A model describing adsorption and desorption in a bed of porous catalyst pellets is presented. The model has been used to simulate temperature-programmed desorption. In particular the effect of a coverage-dependent heat of adsorption has been investigated and the consequences thereof for commonly used interpretation methods are shown. It appears that the method in which the heating rate is varied and the method using desorption rate isotherms yield values which roughly approach the heat of adsorption used for the calculation of the desorption profiles in the case of the coveragedependent heat of adsorption. Adsorption experiments, either in a flow of adsorbate or under static conditions, have also been simulated. If the net rate of adsorption is high, the catalyst surface is covered frontwise. When the amount of adsorbate supplied from the gas phase is insufficient to bring about complete surface coverage, nonuniform coverage results.