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  • oxygen  (3)
  • surface oxygen  (3)
  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: Silver ; oxygen ; selective oxidation ; thermal desorption ; subsurface compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00764316
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Keywords: Ion-scattering spectroscopy (ISS) ; methanol oxidation ; oxygen ; Raman spectroscopy ; reflection electron microscopy (REM) ; silver ; X-ray photoelectron spectroscopy (XPS)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00810368
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of water on the formation of strongly bound oxygen on silver surfaces (1995)
    Springer
    Catalysis letters 32 (1995), S. 171-183 
    Details
    ISSN: 1572-879X
    Keywords: oxygen ; partial oxidation ; reconstruction ; reflection electron microscopy ; Raman spectroscopy ; silver ; water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Interaction of water with an oxygenated Ag(111) surface leads to an enhancement of the surface restructuring and an activated formation of hydroxyl groups (OH) located stably on the surface and incorporated in the subsurface region, as evidenced by means of reflection electron microscopy (REM) and in situ Raman spectroscopy. Dehydroxylation of OHads at elevated temperatures releases the strongly bound oxygen species labelled Oγ at the surface, and offers an alternative to the energetically less favorable pathway for the direct formation of the Oγ species from molecular oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806112
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  • 4
    Electronic Resource
    Electronic Resource
    On the relation between catalytic performance and microstructure of polycrystalline silver in the partial oxidation of methanol (1995)
    Springer
    Catalysis letters 33 (1995), S. 305-319 
    Details
    ISSN: 1572-879X
    Keywords: methanol oxidation ; conversion to formaldehyde ; silver ; surface oxygen ; STM ; IMR-MS ; adsorption-induced restructuring ; atomic structure ; texture ; X-ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Electrolytic silver was investigated as partial oxidation catalyst for the conversion of methanol to formaldehyde. Using the mass spectrometric technique as on-line detector the relation between feed composition and temperature was determined allowing us to conclude that two simultaneous reaction pathways operate under steady state conditions. The microstructure was analysed by XRD and STM. A pronounced restructuring of the surface on the mesoscopic scale was detected. The atomic structure of the γ oxygen phase was determined on the (111) face of facets grown during reaction. The two reaction pathways find their counterparts in two distinctly different surface microstructures providing different geometries for the respective active sites. After prolonged time on stream the high surface mobility of the silver atoms removes all mesoscopic restructuring without changing the conversion characteristics. The observed restructuring is thus considered as a frozen large scale image of the continuously changing surface under reaction conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00814233
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  • 5
    Electronic Resource
    Electronic Resource
    Surface composition and possible rearrangement of disperse Pt and Rh catalysts: does the presence of carbon and oxygen contribute to different catalytic properties? (2000)
    Springer
    Catalysis letters 67 (2000), S. 93-98 
    Details
    ISSN: 1572-879X
    Keywords: rhodium black ; platinum black ; surface carbon ; surface oxygen ; methylcyclopentane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The surface composition of Rh and Pt blacks (as determined by XPS) shows carbon and oxygen impurities in the untreated state. Oxygen on Pt is present as adsorbed O as well as OH/H2O groups and oxidized carbon. Rh was partly oxidized to Rh2O3, in agreement with UPS showing hardly any Fermi‐edge intensity in untreated Rh as opposed to untreated Pt. High Fermi‐edge intensities indicated a predominant metallic surface after an in situ treatment with H2 at 483 K, increasing the purity (XPS) to ∼90%. This treatment reduced Rh to metal and removed its C impurity. Pt, in turn, retained much carbon after H2 treatment, present mainly as graphitic carbon. A minor amount of CO was also detected, some of the O 1s peak belonging to it. The two metals were tested in methylcyclopentane reactions. Considering the necessity of carbon for nondegradative reactions and oxygen enhancing fragmentation, a correlation is suggested between the typical impurities of Pt and Rh and their respective catalytic propensities: the high fragmentation activity of Rh and the predominant nondegradative reactions to C6 “ring opening products” on Pt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019061420659
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  • 6
    Electronic Resource
    Electronic Resource
    An attempt to bridge the pressure and material gap with a disperse model catalyst for low-temperature alkane reforming (2000)
    Springer
    Catalysis letters 65 (2000), S. 19-23 
    Details
    ISSN: 1572-879X
    Keywords: Pt black ; n-hexane ; XPS ; UPS ; XRD ; surface carbon ; surface oxygen ; catalyst restructuring ; crystal anisotropy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Pt black was exposed to n〉-hexane/H2 mixtures between 483 and 663 K followed by O2 and H2 treatments at 603 K. XP and UP spectra were measured without exposing the samples to air. 20–30% carbon accumulated after hydrocarbon exposures. O2 removed most carbon. The surface C content increased after a subsequent contact with H2, C 1s showing more “atomic carbon” as opposed to graphite after n-hexane exposure. Anisotropic recrystallization of Pt black favoring (220) and (311) lattice planes occurred under hydrogen-rich conditions. Both findings were attributed to a H2-induced solid-state rearrangement; H atoms penetrating into the crystal lattice, force subsurface carbon and oxygen atoms to the surface and a concomitant restructuring would occur. Thus another “hydrogen effect” has been recognized, leading to structures favorable for skeletal reactions of alkanes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019037926168
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