Template-Free Synthesis of ZSM-5 Type Zeolite Layers on Porous Alumina Disks


Abstract: ZSM-5 crystals were synthesized from template-free batches on macroporous \alpha-alumina disks. The SiO_2/Al_2O_3 ratio of the synthesis gel influenced the crystal morphology, surface coverage and intergrowth among the crystals. Prismatic ZSM-5 crystals covered the disk surface when the SiO_2/Al_2O_3 ratio of the batch was higher than 100, whereas spherical polycrystalline particles of ZSM-5 were obtained from batches with a SiO_2/Al_2O_3 ratio of 80. Mordenite type zeolite was formed on the disk surface due to the incorporation of alumina dissolved from the disk when the time of crystallization was extended. The effects of silica source and seeding of the support surface with 0.3 and 2 \mu m ZSM-5 crystals on the morphology of zeolite layer were also investigated. The purity, surface coverage and SiO_2/Al_2O_3 ratio of ZSM-5 crystals increased in the order of silica sol containing methanol, silica sol, and silicic acid. Seeding decreased the length of prismatic ZSM-5 crystals from 45 \mu m 10 \mu m and increased the surface coverage.

Keywords: ZSM-5, template-free synthesis, zeolite layer, zeolite membrane

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