Facile preparation of extra-large pore zeolite ITQ-37 based on supramolecular assemblies as structure-directing agents

Abstract

The chiral germanosilicate zeolite ITQ-37 was prepared using a readily-obtained, semi-rigid achiral organic structure-directing agent (SDA) 1,1′,1′′-(2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene)tris-(3-methyl-1H-imidazol-3-ium) (denoted tmbi). The synthetic factors, including crystallization temperature, water content, germanium and tmbi concentrations for the crystallization of ITQ-37, were studied by means of single crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis, liquid and ¹³C/¹⁹F/²⁹Si solid NMR and photoluminescence spectroscopy. The results showed that high Ge content, high tmbi concentration and low temperature (150 °C) conditions favor the formation of extra-large pore ITQ-37 when supramolecular interactions between tmbi molecules occur. On the other hand, a much diluted tmbi solution and a higher reaction temperature favor the crystallization of an unknown lamellar phase, wherein tmbi is present as monomers. These studies revealed that supramolecular assemblies of tmbi were formed during the zeolite synthesis and acted as SDAs for crystallization of ITQ-37, providing a general and applicable strategy for synthesizing large and extra-large pore zeolites.