Multi-species diffusion/heterogeneous reaction coupled problem in porous media involving a boundary layer problem is studied. The spectral approach developed in our previous work allows to derive a macroscopic model in the high Damköhler number regime combining homogenization technique and spectral approach. Such a homogenized model cannot describe the perturbation at the external boundary where the chemical equilibrium is not necessarily satisfied. We construct herein a modified model involving additional variables, which are rapidly-decaying functions, to capture the complex physics in the boundary layer. Numerical simulations underline the accuracy of the proposed correction in both steady and transient states.