Visualization of hierarchically structured zeolite bodies from macro to nano length scales Sharon Mitchell 1† , Nina-Luisa Michels 1† , Karsten Kunze 2 and Javier Pe ´rez-Ramı ´rez 1 * A major challenge in the implementation of laboratory-designed catalysts is the scale-up into technically relevant forms. Advanced characterization is essential to understand and optimize catalyst assembly and function in industrial reactors. This Article presents an integrated approach to visualizing millimetre-sized extrudates and granules of a hierarchical MFI- type zeolite, displaying trimodal networks of micropores (0.56 nm), intracrystalline mesopores (∼10 nm) and macropores (∼200–300 nm). As exemplified for the conversion of methanol to olefins, the hierarchical zeolite yields a superior performance compared to its conventional analogue. The combination of dedicated specimen preparation with state-of-the- art optical, X-ray and electron-based microscopic and tomographic techniques proves a powerful methodology to reveal otherwise inaccessible information regarding structural organization over the whole range of length scales. It is expected that these tools will play a crucial role in the rationalization of scale-up principles in catalyst development. P rocesses that incorporate porous solids, often as catalysts or sorbents, are typified by their multidimensionality (Fig. 1). Bridging these length scales is the main challenge for technol- ogy development 1 . Materials’ properties can be optimized and diver- sified by controlling the nanostructure 2–5 . However, to profit from the resulting scientific advancements, they have to be put into a practical context. A critical task is the scale-up of laboratory leads into technical materials, which involves the translation of prepara- tive routes from gram-to-tonne scale, with the derived powders then formed with the aid of binders and other additives into mechanically stable macroscopic bodies 6,7 . Advanced characterization methods for the study of porous solids in technical forms, in particular for their integrated visualiza- tion, are essential for understanding the assembly of such solids in large-scale manufacture and subsequent function in industrial reac- tors. Such insight will obviously increase the odds of successfully implementing improved technologies. Predominantly left to the realm of industry, fundamental knowledge is scarce regarding the scale-up and, correspondingly, the characterization of shaped bodies. Two major challenges are linking findings at different length scales (Fig. 1) and accounting for the co-existence of several interacting component species, such as the active phase and binder. A variety of techniques, including Raman, UV–vis–NIR and infrared microspectroscopies, magnetic resonance imaging, and X- ray absorption and diffraction microtomography (micro-CT) have been applied by de Jong, Weckhuysen and colleagues to investigate the evolution of metal species during the preparation and reaction of impregnated Al 2 O 3 extrudates 8–12 . However, visualization was limited to micrometre resolutions in most cases, rendering these techniques powerless to access nanostructural details of the external and internal architecture, which are of crucial importance for the design of porous materials. Moreover, the imaging techniques were often used on an individual basis. Solving the complex struc- ture of a technical porous material from macro- to nanoscale requires full integration of state-of-the-art methods, a challenge that to date remains unfulfilled. Hierarchically structured zeolites are currently attracting sub- stantial attention on a laboratory scale because of their huge techno- logical potential in catalytic, adsorption and ion-exchange processes 13 . This class of crystalline aluminosilicates, which inte- grate networks of interconnected micro-, meso- and macropores, was developed in response to the inefficient utilization of conven- tional (purely microporous) zeolites in transport-based applications due to the constrained access and diffusion of bulky molecules 13–17 . The large-scale preparation of mesoporous ZSM-5 zeolites has recently been achieved by alkaline treatment of commercial specimens 18 . With a view to industrial implementation, the powders obtained have been subsequently shaped with conventional binders (for example, natural clays such as attapulgite or kaolin) into millimetre-sized granules and extrudates. To refine scale-up principles, it is vital to establish the arrange- ment and interaction of individual constituents within macroscopic bodies, as well as the location and interconnectivity of the associated pore network. Although valuable, standard techniques for porosity assessment (gas adsorption and mercury intrusion porosimetry 19 ) provide insufficient insight to correlate the textural properties of complex systems with their structural origins and can fail to account for inaccessible pores 20 . The present study focuses on unra- velling the complex organization of hierarchically structured ZSM-5 zeolites in a technical form. For this purpose, optical, X-ray and electron microscopic and tomographic techniques have been appro- priately integrated to tackle a complex material with high potential to revolutionize zeolite catalysis. We stress that, although it has been used prevalently for the characterization of hierarchical zeolites, transmission electron microscopic (TEM) methods have so far only been applied to pure zeolite powders 21,22 , which are not fully illustrative of their technical counterparts. Here, a concerted effort is made to ensure that our representative visualization specifically focuses on non-invasive imaging modes and dedicated preparation methods to minimize alteration of the sampled volume. For the first time, we also demonstrate the outstanding performance of the scaled-up hierarchical ZSM-5 bodies in the conversion of methanol to light olefins. 1 Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zu ¨rich, Wolfgang-Pauli-Strasse 10, CH-8093 Zu ¨rich, Switzerland, 2 Electron Microscopy Center, ETH Zu ¨rich, Wolfgang-Pauli-Strasse 16, CH-8093 Zu ¨rich, Switzerland, † These authors contributed equally to this work. *e-mail: jpr@chem.ethz.ch ARTICLES PUBLISHED ONLINE: 19 AUGUST 2012 | DOI: 10.1038/NCHEM.1403 NATURE CHEMISTRY | ADVANCE ONLINE PUBLICATION | www.nature.com/naturechemistry 1 © 201 2 M acmillan Publishers Limited. All rights reserved.