Facile and selective synthesis of zeolites L and W from a single-source heptanuclear aluminosilicate precursor

Abstract

Zeolites are usually synthesized by hydrothermal reactions using monomeric or polymeric Al- and Si-containing precursors, whereas simple and direct routes for the rational synthesis of zeolites remain elusive. In this...

Does Water Enable Porosity in Aluminosilicate Zeolites? Porous Frameworks versus Dense Minerals

“…Megakalsilite was first discovered in 2002, and only very few reports describe its synthesis. Recently, it was also obtained using a very specific aluminosilicate source, a single molecular precursor (PyH)­[Al­{Ph 2 Si­(OSiPh 2 O) 2 } 2 ] (PyH = pyridinium cation) . Megakalsilite and related potassium feldspars are precursor phases for leucite production, which find applications in ceramics and porcelain-fused-to-metal systems …”

“…32 With increasing water content, the K + signal narrows from 170 to 30 Hz and shifts downfield from 3.7 to 0.0 ppm. Increasing the availability of water increases the average coordination number of oxygen atoms from water, thus modifying the cation environment, as indicated by the change in 39 K chemical shift toward a more shielded environment. The associated weakening of the ionpairing strength simultaneously can be expected to enhance the kinetics of chemical exchange between potassium in different local environments, similar to what has been reported in literature for Na.…”

“…Recently, it was also obtained using a very specific aluminosilicate source, a single molecular precursor (PyH)[Al{Ph 2 Si(OSiPh 2 O) 2 } 2 ] (PyH = pyridinium cation). 39 Megakalsilite and related potassium feldspars are precursor phases for leucite production, which find applications in ceramics and porcelain-fused-to-metal systems. 40 Zeolite W, the zeolite product obtained when increasing the water content in the same K-HSIL based synthesis 37,41 exhibits the MER topology, which bears no structural relationship to megakalsilite.…”

“…By using a Si-background-free probe in combination with 10 mm quartz tubes, the short repetition delays enabled to saturate the background signal resulting from quartz. Direct excitation 27 Al NMR spectra were obtained by accumulating 1024 transients using a π/12 excitation pulse of 1.9 μs, an acquisition time of 0.4 s and a recycle delay of 0.1 s. 39 K NMR spectra were recorded on a Bruker Avance 400 spectrometer operating at 18.672 MHz, with a pulse of 9.1 μs (π/8), a recycle delay of 0.1 s, an acquisition time of 0.5 s, and an accumulation of 1024 scans. Spectra were referenced to tetramethylsilane (TMS) for 29 Si, 1 M Al(NO 3 ) 3 in water for 27 Al, and 2 M KCl in water for 39 K.…”

Synthesis of Microporous Aluminosilicate by Direct Thermal Activation of Phenyl-Substituted Single-Source Aluminosilicate Molecular Precursors

“…MPs with Si–CR-type leaving groups have been considered as a potential alternative to those with Si–OR-type leaving groups for the construction of aluminosilicates. Si–C bonds are easy to handle and can be activated, − they are thermally more active than Si–O bonds, and numerous compounds with Si–C bonds have already been reported. , Among the MPs with Si–CR-type leaving groups, we focused on those with Si–Ph bonds, for which a variety of secondary building unit (SBU)-like MPs have been reported. − We have previously demonstrated that a molecule that consists of a tetrahedral Al and six Si atoms with a spiro-7 core supported by 12 Si–Ph bonds, (PyH + )­[Al­{Ph 2 Si­(OSiPh 2 O) 2 } 2 ] − ( PyH + [AlSi 6 ] − ; PyH + = pyridinium cation; Figure ), can be transformed into two zeolites (zeolites L and W) in the presence of KOH under hydrothermal conditions accompanied by base-assisted Si–Ph bond activation . It should be emphasized here that the use of PyH + [AlSi 6 ] − has advantages over synthetic routes that use conventional separate precursors in terms of reproducibility, selectivity, and crystallinity of the two zeolites. − On the other hand, the studies also demonstrated that the resulting zeolites L and W possess Si/Al ratios of 1.0–1.2, which are lower than that of PyH + [AlSi 6 ] − ( i .…”