We describe the surface reaction steps through a mean-field microkinetic model, while mass transport is simply included as one-dimensional Fickian diffusion (in the direction perpendicular to the surface). The two model components are then coupled via the flux of species X ( * ) and we solve the problem iteratively for steady-state solutions. In practice, the steady-state assumption reduces the transport modeling to a simple analytical expression of Fick's first law. A converged solution is one where the diffusion flux J diff of species X ( * ) equals the corresponding flux output from the microkinetic model J mkm (=turnover frequency × active site density) after normalizing the rate to account for the density of catalytically active sites: