The effect of thermal treatment and of grinding on silicalite-1 synthesized in the presence of fluoride ions

Abstract

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 + decomposition are identified as being due to the Hoffmann degradation of the TPA + ion (first peak) and to the decomposition of the products of TPA + ion (second peak).