To investigate how the properties of model mixed metal oxide catalysts can be influenced by the choice of evaporating species during physical vapor deposition, we have compared MoOx on Al2O3/NiAl(110) prepared via an oxidic and a metallic precursor. In the former case, MoOx was prepared via direct deposition of MoOx, while in the latter case, metallic Mo was deposited in an O2 background. The structure of the resulting catalysts was compared to that of metallic Mo deposited on Al2O3/NiAl(110) in the absence of O2. For directly deposited MoOx, we observe predominantly point defect nucleation and high particle densities. In contrast, when MoOx is prepared by deposition of metallic Mo in 5 × 10-7 mbar O2, we find lower particle densities and preferential nucleation at step edges and domain boundaries, thus reflecting the particle dispersion of metallic Mo. This suggests that the Mo atoms are oxidized typically only after having attached to a stable Mo or MoOx nucleus. We interpret our findings in terms of the interaction between the deposited material and the support, which is stronger for MoOx than for Mo. These results demonstrate that the choice of evaporating material crucially influences the catalyst structure and is therefore a useful parameter in tuning the properties of model mixed oxide catalysts.