Solid-State Synthesis of Aluminophosphate Zeotypes by Calcination of Amorphous Precursors

Because of the growing interest in the applications of zeolitic materials and the various challenges associated with traditional synthesis methods, the development of novel synthesis approaches remains of fundamental importance. Herein, we report a general route for the synthesis of aluminophosphate (AlPO) zeotypes by simple calcination of amorphous precursors at moderate temperatures (250-450 degrees C) for short reaction times (3-60 min). Accordingly, highly crystalline AlPO zeotypes with various topologies of AST, SOD, LTA, AEL, AFI, and-CLO, ranging from ultra-small to extra-large pores, have been successfully synthesized. Multinuclear multidimensional solid-state NMR techniques combined with complementary operando mass spectrometry (MS), powder X-ray diffraction, high-resolution transmission electron microscopy, and Raman characterizations reveal that covalently bonded fluoride in the intermediates catalyze the bond breaking and remaking processes. The confined organic structure-directing agents with high thermal stability direct the ordered rearrangement. This novel synthesis strategy not only shows excellent synthesis efficiency in terms of a simple synthesis procedure, a fast crystallization rate, and a high product yield, but also sheds new light on the crystallization mechanism of zeolitic materials.

Automated summary

Due to the interest in applications of zeolitic materials and challenges associated with traditional synthesis methods, a new synthesis approach for aluminophosphate (AlPO) zeotypes has been developed. By calcinating amorphous precursors at moderate temperatures and short reaction times, highly crystalline AlPO zeotypes with various topologies have been successfully synthesized. Multinuclear multidimensional solid-state NMR techniques combined with complementary characterizations reveal the catalytic role of fluoride and the directing role of organic structure-directing agents in the synthesis process. This novel synthesis strategy not only shows excellent efficiency, but also sheds new light on the crystallization mechanism of zeolitic materials.