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TON-type zeolite crystals in the shape of short needles were synthesized using inhibitors of crystal growth along the 001 direction. When fluoride was used as a mineralizer, bulky amines incorporating structure-directing agents acted as inhibitors, while nonionic surfactants were more effective as inhibitors for decreasing the crystal length of TON-type zeolite. The amount of surfactant adsorbed on the zeolite increased with the surface area of the face containing pore mouths. This indicates that the surfactant was trapped in the pore mouths to inhibit crystal growth along the long axis of the needle-shaped crystals. By microscopic observation of the crystals, we confirmed inhibition of crystal growth by adsorption of the surfactant. After adsorption of Nile red, a lipophilic stain that is intensely fluorescent in surfactants, on as-synthesized zeolite, only the edges of the needle-shaped crystals were luminous, also indicating adsorption of the surfactant in pore mouths. When hydroxide was used as a mineralizer, the bulky amines acted as inhibitors. Nonionic surfactants, however, did not work. We used the obtained shorter crystals of TON-type zeolites as catalysts for hydroisomerization of n-tetradecane. Use of the shorter crystals improved the selectivity for skeletal isomerization.
Okamoto et al. (Wed,) studied this question.