A new experimental reactor concept is presented for spatially resolved DRIFTS surface analysis in a microstructured catalytic reactor. Both gas and surface adspecies concentration profiles can be established along the channels coated with a catalyst. The oxidation of carbon monoxide was studied from 25 to 300 degrees C over a Pt/Al2O3 and a Pt/CeO2-Al2O3 catalyst. For these operating conditions, nearly isothermal conditions were observed for the microstructured reactor, with a continuous linear increase in the reaction product along the micro-channels. In contrast, an important thermal effect with the characteristic light-off was obtained in a fixed bed DRIFTS reactor, underlining the unique behavior of the microstructured system. Modeling of the CO conversion and surface adspecies concentration as a function of the temperature along the channels was performed based on a mono-functional reaction mechanism for the case of the alumina-supported catalyst or a bifunctional one taking into account sites on the platinum particles and on the ceria support for the case of the ceria-supported system. The model permits an adequate description of the data along the reactor axis over both catalysts. It underlines the important role of ceria in the creation of an additional site for oxygen chemisorption and the transfer of oxygen to the active site on the Pt/support interface. It also provides new insights in the change of the rate-controlling step from being the oxygen chemisorption on platinum to the CO2 production at the platinum/ceria interface. (C) 2010 Elsevier Inc. All rights reserved.