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  • 1
    Electronic Resource
    Electronic Resource
    On the structure-function relationship of nitrogenase M-cluster and P-cluster pairs (1995)
    Springer
    Journal of cluster science 6 (1995), S. 485-501 
    Details
    ISSN: 1572-8862
    Keywords: Nitrogenase MoFe-protein ; M-cluster cage ; molecular-sieve effects ; substrates binding modes ; homocitrate-mediated proton-transport relay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract It A proposed that the M-cluster cage (Kim-Rees model) in active N2-ase can exert shape-selective “molecular-sieve” effects in molecular recognition of exogenous substrates, by providing inside multinuclear active-sites the cavity for N2, C2H2, cyclopropene, and N2O reduction, with [Mo-3Fe]-site available only for N2 reduction: on the other handn-RC— CH,n-RC— N,n-RN-C , C—N− and N3 −, are bound outside the cavity at the [2Fe]-site left by the labilizable ligand “Y”. A terminal carboxylate of the Mo-bound (R)-homocitrate is just in position to protect a H2-evolution site on the P-cluster pair from CO inhibition, and also to take part in mediating a P-cluster-to-Mo-site H+-relay system (involving two hydrogen-bonded H2O) specifically required for N. reduction. The nonreducibility of CO at the [Mo-3Fe]-site is also explained. Experimental support for molecular-sieve effects of M-cluster cage has been obtained from the observed decrease in ethene-cis-d: selectivity by competitive inhibition of HC—CH reduction in D2O by N—N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165769
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  • 2
    Electronic Resource
    Electronic Resource
    Oxidative coupling of methane over LaF3/La2O3 catalysts (1994)
    Springer
    Catalysis letters 23 (1994), S. 377-386 
    Details
    ISSN: 1572-879X
    Keywords: Oxidative coupling of methane ; LaF3 ; La2O3 ; rhombohedral LaOF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We studied the oxidative coupling of methane over the LaF3/La2O3 (50∶50) catalyst. The catalyst was found active even at 873 K. At 1023 K, the C2 yield was 12.7% at 26.0% CH4 conversion and 49.1% C2 selectivity. It was found to be stable and had a lifetime not less than 50 h at 1023 K. The catalyst was effective in C2H6 conversion to C2H4. XRD results indicated that the catalyst was mainly rhombohedral LaOF. It is suggested that the catalyst has ample stoichiometric defects and generates active oxygen sites suitable for methane dehydrogenation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811372
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  • 3
    Electronic Resource
    Electronic Resource
    The oxidative coupling of methane and the activation of molecular O2 on CeO2/BaF2 (1994)
    Springer
    Catalysis letters 29 (1994), S. 177-188 
    Details
    ISSN: 1572-879X
    Keywords: OCM ; metal oxide-fluoride ; electron-enriched lattice oxygen ; quasi-free electrons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract CeO2/BaF2 was used as the catalyst for the oxidative coupling of methane (OCM). At 800°C and CH4∶O2=2.7∶1,CH4 conversion of 34% with C2 hydrocarbon selectivity of 54.3% was obtained. XRD measurement showed that partial anion (O2−,F−) and/or cation (Ce4+,Ba2+) exchange between CeO2 and BaF2 lattices occurred. ESR study showed that O− species existed on degassed catalyst. XPS study revealed that, when BaF2 was added to CeO2, the binding energy of Be 3d5/2 was 2.2 eV lower than that in CeO2, and the “electron-enriched lattice oxygen” species was detected. XPS, ESR and Raman study showed that, under O2 adsorbing conditions, O 2 2− and O − 2 species were detected on CeO2/BaF2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00814264
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  • 4
    Electronic Resource
    Electronic Resource
    The activation of O2 and the oxidative dehydrogenation of C2H6 over SmOF catalyst (1996)
    Springer
    Catalysis letters 40 (1996), S. 101-104 
    Details
    ISSN: 1572-879X
    Keywords: ethane oxidative dehydrogenation ; O2 activation ; SmOF ; dioxygen species and mono-oxygen species
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The activation of O2 over SmOF was studied by in situ laser Raman spectrometry and temperature programmed desorption (TPD). When the hydrogen- and helium-treated (1 h for each gas at 973 K) SmOF sample was cooled to 303 K in oxygen, Raman bands which correspond to the existence of O 2 2− , O 2 n− (2 〉n 〉 1), O 2 − and O 2 δ- (1 〉δ 〉 0) species were observed. From 303 to 973 K, there was no O2 desorption but the Raman bands observed at 303 K reduced in intensity and vanished completely at 973 K, even though the sample was under an atmosphere of oxygen. We suggest that as the sample temperature increased, dioxygen species were converted to mono-oxygen species such as O− which were undetectable by Raman spectrometry. O2 desorption occurred above 973 K, giving a TPD-peak at 1095 K. When C2 H6 was pulsed over the sample pretreated with oxygen and helium at 973 K, C2H4 selectivity was 91.8%. We conclude that the mono-oxygen species is responsible for the oxidative dehydrogenation of ethane to ethene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807464
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  • 5
    Electronic Resource
    Electronic Resource
    Methane activation over unsupported and La2O3-supported copper and nickel catalysts (1996)
    Springer
    Catalysis letters 36 (1996), S. 159-163 
    Details
    ISSN: 1572-879X
    Keywords: methane activation ; Cu/La2O3 and Ni/La2O3 catalysts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Methane was pulsed over pure CuO and NiO as well as Cu/La2O3 and Ni/La2O3 catalysts at 600° C. Results indicate that the mechanisms for methane activation over copper and nickel are quite different. Over CuO, methane is converted to CO2 and H2O, most likely via the combustion mechanism; whereas metallic copper does not activate methane. Over NiO in the presence of metallic nickel sites, methane activation follows the pyrolysis mechanism to give CO, CO2, H2 and H2O. Similar results were obtained over the Cu/La2O3 and Ni/La2O3 catalysts. XRD investigations indicate that copper and nickel existed as CuLa2O4 and LaNiO3 respectively in the La2O3-supported catalysts. The effect of La2O3 on the activation of methane is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807613
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  • 6
    Electronic Resource
    Electronic Resource
    Preparation and characterization of rare earth orthovanadates for propane oxidative dehydrogenation (1996)
    Springer
    Catalysis letters 37 (1996), S. 241-246 
    Details
    ISSN: 1572-879X
    Keywords: rare earth orthovanadates ; citrate method ; propane oxidative dehydrogenation ; redox property
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract High purity rare earth orthovanadates (REVO4), YVO4, LaVO4, CeVO4, NdVO4, SmVO4 and EuVO4, were prepared by the citrate method. XRD, FT-IR, LRS and TPR techniques were employed to characterize these orthovanadates. The catalytic performance of SmVO4, LaVO4 and YVO4 in the oxidative dehydrogenation of propane can compete with that of Mg3V2O8. The selectivity of propene over CeVO4, NdVO4 and EuVO4 was relatively lower. The correlation between the reducibility and the selectivity of the catalysts implied that the V4+/V3+ couple might be involved in the dehydrogenation process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807761
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  • 7
    Electronic Resource
    Electronic Resource
    Pulse studies of CH4 interaction with NiO/Al2O3 catalysts (1994)
    Springer
    Catalysis letters 27 (1994), S. 199-206 
    Details
    ISSN: 1572-879X
    Keywords: pulse reaction ; NiO/Al2O3 catalysts ; methane activation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Pulse studies of the interaction of CH4 and NiO/Al2O3 catalysts at 500°C indicate that CH4 adsorption on reduced nickel sites is a key step for CH4 oxidative conversion. On an oxygen-rich surface, CH4 conversion is low and the selectivity of CO2 is higher than that of CO. With the consumption of surface oxygen, CO selectivity increases while the CO2 selectivity falls. The conversion of CH4 is small at 500°C when a pulse of CH4/O2 (CH4∶O2=2∶1) is introduced to the partially reduced catalyst, indicating that CH4 and O2 adsorption are competitive steps and the adsorption of O2 is more favorable than CH4 adsorption
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806993
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