Figure shows the normalized velocity magnitudes, temperatures, n-butane and CO 2 mass fractions at a plane containing the packed bed center axis. The flow direction is from left to right with a particle Reynolds number of 200, i.e., in the laminar flow regime. The velocity is non-uniformly distributed over the tube length-section, indicating a strong deviation from plug-flow behaviour. The concentration of C 4 H 10 is reduced in axial direction by the reaction, whereas CO 2 is formed from C 4 H 10 and MA. Similar to the observations made for the flow around a single VPO particle described in section 5.2 and in line with the results of for a fixed bed containing spherical catalysts, the mass fraction gradients inside the particles are steep due to the limitation by pore diffusion. However, a gradient of the n-butane and CO 2 mass fraction towards the tube wall cannot be found different to the study of because in the presented work a shorter fixed bed with smaller tube-to-particle diameter-ratio ( Dt /dp,outer = 3.75) is investigated. Due to the exothermic reaction, the temperature increases along the packed bed length and decreases towards the cooling tube wall. As already reported by , local temperature differences exceeding 40 K are observable within a single particle close to the tube wall. Moreover, the local packed bed structure and flow regime can lead to a reduced heat transport in some regions of the packed bed, resulting in overheating of individual particles. The C 4 H 10 consumption significantly grows in these regions.