Solid solution of a zeolite and a framework-bound OSDA-containing molecular sieve

Abstract

The structure of the as-made, hydrated form of ECR-40C, synthesized in the presence of (2-hydroxyethyl)trimethylammonium (HTMA⁺) ions as an organic structure-directing agent (OSDA) and 2 wt% (relative to alumina in the synthesis mixture) of aluminosilicate zeolite UZM-22 with the MEI topology as seeds, has been determined using synchrotron powder X-ray diffraction and Rietveld analyses. Two different types of organic species were suggested to exist in ECR-40C: the encapsulated HTMA⁺ ions with one intramolecular C–H⋯O hydrogen bond, typical of OSDA molecules in as-made UZM-22, and the framework-bound cations. A combination of elemental and thermal analyses, Na⁺ ion exchange, and multinuclear MAS NMR and IR spectroscopies clearly shows the coexistence of the zeolite and framework-bound OSDA-containing molecular sieve (FOMS) domains with a proportion of approximately 3 : 2 in ECR-40C crystals. TEM elemental mapping reveals that the Na⁺ ions exchanged with the HTMA⁺ ions into as-made ECR-40C are uniformly distributed throughout the ECR-40C crystals. Therefore, ECR-40C is not a pure FOMS but a solid solution of a zeolite and a FOMS (i.e., UZM-22 and ECR-40-type FOMS), which has never been recognized or addressed before. The overall characterization results of this work demonstrate that the proportion of the zeolite domain in such solid-solutions varies significantly with the number of OH groups in OSDAs.