Different Pt-based catalyst layers have been prepared and tested in a stacked foil microreactor for CO oxidation and preferential oxidation of CO in presence of hydrogen. The reactions were performed on Pt without support by impregnation of a pre-oxidized microstructured metal plate, Pt/Al2O3 and Pt/CeO2 based on sol methods as well as Pt/nano-Al2O3, a combined method of sol-gel and nanoparticle slurry coating. The ceria based sol-gel catalyst was much more active for CO oxidation than alumina based sol-gel catalysts at low temperature. However, total oxidation was only obtained at higher temperature on the alumina based catalysts. The combined method seems to have advantages in terms of less internal mass transfer limitation when trying to increase the catalyst coating thickness based on sol-gel approaches due to no reduction of CO selectivity up to 300 degrees C reaction temperature. Experiments on CO oxidation with the Pt/CeO2 catalyst have been conducted in an oxygen supply microreactor to evaluate the catalyst performance under sequential oxygen supply to reaction zone (CO excess).