Some factors, such as calcination, ion-exchange, acid leaching etc., were studied on influencing the hydrothermal stability of natural CXN zeolite. Characterization with XRD, XRF and 27Al MAS NMR proves that the type and location of cations obviously influence the hydrothermal stability of the zeolite, and NH4-type CXN zeolite possesses the best stability. Although the framework SiO2/Al2O3 ratio of calcined NH4-CXN zeolite was enhanced, but the increase of followed framework defects greatly reduced the hydrothermal stability. The effects of steam volume, treatment temperature and time on the evolution rules of zeolite framework were also studied in this paper. The results indicate that raising the treatment temperature and steam volume decrease the zeolite crystallinity, while the effect of treatment time is negligible.

Key words: CXN zeolite, STI zeolite, hydrothermal stability, non-framework aluminum, steam treatment