Insights into the aminothermal crystallization process of SAPO-34 and its comparison with hydrothermal system

Aminothermal synthesis reported by our group recently, in which organic amine is used as the solvent and template, could obviously enhance the solid yield and crystallization rate of SAPO-34 as compared with the corresponding hydrothermal one. Herein, aminothermal crystallization process of SAPO-34 is investigated to gain insights into this novel synthetic method by XRD, SEM, IR, UV-Raman and various solid-state NMR techniques. It is found that aminothermal environment facilitates the fast formation of a semicrystalline AIPO layered phase, which further promotes the quick activation of Al source. The lamellar phase, which is water-soluble and contains double 6-rings in the framework, could be stabilized by protonated triethylamine (TEA(+)). SAPO-34 nucleates from the rearrangement of the double 6-rings in the layered phase through bond breaking, reforming and Si incorporation after heating at 160 degrees C for 3 h. For the hydrothermal process, the interaction between TEA(+) and inorganic species is weak and the formation of layered phase is retarded due to its high solubility in water. Correspondingly, the activation of Al source is slow and SAPO-34 appears after 24 h. This work demonstrates the importance of water concentration in the synthetic system, which may influence the formation of intermediate species and alter the crystallization process and rate. (C) 2017 Elsevier Inc. All rights reserved.