Raman and UV−vis diffuse reflectance spectroscopy were used to characterize the structure of vanadia dispersed on high surface area zirconium oxide. Two-dimensional vanadia species with tetrahedral coordination appear on the surface of the ZrO2 and expand in size with increasing V loading. Crystalline V2O5 appears when the vanadia loading exceeds an apparent surface density of 7.0 V atoms/nm2, and ZrV2O7 is formed as a consequence of zirconia migration into the V2O5 crystallites. A model for the structure of two-dimensional vanadia overlayer is proposed based on the experimental data and information taken from the literature. Vanadia is found to absorb the light scattered by the support, and this gives rise to a reduction in the intensity of the Raman bands for zirconia as the surface loading of vanadia increases. Partial reduction of the dispersed vanadia increases the absorbance of the vanadia and alters the profile of absorbance versus frequency in such a manner as to increase the intensity of the Raman bands for zirconia relative to those for vanadia. Examination of Raman spectra taken after repeated reduction−oxidation cycles suggests that reduction occurs via removal of oxygen from the vanadia monolayer without agglomeration or reorganization of the surface species.
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