Investigation of the Evolution of Intermediate Phases of AlPO4-18 Molecular Sieve Synthesis

• Published in: Chemistry of materials 2003-06, Vol.15 (12), p.2437-2444
• Main Authors: Huang, Yining, Demko, Bryan A, Kirby, Christopher W
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Porous materials
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm021728c

In the present work, we examined the intermediate phases formed during the hydrothermal synthesis of microporous material, AlPO4-18. The evolution of the long-range ordering of the gel samples as a function of crystallization time was followed by powder X-ray diffraction. The development of the local environments of P and Al atoms was monitored by 31P and 27Al magic angle spinning (MAS) NMR. Several representative intermediate phases were further characterized by 27Al multiple quantum MAS and 27Al → 31P cross-polarization experiments. Our results show that the formation of AlPO4-18 undergoes several stages. Mixing phosphorus and aluminum sources together with a template at room temperature yielded a mixture containing an ordered aluminophosphate (AlPO) phase and a phosphate material. These materials were converted to an amorphous AlPO phase under hydrothermal conditions. Continuous heating resulted in the transformation of the amorphous phase into a crystalline microporous material, AlPO4-5. A further increase in heating time led to the disappearance of AlPO4-5 and the formation of AlPO4-18.