The oxidative dehydrogenation of propane to propylene with molecular O2 (PPD) has been investigated on commercial bare SiO2 and medium loaded V2O5 and MoO3 catalysts at 450–525°C. The direct relationship between the density of reduced sites (ρ, 1016 sr g cat− 1 ), evaluated in steady-state conditions by O2 chemisorption, and the POD reaction rate proves the occurrence of a “concerted” reaction mechanism involving the activation of gas-phase O2 on the reduced sites of the catalyst surface. A straight-line correlation between the activity of such silica based catalysts in POD and methane partial oxidation to formaldehyde (MPO) at 525°C has been disclosed.