Synthesis and real structure of RUB-11, a novel high-density silica zeolite based on magadiite layers

Isabel Grosskreuz; Yaşar Krysiak; Hermann Gies; Enrico Mugnaioli; Bernd Marler

doi:10.1039/D3NJ03424K

Synthesis and real structure of RUB-11, a novel high-density silica zeolite based on magadiite layers†

Isabel Grosskreuz,

^a Yaşar Krysiak,

^bc Hermann Gies,

^a Enrico Mugnaioli^d and Bernd Marler*^a

Author affiliations

* Corresponding authors

^a Institute of Geology, Mineralogy and Geophysics, University of Bochum, Universitaetsstrasse 150, D-44801 Bochum, Germany
E-mail: bernd.marler@rub.de
Fax: +49 0234 32 14433
Tel: +49 2332 665580

^b Department of Structure Analysis, Institute of Physics, Czech Academy of Sciences, Cukrovarnická 10/112, CZ-17000 Prague, Czech Republic

^c Institute of Anorganic Chemistry (ACI), Leibniz University Hannover (LUH), Callinstraße 9, Building 2501, Room 189, D-30167 Hannover, Germany

^d Instituto Italiano di Tecnologia, Center for Nanotechnology Innovation, NEST, Piazza San Silvestro 12, I-56127 Pisa, Italy

Abstract

The discovery of new zeolite framework types plays an important role in producing new porous materials for applications such as adsorption, catalysis, separation, etc. RUB-11, a new all-silica zeolite with high density (2.11 g cm⁻³), was synthesised at 160 °C from reaction mixtures consisting of SiO₂/ethylenediamine/H₂O in a xenon atmosphere of 30 bar for a long reaction time (140 d). Physico-chemical characterisation using solid-state NMR spectroscopy, SEM, TG-DSC and ATR-FTIR spectroscopy confirmed that RUB-11 is a framework silicate. The atomic structure was solved by 3D electron diffraction using the fast-automated diffraction tomography method. The structure model of monoclinic symmetry with lattice parameters of a₀ = 7.3929(5) Å, b₀ = 7.3942(3) Å, c₀ = 26.1786(13) Å and β = 98.372(7)° (space group: Pc) was refined against electron diffraction data (dynamical refinement) and powder diffraction data. An additional distance-least-squares refinement confirmed the feasibility of forming a stress-free silica framework of RUB-11 topology. The chemical composition of RUB-11 per unit cell is 30 SiO₂. The framework silicate RUB-11 is structurally closely related to layer silicate magadiite and can be regarded as an interlayer expanded zeolite (IEZ) based on magadiite-type layers. Both materials contain topologically identical, dense layers, named [m with combining low line] [a with combining low line] [g with combining low line] layers. In the case of RUB-11, these layers are interconnected via additional silicon atoms leading to a complete framework with a 2-dimensional pore system consisting of intersecting 8-ring channels. The synthesis route leading to RUB-11 is in contrast to typical IEZs, which are obtained in a two-step process. According to the electron diffraction data and the XRD powder patterns, RUB-11 has a disordered structure. A detailed analysis revealed that two different types of disorder concerning the stacking of layer-like building units (consisting of [m with combining low line] [a with combining low line] [g with combining low line] layers plus interconnecting silicon atoms) contribute to the real structure of RUB-11. It is surprising that the channel-like pores of RUB-11 are completely empty when separated from the reaction mixture.