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 WO bond nature of complex formed by the interaction between WO3 and ZrO2.

Spectroscopic Studies on ZrO2Modified with MoO3and Activity for Acid Catalysis

“…24,25 The catalyst in a glass tube was pretreated at 400 o C for 1 hr and filled with dry nitorgen. For the determination of acid strength of the catalyst the color changes of indicators were observed by spot test.…”

“…The superacidic property is attributed to the double bond nature of the Mo=O in the complex formed by the interaction of ZrO 2 with molybdate, in analogy with the case of ZrO 2 modified with tungstate, chromate, and sulfate ion. 21,22,25,27 The acidity of catalysts calcined at 500 o C, as determined by the amount of NH 3 irreversibly adsorbed at 230 o C, 21,24 is listed in Table 1. As listed in Table 1, the acidity increases upon the addition of 1 wt% molybdenum oxide to ZrO 2 , giving a maximum at 3 wt% of MoO 3 , and then the acidity decreases with increasing molybdenum oxide content.…”

Surface modification of a fuel cell material by ion implantation

“…But nevertheless it is interesting to see how vanadia behaves on the zirconia sample. Zirconia supported tungsten oxide is also frequently used as a catalyst for hydracarbon conversion [14], but less is known about the chemica} structure tungstenoxide forms at the surface.…”

Effect of Al2O3Addition and WO3Modification on Catalytic Activity of NiO/Al2O3-TiO2/WO3for Ethylene Dimerization

“…The infrared single band at 1003-1012 cm −1 is due to the symmetrical W=O stretching mode of the tungsten oxide complex coordinated to the Al 2 O 3 -TiO 2 surface. 40 As shown in Figure 1, as evacuation temperature increases, the W=O stretching mode shifts upward from 1003 to 1012 cm −1 , the band becomes sharper, and the intensity increases. The similar results have been obtained with the other samples.…”