Hydrothermal synthesis of SAPO-5 with novel morphologies from hydrogels containing acetic acid and high concentration of triethylamine under neutral or alkaline conditions

Abstract

SAPO-5 with novel morphologies was hydrothermally synthesized from neutral or alkaline hydrogels containing acetic acid and high concentration of triethylamine (TEA) at 180 °C for 48 h. Bullet-like, pine cone-like and disk-shaped crystals were prepared at the TEA/Al₂O₃ molar ratio of 14 and the HAc/Al₂O₃ molar ratios of 5–17. All the samples are constructed from flakes with thicknesses ranging from 100 to 300 nm stacked together to form various geometries. Their aspect ratio decreases with increase in the HAc/Al₂O₃ molar ratio. Substitution of HCl for HAc results in the formation of SAPO-5 with hexagonal disk flower-like morphology at a TEA/Al₂O₃ molar ratio of 14 and HCl/Al₂O₃ molar ratio of 4.3. The above SAPO-5 with novel morphologies contains mesopores and exhibits higher ratios of the amounts of the weak acid site to intermediate acid site than those of the conventionally synthesized SAPO-5. The effect of interaction between acetic acid and TEA on formation of the novel morphology is discussed.