This work presents a detailed investigation of the preparation routine for the multi-metal oxide Mo1V0.30Te0.23Nb0.125Ox used as catalyst for the selective oxidation of propane to acrylic acid. In situ Raman spectroscopy on the initial aqueous polyoxometalate solution prepared from ammonium heptamolybdate, ammonium metavanadate and hexaoxotelluric acid reveals the coexistence of Anderson-type anions [TeM6O24](n-), M = Mo, V; n >= 6 and protonated decavanadate species [HxV10O28]((6-x)-). Raman analysis showed that the monomeric motif of the Anderson-type tellurate is preserved after addition of the Nb precursor and the subsequent spray-drying process. Calcination of the X-ray amorphous spray-dried material in air at 548 K seems to be the essential step, leading to a re-arrangement of the tellurate building blocks, generating nanocrystalline precursors of the phases finally established during treatment in helium at 873 K. (c) 2006 Elsevier B.V. All rights reserved.