In our study of CO preferential oxidation (PrOx) on Pt/Al 2O 3 with a thin-film catalyzed microreactor, systematic differences of kinetic study results and characteristic curves of CO conversion were identified between the microreactor and conventional minimized packed-bed lab reactors (m-PBR's). Evidence suggested that the difference in heat transport limitations is the origin of these differences. In this paper, these differences were examined systematically. First, based on existing criteria for mass and heat transport limitations, we found negligible mass transport resistance for both types of reactors within typical PrOx operating conditions, but strong heat transport limitations for m-PBR's. Further, a non-isothermal reactor model was built to quantitatively study the effect of the heat transport limitations on PrOx reaction behavior. Model results showed that the temperature gradients in m-PBR's favor the r-WGS reaction, thus causing a much narrower range of permissible operating temperature compared to the microreactor. Accordingly, a more direct access to PrOx reaction kinetics is permitted by the microreactor because of its excellent heat transfer efficiency.