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  • copper suboxide  (2)
  • oxidation  (2)
  • 36.40  (1)
  • 1
    ISSN: 1572-879X
    Keywords: catalytical oxidation of methanol over copper ; partial oxidation ; copper suboxide ; copper(I) oxide ; total oxidation ; in situ O K-XANES
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The active phase of a bulk metallic copper catalyst is investigated by surface sensitive X-ray absorption spectroscopy at the oxygen K-edge and the Cu L-edges in the total electron yield mode under practical steady state flow-through conditions. The active catalyst surface contains oxygen atoms revealing significant spectral differences compared to those of known copper oxides. The partial oxidation of methanol to formaldehyde is correlated to the abundance of this copper suboxide. These oxygen atoms probe defects of the copper lattice, which represent catalytically active sites. The suboxide is undetectable under UHV conditions. The total oxidation of methanol is catalysed by a conventional copper(I) oxide species and the abundance of carbon dioxide in the gas phase is increasing with decreasing integrated intensity of the oxide species.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 64 (2000), S. 113-118 
    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
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Microchimica acta 125 (1997), S. 401-406 
    ISSN: 1436-5073
    Keywords: fullerenes ; intercalation ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The investigation of structural and electronic properties of the novel family of fullerenes depends on the existence of pure reference materials. Sublimation of the van-der Waals solids is a suitable purification method. Little attention has been paid to the question about the air stability of such sublimed samples in form of crystals or thin films. A combination of thermal desorption spectroscopy, thermal analysis and diffuse reflectance FT-IR spectroscopy is used to show the extent to which oxygen from dry air is intercalated into fullerenes and which detrimental reactivity occurs from attempts to thermally remove („nneal”) air-exposed samples. The conclusion is that any fullerene sample exposed to air will be transformed in part into a polymeric non-fullerene carbon upon thermal treatment to above 400 K irrespective of its initial purity.
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  • 4
    ISSN: 1432-0630
    Keywords: 36.40 ; 61.1.P ; 68.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Fullerene powder mixtures with different C60/C70 ratios have been analyzed by a variety of techniques, and results have been compared. The fullerence mixtures have been characterized as solutions in n-hexane by high-pressure liquid chromatography (HPLC) and UV-VIS spectroscopy. Thin films of fullerenes on Au(111) have been prepared from the mixtures by sublimation. The sublimation process has been studied by simultaneous thermogravimetric and differential thermal analyses. Thin fullerene films on Au(111) have been investigated by scanning tunneling microscopy (STM). The STM images show primarily two types of ballshaped molecules arranged in a lattice with hexagonal symmetry (fcc(111) face, nearest neighbour distance: 1 nm). The two species differ in diameter. STM images of films made of mixtures of different C60/C70 ratios show that C70 molecules display a larger apparent diameter (0.8 nm) and corrugation than C60 molecules (0.7 nm). The C60/C70 ratios obtained by counting the corresponding molecular species in the STM images of the thin films are compared to the C60/C70 ratios determined by HPLC on hexane solutions of the mixtures. The observed differences might be explained by different rates of sublimation for the two species. The STM images reveal film defects (vacancies and boundaries) and dynamic processes (displacement of C70 molecules and vacancies). In films prepared to have a C60 coverage of less than one monolayer, stable structural units of the C60(111) surface consisting of three or seven C60 molecules are revealed by STM. Occasionally, substructure within individual fullerene molecules is observed.
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  • 5
    ISSN: 1572-9028
    Keywords: O K-NEXAFS ; Cu L-NEXAFS ; catalytic oxidation of methanol over copper ; copper suboxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An instrumentation is presented allowing to study the X-ray absorption edge spectra of light elements (z=3–15) in the surface-sensitive Auger yield detection at elevated pressures (mbar range). Heterogeneous catalysts can be studied for their surface electronic structure under working conditions in a flow-through reactor mode. An example of methanol oxidation to formaldehyde over copper metal is studied in detail. A new form of weakly bound atomic oxygen was found which only exists under reaction conditions. Its existence is linked to defect sites on the Cu. Several mechanistic predictions from earlier low-pressure studies could be verified with this in situ experiment.
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