Abstract
Abstract SAPO-11 was synthesized with fluoride ions via a grinding synthesis method. After introducing fluoride ions, (hydro)thermal stability of SAPO-11 was improved. Zeolitic framework keeps stable up to 1000 °C and distortion is inhibited at 800 °C. When tested in hydrothermal conditions (450 °C, 4 h), the retention rate of relative crystallinity and micropore increase by 28% and 7%. A potential mechanism is proposed to explain the role of fluoride ions to enhance the stability of SAPO-11. At the hydrothermal atmosphere, fluoride species enhance surface hydrophobicity, which inhibits the adsorption of water on SAPO-11. Three types of fluoride ions are confirmed: (i) fluoride ions in the pore channel and on the surface, (ii) fluoride ions interacting with silicon atoms and (iii) aluminum atoms. Fluoride ions interacted with aluminum atoms increase Al-O bond strength. The current research proposes a fluoride-assisted method for stability enhancement of SAPO molecular sieves and is important for expanding application of SAPO molecular sieves in severe (hydro)thermal environment.
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