Formation of Al-rich nanocrystalline ZSM-5 via chloride-mediated, abrupt, atypical amorphous-to-crystalline transformation

The efficient hydrothermal synthesis of highly crystalline, nano ZSM-5 particles, rich in framework Al content (Si/Al = 25) and low in the degree of intergrowth, in a medium of unusually high NaCl concentration was followed by examining the solids formed with ²⁹Si, ²⁷Al, ¹³C MAS NMR, TEM, DRIFT, and XRD spectroscopies. ZSM-5, in the form of 60 nm primary crystallites present as 100-150 nm dispersed cubic clusters, were crystallized from an amorphous phase via an abrupt, solid state transformation within 15 min at 165 °C. A model of the crystallization process was proposed, different from the typical nucleation-crystal growth process, in which aluminosilicate oligomers of low connectivity was salted out as amorphous solid as a result of high NaCl concentration immediately upon mixing of the ingredients.