The influence of different reaction conditions on the catalytic activity of vanadium-aluminium oxynitride "VAlON" in propane ammoxidation is investigated. This new catalytic material exhibits amorphous character, high specific surface area, basic-redox properties and remarkable acrylonitrile production per hour and amount of catalyst. Optimal performance is achieved when the reaction temperature is 500 degreesC and the molar ratio of propane, oxygen, and ammonia in the gas feed is 1.25:3: 1. Under these optimal reaction conditions, the catalyst showed a propane conversion level of 60%, an acrylonitrile selectivity of 56%, and an acrylonitrile productivity of 8121/kg h. The formation of a propylene intermediate compound as well as hydrogen cyanide was detected only for those reaction conditions where the NH3:C3H8 ratio was lower than 1. This suggests differences in the reaction mechanism with respect to conventional V-Me-oxide propane ammoxidation catalysts. In propane ammoxidation over VAlON catalysts, ammonia seems to play a double role: (i) as a reagent necessary for the thermal nitridation and generation of nitrogen species, (ii) participating in N-insertion step for the acrylonitrile formation from propane. The catalytic performances depend on the generation of nitrogen species as a function of the reaction conditions, which determine the level of propane conversion and selectivity to the reaction products. (C) 2003 Elsevier B.V. All rights reserved.