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  • XPS  (5)
  • silver  (5)
  • surface carbon  (2)
  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Oxidative coupling of methane on silver catalysts (1995)
    Springer
    Catalysis letters 32 (1995), S. 185-194 
    Details
    ISSN: 1572-879X
    Keywords: methane ; silver ; oxidative coupling ; C2 selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bulk silver catalysts were found to be active for the oxidative coupling of methane to ethane and ethylene if operated under oxygen-limited conditions at atmospheric pressure and at temperatures above 1020 K. The addition of small amounts of sodium phosphate as promoter increases markedly the C2 selectivity (to values above 90%) and yield (〉10%) by efficient suppression of reaction steps leading to total oxidation. Further improvement of the yields might be achieved by more appropriate reactor design.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806113
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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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  • 7
    Electronic Resource
    Electronic Resource
    Selectivity of hydrogen chemisorption on clean and lead modified palladium particles; a TPD and photoemission study (1990)
    Springer
    Catalysis letters 6 (1990), S. 301-315 
    Details
    ISSN: 1572-879X
    Keywords: Palladium ; hydrogen chemisorption ; decomposition of PdO ; Head as surface modifier ; XPS ; UPS ; TPD
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This work describes hydrogen chemisorption on clean and lead modified palladium particles obtained from decomposition of PdO. TPD is used as a chemical probe to test the surface properties of several states of metallic palladium relevant in practical selective hydrogenation catalysts. These states differ in oxygen content and the presence of a lead modifier. XPS and UPS data serve as a basis for identifying the surface properties. TPD spectra show a very broad low temperature peak-likely bulk hydride decomposition-and a sharp TPD peak between 330 and 380 K. This latter can be devided into three rather poorly separated subpeaks; addition of Pb does not shift peak maxima but decreases the central subpeak and eliminates the high temperature peak completely. This points to the interaction of Pb with specific surface sites rather than to bulk alloy formation. The enhancement of selectivity in hydrogenation obtained from lead modification is considered as a geometric site blocking effect rather than to arise from a bulk modification of the valence electronic structure of palladium metal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00763996
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  • 8
    Electronic Resource
    Electronic Resource
    Formation of a liquid film of AgNO3 on a silver surface (2000)
    Springer
    Catalysis letters 64 (2000), S. 113-118 
    Details
    ISSN: 1572-879X
    Keywords: X‐ray photoelectron spectroscopy (XPS) ; scanning electron microscopy (SEM) ; silver ; oxidation ; surface chemical reaction ; NO ; NO x
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The behavior of a AgNO3/Ag2O/Ag “sandwich” upon heating in vacuum was studied by in situ X‐ray photoelectron spectroscopy (XPS) and ex situ scanning electron microscopy (SEM). The AgNO3/Ag2O/Ag “sandwich” was prepared by exposure of a silver foil to a NO : O2 mixture. The upper layer of the “sandwich” consists of AgNO3 crystals of a mean size between 0.1 and 0.4 μm. Heating at 550 K in vacuum results in melting of the AgNO3 crystals. A liquid film of AgNO3, readily wetting the silver, covers the surface. Cooling below the melting point of AgNO3 leads to the agglomeration of silver nitrate to long islands with a size reaching a few tens of micrometers (μm). The possible effects of AgNO3 liquid‐phase formation on surface processes are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019015826651
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  • 9
    Electronic Resource
    Electronic Resource
    Microstructure of the activated industrial ammonia synthesis catalyst (1991)
    Springer
    Catalysis letters 11 (1991), S. 19-31 
    Details
    ISSN: 1572-879X
    Keywords: Ammonia synthesis ; iron catalyst ; surface characterization ; promoter effects ; nitrides ; ion scattering spectroscopy ; XPS ; HRTEM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00866897
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  • 10
    Electronic Resource
    Electronic Resource
    Methanation of carbon dioxide over Ru/Titania at room temperature: explorations for a photoassisted catalytic reaction (1991)
    Springer
    Catalysis letters 11 (1991), S. 157-168 
    Details
    ISSN: 1572-879X
    Keywords: Carbon dioxide methanation ; Ru/TiO2 catalyst ; in-situ UV-VIS spectroscopy ; XPS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The methanation of CO2 has been investigated over a special Ru/TiO2 catalyst suggested by Thampi, Kiwi and Graetzel [4]. This paper deals with the analysis of the material and the investigation of the reported photoenhancement of the activity. The catalyst is characterised by in situ UV-VIS spectroscopy and by XPS. Conversion experiments at atmospheric pressure were carried out with and without UV light irradiation. The irradiation increases the conversion significantly. From various experiments it can be shown, however, that this effect is due to a thermal effect and does not involve an intrinsic photochemical step. Localised Ti3+ states sensitise the support to convert visible light into heat resulting in the observed increase in conversion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00764081
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