Hierarchically Structured Zeolite Bodies: Assembling Micro-, Meso-, and Macroporosity Levels in Complex Materials with Enhanced Properties

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Abstract

Engineering levels of porosity in hierarchical zeolites is a vibrant area of research with remarkable application potential. To gain practical relevance, the superior properties observed for the as-synthesized powders have to be preserved when they are shaped into suitable technical geometries. Herein, mechanically stable millimeter-sized bodies are prepared by granulation of mesoporous ZSM-5 zeolite powders using an attapulgite clay binder. Alkaline treatment of conventional zeolite granules is demonstrated to be unsuitable for this purpose. Multiple techniques are applied to characterize mesoporous zeolite granules with respect to their conventional zeolite counterparts, thus establishing the impact of binder inclusion and granulation on their respective properties. The intrinsic structure and acidity of the zeolite are retained post-structuring. Gas adsorption and mercury porosimetry confirm the presence of interconnected micro-, meso-, and macropores. A wide range of imaging techniques permits visualization of the particle properties, phase distribution, and consequent origins of the distinct levels of porosity within the zeolite granules. The superior adsorption properties of the hierarchical ZSM-5 zeolite granules are demonstrated using cyclohexane, toluene, and isopropyl alcohol as probe molecules.

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