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

Abstract

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.