Supercritical fluids are often proposed as a means of extending the lifetimes of heterogeneous catalysts that deactivate by deposition of solid carbonaceous deposits, often called 'coke'. This is because the higher density of the supercritical state, compared to the gaseous state, permits the dissolution and removal of coke precursors and coke, before coke can build up and inhibit mass transfer. However, the impact of this process on the extension of catalyst lifetime achieved depends strongly upon the nature of the pore space of the catalyst support, as this dictates the rates of mass transport and the susceptibility of the pellet to pore blockage. In order to optimise the design for running a catalytic process under supercritical conditions, it is vital to be able to predict the interaction between mass transport rates and structural evolution. Previous work has neglected the full complexity of the void space of heterogeneous catalysts, but capturing this in the model is essential to fully understand the evolution of that void space during coking. In this work, a novel structural model that captures the key features of the void space that control mass transport and structural evolution has been employed. Simulations of various reaction schemes, capturing the important aspects of the real reaction pathways, coupled with mass transport, have enabled the prediction of the particular trajectories of structural evolution to be expected. These simulations have been compared with experimental observations of the structural evolution of a real catalyst under supercritical conditions. A comparison of simulation with experiment has enabled a validation of the structural model and particular reaction scheme used in the simulations. (C) 2010 Elsevier Ltd. All rights reserved.