catalysis letters 53 (1998), S. 77-81 
    ISSN: 1572-879X
    Schlagwort(e): SCR of NO ; Ru ; MgO ; frontal chromatography ; TPD ; TPSR
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Ruthenium supported on magnesia was found to be a highly active and selective catalyst for the reduction of NO to N2 with H2. The adsorption of NO on Ru/MgO was studied at room temperature by applying frontal chromatography with a mixture of 2610 ppm NO in He. Subsequently, temperature‐programmed desorption (TPD) and temperature‐programmed surface reaction (TPSR) experiments in H2 were performed. The adsorption of NO was observed to occur partly dissociatively as indicated by the formation of molecular nitrogen. The TPD spectrum exhibited a minor NO peak at 340 K indicating additional molecular adsorption of NO during the exposure to NO at room temperature, and two N2 peaks at 480 K and 625 K, respectively. The latter data are in good agreement with previous results with Ru(0001) single‐crystal samples, where the interaction with NH3 was found to lead to two N2 thermal desorption states with a maximum coverage of atomic nitrogen of about 0.38. Heating up the catalyst after saturation with NO at room temperature in a H2 atmosphere revealed the self‐accelerated formation of NH3 after partial desorption of N2, whereby sites for reaction with H2 become available. As a consequence, the observed high selectivity towards N2 under steady‐state reduction conditions is ascribed to the presence of a saturated N+O coadsorbate layer resulting in an enhanced rate of N2 desorption from this layer and a very low steady‐state coverage of atomic hydrogen. The formation of H2O by reduction of adsorbed atomic oxygen is the slow step of the overall reaction which determines the minimum temperature required for full conversion of NO.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 89-98 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The occurrence of instabilities in chemically reacting systems, resulting in unsteady and spatially inhomogeneous reaction rates, is a widespread phenomenon. In this article, we use nonlinear signal processing techniques to extract a simple, but accurate, dynamic model from experimental data of a system with spatiotemporal variations. The approach consists of a combination of two steps. The proper orthogonal decomposition [POD or Karhunen-Loève (KL) expansion] allows us to determine active degrees of freedom (important spatial structures) of the system. Projection onto these “modes” reduces the data to a small number of time series. Processing these time series through an artificial neural network (ANN) results in a low-dimensional, nonlinear dynamic model with almost quantitative predictive capabilities.This approach is demonstrated using spatiotemporal data from CO oxidation on a Pt (110) crystal surface. In this special case, the dynamics of the two-dimensional reaction profile can be successfully described by four modes; the ANN-based model not only correctly predicts the spatiotemporal short-term behavior, but also accurately captures the long-term dynamics (the attractor). While this approach does not substitute for fundamental modeling, it provides a systematic framework for processing experimental data from a wide variety of spatiotemporally varying reaction engineering processes.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 80 (1968), S. 244-244 
    ISSN: 0044-8249
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 7
    ISSN: 0009-286X
    Schlagwort(e): Chemistry ; Industrial Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 41 (1969), S. 289-294 
    ISSN: 0009-286X
    Schlagwort(e): Chemistry ; Industrial Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Primärvorgänge bei der heterogenen Katalyse können mit atomar reinen Einkristall-Oberflächen untersucht werden. Aussagen über die Struktur von Oberflächenphasen werden mit der Methode der Beugung niederenergetischer Elektronen (LEED) erhalten, mit deren Hilfe eine allgemeine Charakterisierung von Adsorptionserscheinungen und katalytischen Reaktionen möglich ist. Es wird über ausgewählte Beispiele berichtet.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 48 (1976), S. 502-502 
    ISSN: 0009-286X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 12 (1988), S. 233-238 
    ISSN: 0142-2421
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: An X-ray photoelectron spectroscopic study is presented for an industrial catalyst surface, which is in its active form only accessible after reaction under technical conditions. A high pressure-high temperature reactor was attached to a surface analysis system. It allowed rapid transfer of a sample between the reaction environment and the UHV required for surface analysis. The active phase was identified as a ternary iron potassium oxide. No evidence was found for the previously suggested presence of a binary potassium hydroxide or carbonate phase in solid or liquid form. A new model of the active catalyst is proposed.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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