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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 3082-3091 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study a model of the CO oxidation on percolation clusters which represent the surface of our system in the Monte Carlo simulation. We observe two phase transitions where the surface is completely covered (poisoned) by one species (in our system CO or O). These phase transitions are described by their order and the values of the mole fraction yCO of CO in the gas phase at y1 (O poisoning) and at y2 (CO poisoning). The interval (y1,y2) represents the reactive regime. The influence of the occupation probability p for generating a spanning cluster on the underlying square lattice, of the diffusion of CO and of the lattice size on the value and the character of the kinetic phase transitions is studied. Increasing p leads to a shift of y2 to larger values of yCO for all ratios of adsorption to diffusion events but the value of y1 is increased to a larger value of yCO only if diffusion is not allowed. In the case of diffusion the value of y1 is maximally independent of p. A change in the character of the phase transition at y2 from first order on regular lattices to second order is observed on percolation clusters (p≥pC=0.592 75). Here pC is the percolation threshold on the square lattice. The character becomes again first order if diffusion is allowed or if p exceeds 0.97. The observed effects may be understood as a result of the different ramification of the percolation clusters which strongly depends on p. The cluster structures are characterized by pair correlation functions. The lattice size shows for p near unity no significant effect on the values of y1 and y2 but its influence increases with decreasing p. We will show that the fractal dimension of the surface is not a useful quantity for predicting the positions and the character of the phase transitions for the reaction system studied here.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5037-5044 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we study CO oxidation on a catalyst consisting of a Pt/Sn alloy. On this catalyst the reaction can take place at room temperature. We use for the description two basically different methods: Monte Carlo simulations and a theoretical stochastic ansatz. The stochastic ansatz introduced recently [Mai, Kuzovkov, and von Niessen, Physica A 203, 298 (1994)] is a general method for the description of surface reaction systems including mono- and bimolecular steps. Using the Markovian behavior of these systems we formulate this ansatz in terms of master equations. It turns out that the stochastic ansatz can be used as an interesting and advantageous alternative to the standard Monte Carlo simulations. The particles involved in the reaction system have different tendencies toward building structures on the surface. The coverages show a strong dependency, not only on the composition of the gas phase but also on the initial concentration of the reaction promotor OH and the concentration of Pt sites in the catalyst material. The reaction probability does not influence the qualitative trends of the coverages versus the gas phase concentration of CO. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Chemical Physics Letters 211 (1993), S. 197-202 
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Chemical Physics Letters 196 (1992), S. 358-362 
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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