The effect of Te addition over Mo-V-O catalysts supported on alumina is discussed for the ammoxidation of propane to acrylonitrile. Catalysts were characterized before and after catalytic reaction by XPS, XRD, UV-vis and in situ Raman spectroscopies. The absence of Te in catalysts formulation and the presence of a high amount of vanadium induce the presence of V5+ species and the formation Of V2O5 oxide; associated with a decrease in acrylonitrile selectivity. The presence of heteropolyacids-type structures, such as Al-Mo-V-O or Al-Mo-O, promotes a decreasing of the selectivity to acrylonitrile. The characterization results reveal that the surface of Mo-V-Te-O catalysts is further different from the binary counterparts, due to the presence of stabilized and reduced structures dispersed on the support. The Te incorporation to supported Mo-V catalysts conduces to a better performance during propane ammoxidation. (c) 2008 Elsevier B.V. All rights reserved.