The design of periodically operated trickle-bed reactors requires extensive knowledge of the complex underlying processes occurring at various scales. The development of dynamic models offers detailed insights into system behaviour and allows quantitative investigations over a wide range of operating, conditions without the expense of comprehensive experimental studies. The description of the dynamic behaviour of periodically wetted catalyst particles is an important element in the overall multi-scale model architecture. Unfortunately, very little information is available on the influence of various model assumptions to aid selection of appropriate unsteady-state models. A systematic evaluation of dynamic particle-scale modelling approaches based on various intra-particle concentration profiles and periodic wetting of the external particle surface is presented. (c) 2005 Elsevier Ltd. All rights reserved.