Mechanochemical reaction pathways in solvent-free synthesis of ZSM-5

Abstract

Solvent-free methods for the synthesis of ZSM-5 have been previously reported in the literature. These methods typically involve grinding the starting materials together prior to the hydrothermal reaction step. However, very little is known about the reaction intermediates formed during the mechanochemical pre-reaction or about how the pre-reaction impacts the subsequent hydrothermal synthesis conditions (temperature and length of hydrothermal treatment). In this study, the solvent-free synthesis of ZSM-5 was investigated while varying the length and type of grinding (manual, ball-mill) and the components of the reaction mixture. The initial reactions that occurred between the solid-state raw materials during grinding were monitored by powder X-ray diffraction (pXRD). Extended grinding initiates exchange reactions between several reagents to form NaCl and to liberate ammonia and water. The resulting wet paste undergoes facile thermal conversion to crystalline zeolite ZSM-5 framework structures. These results provide valuable insights used to guide the optimization of the synthesis conditions required to prepare stable, crystalline and high surface area ZSM-5 under solvent-free synthesis conditions. The solvent-free approach contributes to the overall goal of a greener, more sustainable ZSM-5 synthesis.