In this talk I will address the thermal and chemical stability of Rh adatoms adsorbed on Fe3O4(001), and discuss the reactivity of these species with a view to single-atom catalysis. Using a combination of atomic-scale imaging, spectroscopies and DFT-based calculations, I will show that Rh adatoms adsorb in a bulk-continuation cation site at room temperature on Fe3O4(001), where they remain stable upon CO adsorption and can catalyze CO oxidation via a reaction with the support at 500 K. However, at this temperature Rh begins to incorporate within the support lattice, and the higher coordination environment significantly modifies the reactivity. In addition, I will show that Rh1 species efficiently dissociate water, leading to H spillover of H onto the support, and that Rh1 diffusion is induced upon adsorption of O2 and NO.