In the presented work, a physically accurate and numerically stable conjugated heat and mass transfer model is proposed for coupling a catalytic reaction inside a porous catalyst particle with the surrounding fluid flow. Since the CHT and CMT model can be applied to computational meshes with orthogonal and non-orthogonal cells, the approach enables the simulation of even very complex geometries, such as packed beds of non-spherical pellets, that can only be solved computationally efficiently with unstructured meshes. Regardless whether the underlying mesh is structured or unstructured, the imple-mented model is able to reflect the analytical solution of heat and species mass diffusion through two connected slabs. Moreover, the particle Nußelt and Sherwood number as well as the thickness of the temperature and concentration boundary layers at the forward stagnation point are determined from the CFD simulation of the flow around a single spherical VPO particle coupled with reaction inside the porous catalyst. The determined values are in excellent agreement with results obtained from relevant literature correlations. Beside the validation of the CHT and CMT model with analytical solutions and correlations, the impact of the secondary gradient on integral and distributed quantities are investigated for the flow through a short fixed bed containing ring-shaped VPO catalysts, as an illustrative example for a complex geometry resolved by an unstructured mesh. It can be found that the secondary gradient does not have a significant influence on integral quantities but might locally affect the temperature and mass fractions at the fluid-solid interface. Furthermore, considering the secondary gradient does not change the numerical stability and computational effort of the simulation. Therefore, it is advised to apply the secondary gradient, especially for unstructured meshes of complex geometries. The presented approach for coupling the surrounding flow with reaction inside the porous catalyst is exemplary applied on a short packed bed for maleic anhydride synthesis to obtain better insights on catalyst performance. The analysis of temperatures and mass fractions at a plane containing the packed bed center axis indicates that individual particles overheat leading to an increase in CO 2 mass fraction due to the more favored total oxidation of n-butane and MA. Moreover, the catalyst effectiveness factor of the reaction from C 4 H 10 to MA, being calculated for every single particle, is reduced in axial direction and grows towards the tube wall. However, the effectiveness factor can differ for particles with similar axial and radial position due to the influence of the local packed bed structure and flow regime on energy and material transport. The presented method is the base for automated computer-aided shape optimization of catalyst particles. Besides the PRCFD simulation of catalytic fixed bed, the conjugated heat and mass transfer model can be also applied in modeling other applications in which fluid flow must be coupled with transport inside a porous solid phase, such as monolithic catalysts ), membrane filtration ), redox-flow batteries ), or fuel cells ). In order to apply the CHT model for high-temperature processes, the influence of thermal radiation on the heat transfer should be considered. For a more detailed description of the species mass diffusion within multicomponent mixtures, future work should replace the Fickian approach with Maxwell-Stefan type models, as described for the fluid phase by and for diffusion in porous catalyst particles by . Finally, the comparison of the simulated results with spatially resolved measurements of temperature and gas composition in chemical reactors is crucial for further validation of the method.