The reduction reaction of NO by CO over Pd is studied by means of a Monte Carlo simulation. A reaction mechanism similar to that established previously in the literature for Rh and a set of recently published kinetics parameters for Pd determined from experimental work are assumed. The heterogeneous effects of the catalytic substrate are analyzed by simulating various surfaces: a uniform square and hexagonal lattice, the incipient percolation cluster (IPC) fractal, and a lattice formed by a cluster distribution supported on a deterministic fractal. The results interpret reasonably the experimental data published recently in the case of crystals and supported catalysts. (c) 2008 Elsevier B. V. All rights reserved.