Kinetic study of the crystallization of ZSM-5 under organic template-free conditions

Abstract

Here, the ZSM-5 zeolite was prepared under organic template-free conditions at different reaction temperatures and initial gel compositions using a hydrothermal process. A kinetic study of the synthesis of Zeolite was performed based on crystal growth. The crystallinity degree of the prepared samples was calculated from the PXRD and FT-IR results and then the crystallization curves were obtained. From these curves, the kinetic parameters were computed. The obtained results showed that by increasing the Na+ content of the initial gel composition, the activation energy for the crystal growth was reduced and as a result, the crystallization rate of ZSM-5 zeolite was enhanced due to the structure-directing role of Na+ cation. The activation energy of the induction step, transition step and crystal growth step are 122.8, 46.2, and 48.5 kJ/mol respectively for the molar ratios of 29Na2O:63SiO2:Al2O3:2400H2O:16H2SO4 and 141.0, 70.4, and 80.8 kJ/mol respectively for the molar ratios of 16Na2O:31SiO2:Al2O3:2400H2O:16H2SO4.