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

Abstract

V[sub 2]O[sub 5] gels have several potential uses in electronics and catalysis, but the rate and mechanism of the synthesis remain poorly understood. [sup 51]V NMR spectra show the consumption of the dioxovanadium cation (V[sup V]O[sup +][sub 2]) to form vanadate polymers in solution. The only other vanadium-(V) species in solution, decavanadic acid, acts primarily as a source of dioxovanadium cations for the polymerization. The oxovanadium cation (V[sup IV]O[sup 2+]) may act as an initiator for the polymerization reaction with the dioxovanadium cation. The pH remains constant throughout this process, suggesting that hydrolysis of the polymer furnishes hydronium ions. [sup 51]V MAS NMR of the resulting sol indicates that the vanadium environment in the polymer is similar to that of the dioxovanadium cation. These results confirm some aspects of models previously proposed. 48 refs., 6 figs., 1 tab.