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  • XPS  (5)
  • surface carbon  (2)
  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Ruthenium supported on zeolite A: preparation and characterisation of a stable catalyst for ammonia synthesis (1994)
    Springer
    Catalysis letters 25 (1994), S. 61-74 
    Details
    ISSN: 1572-879X
    Keywords: Ammonia synthesis ; supported ruthenium catalyst ; dispersed ruthenium ; instationary kinetics ; lifetime effects ; ruthenium oxidation ; surface analysis ; XPS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00815416
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