Intergrowth segregation in FAU-EMT zeolite materials

Abstract

Intergrowths of cubic (FAU) and hexagonal (EMT) structural phases in a number of faujasite-related zeolite materials have been studied using transmission electron microscopy, and high-resolution powder X-ray diffraction. In Y, CSZ-1, CSZ-3, ZSM-2, ZSM-3, ZSM-20, ECR-35, ECR-30 and EMC-2 materials, the FAU and EMT components segregate non-randomly into contiguous blocks. This segregation is most pronounced in ZSM-20 and ECR-35. ECR-30 and EMC-2 are both predominantly EMT framework materials, within which FAU intergrowths occur in clumps of 1, 2 or 3 layers. No evidence is found for extended superlattice ordering of intergrowths. Intergrowth segregation acts to reduce both the configurational entropy associated with the stacking statistics and the elastic energy associated with coherency strain.