RELATING METAL-PARTICLE GEOMETRY TO THE SELECTIVITY AND ACTIVITY OF SUPPORTED-METAL CATALYSTS - A MONTE-CARLO STUDY

Monte Carlo simulations of adsorption and reaction of polyatomic molec ules have been conducted on regular Euclidean shapes and on random tes sellations to determine the extent to which simple geometric parameter s, such as particle size and the spatial distribution of active sites, determine the selectivity and activity characteristics of supported-m etal catalysts. It is observed that the influence of low coordination metal atoms at the edges and corners of metallic clusters become signi ficant at an average particle size of approximately 5-10 nm. This is i n agreement with experimental results for a range of hydrocarbon react ions catalysed by supported metals. The influence of molecule size and geometry has also been considered in these simulations, and it is dem onstrated that the influence of molecule and particle geometry on the particle effectiveness factor is insignificant. By investigation of va rious combinations of active site distribution and particle size it ha s been possible to reproduce the main features observed from experimen tal studies relating metal particle size and catalyst performance, by consideration of geometric parameters alone. (C) 1998 Academic Press.