Platinum/cerialalumina catalysts have been prepared in the microchannels of stainless steel platelets. These catalysts are very active for the water-gas shift reaction between 250-400 degrees C. The use of microreactors as kinetic devices has a clear advantage that the thin catalyst film allows the determination of the intrinsic kinetics even in the case of fast reactions. However, the channel design should be such that plug flow conditions are favored. The kinetics of the water-gas shift reaction, free from internal diffusion limitations, have been studied over thin catalyst layers over a large range of operation conditions. The reaction rate is almost zero-order in carbon monoxide and strongly inhibited by the partial pressure of hydrogen and to a lesser extent to that of carbon dioxide. An overall activation energy of 76.8 +/- 2 kJ/mol has been measured. The data are best described by a dual-site mechanism, where platinum provides an adsorption site for carbon monoxide and ceria an adsorption site for water. The rate-determining step involves the formation of a complex between a carboxyl species and a hydroxyl group that decomposes over a free platinum site into carbon dioxide and hydrogen. (c) 2006 American Institute of Chemical Engineers.