Perspectives on the multi-functions of aniline: Cases from the temperature-controlled phase transfer hydrothermal synthesis of MWW zeolites

- Multi-functions of aniline in synthesis originated from its properties.
- Solubility of aniline favors easy separation-recovery of HMI.
- Aniline was of poor structure-directing capability because of lower basicity.
- As structure-promoting agent, aniline fills space of MWW zeolites.
- Aniline can modify distribution and stability of Al.

The relationship between properties of aniline and its function was summarized concerning the hydrothermal synthesis of MWW zeolites with hexamethyleneimine as the structure-directing agent. Positive temperature-dependent solubility of aniline makes organics completely dissolved during crystallization and easily separated and recovered by liquid separation, which is defined as temperature-controlled phase transfer hydrothermal synthesis. For aniline, p-π conjunction significantly decreased basicity (determined by electronegativity) of amino groups, which accounted for poor charge-balancing and structure-directing capability. With hexamethyleneimine as the structure-directing agent, Aniline could promote crystallization as space-filling agent at much lower HMI/SiO2 ratio without being trapped within as-made MWW zeolites. Furthermore, the utilization of aniline as the structure-promoting agent could modify morphology into disorder packing of MWW platelets via directing gel method. HMI/SiO2 is the key to the distribution and stability of Al within final MWW zeolites. All referred advantages were originated from structure and properties of aniline. In future studies, efforts could be focused on property-oriented function design of hydrothermal synthesis.

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