51V NMR and EPR Study of Reaction Kinetics and Mechanisms in V2O5 Gelation by Ion Exchange of Sodium Metavanadate Solutions

V2O5 gels produced by sol-gel methods have several potential uses in electronics and catalysis, but the rate and mechanism of the synthesis remain poorly understood. Recent results disagree with models previously proposed. 51V NMR spectra show that the initial reactions involve the consumption of the dioxovanadium cation V (V) 02 (+). The only other vanadium (V) species in solution, decavanadic acid, acts only as a source of dioxovanadium cations for the polymerization through a dimerization reaction with the dioxovanadium cation. Hydrolysis of the polymer allows further decavanadic acid decomposition to the dioxovanadium cation by furnishing protons. 51V MAS NMR of the resulting colloidal suspensions indicates that the vanadium environment in the polymer is similar to that of the dioxovanadium cation.