The effect of total coverage on alumina is evaluated for Mo(5)V(4)Nb(1)/Al(2)O(3) catalysts by operando Raman-GC spectroscopy during reaction, demonstrating structural changes during reaction that do not occur during catalyst calcination. XRD detects show no appreciable change but Operando Raman-GC studies are sensitive to changes occurring in the nanometer scale, which modulate the performance during propane oxidation, delivering the structure-activity relationship for deactivation. Raman spectra confirm the formation of nanocrystalline MoO(3)-type structures during reaction up to 375 degrees C, accompanied by coke deposits, able to block the active sites, being detrimental for the acrylic acid formation. Three new catalysts were preparing by the addition of tellurium as dopant, in this case, the presence of MoO(3) is not detected under reaction conditions, since the formation of a distorted rutile structure under reaction conditions is observed, and in this case acrylic acid is obtained as the main reaction product with a yield of ca. 25% at 400 degrees C. (C) 2011 Elsevier B.V. All rights reserved.