Zeolite Beta Formation from Clear Sols: Silicate Speciation, Particle Formation and Crystallization Monitored by Complementary Analysis Methods.
The formation of silicate nanoaggregates (NAs) at the very early stages of precursor sols and zeolite beta crystallization from silicate nanoparticles (NPs) are investigated in detail using a combination of different analysis methods, including liquid-state29Si,27Al,14N, and1H NMR spectroscopy, mass spectrometry (MS), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy at cryogenic temperatures (cryo-TEM). Prior to hydrothermal 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 aggregation. These results are in agreement with general trends observed for other systems. Silicate NAs are essential intermediates for zeolite formation and are generated by the aggregation of hydrated oligomers, aluminate, and templating cations. Subsequent further intra-nanoaggregate silicate condensation results in the formation of NPs.1H and14N liquid NMR as well as diffusion ordered spectroscopy (DOSY) experiments provide evidence for weakly restricted rotational and translational mobility of the organic template within NAs as a consequence of specific silicate-template interactions. 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.
Department of Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany.
Maria
M
Castro
Institut Lavoisier de Versailles, University of Versailles, Versailles, France. mohamed.haouas@uvsq.fr.
Mohamed
http://orcid.org/0000-0002-2133-702X
M
Haouas
Department of Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany.
Ivy
I
Lim
Department of Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany.
Hans J
HJ
Bongard
Department of Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany.
Ferdi
F
Schüth
Institut Lavoisier de Versailles, University of Versailles, Versailles, France.|Center for Surface Chemistry and Catalysis, KU Leuven, Leuven, Belgium.
Francis
http://orcid.org/0000-0002-8263-4802
F
Taulelle
National Center for High Resolution Electron Microscopy, Lund University, Lund, Sweden.
Gunnel
G
Karlsson
Division of Physical Chemistry, KILU, Lund University, Lund, Sweden.
Viveka
http://orcid.org/0000-0002-9733-2735
V
Alfredsson
Center for Surface Chemistry and Catalysis, KU Leuven, Leuven, Belgium.
Eric
http://orcid.org/0000-0003-3499-0455
E
Breyneart
Center for Surface Chemistry and Catalysis, KU Leuven, Leuven, Belgium.
Christine E A
CE
Kirschhock
Department of Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany. schmidt@kofo.mpg.de.
Wolfgang
http://orcid.org/0000-0001-5166-1202
W
Schmidt
NMR spectroscopy; clear sols; crystal growth; mass spectrometry; nanoparticles; oligomers; small angle scattering; transmission electron microscopy; zeolites