“…The most important V(V) species on the catalyst supports are monomeric [VO 4 ] À , vanadate dimeric or oligomeric chain-or sheet-like structures, polyvanadate anions, and 3-D nano-and microstructures of V 2 O 5 at higher V-loadings. Crystalline V 2 O 5 is most reliably detected by X-ray diffraction [3,6,7], while non-crystalline V(V) species are mostly detected by UV-vis spectroscopy (DRS), Raman or IR spectroscopy [2][3][4][5][7][8][9], and temperature programmed reduction (TPR) [5,7,9,10]. Electron spectra are sensitive to the degree of V-oxide oligomerization or polymerization to oxides: the more extensive condensation of VO x polyhedra producing V-O-V bonds, the more the absorption bands are shifted from UV region to Vis region [11,12].…”