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Synthesis in fluoride-containing medium leads to large silicalite crystals without SiOX defect groups. The four occluded tetrapropylammonium (TPA + ) ions/unit cell are ion pairs with 2 F - and 2 OH - . Grinding the samples in the presence of water leads to SiOH groups that are eliminated during calcination. The two endothermic peaks at 420 and 560°C of the TPA + ...
Silica gels containing tetraalkylammonium bromide (TAA), hexamethonium (HM) bromide, and 1,2-diaminododecane (DADD) have been prepared in fluoride medium: 10 NaF - (x TAABr -y HMBr 2 - z DADD) - 10 SiO 2 - 330 H 2 O with x + y + z = 1.25. TAA = tetramethyl-, tetraethyl-t tetrapropyl-, and tetrabutylammonium. Silicalite-1 (with TPA), silicalite-2 (with TBA), and ZSM-48 (with...
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