WO₃ microcrystallites: One of the crucial factors controlling the isomerization activity of Pt/WO₃-ZrO₂

A series of hydrous zirconia supports were prepared by hydrothermal method and Pt/WO₃-ZrO₂ catalysts were prepared by impregnation method. The catalytic activity of Pt/WO₃-ZrO₂ in n-hexane isomerization was evaluated in a fixed-bed reactor. In order to investigate the crystalline structure, acidity, and textural properties, the catalysts were characterized by XRD and Raman spectroscopy, NH₃-TPD, FTIR, and N₂ adsorption. The results indicated that the crystalline structure of hydrous zirconia support and the state of tungsten oxide species over the catalyst varied obviously with the hydrothermal temperature, while no distinct change in the acidity of the catalyst occurred. The isomerization activity of Pt/WO₃-ZrO₂ could not well be correlated with the crystalline structure of hydrous zirconia support and the acidity. It was proposed that the presence of considerable microcrystalline WO₃ in catalyst was indispensable for achieving high isomerization activity.