The inner heterogeneity of ZSM-5 zeolite crystals

Abstract

The inner architecture of zeolite crystals beneath the zeolite surface is the missing part in understanding the crystallization of zeolites and in their thoughtful post-synthesis engineering. In this work, both the defect-zoning and Al-zoning in pseudo-single ZSM-5 crystals were revealed using unbiased NH₄F etching of as-synthesized and calcined samples. The formation of defect-zoning leading to a multiple core–shell structure was described with a three-stage process involving (i) nucleation resulting in the innermost core formation, (ii) fast aggregate growth leading to defect-rich zones, and (iii) layer-by-layer growth shaping the final morphology of the zeolite crystals. A clear correlation between Al zoning and the spatial distribution of C and Na was established. This distinct inner heterogeneity in the ZSM-5 crystals reveals the particularities of the crystal growth process of this very important zeolite, and this knowledge can be translated into novel framework structures with targeted properties.