(129a) Bead-Milling and Post-Milling Recrystallization: An Organic Template-Free Methodology for the Production of Nano-Zeolite Catalyst

A new method for the production of nanosized zeolite powder by a top-down approach has been performed. [1,2] In this study, ZSM-5 (MFI type structure) was first milled to produce a nanopowder. This technique can destroy the outer portion of the zeolite framework, which lowers the micropore volume of ZSM-5 zeolite. To remedy this, the damaged part was recrystallized using a dilute aluminosilicate solution after bead milling. From the combined bead milling and post-milling recrystallization, nanosized ZSM-5 zeolite approximately 50 nm in size with high crystallinity was obtained successfully.

Commercial ZSM-5 was milled using a bead milling apparatus (Minicer, Ashizawa Finetech, Ltd., Tokyo, Japan) for 2-6hours. Recrystallization of the milled ZSM-5 was performed using dilute silicate solution with the composition of 0.0525 Na₂O : 0.117 SiO₂ : 10.0 H₂O. The importance of this particular ratio is that it provides a solution nearly in equilibrium with ZSM-5. This means that ZSM-5 neither undergoes macroscopic growth nor dissolution. Under these conditions, the remaining ZSM-5 crystallites act as seeds and the poorly crystalline parts of the milled ZSM-5 are more easily recrystallized back onto the ZSM-5, resulting in a more ordered product. Obtained samples were evaluated as acid-catalysts for cumene cracking. The test reactions were conducted so that diffusion through the zeolite pore structure was the rate-determining step of the catalytic reaction. As a result, ZSM-5 zeolite powder showed a higher catalytic activity in cumene cracking in comparison with the raw ZSM-5 zeolite. Furthermore, the decrease in crystal size suppresses catalyst deactivation through coke deposition during cumene cracking.

References

[1] T. Wakihara et al., Crystal Growth & Design, 11, 955-958 (2011).

[2] T. Wakihara et al., Crystal Growth & Design, 11, 5153-5158 (2011).