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  • 1990-1994  (4)
  • oxygen  (2)
  • HRTEM  (1)
  • carbon monoxide oxidation on Pt(110)  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Surface and subsurface products of the interaction of O2 with Ag under catalytic conditions (1991)
    Springer
    Catalysis letters 11 (1991), S. 253-265 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Silver ; oxygen ; selective oxidation ; thermal desorption ; subsurface compounds
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Polycrystalline Ag treated with O2 at pressures up to 1 bar and at temperatures up to 920 K was examined by TDS. It was found that the peak commonly observed at 595±25 K and assigned to adsorbed atomic oxygen (Oa) is shifted to higher desorption temperatures with rising dosing temperatures. Since saturation of the uptake was not possible either, this peak was identified as dissolved atomic oxygen (Od). The existence of a maximum for the O2 uptake after exposure at 820 K was found. Hence, under conditions of formaldehyde synthesis (≈ 920 K) the ability of the catalyst to dissolve oxygen is near its maximum.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00764316
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  • 2
    Digitale Medien
    Digitale Medien
    On the nature of the active state of silver during catalytic oxidation of methanol (1993)
    Springer
    Catalysis letters 22 (1993), S. 215-225 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Ion-scattering spectroscopy (ISS) ; methanol oxidation ; oxygen ; Raman spectroscopy ; reflection electron microscopy (REM) ; silver ; X-ray photoelectron spectroscopy (XPS)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Under the applied high reaction temperatures (∼900 K) the Ag surface is restructured and a tightly held oxygen species is formed on the surface (Oγ) apart from O atoms dissolved in the bulk (Oβ). Methanol oxidation to formaldehyde proceeds through this Oγ species as demonstrated by application of a variety of spectroscopic techniques.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00810368
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  • 3
    Digitale Medien
    Digitale Medien
    Temporal and spatial self-organisation in catalysis at single crystal surfaces (1991)
    Springer
    Catalysis letters 9 (1991), S. 219-230 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Oscillatory catalytic reactions ; spatial differences in surface concentrations of reactants ; carbon monoxide oxidation on Pt(110)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The elementary steps underlying the mechanism of a catalytic reaction are also responsible for its rate under steady-state conditions. In special cases the rate will no longer be stationary, but may become oscillatory or even chaotic. These phenomena have to be ascribed to the nonlinear character of the coupled differential equations modelling the temporal behavior of the surface concentrations of the reacting species. As a consequence, these concentrations may also exhibit spatial differences, even on ana priori uniform single crystal surface, leading to spatiotemporal patterns such as propagating and standing waves as well as ‘chemical’ turbulence. Experimental evidence for these effects is presented for a particular system, the oxidation of CO on a Pt(110) surface.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00773180
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  • 4
    Digitale Medien
    Digitale Medien
    Microstructure of the activated industrial ammonia synthesis catalyst (1991)
    Springer
    Catalysis letters 11 (1991), S. 19-31 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00866897
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