. The observed distributions of metals differed substantially from those observed in the bulk through EDX measurements. For all analyzed samples, the ratio between the amount of Co and the amount of guest metal M (Mn, Ni, or Zn) deviated from the nominal value of 2. The surface of NiCo2O4 was enriched in Co, while those of MnCo2O4 and ZnCo2O4 were enriched in Mn and Zn, respectively. The spectrum of Co3O4 includes the two spin-orbit split peaks (2p1/2 and 2p3/2) associated with the 2p electron energy level of Co, and their satellites (Figure ). The presence and the abundance of different oxidation states of Co affects the shape of these peaks. Comparing the spectra of Co3O4 before and after catalytic tests with other spectra reported in the literature, it appears that both the divalent and the trivalent oxidation state of Co were present on the surface, and that no substantial changes occurred during the reaction. In line with our expectations, this suggests that the catalyst was not reduced to CoO or metallic Co, which could happen in case of an intense oxidation-via-dehydrogenation (but is unlikely due to the highly oxidative environment), or hydroxylated to Co(OH)2, due to reaction with water.