Structure Characterization of W03/Zr02 Catalysts by Raman Spectroscopy

WO,/ZrO, catalysts prepared by different methods are distinct in their catalytic behaviour. In this work, WO,/ZrO, catalysts prepared by impregnating Zr(OH), and crystallized ZrO, and then calcining at selected temperatures were characterized by means of qualitative and quantitative Raman spectroscopy. The results showed that ZrO, in WO,/ZrO, obtained from crystallized ZrO, (referred to as WZ) is monoclinic, whereas ZrO, in WO,/ZrO, obtained from Zr(OH), (referred to as WZH) is in a metastable tetragonal phase as long as the WO, content is high enough. In both WZ and WZH, WO, is dispersed on ZrO, as a monolayer, and the dispersion capacity per 100 m2 of ZrO, is in good agreement with that estimated from the close-packed monolayer model. However, since the specific surface areas of WZH samples are larger than those of WZ samples, the dispersion capacity per gram of ZrO, of WZH is larger than that of WZ. A chemical reaction may occur between WO, and the surface of Zr(OH), (or tetragonal ZrO,) at high temperature, and then some superacid sites are created on the surface of the WZH sample.