Determination of local structures of layered niobate, niobate nanosheet and mesoporous niobium oxide by solid state NMR and PXRD

A complete understanding of the relationship between structure and acidity is necessary to tailor the heterogeneous catalytic properties of the materials. However, it is difficult for X-ray diffraction to extract the structural information for amorphous or nanoscopic materials because of the lack of long range order due to disorder in the amorphous systems or due to physical lack of space in nanoscopic materials. Solid state NMR can probe the local environment of the nucleus and be an ideal technique to study these materials. The aim of the research work in this dissertation is (1) to investigate how the local structure of the niobium atom is altered in layered niobates when alkaline cations or alkaline earth cations are changed and (2) to investigate the structures of mesoporous niobium oxide and the niobate nanosheet by solid state NMR (short range) and XRD (long range) techniques. In this dissertation, a series of the layered niobates (AB2Nb3O10 (A = K, Rb, Cs and H; B = Ca, Sr and Ba)), mesoporous niobium oxide and HCa 2Nb3O10 nanosheet were prepared and the local structures of these compounds were investigated with quadrupolar solid state NMR spectroscopy. Variable quadrupolar solid state NMR techniques, such MQMAS, QPASS, DFS, VOCS and CP were used to determine the chemical shift anisotropy (CSA) and electric field gradient (EFG) tensors of the different niobium environments in these compounds.