Density functional theory (B3LYP) is used to study elementary reaction steps of the selective oxidation of propane to propene and further on to acrolein and acrylic acid, as well as of reactions leading to combustion. Monomeric vanadyl and peroxovanadate sites on silica are considered together with their V-O-Si bridging sites. Vanadyl sites are reduced from V-V to V-III. On reoxidation with O-2, peroxovanadate is formed that can easily oxidize propene to propene oxide. Propene oxide as common intermediate couples formation of acrolein as main product with the formation of acetone as main by-product. Whereas acrolein is further oxidized to acrylic acid, acetone undergoes C-C bond rupture, decomposes to formaldehyde, and is finally oxidized to CO/CO2 by peroxovanadate species. Peroxovanadate (electrophilic oxygen) is found to be the main factor for the total oxidation (combustion) reactions. The results are compatible with experimental observations for varying reaction conditions. (C) 2014 Elsevier Inc. All rights reserved.