The structure of an iron oxide cluster incorporated into zeolite Y, determined by HRTEM and SAED

Abstract

The atom positions of an iron cluster (Fe₆O _n ) inside the framework of a zeolite (FAU, Na₄₈(Fe₂O₃)₃₈Al₄₈Si₁₄₄O₃₈₄) were determined through the use of electron crystallography methods for three-dimensional reconstruction of atomic positions within the cluster from high-resolution electron micrographs and selected-area electron diffraction. The iron-containing FAU structure was determined in the space group Fd3m (a = 24.7 Å) by the use of 42 unique reflections. The Fe₆O _n molecule is situated in the sodalite cage with the iron atoms facing the square windows of the cage. The iron-iron distance is 3.6 Å and the distances between iron atoms and the nearest oxygen atoms in the sodalite cage are close to 2.2 Å. As a verification of the method, the same technique was used for the dermination of the structure of Na₄₈Al₄₈Si₁₄₄O₃₈₄ without iron, and the Si/Al atom positions of the zeolite framework were found to coincide with those determined from single crystal X-ray diffraction methods.