Synthesis of PST-11 and PST-12 Zeolites via a Charge Density Mismatch Approach and Their Characterization

Abstract

The synthesis of aluminosilicate zeolites are carried out based on the charge density mismatch (CDM) approach and the characterization of the representative products are described. We report the synthesis of a new MEI-type zeolite, denoted PST-11 (POSTECH no. 11) and that of a nano-crystalline BPH, denoted PST-12 (POSTECH no. 12) using the two most studied simple organic molecules, tetraethylammonium and tetramethylammonium, together with Sr2+ and Li+. Although the comprehensive cooperation of all four different types of molecules is responsible for the formation of these peculiar zeolite structures, we found that the PST-11 primarily contained tetramethylammonium in the pores. We also discovered that PST-12 included both tetramethylammonium and tetraethylammonium in the pores. We have also estimated the formation pathway of PST-11 that the very small crystals with BPH like structure were initially formed. The presence of PST-11 and PST-12 are evidenced by a combination of powder XRD, IR, and 13C, 27Al, and 29Si MAS NMR spectra. From the overall results of these study, it is clear that PST-11 is transformed from BPH-like structure to MEI structure with not only decreasing its Sr/Al ratio, but also increasing its Si/Al ratio and PST-12 is formed nano-crystalline UZM-4.