One of the challenges in the numerical modelling of chemically reacting multi-phase flows, e.g. including solid particles and a gas phase, is the complexity of transport processes occurring on the particle surface. This complexity is the result of coupling between the gas flow in the void spaces, which is three-dimensional a priori, and heterogeneous reactions on the particle surface. This complexity and three-dimensionality of the flow requires the use of computationally expensive numerical grids to resolve the particle surface and the void space between particles. Thus, as of yet it is not feasible to simulate the heat and mass transfer in different fixed-bed reactors (with as many as hundreds of thousands of particles) resolving all particles. At the same time, the accuracy of existing 1-D models depends on the empirical closure relations describing the heat and mass transfer between particles and the fluid flow. In this view, one way to solve this problem applied to a structured packed bed is to approximate the particulate beds using 2-D geometry, which will still allow us to calculate the heat and mass transfer directly without using any empirical relations. Thus, the main subject of this work is the development and validation of an axisymmetric representative element approximating the heat and species transport, and gas flow in a 3-D structured fixed bed with different porosities. Comparative analysis of 3-D and 2-D simulations shows acceptable agreement. Finally, we explore the influence of the void fraction on the gas-phase temperature behaviour between particles.