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

Maria Castro (1) , Pit Losch (2, 1) , Woojin Park , Mohamed Haouas (3) , Francis Taulelle (3) , Claudia Loerbroks (1) , Gert Brabants (4) , Eric Breynaert (4) , Christine Kirschhock (4) , Ryong Ryoo , Wolfgang Schmidt (1)

1 Max-Planck-Institut für Kohlenforschung (Coal Research)
2 LMSPC - Laboratoire des Matériaux, Surfaces et Procédés pour la Catalyse
3 ILV - Institut Lavoisier de Versailles
4 KU Leuven - Catholic University of Leuven = Katholieke Universiteit Leuven

A case study on the understanding of the formation of hierarchical Beta zeolites using gemini-type piperidine based multi-ammonium surfactant (N 6-diphe) is reported. Complementary techniques were used to investigate N 6-diphe's structure directing effect at the molecular level. The herein developed toolbox applicable to clear solutions and dense gels, combined with a characterization of the resulting zeolite materials disclosed a series of self-assembly processes that govern the growth (and growth inhibition) of nano-Beta zeolite crystals, which assemble in micron-sized aggregates. In clear solution, small angle X-ray scattering and liquid state NMR provide insights about the formation of nanoparticles and their degree of order. 14 N and 1 H-DOSY NMR probe the dynamics and mobility of soluble species. In a dense gel, on the other side, 27 Al-and 29 Si-(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 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.

Mots clés: Nano-Beta; self-assembly mechanism; spinodal decomposition

Domaines: Matériaux

Maria Castro, Pit Losch, Woojin Park, Mohamed Haouas, Francis Taulelle, et al.. 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. Chemistry of Materials, 2018, 30 (8), pp.2676-2686. ⟨10.1021/acs.chemmater.8b00109⟩. ⟨hal-02335593⟩