Thermal activation of a nanocrystalline Mo(5)0O(14)-type Mo0.64V0.25W0.09Ox, catalyst leads to enhanced catalytic performance in the partial oxidation of methanol, propylene and acrolein. This thermal activation process was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman microspectroscopy. Thermal activation of the nanocrystalline Mo0.64V0.25W0.09Ox precursor oxide in inert atmospheres induces partial crystallization of a Mo5O14-type oxide only in a narrow temperature range ending at 818 K. The Raman spectrum of the crystalline Mo5O14 oxide was identified by statistical analysis and by comparison with XRD and TEM results. The observed Raman bands in the M=O stretching mode regime were attributed to the different Mo=O bond distances in Mo5O15. A fraction of the precursor oxide remains nanocrystalline after activation as shown by Raman. HRTEM identified amorphous surface layers on top crystalline cores. Above 818 K, the Mo5O14-type structure disproportionates into the stable phases MoO2 and MoO3. This disproportionation occurs via an intermediate state which is formed by bundles of molybdenum oxide chains exhibiting structural order in only one dimension as shown by HRTEM. These results from the combined structural analysis suggest that the improvement of the catalytic performance of the MoVW oxide catalyst in the partial oxidation of methanol is related to the formation of the Mo5O14 type mixed oxide.