Effects of adding alcohols on ZSM-12 synthesis

• Di-ols and glycols are applied to modulate the morphology of MTW crystals.
• Anisotropic growth of MTW along b-direction is observed using HD and TEG.
• Potential synthesis route to control MTW membrane with preferred orientation.

This work systematically studies on adding alcohols to alter the crystal growth behavior of ZSM-12, using 1-propanol (1P), 2-propanol (2P), ethylene glycol (EG), 1,3-propanediol (PD), 1,6-hexanediol (HD), diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene glycol (TTEG) as co-solvents. The effects of co-solvent content, temperature, and excess mineralizer content were studied as well. Except 2P, all other co-solvents are observed to tune the crystal morphology into a discrete round-shape. Except DEG and TTEG, all other co-solvents promote the crystallization rate of MTW phase, verified by larger zeolite crystal size in SEM images. The observation is corroborated with the formation of cristobalite, possibly via Ostwald ripening mechanism. The finding enlightens us using a lower synthesis temperature to attain high purity MTW phase, with an adequate amount of co-solvents. It is noteworthy that using HD as co-solvent facilitate the anisotropic growth of MTW crystals along the b-axis (2θ of 8.5°), possibly due to the effect of co-solvent’s hydrophobicity as well as the backbone length. The blue shift of symmetric and asymmetric Si-O vibration modes in FTIR spectra implies that TEG and HD are incorporated within the ZSM-12 pore structure. This work provides potential synthetic route to form anisotropic ZSM-12 membranes with preferred orientation.

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