Vanadia Gel Synthesis via Peroxovanadate Precursors. 1. In Situ Laser Raman and ⁵¹V NMR Characterization of the Gelation Process

Vanadium oxide gels derived from aqueous solutions of V₂O₅ and H₂O₂ have been investigated using in situ ⁵¹V NMR and laser Raman spectroscopic techniques. On the basis of this characterization, a pathway for peroxovanadate decomposition has been proposed, including the presence of two peroxovanadate dimers. New Raman bands and assignments for these species are reported. Gelation was observed to begin both during and after the peroxovanadate decomposition, depending on the initial molar ratios of H₂O₂/V and the total concentration of vanadium. Experimental ⁵¹V NMR evidence suggested that the VO₂⁺ species was directly involved in the formation of the gel.