Theoretical and experimental insights into applicability of solid-state 93Nb NMR in catalysis

Abstract

Ab initio DFT calculations of ⁹³Nb NMR parameters using the NMR-CASTEP code were performed for a series of over fifty individual niobates, and a good agreement has been found with experimental NMR parameters. New experimental and calculated ⁹³Nb NMR data were obtained for several compounds, AlNbO₄, VNb₉O₂₅, K₈Nb₆O₁₉ and Cs₃NbO₈, which are of particular interest for catalysis. Several interesting trends have been identified between ⁹³Nb NMR parameters and the specifics of niobium site environments in niobates. These trends may serve as useful guidelines in interpreting ⁹³Nb NMR spectra of complex niobium oxide systems, including amorphous samples and niobium-based multicomponent heterogeneous catalysts. Potential applications of ⁹³Nb NMR to study solid polyoxoniobates are discussed.