Solid-State NMR Studies Of Ni/CeO₂ And γ-Al₂O₃

Metal oxide materials have been widely used in energy storage,catalysis,environmental treatment and other fields.It is of great importance to study the structurefunction relationship of metal oxides with various advanced characterization techniques.Different from traditional characterization methods,solid-state NMR can detect the local environment of specific nuclei and provide short-range information,and it has the advantages of nondestructive detection and quantitative analysis.Ni/CeO2 and γ-Al2O3 are studied in this dissertation by solid-state NMR methods,the results are as follows:1.The ceria nanorods exposing {111} facets have been prepared by the hydrothermal method,and Ni/CeO2 samples with different Ni concentrations have been prepared by the impregnation method at different calcination temperatures.17O MAS NMR spectra show that the peaks of the O ions in the second and third layers in Ni/CeO2 are weaker than those in ceria nanorods,because paramagnetic Ni ions have been incorporated into the lattice of ceria.Taking into account of the coordination of Ni and O ions,as well as the distribution of Ni in the first and second layers of ceria nanorods,quantitative relationships have been established between the Ni amounts in first two metal ion layers and the relative peak intensities of oxygen ions in the second and third layers.Analysis shows that the Ni concentrations in first two metal ion layers of 10%NiCe-500 and 20%NiCe-300 are within the ranges of 9～17%and 8～15%,respectively.This method can be extended to other complicated oxides to extract the relative concentrations of the doped paramagnetic ions.2.γ-Al2O3 nanoparticles haven been prepared by calcining the alumina sol.In-situ 27Al,1H and 17O MAS NMR experiments have been performed to investigate the interaction of γ-Al2O3 and water.Tetra-coordinated,penta-coordinated and hexacoordinated Al can be distinguished in 27Al MAS NMR spectra,however,the signals of new species cannot be observed in the 27Al NMR spectra.Terminal as well as doubly and triply bridging hydroxyls can be observed in 1H MAS NMR.In-situ NMR results show that the majority of water molecules are transformed to triply bridging hydroxyls with a 1H shift of around 4.4 ppm.In-situ 17O MAS NMR and 17O-1H REDOR spectra show the dissociation of water and the formation of surface hydroxyl groups.In addition,170 in the surface hydroxyl groups are exchanged to the sub-surface OAl4 sites.Finally,17O-1H HETCOR NMR experiments are performed to investigate the correlation between 17O and 1H.