XPS characterization of Ni and Mo oxides before and after “in situ” treatments

The characterization of oxide surfaces is often made by means of the XPS technique: in this paper results obtained by treating nickel and molybdenum oxides at a temperature of 523 K, at 10-4 Pa (in vacuo) and at 105 Pa (in hydrogen), are reported. These treatments were performed in a reaction chamber and the samples were subsequently analyzed in the main chamber without exposing them to the atmosphere. The results indicate that it is possible to completely reduce nickel oxide to metal by treating it in hydrogen, while the heating in vacuo leaves a fairly large amount of oxide not reduced on the surface (77.8%, atomic percentage). On the other hand, on the two molybdenum oxides (MoO3 and MoO2) it is possible to notice the presence of a large amount of intermediate not reduced oxides, at 523 K, both in hydrogen and in vacuo.