When searching for a design concept in which a catalytic combustor is utilised, or looking for areas where improvements can be made to an existing design, then mathematical modelling is an important tool. However, models are only as good as the way in which the physico-chemical processes are modelled and the quality of the physical and chemical parameters (e.g. kinetic expressions, physical properties) acquired for use in the models. When selecting a basis for a model, there are many questions that need to be asked and answered by the developer of the chemical reaction engineering model of the catalytic combustor. Many challenges arise from having to make decisions on compromises that need to be made, and in recognising the consequences of such action. Examples of such challenges are outlined and, for some, clues are offered as to where the answers may lie. The examples include challenges in: the selection of appropriate kinetic expressions, recognition of the role that intraphase diffusion may play, the choice of pressure for catalytic kinetic and pilot scale studies, the selection of heat and mass transfer correlations, and the modelling of transients.