A one-dimensional model (ID), called generalized cylinder (GC), for the diffusion-reaction problem in commercial catalytic pellets is presented. The GC model free parameter (a) is fitted so as to reproduce the behaviour of the actual pellet at high reaction rates. A simple analytical expression allows obtaining a straightforwardly and the maximum deviation of the GC model is evaluated at around 2%. (C) 2007 Elsevier B.V. All rights reserved.