Structural study of surface tungstate in WO 3 Al 2 O 3 : Effects of Hydration and 18 O Exchange

The Raman spectra of a series of WO 3 AI 2 O 3 catalysts containing 1‐30 wt‐% of WO 3 were investigated with respect to the effect of O 2 calcination and H 2 OD 2 O exposure. These studies showed that the frequencies of bands due to surface tungstate species can be shifted reversibly by as much as 6% of their values during alternate O 2 calcination and H 2 O exposure cycles. The exchange of 18 O for l6 O in the surface tungstate was also investigated with Raman spectroscopy and ion‐scattering spectrometry. The results were used to assign Raman bands to fundamental vibrations of the surface tungstate and to propose a mechanism of interaction between H 2 O and the surface tungstate that hitherto has not been addressed for WO 3 AI 2 O 3 .