Directional Transport\nin Hierarchically Aligned ZSM‑5\nZeolites with High Catalytic Activity

Zeolites, the most technically important crystalline\nmicroporous\nmaterials, are indispensable cornerstones of chemical engineering\nbecause of their remarkable catalytic properties and adsorption capabilities.\nNumerous studies have demonstrated that the hierarchical engineering\nof zeolites can maximize accessible active sites and improve mass\ntransport, which significantly decreases the internal diffusion limits\nto achieve the desired performance. However, the construction of hierarchical\nzeolites with ordered alignments and size-controlled substructures\nin a convenient way is highly challenging. Herein, we develop a facile\nprocedure using two common structure-directing agents, tetrapropylammonium\nhydroxide (TPAOH) and tetraethylammonium hydroxide (TEAOH), to synthesize\nhierarchically aligned ZSM-5 (Hie-ZSM-5) crystals with <i>a</i>-axis alignment substructures of controllable size. The control of\nthe substructure size (α) in the range of 10–60 nm and\nthe corresponding similarity (<i>r</i> = α/β,\nwhere β is the size of Hie-ZSM-5) ranging from 0.004 to 0.033\ncan be tuned by varying the Si/Al ratios (40–120). A systematic\ninvestigation of the overall crystallization process, using time-dependent\nXRD, SEM, TEM, and solid-state magic-angle spinning NMR (<sup>13</sup>C, <sup>27</sup>Al, <sup>29</sup>Si) methods, enable us to construct\na solid mechanism for the generation of Hie-ZSM-5. Most importantly,\ndirectional transport in the unique structures of Hie-ZSM-5 efficiently\nenhances mass diffusion, as well as catalytic activity and stability.\nThese findings improve our understanding of the zeolite crystallization\nprocess and inspire novel methods for the rational design of hierarchical\nzeolites.