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 13C 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 27Al 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 cell c-parameter.