In addition to the alkane oxidation reactions, all catalysts were investigated in CO oxidation in oxygen-rich and oxygen-poor feeds. Only three catalysts are active for CO oxidation below 420°C: SmMnO3, MnWO4, and αII-VWOPO4 (see light-off curves in Fig. ). The temperature at which 50% conversion is achieved increases in the following order: SmMnO3 < MnWO4 < αII-VWOPO4. Although the ranking of these three catalysts matches their ranking in terms of activity in all three alkane oxidations, there are other catalysts that are also very active in alkane oxidation but cannot oxidize CO. Therefore, CO oxidation cannot serve as a simple probe reaction for the alkane consumption rate.