The structural diversity of zeolites depends strongly on the use of organic structure-directing agents (OSDAs) that guide their formation. Low-dimensional zeolitic materials, such as layered or chain-like phases, can serve as key intermediates in topotactic condensation pathways, yet the mechanisms governing their formation and transformation remain poorly understood. Here, we report three low-dimensional zeolitic materials, EMM-75P, EM-L01, and EM-L02, synthesized using benzimidazolium cations as OSDAs. Their structures were determined by three-dimensional electron diffraction (3D ED), including the atomic structure of the OSDAs, revealing their confinement within the framework to shed light on their structure-directing role. The bulky benzimidazolium OSDAs prevent the formation of materials with three-dimensional framework structures and instead direct the formation of low-dimensional zeotypes. Upon calcination, the two-dimensional layered aluminosilicate zeotype EMM-75P undergoes topotactic condensation to form a three-dimensional zeolite, EMM-75, with a previously unreported zeolite framework topology. Aluminosilicate EM-L01 is a 2D analogue of STF/SFF zeolite frameworks and partially condensed to an STF-topology upon calcination, whereas EM-L02, a 1D silicate composed of double 6-ring chains, packed analogous to the CHA zeolite framework, collapses during the thermal treatment. The detailed structural characterization of these three materials provides insights into the mechanism of topotactic condensation and demonstrates how such pathways can lead to new zeolite materials.

Cu-exchanged chabazite zeolites are used industrially as catalysts for abatement of NO_x pollution from diesel engines; however, catalyst activity is adversely impacted by exposure to high temperature steam. This occurs due to both dealumination of the zeolite framework and aggregation of Cu²⁺ cations into larger oxide agglomerates that are less active. Under oxidation-limited conditions in the presence of coadsorbed NH₃, hydrothermal aging of Cu-chabazite leads to a surprising increase in the rate of NO_x reduction per redox-active Cu cation at low temperatures (200 °C). A combination of electron microscopy, electron diffraction, NMR spectroscopy, and reaction kinetics analyses reveals that, although a portion of Cu species sinter into large agglomerates during aging, activity is maintained by the remaining Cu²⁺ cations that are stabilized by pairs of framework aluminum sites. These sites exhibit lower activation enthalpies for ammonia exchange dynamics, manifesting enhanced mobility of Cu²⁺ ions that persist as the extent of aging increases. The results yield insights into the complicated physicochemical processes and ramifications associated with deactivation of technologically important Cu-CHA zeolite catalysts, including the dynamics of adsorbed intermediates and the macroscopic reaction properties of the selective catalytic reduction of NO_x over active Cu species.

We report the one-pot synthesis of a chabazite (CHA)/erionite (ERI)-type zeolite intergrowth structure characterized by adjustable extents of intergrowth enrichment and Si/Al molar ratios. This method utilizes readily synthesizable 6-azaspiro[5.6]dodecan-6-ium as the exclusive organic structure-directing agent (OSDA) within a potassium-dominant environment. High-throughput simulations were used to accurately determine the templating energy and molecular shape, facilitating the selection of an optimally biselective OSDA from among thousands of prospective candidates. The coexistence of the crystal phases, forming a distinct structure comprising disk-like CHA regions bridged by ERI-rich pillars, was corroborated via rigorous powder X-ray diffraction and integrated differential-phase contrast scanning transmission electron microscopy (iDPC S/TEM) analyses. iDPC S/TEM imaging further revealed the presence of single offretite layers dispersed within the ERI phase. The ratio of crystal phases between CHA and ERI in this type of intergrowth could be varied systematically by changing both the OSDA/Si and K/Si ratios. Two intergrown zeolite samples with different Si/Al molar ratios were tested for the selective catalytic reduction (SCR) of NOx with NH3, showing competitive catalytic performance and hydrothermal stability compared to that of the industry-standard commercial NH3-SCR catalyst, Cu-SSZ-13, prevalent in automotive applications. Collectively, this work underscores the potential of our approach for the synthesis and optimization of adjustable intergrown zeolite structures, offering competitive alternatives for key industrial processes.

Structure determination of disordered zeolites is a challenging task and often requires a combination of several characterization techniques. Here, we report the structure elucidation of aluminosilicate zeolite, EMM-41, by electron crystallography. Despite the fact that EMM-41 possesses a highly disordered structure and is only several unit cells along the shortest crystal dimension, the structure was determined and found to possess a two-dimensional channel system built from two paired 10-ring channels interconnected by paired 12-ring channels. The material can be described as an intergrowth of two different polymorphs. Each of them consists of two distinct layers, one of which is related to the structure of zeolite Beta and contains disorders that alter the straight paired 10-ring channels to a zig-zag configuration,while the interconnected 12-ring channels remain unaffected. Furthermore, the structure of EMM-41 was found to be closely related to the highly disordered zeolite catalyst NU-88. These findings provide important insights to help resolve the longstanding question of the NU-88 structure.