STRUCTURE CHARACTERIZATION OF WO3 ZRO2 CATALYSTS BY RAMAN-SPECTROSCOPY/

WO3/ZrO2 catalysts prepared by different methods are distinct in their catalytic behaviour. In this work, WO3/ZrO2 catalysts prepared by imp regnating Zr(OH)(4) and crystallized ZrO2 and then calcining at select ed temperatures were characterized by means of qualitative and quantit ative Raman spectroscopy. The results showed that ZrO2 in WO3/ZrO2 obt ained from crystallized ZrO2 (referred to as WZ) is monoclinic, wherea s ZrO2 in WO3/ZrO2 obtained from Zr(OH)(4) (referred to as WZH) is in a metastable tetragonal phase as long as the WO3 content is high enoug h. In both WZ and WZH, WO3 is dispersed on ZrO2 as a monolayer, and th e dispersion capacity per 100 m(2) of ZrO2 is in good agreement with t hat estimated from the close-packed monolayer model. However, since th e specific surface areas of WZH samples are larger than those of WZ sa mples, the dispersion capacity per gram of ZrO2 of WZH is larger than that of WZ. A chemical reaction may occur between WO3 and the surface of Zr(OH)(4) (or tetragonal ZrO2) at high temperature, and then some s uperacid sites are created on the surface of the WZH sample.