Synthesis of ZSM-12 (MTW) with different Al-source: Towards understanding the effects of crystallization parameters

• Effects of Si/Al ratio and alkalinity on morphology of ZSM-12 were studied.
• Selection of the Si/Al and temperature were critical to obtain pure ZSM-12.
• Different types of ZSM-12 agglomerates were observed at different Si/Al ratio.
• Prolonged aging time up to 6 h induced the nucleation of competing phase.

The effect of synthesis parameters on morphology of ZSM-12 (MTW) zeolite with tetra ethyl ammonium bromide (TEABr) as an organic-structure directing agent was investigated systematically. Aluminum sulfate octahydrate (Al2(SO4)3·18H2O) was used as an aluminum (Al) source. The Si/Al ratio was varied from 40 to 180 and alkalinity ratio (NaOH/Si) was set between 0.132 and 0.160. Effects of crystallization temperature and time were studied. The contribution of the aging period on the final morphology of ZSM-12 was investigated in the range of 1.5–6 h. Phase identification of as-synthesized ZSM-12 was confirmed by X-ray diffraction and morphology of crystals was studied by electron microscopy. The alkalinity was one of the most substantial factors that induced the formation of ZSM-5 (MFI) nuclei as a competing phase. Pure ZSM-12 was obtained with Si/Al of 80 at 145 °C. Different agglomeration shapes of ZSM-12 were observed by changing Si/Al ratio. Prolonged aging time up to 6 h induced the formation of ZSM-5 nuclei.

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