Epitaxial growth of core-shell zeolite X-A composites

A core-shell zeolite composite consisting of a single-crystal FAU-type zeolite (zeolite X) as the core and the LTA-type zeolite (zeolite A) as the shell has been synthesized. The growth of the zeolite shell has been studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and single crystal X-ray diffraction. Cross-sections for SEM and TEM studies were prepared by argon ion cross-section polishing (CP) and focused ion beam (FIB), respectively. The results show that crystals of zeolite A grew epitaxially and uniformly on zeolite X with well-defined orientation relationships. Three possible models of the X-A interface have been proposed, all indicating that the pores in zeolites X and A are interconnected. The different techniques used for studying the composite materials are described in detail, which are general and can be applied for studying other composite materials.