The samples of ultra-stable high-silica H-STI-I and H-STI-II zeolites were prepared using the method of ion-exchange combined with controlled calcinations. Characterizations with EDX, ²⁹Si MAS NMR, ²⁷Al MAS NMR and FT-IR indicate that the framework Si/Al ratios of H-STI-I and H-STI-II are 4.43 and 10.62, respectively. Investigations of the samples obtained in the processs of stage-temperature-programmed calcinations with XRD proved that the structure stability of both samples could be kept at temperature up to 1000 ℃. Type I isotherms of N₂ adsorption at 77 K illuminated that the ultra-stable H-STI samples possessed perfect channel systems with opening micro-pore structures. The more structural defects in the framework of H-STI-II, which has been treated with acid in the process of preparation, led to worse thermal stability, lower surface area and pore volume than those of H-STI-I.

Key words: STI zeolite, ultra-stability, ion-exchange, temperature-programmed calcinations, solid NMR, N₂ adsorption, FT-IR