Interzeolite conversion of zeolite MCM-49 into zeolite ZSM-35 in cyclohexylamine–hexamethyleneimine–Na2O–H2O containing systems

Abstract

The interzeolite conversion of zeolite MCM-49 into zeolite ZSM-35 in “cyclohexylamine (CHA)–hexamethyleneimine (HMI)–Na₂O–H₂O” systems, consisting of “CHA–Na₂O–H₂O”, “HMI–Na₂O–H₂O” and “Na₂O–H₂O”, was investigated in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) characterization techniques. Both CHA and HMI play important roles in directing the interzeolite conversion of MCM-49 into ZSM-35, and the conversion speed is much faster in systems containing CHA than those containing HMI. Even in the Na₂O–H₂O system without any organic amine, MCM-49 can still transform into some other zeolites with more stable topological structures than itself, such as ZSM-35, ZSM-5, and mordenite, but the product of the interzeolite conversion is more complicated than that in the systems containing organic amines (CHA and/or HMI). In the Na₂O–H₂O system, alkalinity has been proved to be a crucial factor influencing the conversion trend of MCM-49. Zeolites ZSM-5 and mordenite will appear in the products besides ZSM-35 with the increase of the alkalinity. The conversion process of zeolite MCM-49 in the systems investigated accords well with the solution-mediated transformation mechanism.