Influence of spatial distribution of active centers on the kinetics of model heterogeneous catalytic processes

The kinetics of two model catalytic processes, one with a unimolecular and the other with a bimolecular Langmuir-Hinshelwood surface reaction mechanism was investigated using dynamic Monte Carlo simulations. The catalytic processes proceeded on the surfaces with heterogeneous surface centers and the influence of the arrangement of the centers active in the surface reaction on dynamics of processes was considered. The conditions in which the spatial distribution of active centers is important were found qualitatively and among them the surface diffusion of reactant particles with a rate comparable with other processes was the most important. The influence of the arrangement of active centers on the ratio of the two model processes was investigated and explained. In the case of the unimolecular surface reaction mechanism, increasing the ordering in the arrangement of active centers decreased turnover number. In the systems with the bimolecular reaction mechanism the highest turnover number values were observed for the surfaces with moderate order in the arrangement of active centers. The mean fraction of active centers neighboring an average active center n(A-A) was proposed as a measure of the order of active centers arrangement. (C) 2004 Elsevier B.V. All rights reserved.