Synthesis of ZSM‐5 from template‐free batches which preceded the preparation of template‐free ZSM‐5 layers on porous supports was studied to ascertain the effect of nature of silica source on the purity of template‐free ZSM‐5. Silicic acid and two colloidal silica sols were used as silica sources to prepare the template‐free batches with a molar composition of 6.5Na2O:Al2O3:80SiO2:3196H2O. One of the colloidal silica sols contained methanol as stabilizer while the other did not. The product purity and rate of crystallization increased when colloidal silica sols were used as silica source, however, use of silicic acid led to low purity and slow crystallization rate. The methanol in the colloidal silica sol appeared to act as template to promote the crystallization and was occluded in the resultant ZSM‐5 pores. The dissolution of the meta‐stable ZSM‐5 phase and formation of quartz was observed regardless of the nature of the silica source in case of prolonging the crystallization time more than 90 h at 200°C.
Although clinoptilolite is the most abundant zeolite mineral in nature, its synthesis under laboratory conditions has been difficult. A partial crystallization field study was done for the synthesis of clinoptilolite based on a nominal batch composition of 2.1Na 2 O:Al 2 O 3 :10Si 2 O:110H 2 O to delineate the limits of composition and temperature within which sodium clinoptilolite can be produced as a single phase in high yields. Effects of temperature, SiO 2 /Al 2 O 3 molar ratio in the batch composition, and the use of different raw materials in batch preparation were studied. The need for the use of seed crystals for reproducible synthesis of clinoptilolite was established.
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