Controlling Crystal Transformation between Zeolite ZSM-5 and Mordenite without Organic Structure-Directing Agent

Zeolite crystals were synthesized at a lower temperature (150 degrees C) by adding a nucleation solution prepared at higher temperature (190 degrees C) to the mother solution. The effects of the Na2O/SiO2 ratio, nucleation time of the nucleation solution, and the ratio of Na2O/SiO2 ratio in the mother solution on crystal transformation between ZSM-5 and mordenite were investigated. The transformation between zeolite ZSM-5 and mordenite could be controlled effectively by changing the overall Na2O/SiO2 ratio in the overall solution. A Na2O/SiO2 ratio of 0.18 formed a boundary between ZSM-5 and mordenite phases when the overall solution had a composition of xNa(2)O:100SiO(2):2.5Al(2)O(3): 12SO(4)(2-):4000H(2)O. When the Na2O/SiO2 ratio was increased higher than 0.18 by altering the composition of the mother solution, the ZSM-5 product formed by nucleation at higher temperature (190 degrees C) could be transformed into mordenite crystals during crystallization at lower temperature (150 degrees C). When the Na2O/SiO2 ratio was <= 0.18, a product containing both ZSM-5 and mordenite crystals was obtained during nucleation at higher temperature that could be transformed into ZSM-5 crystals during crystallization at lower temperature. A precondition for crystal transformation between ZSM-5 and mordenite was that the crystallinity of the product formed during nucleation at higher temperature must be <= 30%.