Elucidation of the solid-state ion exchange mechanism of MoCl5 into ZSM-5 zeolite

- Hygroscopic MoCl5 decomposes into MoO3 between room temperature and 573 °C.
- Thermodynamic calculations illuminate the physical states of decomposition products.
- The dehydration of NH4+-ZSM-5 zeolite is crucial to produce MoO2(OH)2(g).
- The exchange of MoO2(OH)2(g) into zeolite occurs between 342 and 523 °C.

The highly hygroscopic MoCl5 exhibited, under helium stream, several transformations between room temperature and 387 °C. At low temperatures (between 77 and 202 °C), the salt transforms into the stable MoO3 oxide and the less-stable oxochloride, MoOCl4, which evaporates and decomposes into MoOCl3. The former compound evaporates at 313 °C, while the entire vanishing of MoCl5 occurs at 387 °C. In the presence of NH4+-ZSM-5 zeolite, the starting salt is transformed into MoOCl4 and then into the volatile MoO2(OH)2. The non-isothermal solid-state ion exchange of MoO2(OH)2(g) into H+-ZSM-5 zeolite occurs between 342 and 523 °C. Nonetheless, the isothermal exchange is highly recommended at a temperature below 523 °C in order to avoid the irreversible zeolite dealumination. In this study, thermodynamical calculations were used for the elucidation of the physical states of decomposition products.

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