Solid-state NMR strategies for characterizing high surface area niobates

Layered niobates have been found to be strong solid-acid catalysts and have high surface areas while maintaining their crystalline structure. These materials can serve as model compounds for the metal environments at the surface of amorphous solid-acid niobates. The niobium environment in KCa2Nb3O10 and its acid exchanged version were studied using 93Nb solid-state NMR. As 93Nb is a quadrupolar nucleus, both the electric field gradient (EFG) and chemical shift anisotropy (CSA) for a given site can yield information about the symmetry of the local structure and relate its influence on the acid site. The change in the local environment of surface niobium sites upon acid exchange is observed via NMR and attributed to changes in the terminal niobium–oxygen bonds.

Graphical abstractThe niobium environment in KCa2Nb3O10 and its acid exchanged version were studied using 93Nb solid-state NMR. The change in the local environment of surface niobium sites upon acid exchange is observed via NMR derived electric field gradient information and attributed to changes in the terminal niobium–oxygen bonds. Figure optionsDownload full-size imageDownload as PowerPoint slide