A stagnation-flow on a catalytic porous plate is modeled one-dimensionally coupled with multi-step surface reaction mechanisms and molecular transport (diffusion and conduction) in the flow field and the porous catalyst. Internal mass transport inside the porous catalyst is studied with three different models: instantaneous diffusion (infinitely fast mass transport), effectiveness factor, and one-dimensional reaction-diffusion equations. A new computer code, DETCHEMswr, is presented to execute the numerical model. The oxidation of CO over a porous Rh/Al2O3 surface is studied exemplarily. Experimental measurements are carried out to apply the developed model and the computer code. External and the internal mass transfer effects in front of and inside the porous catalyst are discussed. Internal mass transfer limitations become important in case of a thick catalyst layer for accurately predicting the experimental results. (C) 2013 Elsevier Ltd. All rights reserved.