An Au/alpha-Fe2O3-gamma-Al2O3 catalyst (0.96% (w/w) of Au and 4.8% of Fe2O3) was tested for activity and selectivity in an isothermal flat-bed reactor. Very good activity and selectivity values were measured for different operation temperatures and compositions. The reaction rate parameters of carbon monoxide and hydrogen oxidation were fitted. Activation energies of 11 and 36.9 kJ/ mol for CO and H-2 oxidation, respectively, were obtained. A folded-plate reactor concept with three side ports and one front port for air injection has been proposed to carry out the preferential oxidation (PrOx) reaction. By means of a mathematical model of the reactor, design and optimization studies were conducted. Simulation results indicate a remarkable uniformity of the axial temperature profile in the reactor. For the calculated heat-transfer parameters, a reactor configuration with only one air-side-feed injection port, is the preferred design, combining good operation performance, simplicity of design, and sufficient oxygen conversion. On the basis of the simulation results, a folded-plate reactor for CO-PrOx has been built up and is presently under testing for an experimental proof of concept.