Zeolite MCM-49: A three-dimensional MCM-22 analogue synthesized by in situ crystallization

As-synthesized MCM-49 is a three-dimensional (3D) microporous aluminosilicate zeolite with the MCM-22 framework topology. It is formed hydrothermally in a reaction gel and is the first example of a zeolite with this topology to be produced by direct synthesis, in contrast with the conventional procedure in which a precursor is formed first and is then calcined. When hexamethyleneimine (HMI) is used as the directing agent, a SiO2/Al2O3 ratio of the framework as low as 17/1 can be achieved. X-ray powder diffraction (XRD), temperature programmed base desorption (TPBD) experiments, and multinuclear NMR analyses of this zeolite and others in this series (viz., calcined MCM-22 and its precursor) provide new insights into the novelty of this class of materials. TPBD and C-13 NMR experiments, for example, provide experimental evidence that support the coexistence of different dual pore systems within both the MCM-22 precursor and MCM-49. The Al-27 MAS NMR spectra of MCM-22 and calcined MCM-49 exhibit three distinct Td resonances, a feature not previously observed for any other zeolite. And finally, aluminum enrichment of the T1-O1-T1 bridge in MCM-49 is postulated on the basis of the length of its unit eel c-parameter.