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Unraveling Direct Formation of Hierarchical Zeolite Beta by Dynamic Light Scattering, Small Angle X‑ray Scattering, and Liquid and Solid-State NMR: Insights at the Supramolecular Level
journal contribution
posted on 2018-03-12, 00:00 authored by Maria Castro, Pit Losch, Woojin Park, Mohamed Haouas, Francis Taulelle, Claudia Loerbroks, Gert Brabants, Eric Breynaert, Christine E. A. Kirschhock, Ryong Ryoo, Wolfgang SchmidtA case
study on the understanding of the formation of hierarchical
Beta zeolites using gemini-type piperidine based multiammonium surfactant
(N6-diphe) is reported. Complementary techniques were used
to investigate N6-diphe’s structure-directing effect
at the molecular level. Combining characterization of the resulting
zeolite materials with the toolboxes herein developed for studying
clear solutions and dense gels discloses self-assembly processes that
govern the growth (and growth inhibition) of nano-Beta zeolite crystals.
In clear solution, small-angle X-ray scattering and liquid-state NMR
provide insights about the formation of nanoparticles and their degree
of order. 14N and 1H-DOSY NMR probe the dynamics
and mobility of soluble species. In a dense gel, on the other side, 27Al- and 29Si-(MAS) NMR elucidate the varying local
connectivity between initial nano-objects and the final solid products.
It has been found that cylindrical micelles control the transformation
of solubilized silica and alumina during the formation of zeolite
nuclei and guide their crystal growth to nano-Beta rods with bimodal
mesoporosity. The predominant smaller mesopores (6 to 8 nm) originate
from the template’s hydrophobic alkyl chains, while larger
mesopores (10 to 30 nm) are supposed to result from a spinodal decomposition-type
segregation of phases consisting of as-formed hydrophobic zeolite
rods and an aqueous solution.