Structural Characterization of Large-Pore Intergrowth Zeolites SSZ-31 and PST-38

The structure determination of multiple-phase intergrowth zeolites faces more challenges than that of single-phase ordered zeolites because of their structural complexity and diversity. Here, we directly visualized the atomic structure and one-dimensional stacking disorder of the pure-silica large-pore intergrowth zeolites SSZ-31 and PST-38, using aberration-corrected scanning transmission electron microscopy. The atomic-resolution images revealed the presence of distinct polymorphs, their intergrowth boundaries, and cages formed through local connectivity variations. It was found that while SSZ-31 is an almost pure (ca. 90%) polymorph A, E, or their intergrowth, with the ABC stacking of 12-ring channels, PST-38 is a predominant intergrowth between SSZ-31 polymorph C and a 1D 10-ring structure, denoted as PST-39, along the same axis. Furthermore, the latter material also contains a region where the 8-membered rings are connected to the 12- and 10-membered rings. The structural features of SSZ-31 and PST-38 presented here provide insights into the design and synthesis of intergrowth zeolites.