In this study, a geometrical model is combined with the network of pores analogue to yield a structural-phenomenological description for diffusion and adsorption in pellets compacted from bidisperse and non-porous grains. Simulation results from both steady-state (single-pellet) and transient (chromatographic column) systems demonstrate how grain size and relative proportion affect mass transport in the pellet. For the steady-state case, it is shown that the effective medium approximation (EMA) can be readily applied to predict effective diffusivities which are in excellent agreement with network model simulations. Some specific guidelines are then outlined which suggest how to develop improved catalysts in terms of pellet structure and performance.