DOI: 10.1002/chem.201200544 Nanofusion: Mesoporous Zeolites Made Easy Karin Mçller,* [a] Bilge Yilmaz, [b] Ulrich Müller, [b] and Thomas Bein* [a] Zeolites are crystalline microporous materials with tuna- ble pore dimensions and topologies that present an enor- mous diversity of structures and well-defined nanoscale re- actors. [1, 2] Despite their industrial success, one remaining great challenge is to overcome the transport limitations for many molecules associated with the narrow pore sizes of zeolites. Significant efforts are therefore being undertaken to enrich the catalytically active zeolites with mesopores in- tended to enhance mass transport. [3] Such hierarchically structured zeolitic materials can be more effective in catalyt- ic reactions than conventional zeolites. [4] However, the strat- egies for implementing mesopores often involve complex multistep or multitemplated processes that might compro- mise industrial implementation. Mesopores can exist as intrazeolite pores in zeolite crys- tals or as interzeolite voids in nanozeolite aggregates, re- spectively. [5, 6] Intrazeolite mesopores can be prepared through controlled leaching procedures [7] or by application of various secondary templates, such as hard scaffolds, [8] or- ganosilane additives, [9] or bifunctional surfactants. [10] Anoth- er strategy is to co-assemble zeolitic precursor units [11] or nanozeolites [12] with surfactants, effectively combining the properties of a mesopore architecture with the benefits of nanozeolites. Nanozeolite building blocks for mesoporous zeolite mate- rials are ideal candidates to address the above-mentioned mass-transport issues based on their large surface area and small internal diffusion pathways. Additionally, they can form mesopores when compacted to powders. [13] For exam- ple, compacted beta nanozeolites obtained from colloidal solutions by centrifugation were shown to provide higher catalytic conversion than larger zeolite beta crystals. [14] How- ever, nanozeolites are often obtained at low yields and their isolation is difficult and costly. [15c] Direct aggregation of nanozeolites through additional pre- treatments or cationic polymers has also been reported. [5–6, 16] Alternatively, we have recently shown that in situ nanoparti- cle assembly is possible through steam-assisted conversion (SAC). [17] This SAC process provides excellent mesoporosity, although it is not easily scaled up. To take the potential of hierarchical zeolite materials from academic research to industrial applications, simple and efficient protocols are required. Herein, we present a single-step approach based on conventional hydrothermal conversion that does not require any additional gel manipu- lations or secondary templates and results in an unprece- dented high space–time yield (STY) of mesoporous zeolite beta. Our “nanofusion” strategy is based on the formation of nanozeolite beta particles of 20–40 nm diameter that are instantly fused into stable zeolite aggregates, which can be easily isolated by filtration. Moreover, nanofusion offers a simple means to tune the size of the interstitial mesopores. Typically, nanozeolite beta is synthesized from clear solu- tions with a SiO 2 /H 2 O molar ratio between 1:12–16 or higher resulting in low-yield colloidal solutions. [15a, 18] In con- trast, our samples were prepared by using a highly concen- trated precursor solution of 1 SiO 2 :0.023 Al 2 O 3 : 0.049 NaOH:0.42 tetraethylammonium hydroxide (TEAOH): 6.8 H 2 O that is completely converted after 72 h at 150 8C into a translucent gel of nanosized beta particles. Important- ly, the converted gel consists of individual nanoparticles: when it is dispersed in water, a colloidal solution results. After threefold washing by centrifugation, the solution showed a small average particle size of 78 nm (with dynamic light scattering (DLS), number weighted; sample CBNa15- 72; see the Experimental Section and the Supporting Infor- mation for sample naming) and an extremely high isolated yield of about 80 %. In contrast, when applying the nanofusion process, we do not isolate the nanozeolites, but immediately dry the viscous gel to obtain a coarse powder of compacted particles. Con- ventional calcination directly converts the dry powder into a self-sustaining hierarchical material (sample FBNa15-72, Scheme 1). This way, the nanoparticles are fused into robust and easily handled aggregates that can sustain long-term stirring in water or sonication in a 500 W ultrasonic bath. We propose that the fusion/condensation of the nanozeolites is enabled by the dissolved aluminosilicate species still pres- ent in the gel. Therefore, losses of material occurred only due to handling, such that the yield approaches 100 %. Both materials, the compacted powder consisting of isolated nanozeolites and the fused zeolite beta sample show high surface areas, micropore volumes, and, importantly, large [a] Dr. K. Mçller, Prof. Dr. T. Bein Department of Chemistry and Center for NanoScience (CeNS) University of Munich (LMU), Butenandtstrasse 11 (E), 81377 Munich (Germany) Fax: (+ 49) 89-218077622 E-mail : bein@lmu.de [b] Dr. B. Yilmaz, Dr. U. Müller Chemicals Research & Engineering, BASF SE 67056 Ludwigshafen (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201200544. Chem. Eur. J. 2012, 18, 7671 – 7674 # 2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 7671 COMMUNICATION