© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 wileyonlinelibrary.com COMMUNICATION Micro/Macroporous System: MFI-Type Zeolite Crystals with Embedded Macropores Albert G. Machoke, Ana M. Beltrán, Alexandra Inayat, Benjamin Winter, Tobias Weissenberger, Nadine Kruse, Robert Güttel, Erdmann Spiecker, and Wilhelm Schwieger* A. G. Machoke, Dr. A. Inayat, T. Weissenberger, Prof. W. Schwieger Friedrich-Alexander-Universität Erlangen-Nürnberg Department of Chemical and Bioengineering Institute of Chemical Reaction Engineering Egerlandstraße 3, 91058 Erlangen, Germany E-mail: wilhelm.schwieger@crt.cbi.uni-erlangen.de Dr. A. M. Beltrán, B. Winter, Prof. E. Spiecker Friedrich-Alexander-Universität Erlangen-Nürnberg Department of Materials Science and Engineering Center for Nanoanalysis and Electron Microscopy (CENEM) Cauerstraße 6, 91058 Erlangen, Germany N. Kruse, Prof. R. Güttel Clausthal University of Technology Institute of Chemical Process Engineering Leibnizstr. 17, 38678 Clausthal-Zellerfeld, Germany DOI: 10.1002/adma.201404493 macropores as reported in the literature. [3] Furthermore, zeolite nanocrystals have poor thermal as well as hydrothermal sta- bility and are difficult to recover from the synthesis mixture, which is not the case for macroporous crystals with diameters in the micrometer range. Despite of this, the development and utilization of micropo- rous zeolite crystals with embedded macropores is still a chal- lenge due to the lack of simple methods to introduce macropores into zeolite crystals directly. Currently, macropores are being introduced in zeolites through sphere templating, [4] postsyn- thetic modifications, [4] and templating with macroporous sup- ports. [5] Among these techniques, the use of hard templates like latex spheres or silica spheres has been widely adopted to form different macroporous zeolitic structures like 3D-ordered zeolitic macroporous structures [6] or hollow zeolite capsules. [7] However, the hard templating technique is still limited by the low wettability of the hard templates with zeolite precursors, [7] poor thermal stability of the template under zeolite synthesis conditions, [6] difficulties in controlling the thickness of the zeolitic walls, [6] and the template removal after hydrothermal synthesis. [8] The strategies adopted to overcome such limitations have resulted into multistep procedures that require the use of surface modification techniques and pseudosolid-state transfor- mation procedures to improve the wettability of these templates with the precursor solution and to prevent melting of the tem- plate during the hydrothermal transformation, [6] respectively. In addition, huge amounts of template for the formation of the zeolite network (template/SiO 2 molar ratios above 0.35) [6,7,9] have been used to control the thickness of zeolitic walls, and harsh conditions have been employed to remove the hard tem- plate after the synthesis. [8] These drawbacks are still retarding the development of macroporous zeolites. Another strategy to prepare zeolite assemblies with additional macropores without utilizing any external template is the use of mesoporous silica particles (MSPs) both as a silica source as well as a sacrificial template for macropore formation. [2] However, currently avail- able methods [10–12] involve the coating of these MSPs with zeo- lite seeds via a layer-by-layer deposition procedure [12] and result into hollow zeolite capsules [10] or 3D structures with isolated macropores or they additionally need an extra silica source to form a polycrystalline zeolitic phase, which surrounds the inter- connected macropores. [11] The preparation and coating of zeo- lite seeds on MSPs make this procedure laborious. Thus, no procedure is available to prepare zeolite crystals with a nearly classical morphology and an intracrystalline macropore system that is embedded in the zeolitic matrix. To overcome the limitations of existing macroporous zeolite assemblies, crystals of MFI-type zeolites with a Hierarchically organized systems are commonly encountered in our natural environment. [1] Such hierarchical systems are related mostly to structural properties (e.g., stem of trees, bones) or fluid dynamic properties (e.g., in the lung or the blood circle). [1] The ability of these systems to maximize the efficiency of trans- port processes has always been an inspiration for their imple- mentation in different artificial systems reaching from watering systems up to catalytic reactors. Zeolite crystals can be regarded as an assembly of miniaturized catalytic reactors with their micropores providing large specific surface area, a defined envi- ronment of active sites as well as shape selectivity at each single pore entrance. [2] Thus, zeolites belong to the most important cat- alytic materials used today. However, their utilization in catalysis is limited due to the slow transport of the reacting species within the micropores. In order to minimize these transport limita- tions, it is highly desirable to reduce the diffusion path lengths. The preparation of either nanozeolites or zeolitic systems with intracrystalline meso- or macropores belongs to the versatile strategies adopted so far to reach the aforementioned goal. [2] Mesoporous zeolites have been prepared using different strategies and the positive effect of such additional mesopores on the rate of diffusion has already been demonstrated for different reactions. [2] In contrast to mesoporous zeolites, macroporous zeolitic systems should diminish transport limi- tations even more and are expected to have better resistance to coke formation and thus, could drastically extend the cata- lyst lifetime. [2] In terms of diffusion, the benefits of combining macroporosity with zeolite microporosity may resemble to some extent to those of nanozeolite assemblies. However, it is worth mentioning that the reduction of zeolite crystal dimen- sions mostly results in intercrystalline mesopores rather than Adv. Mater. 2014, DOI: 10.1002/adma.201404493 www.advmat.de www.MaterialsViews.com