III International Conference

PP-I-18ORIGINAL MONTE CARLO METHOD FOR HETEROGENEOUS CATALYTICREACTIONS SIMULATION IN TIME MODE OF REAL EXPERIMENTSEfremov D.K., Pinaeva L.G., Sadykov V.A., Mirodatos C. 1Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia1 Institut de Recherches sur la Castalyse, 2 av. A. Einstein, F-69626 Villeurbanne Cedex, FranceE-mail: claude.mirodatos@catalyse.cnrs.fr ; d_efremov@inbox.ru16 O/ 18 O isotopic exchange over CeO 2 -ZrO 2 and CeO 2 -ZrO 2 -La 2 O 3 at T = 923 K andP = 760 Torr was analyzed by original Monte Carlo method simulating these processes in thetime mode of real transient kinetic experiments. The values of the rate constants of elementarystages of isotopic exchange were found at which the excellent agreement between calculatedand experimental isotopic transient curves was obtained. All these kinetic data are requiredfor the further steps of modeling isotopic exchange over Pt/CeO 2 -ZrO 2 and Pt/CeO 2 -ZrO 2 -La 2 O 3 , and then partial oxidation of hydrocarbons.Fluorite-like ceria-zirconia based catalysts are known to have high surface/bulk oxygenmobility and storage capacity, which is supposed to play a key role in the number of catalyticreactions and therefore deserves to be investigated carefully for elucidation of detailedkinetics and mechanistic pathways.In our numerical experiments several assumptions were made as follows. a) thetopological equivalent of the model fluorite-like structure in our simulations consisted ofoxygen atoms and/or oxygen vacancies only, and its surface, subsurface and innermost layerswere hexagonally packed; b) each Monte Carlo step considered a tiny time interval dt for allelementary stages of the overal process: inlet (outlet) stream, adsorption, desorption,diffusion, etc. It was supposed that during this interval dt concentrations of oxygen isotopemolecules are constant in all the reactor volume; c) the kinetics of oxygen adsorption,desorption, bulk and surface diffusion follows a mass action low: for example, the rate of O 2adsorption onto the surface may be represented by W ads = k ads C O2 Θ Z 2 , where k ads is a functionof temperature only; C O2 is a gas oxygen concentration of any isotope composition; Θ Z is thesurface vacancy fraction. If we have square layers L*L in area (where L measured by oxygendiameters) and small time step dt ca. 0.02 - 0.05 s (vide supra), then quantity N ads ofelementary acts of O 2 adsorption may be written asN ads = [L 2 dt k ads C O2 Θ Z 2 ] + n ads40