1H and 93Nb Solid-State NMR and IR Study of Acidity of Nanodisperse Nb2O5·nH2O

Abstract

Niobium oxide hydrate is a promising material for various heterogeneous catalytic processes due to its strong acidity and stability in aqueous medium. While different synthesis conditions may lead to various particle morphologies, the effect of morphology of Nb₂O₅·nH₂O particles on their acidic properties is not fully understood yet. In this paper, we have successfully synthesized and characterized nanodisperse niobium oxide hydrate. Using infrared (IR) spectroscopy, we demonstrated that the sample exhibits strong Brønsted acidity close in strength to sulfuric acid. Furthermore, solid-state nuclear magnetic resonance (NMR) spectroscopy in combination with ab initio calculations gave additional insight into the nature of strong acidic sites and proved to be a useful tool for identification of acidic sites in Nb₂O₅·nH₂O systems. Thus, we have shown that it is not necessary to follow difficult high-temperature solid-state processes or processes with ammonia, which often contaminates the material, to synthesize highly acidic nanodisperse Nb₂O₅·nH₂O.