1H and 93Nb Solid-State NMR and IR Study of Acidity of Nanodisperse Nb2O5·nH2O
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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.
This work was conducted within the framework of the budget project for Boreskov Institute of Catalysis. The authors also acknowledge the financial support from Russian Foundation for Basic Research (RFBR, project № 17-03-00531). The Siberian Branch of the Russian Academy of Sciences (SB RAS) Siberian Supercomputer Center is gratefully acknowledged for providing supercomputer facilities. We also would like to thank Dr. D. F. Khabibulin for the help with 93Nb NMR, Dr. A. N. Salanov for the SEM micrographs and T. Ya. Efimenko for the nitrogen adsorption experiments.
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