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  • 11
    Electronic Resource
    Electronic Resource
    An ab initio study of methane activation on lanthanide oxide (1997)
    Springer
    Catalysis letters 49 (1997), S. 53-58 
    Details
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ab initio MP2 calculations have been carried out to study the activation of methane on lanthanide oxide La2O3. O- and O2 2- are assumed to be the active species on the oxide surface. The possible roles of O2- and O2 4- on the oxide surface in C-H bond activation are also investigated. It is shown that the CH4 oxidative dehydrogenation occurs much more readily on O- and O2 2- than on O2- and O2 4-. The results indicate that O- and O2 2- are the active species and therefore support the O- and O2 2- mechanisms assumed for the reactions. The promoter compound containing Br- is found to be favorable for the methane activation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019040902099
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  • 12
    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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  • 13
    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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  • 14
    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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  • 15
    Electronic Resource
    Electronic Resource
    Pulse study of methane partial oxidation to syngas over SiO2-supported nickel catalysts (1996)
    Springer
    Catalysis letters 41 (1996), S. 159-163 
    Details
    ISSN: 1572-879X
    Keywords: methane oxidation ; syngas ; SiO2-supported nickel (Ni/SiO2) ; deuterium isotope effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reaction behaviors of CH4/O2 (2/1) with unreduced and reduced SiO2-supported nickel (10 wt% metal) catalysts were investigated in a pulse micro-reactor at temperatures ranging from 600 to 800° C. In the interaction of CH4/O2 with unreduced NiO/SiO2, the products are exclusively CO2 and H2O at or below 700°C. At 800° C, besides CO2 and H2O, CO and H2 are formed. The reactivity at 800°C can be ascribed to the net generation of metallic nickel site at this temperature. In the reaction of CH4/O2 over reduced Ni/SiO2, the main products are CO and H2 with CO2 and H2O being the minor ones. The results indicate metallic nickel is the active site for methane partial oxidation to syngas. Normal deuterium isotope effects of similar magnitude were observed on the overall, as well as on the CO and CO2 formation reactions with insignificant change in the product selectivities when CD4 was used instead of CH4, indicating that methane dissociation is a key step and that CO and CO2 are formed via some common intermediates which are subject to kinetic deuterium isotope effect. The results of deuterium isotope effects can be reasonably explained based on the methane pyrolysis mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811484
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  • 16
    Electronic Resource
    Electronic Resource
    Exact two-soliton solutions to the Einstein gravitational field equations (1991)
    Springer
    Astrophysics and space science 184 (1991), S. 313-330 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Following our previous work on the existence of 1-soliton solution to the Einstein gravitational field equations in the presence of a spherically-symmetric static background field, we have found six sets of analytical 2-soliton solutions to the Einstein field equations under a certain ansatz in the absence of the stated background field. Numerical analysis shows that if the two solitons of the transverse nature are injected at space variable z→±∞, the longitudinal field componentg 33 will acquire non-zero values for a bounded spatial region at later time. The nature of the solitons becomes rather complex when they interact. The amplitudeg μν of each soliton may change its magnitude resulting from the interaction. We have found that we might interpret the evolution of one field component as the gravitational instanton in our solutions. We must remark also that the total energy of the interacting solitons remains constant, as expected, at all time. These solutions correspond to the situation where the Riemann tensor is in general non-zero and are truly non-trivial solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642979
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  • 17
    Electronic Resource
    Electronic Resource
    Perturbation theory via the Ricatti equation (1982)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 21 (1982), S. 179-190 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present summary results of a bound-state perturbation theory for a one-space and one-time dimension nonrelativistic spinless (Schrödinger) particle, a relativistic spinless (Klein-Gordon) particle, and a relativistic spin-half (Dirac) particle in central fields due to scalar or fourth-component vector-type interactions for an arbitrary bound state. This is accomplished by the reduction of the wave equations to Ricatti form. This enables a decoupling between the pair of coupled first order differential equations on the large and small component Dirac wave functions or a decoupling of the second order differential equation in the Schrödinger or Klein-Gordon equations. All corrections to the energies and wave functions, including corrections to the positions of the nodes in excited states, are expressed in quadratures in a hierarchial scheme, without the use of either the Green's function or the sum over intermediate states. For the ground states of a Schrödinger particle, it is possible to extend this technique to multidimension in the case where the perturbation is due to noncentral fields, for example, in the problem of a nonrelativistic hydrogen atom in a linear combination of multiple fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560210114
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