On the synthesis of AlPO₄-21 molecular sieve by vapor phase transport method and its phase transformation to AlPO₄-15 molecular sieve

Abstract

An experimental design was applied to the synthesis of AlPO₄-21 molecular sieve (AWO structure) by vapor phase transport (VPT) method, using tetramethylguanidine (TMG) as the template. In this study, the effects of crystallization time, crystallization temperature, phosphor content, template content and water content in the synthesis gel were investigated. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy and fourier transform infrared spectroscopy (FT-IR). Microstructural analysis of the crystal growth in vapor synthetic conditions revealed a revised crystal growth route from zeolite AlPO₄-21 to AlPO₄-15 in the presence of the TMG. Homogenous hexagonal prism AlPO₄-21 crystals with size of 7 × 3 μm were synthesized at a lower temperature (120 °C), which were completely different from the typical tabular parallelogram crystallization microstructure of AlPO₄-21 phase. The crystals were transformed into AlPO₄-21 phase with higher crystallization temperature, longer crystallization time, higher P₂O₅/Al₂O₃ ratio and higher TMG/Al₂O₃ ratio.

Keywords:

• AlPO₄-21
• AlPO₄-15
• phase transformation
• tetramethylguanidine
• vapor phase transport

Acknowledgements

This work was supported by a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.

Additional information

Funding

This work was supported by National Natural Science Foundation [grant number 21276029]; Natural Science Foundation of Jiangsu [grant number BK20131142]; Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology [grant number BM2012110].