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  • 1
    Electronic Resource
    Electronic Resource
    Dissociative sticking of CH4 on Ru(0001) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2637-2642 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this study the CH4 dissociation probability on Ru(0001) is found for various translational and vibrational energies. The absolute sticking values are determined from King and Wells experiments and carbon uptake curves. The carbon amount is determined from the recombination signal of carbon with oxygen obtained after the beam exposure when heating in an oxygen atmosphere. The measured sticking coefficient of CH4 is strongly enhanced both by increasing the translational and the vibrational energy of the CH4 molecule. A model is applied to the data and an estimate of the thermal activation energy for CH4 dissociation is found to be in good agreement with previous bulb experiments. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477985
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Modification of Ni(111) reactivity toward CH4, CO, and D2 by two-dimensional alloying (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 7289-7295 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Alloying Au into the outermost atomic layer of Ni(111) significantly alters the physical and chemical properties of the surface. The reactivity is investigated by the use of seeded supersonic molecular beams of CH4 and it is found that the nobleness of Au reduces the overall reactivity toward CH4. This is accounted for in an ensemble model resolving the sticking probability on Ni atoms having different nearest neighbor surroundings. Although a mean field description of site distributions is found to be a very good approximation it is improved by using experimentally determined ensemble statistics from STM images. The strong influence of the vibrational temperature on the sticking coefficients of CH4 vs translational energy on the pure Ni(111) is also demonstrated. Desorption energies of CO and D2 is observed to decrease approximately 25–30 kJ/mole as the coverage of Au is increased from 0.0 to 0.7 ML. In TPD spectra of deuterium saturated surface alloys a new clearly resolved desorption state is observed at 180–220 K with maximum intensity around θAu=0.3–0.4 ML. This state is clearly related to chemisorption sites involving both Au and Ni. A site model based on mean field statistics adequately accounts for the appearance of this state. The effect of Au is also evident in the TPD spectra of CO saturated Au/Ni(111) surface alloys where the saturation coverage decreases and new structure develops. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471395
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular beam study of dissociative sticking of methane on Ni(100) (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8255-8263 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper reports a detailed molecular beam study of the dissociative sticking of methane incident on clean Ni(100). It is demonstrated that the sticking coefficient depends strongly on the translational energy of the molecule. It is also observed that an increase in the vibrational energy of the methane leads to a dramatic enhancement of the sticking, emphasizing that the initial vibrational state is of crucial importance. These results are consistent with a mechanism of direct activated dissociative chemisorption where the dynamics is dominated by a barrier in the potential energy surface mainly located in the vibrational coordinates. Normal-energy scaling is only approximately observed. The effect of surface temperature is also investigated but is found to be smaller than activation by translational or vibrational energy. A simplified analysis in terms of state resolved sticking curves, Sν(Ei), considering only the vibrational C–H stretch modes of methane as relevant for the sticking, gives a good description of the data. These sticking curves enables a calculation of the thermal sticking coefficient which is found to be in excellent agreement with bulb experiments directly probing this. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468955
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  • 4
    Electronic Resource
    Electronic Resource
    Designing surface alloys with specific active sites (1996)
    Springer
    Catalysis letters 40 (1996), S. 131-135 
    Details
    ISSN: 1572-879X
    Keywords: active sites ; surface alloys ; STM ; molecular beams ; activation barriers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This report describes a combined experimental and theoretical approach to the problem of designing surface alloys with specific chemical properties. Au-Ni(111) surface alloys were prepared and the distribution of active sites was determined by atomically resolved STM as a function of Au coverage. Using density functional theory the difference in activation energy for methane over the various sites was determined. The activity of the surface could be predicted directly by combining this information with the distribution of sites. Subsequent measurements of the activity proved this method to be quantitative and demonstrated that surface alloys with specific activity can be synthesized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00815272
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  • 5
    Electronic Resource
    Electronic Resource
    Methanol synthesis on Cu(100) from a binary gas mixture of CO2 and H2 (1994)
    Springer
    Catalysis letters 26 (1994), S. 373-381 
    Details
    ISSN: 1572-879X
    Keywords: methanol ; synthesis ; Cu(100) ; hydrogenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The rate of methanol synthesis over a Cu(100) single crystal from a 1 ∶ 1 mixture of CO2 and H2 has been measured at a total pressure of 2 bar and a temperature range of 483–563 K. At these conditions the apparent activation energy is determined to be 69 kJ mol−1, and at 543 K the turnover rate is 2.7 × 10−4 (site s)−1. A kinetic model for the methanol synthesis is presented. Predictions from this model are in good agreement with the rates of methanol synthesis observed on real catalysts at industrial conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00810611
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  • 6
    Electronic Resource
    Electronic Resource
    Activated dissociative chemisorption of methane on Ni(100): a direct mechanism under thermal conditions? (1995)
    Springer
    Catalysis letters 32 (1995), S. 15-30 
    Details
    ISSN: 1572-879X
    Keywords: thermal sticking ; direct dissociation mechanism ; thermal finger ; equilibration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The dissociative chemisorption of methane on a Ni(100) single crystal has been studied under thermal conditions as a function of pressure and temperature. The initial sticking coefficient was measured in the pressure range of 0.010–7.0 mbar at temperatures ranging from 375 to 500 K. A strong pressure dependence was observed, consistent with a direct dissociation mechanism under these thermal conditions. This was further confirmed by experiments where the gas at a low pressure was heated by a thermal finger facing the crystal surface. With the thermal finger at the same temperature as the surface, it was possible to ensure that the methane was fully equilibrated to the crystal and an activation energy of 59±1.5 kJ/mol was determined under isothermal conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806098
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