A goal of single-atom catalysis (SAC) is to find a support that stabilizes single metal adatoms in geometries that make them catalytically active.1 For this to be possible, the adatoms must be able to change their coordination state by forming and breaking bonds. Iron oxides are popular supports used in SAC because of their low cost, chemical stability, and non-toxicity.2 Given its ubiquity in catalysis, platinum is an attractive metal to be used in SAC. I will discuss the similarities and differences between Pt adatoms on hematite, α-Fe2O3(012)-(1x1), and magnetite, Fe3O4(001). Scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) were used to characterize these surfaces and how Pt atoms bind to them. In both cases, Pt is 2-fold coordinated to lattice oxygen atoms, but the reactivity differs. Interestingly, we find that the second coordination sphere plays an important role defining the reactivity to molecular oxygen.