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  • 1990-1994  (3)
  • pressure  (2)
  • 33.20.Rm  (1)
  • 07.75. + h
  • Radioactivity
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  • 1
    Electronic Resource
    Electronic Resource
    In situ high temperature and high pressure exafs studies of Pt/Al2O3 Catalysts. Part II: Carbon removal (1991)
    Springer
    Catalysis letters 8 (1991), S. 297-304 
    Details
    ISSN: 1572-879X
    Keywords: EXAFS ; Pt/Al2O3 catalyst ; temperature ; pressure ; carbon deposition ; carbon removal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract EXAFS has been used to follow in situ the structural evolution of a Pt/Al2O3 catalyst during removal of carbon by hydrogenation, after reduction and carbon deposition. After reduction at 350 °C, the total hydrogen pressure was raised to 3 atm. and n-heptane was injected over the sample. EXAFS measurements at the Pt edge were carried out with simultaneous on-line EXAFS analysis of the spectra. After observing the rapid formation of a carbon-platinum bond which is unmodified with time, we stopped the heptane flow, raised the temperature to 450 °C, and maintained hydrogen flow at 3 atm. The disappearance of the platinum-carbon bond during heat treatment in hydrogen was monitored via on-line analysis. No sintering of the metal particles was observed. EXAFS is thus proven to be an efficient tool to study not just structural changes of a catalyst during a hydrocarbon reaction [1], but also to use it as a technique to study other catalytic phenomena as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00764191
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    In situ high temperature and high pressure exafs studie of Pt/Al2O3 catalysts. Part I: Reduction and deactivation (1991)
    Springer
    Catalysis letters 8 (1991), S. 283-295 
    Details
    ISSN: 1572-879X
    Keywords: EXAFS ; Pt/Al2O3 catalysts ; chlorine ; temperature ; pressure ; reduction ; deactivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract EXAFS has been used to follow in situ the structural evolution of a chlorinated and non-chlorinated Pt/Al2O3 catalyst during reduction in the temperature range of 300–500 °C. Smaller metal clusters are formed from the hydrogen reduction of the chlorinated catalyst, in contrast to the larger cluster formed from the non-chlorinated one. At 460 °C, the total hydrogen pressure was raised to 5 atm. and n-heptane was injected over the samples. EXAFS measurements at the Pt edge were carried out while hydrocarbon conversion was monitored with a gas Chromatograph. We observe the rapid formation of a carbon-platinum bond. This is unmodified while turnover rates and selectivities indicate evidence for deactivation. From this structural information supplied by EXAFS, correlated with the data obtained from gas chromatography, we find that our results are consistent with a model proposed by others where deactivation is due to the build-up of a multilayer of carbon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00764190
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Chlorine K shell photoabsorption spectra of gas phase HCl and Cl2 molecules (1990)
    Springer
    The European physical journal 17 (1990), S. 291-298 
    Details
    ISSN: 1434-6079
    Keywords: 33.20.Rm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract High resolution photoabsorption spectra of HCl and Cl2 have been measured near the chlorineK edge in the 2810–2850 eV photon energy range. Below the ClK edge, the strongest resonance is interpreted as a simple core excitation into the unoccupied σ* valence orbital for both molecules, leading to a markedly repulsive state. Higher resonances due to low lying Rydberg states, are observed in both systems, but with a larger oscillator strength for HCl as compared to Cl2. In Cl2, the σ* orbital is deep enough to avoid any mixing with Rydberg orbitals. In HCl, we observe the dipole forbidden Cl 1s → 4s transition which denotes a strong 4s–4p hybridization. Above the ClK edge, the multiplet features seen for HCl are analysed in terms of double-core-valence excited vacancy states. In Cl2, their counterpart are found very close to the ionization threshold because of the deep σ* orbital and possibly because the excited core and valence electrons originates either from the same atomic site or from different ones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437369
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    Paper (German National Licenses)
    Fulltext
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