Rietveld structure refinement of zeolite ECR-1

In this work, we present the structure refinement of ECR-1 to give the first direct evidence of the proposed structure of this synthetic zeolite. In fact, a model of the structure of ECR-1 was proposed on the basis of high-resolution transmission electron microscopy (HRTEM) evidence and the structure solution of the synthetic gallo-silicate TNU-7, but it has not been refined to date. The proposed model consists of structure layers of mordenite (MOR) and mazzite (MAZ) connected in a regular 1: 1 stacking sequence and framework topology EON. Because single crystals of ECR-1 cannot be synthesized, the structure was refined using the Rietveld method. High-resolution synchrotron powder diffraction data were collected on both the synthetic Na-ECR-1 and NH4-ECR-1 samples at ESRF. Na atoms located on the axis of the eight-member ring channels in mordenite and zeolite omega are not present in Na-ECR-1. In Na-ECR-1, the equivalent sites lay near the walls of the eight-membered-ring channels. This difference is presumably at the basis of the formation of ECR-1 because, during growth, the local symmetry deformation of the eight-membered-ring channel prevents the formation of the MOR or MAZ structures and justify the periodical shift from one structure to the other. A quantitative explanation of the anisotropic peak broadening observed in the powder patterns is also given.