& Zeolite Formation Zeolite Beta Formation from Clear Sols: Silicate Speciation, Particle Formation and Crystallization Monitored by Complementary Analysis Methods Maria Castro, [a] Mohamed Haouas,* [b] Ivy Lim, [a] Hans J. Bongard, [a] Ferdi Schüth, [a] Francis Taulelle, [b, c] Gunnel Karlsson, [d] Viveka Alfredsson, [e] Eric Breyneart, [f] Christine E. A. Kirschhock, [f] and Wolfgang Schmidt* [a] Abstract: The formation of silicate nanoaggregates (NAs) at the very early stages of precursor sols and zeolite beta crys- tallization from silicate nanoparticles (NPs) are investigated in detail using a combination of different analysis methods, including liquid-state 29 Si, 27 Al, 14 N, and 1 H NMR spectrosco- py, mass spectrometry (MS), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron mi- croscopy at cryogenic temperatures (cryo-TEM). Prior to hy- drothermal treatment, silicate NAs are observed if the Si/OH ratio in the reaction mixture is greater than 1. Condensation of oligomers within the NAs then generates NPs. Aluminum doped into the synthesis mixtures is located exclusively in the NPs, and is found exclusively in a state that is fourfold connected to silicate, favoring their condensation and aggre- gation. These results are in agreement with general trends observed for other systems. Silicate NAs are essential inter- mediates for zeolite formation and are generated by the ag- gregation of hydrated oligomers, aluminate, and templating cations. Subsequent further intra-nanoaggregate silicate condensation results in the formation of NPs. 1 H and 14 N liquid NMR as well as diffusion ordered spectroscopy (DOSY) experiments provide evidence for weakly restricted rotation- al and translational mobility of the organic template within NAs as a consequence of specific silicate–template interac- tions. NAs thus appear as key species in clear sols, and their presence in the precursor sol favors silicate condensation and further crystallization, promoted either by increasing the Si/OH ratio or by heating. Introduction Zeolites are crystalline aluminosilicates with structures contain- ing periodic networks of cavities and/or channels. The surface chemistry within the pores depends mainly on the Si/Al ratio and on the number and nature of exchangeable cations. Classi- cal zeolite synthesis entails hydrothermal treatment of reactive gels containing aluminosilicate precursors, a mineralizer, and cations acting as structure directors. In some cases, these struc- ture-directing agents (SDAs) consist exclusively of organic mol- ecules. [1] Although zeolite discovery is commonly achieved, [2] the rational design of new zeolites with tailored structural and chemical properties is still rare, and requires a molecular-level understanding of zeolite formation processes. [3] Despite the effort invested, the early stages of crystallization, which may affect significantly the structure and topology, chemical com- position, crystal sizes, and morphologies of phases formed, remain elusive. This results in part from the limited probing range of analytical methods, mostly providing either short- range or long-range information. The processes taking place in the early stages of particle formation, such as nucleation and initial crystallization, proceed on intermediate length scales that are difficult to characterize with a single technique. Conse- quently, the development of a toolbox suitable for studying nucleation processes is still a topic of substantial academic in- [a] Dr. M. Castro, Dr. I. Lim, H.J. Bongard, Prof. F. Schüth, Dr. W. Schmidt Department of Heterogeneous Catalysis Max-Planck-Institut für Kohlenforschung Mülheim an der Ruhr (Germany) E-mail : schmidt@kofo.mpg.de [b] Dr. M. Haouas, Prof. F. Taulelle Institut Lavoisier de Versailles University of Versailles Versailles (France) E-mail : mohamed.haouas@uvsq.fr [c] Prof. F. Taulelle Center for Surface Chemistry and Catalysis KU Leuven Leuven (Belgium) [d] G. Karlsson National Center for High Resolution Electron Microscopy Lund University Lund (Sweden) [e] Prof. V. Alfredsson Division of Physical Chemistry, KILU Lund University Lund (Sweden) [f] Dr. E. Breyneart, Prof. C. E. A. Kirschhock Center for Surface Chemistry and Catalysis KU Leuven Leuven (Belgium) Supporting information and ORCID identification numbers for the authors of this article can be found under http://dx.doi.org/10.1002/ chem.201600511. Chem. Eur. J. 2016, 22, 1 – 14  2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 && These are not the final page numbers! ÞÞ Full Paper DOI: 10.1002/chem.201600511