WOx/ZrO2 catalysts prepared by anionic exchange : In situ raman investigation from the precursor solutions to the calcined catalysts

W/ZrO2 catalysts were prepared using anionic exchange of peroxotungstate species with hydroxyl groups of zirconium hydroxide at low pH. The solids were dried and calcined under air at 700 °C. Each step of this novel method of preparation was investigated by Raman spectroscopy. A reference sample was also prepared by incipient wetness impregnation of ZrO2·n(H2O) with an ammonium tungstate solution and characterized throughout its preparation process. Complementary data were collected from X-ray diffraction, chemical analysis, surface area measurements, and thermal analysis. The Raman spectra of the H2WO4−H2O2 precursor solutions evidenced the presence of (W2O3(O2)4(H2O)2)2- dimers. These low-nuclearity species were exchanged with zirconium hydroxide at low pH. The Raman spectra of the dried solids did not reveal peroxotungstate species but were typical of tetrahedral (WO4)2- species. A slight agglomeration of W species was observed with an increase in the W content. However, for an equivalent W loading, a ...