Thermochemical study of the structural stability of low-silicate CHA zeolite crystals

In this study, the effect of synthesis method on the structural stability of low-silica CHA zeolite crystals were investigated. For this purpose, template-free CHA crystals with similar chemical compositions were synthesized using seeded secondary growth and inter-zeolite transformation approaches. The stability performance of as-synthesized crystals was studied at temperatures, steam flow in a closed system, and acidic media. The results were analyzed using XRD, FTIR, DLS and FESEM. It was found both methods have similar structural stability behavior. The thermal stability investigation proved they have maintained their crystalline structure against heating, up to 800 °C, and at higher temperatures, the amorphous phase prevailed. The CHA crystals synthesized via both methods are stable in terms of hydrothermal stability up to 200 °C. Moreover, the results of chemical resistance showed CHA crystals exhibit excellent resistance to weak acidic medium, but against stronger acids, it has completely lost its crystallinity after 72 h.