Characterization of Zirconia-Supported Tungsten Oxide Catalyst

Abstract

Tungsten oxide−zirconia catalysts were prepared by drying powdered Zr(OH)4 with ammonium metatungstate aqueous solution, followed by calcining in air at high temperature. Characterization of prepared catalysts was performed by using Fourier transform infrared (FTIR), Raman, and X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) and by measuring surface area. The addition of tungsten oxide up to 20 wt % to zirconia shifted the phase transition of ZrO2 from amorphous to tetragonal to higher temperature due to the interaction between tungsten oxide and zirconia, and the specific surface area and acidity of catalysts increased in proportion to the tungsten oxide content. Since the ZrO2 stabilizes the tungsten oxide species, for the samples equal to or less than 5 wt %, tungsten oxide was well dispersed on the surface of zirconia, but for the samples containing 13 wt % or above 13 wt %, the triclinic phase of WO3 was observed at any calcination temperature. Upon the addition of only small amount of tungsten oxide (1 wt % WO3) to ZrO2, both the acidity and the acid strength of catalyst increased remarkably, showing the presence of Brönsted and Lewis acid sites on the surface of WO3/ZrO2. The high acid strength and high acidity were responsible for the WO bond nature of complex formed by the interaction between WO3 and ZrO2.