Modification of sulfated zirconia by tungsten oxide: Acidity enhancement and structural characterization Original Research Article

Tungsten trioxide modified sulfated zirconia is a more active catalyst for hexane conversion at 140°C than unmodified sulfated zirconia. 700°C is the optimum calcination temperature for the activity enhancement. Characterization by means of differential thermal analysis (DTA), X-ray diffraction (XRD), laser Raman spectroscopy (LRS) and other techniques shows that both WO3 and SO2−4 ions prevent the agglomeration of ZrO2 particles and therefore stabilize the ZrO2 particles which form tetragonal zirconia upon crystallization and enhance the surface area of the catalysts. The simultaneous presence of SO2−4 and WO3 exerts a stronger effect than the presence of only one of these modifiers. Tungsten oxide disperses over the zirconia surface up to a coverage of 0.15 g WO3/g ZrO2. The dispersed WO3 stabilizes the SO2−4 ions that are coadsorbed on ZrO2 and the increase of surface sulfate concentration accounts for the activity enhancement. The optimum WO3 loading is equal to its dispersion threshold on zirconia.