A Series of LiCl/γ-Al2O3 samples were prepared by mixing and then heating at 400℃ for 30 hours. 7Li MAS NMR was used to investigated their structures. The 7Li MAS NMR signal of LiCl in the dispersion phase was observed for the first time, and its chemical shift was at 0.25ppm.After the dispersion threshold of LiCl on γ-Al2O3 was achieved, the 7Li signal in the crystallme phase LiCl appears at -1.01ppm and its intensity increases with the increasing in LiCl loading.From the 2D nutation NMR spectra, it can be seen that the electric field gradient surrounding the lithium nuclei in the dispersion state is larger and so the quadrupole interaction is stonger than that in the crystalline state. The dispersion threshold indicated by NMR is in agreement with that deduced from XRD, which is about 0.136gLiCl/gγ-Al2O3.
The preparation of alumina with large surface area, certain phase and porosimetry has always been one of important researches. A new method using much less sucrose (the molar ratio of sucrose to Al 3+=0 5) was developed to prepare γ-Al 2O 3 with large surface area and high thermal stability. Firstly,ammonium hydroxide was dropped to aqueous solution of aluminum nitrate and sucrose. The resulted precipitate in suspension was heated until a homogeneous gel was obtained. Then the gel was dehydrated at 110 ℃ to get a fluffy black precursor. Finally, γ-Al 2O 3 with A=345 m2/g was prepared by calcining the precursor at 600 ℃ for 24 h. The precursor and the obtained γ-Al 2O 3 were characterized by DTA-TG, N 2 adsorption-desorption isotherms, XRD and TEM. According to the dispersion behaviors of organic compounds on supports, the related mechanism was discussed.
