This work investigates the influence of porous catalyst structural parameters on a packed bed reactor's performance, through the application of a multiscale reactor model. Constitutive equations, at the catalytic pellet and packed bed reactor length scales, are derived using the Reynolds transport theorem. Diffusive fluxes in the microscale (catalytic pellet) and macroscale (reactor) domains are calculated using the dusty gas model (DGM) and Stefan Maxwell model (SMM) equations respectively, while Chapman Enskog theory is applied to estimate diffusion and viscosity coefficients. Simulations are carried out for a case study on hydrogen production through steam methane reforming, using a finite element numerical scheme. The employed multiscale model enables the computation of catalyst effectiveness factors throughout the reactor, thus quantifying the effect on reactor performance of various catalyst structural characteristics, such as volumetric fraction, tortuosity, thermal conductivity, and mean pore diameter.