Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-I-23STOCHASTIC MODELS FOR THE IMAGINATIONOF SURFACE WAVES IN CATALYTIC REACTIONSOF CARBON MONOXIDE OXIDATION ON PLATINUM METALSV.I. Elokhin, A.V. Matveev, V.V. GorodetskiiBoreskov Institute of Catalysis SB RAS, Novosibirsk, RussiaFax: 007-383-3308056, e-mail: elokhin@catalysis.ruWe intend to compare the specific features of the statistical lattice models (based on theMonte-Carlo technique) for imitating the oscillatory and autowave dynamics in the adsorbedlayer during carbon monoxide oxidation over Pt(100) and Pd(110) single crystals differing bythe structural properties of catalytic surfaces. The statistical lattice model constructed for(CO+O 2 )/Pd reaction takes into account the change of surface properties due to the reversiblepenetration of the adsorbed oxygen into subsurface layer: O ads ↔ O sub [1]. The statisticallattice model has been constructed for the (CO+O 2 )/Pt(100) reaction which takes into accountthe change of surface properties due to the adsorbate-induced reversible surfacetransformation hex ↔ 1×1 [2]. The model reproduces qualitatively the hysteresis and theoscillations of reaction rate, O ads , CO ads coverages, hex and 1×1 surface phases under theconditions close to the experimental ones. Autowave processes on the model surfaceaccompany the oscillations of the rate of CO 2 formation and the concentrations of theadsorbed species in both cases. The existence of the reaction zone between the movingadsorbate islands characterised by the elevated concentration of the free active centres hasbeen shown [2]. The presence of the narrow reaction zone was found experimentally bymeans of the field ion probe-hole microscopy technique with ~ 5 Å resolutions, Fig. 1 [3].The simulated structure of the reaction zone is shown in Fig. 2.In both cases (Pt(100), Pd(110)) the synchronous oscillations of the reaction rate andsurface coverages are exhibited within the range of the suggested model parameters under theconditions very close to the experimental observations [1,2]. These oscillations areaccompanied by the autowave behaviour of surface phases and adsorbates coverages. Theintensity of CO 2 formation in the CO ads layer is low, inside oxygen island it is intermediateand the highest intensity of CO 2 formation is related to a narrow zone between the growingO ads island and surrounding CO ads layer («reaction zone»), Fig. 2. The boundaries ofoscillatory behavior and hysteresis effects have been revealed. The possibility for theappearance of the turbulent patterns in the case of Pt(100) [2] and Pd(110), the spiral [4] andelliptic waves on the surface in the cases under study has been shown.69