Solid solution of a zeolite and a framework-bound OSDA-containing molecular sieve
نویسندگان
چکیده
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 solidsolutions varies significantly with the number of OH groups in OSDAs.
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