Titania nanotubes synthesized by alkali hydrothermal method were used to support 5-20 wt.% of WOx by wet impregnation method. Samples were characterized by in situ thermo-Raman spectroscopy, electronic microscopy and X-ray diffraction. Initially and below 400 degrees C, WOx species have octahedral coordination as isolated species. After annealing at 500 degrees C, the nanotubular support collapsed and transformed into anatase. This event released Na+ ions that reacted with surface WOx species converting into sub-nanometric sodium tungstate (Na2WO4) particles, homogeneously dispersed on the support. At higher temperature, that is at 700 degrees C and 800 degrees C, Na2WO4 nanoparticles were detected on samples with W content <= 10 wt.%, whereas a mixture of Na2WO4 and Na2W2 O-7 was obtained on samples with W content above 15 wt.%. A very thin layer of sodium tungstate covered the titania (anatase or rutile, depending on W loading) support after annealing at 800 degrees C yielding core-shell particles, with titania phase in the core and Na2WO4 and/or Na2W2O7 on the shell. (C) 2009 Elsevier B.V. All rights reserved.