For instance, according to interrelated pillars 1, 2, and 4, the more activated oxygen the catalyst can offer, the highest its activity. Such redox capacity is captured by the reversible oxygen uptake measured by TPRO. The reversible oxygen uptake per mass and per surface area measured on the fresh catalyst samples (denoted a b,$" * F and a M,$" * F , respectively) are shown in black and red in Fig. , respectively, for the 12 investigated catalysts. The reversible oxygen uptake per mass correlates with the high activity of MoVOx, SmMnO3, and MnWO4 (Fig. , in grey, red and yellow, respectively). However, this parameter does not capture that MoVTeNbOx or V2O5 have moderate activity, since the oxygen uptakes for these materials are comparable to the values corresponding to the low-activity catalysts β-VOPO4, αII-VWOPO4, αII-VOPO4, VOPO4*2H2O, and VWPOx. The reversible oxygen uptake per surface area is not able to fully account for the observed activity trend either.