Although the search for new zeolites has traditionally been based on trial and error, more rational methods are now available. The theoretical concept of inverse σ transformation of a zeolite framework to generate a new structure by removal of a layer of framework atoms and contraction has for the first time been achieved experimentally. The reactivity of framework germanium atoms in strong mineral acid was exploited to selectively remove germanium-containing four-ring units from an UTL type germanosilicate zeolite. Annealing of the leached framework through calcination led to the new all-silica COK-14 zeolite with intersecting 12- and 10-membered ring channel systems. An intermediate stage of this inverse σ transformation with dislodged germanate four-rings still residing in the pores could be demonstrated. Inverse σ transformation involving elimination of germanium-containing structural units opens perspectives for the synthesis of many more zeolites.

SSCI-VIDE+ING+NKS:ATUInternational audienceGe-rich ITQ-13 and ITQ-22 zeolites were degermanated by acid leaching of as-made still containing organic template and calcined forms. These two zeolites could be almost completely degermanated without modifying the framework structure. This behavior is different from IM-12 zeolite, which undergoes framework transformation from UTL to OKO type upon degermanation. All three zeolite types contain double four-ring (D4R) units populated by germanium atoms. The UTL to OKO transformation involves the elimination of Germanate 4 rings (Ge 4R) from double four-ring (D4R) units connecting the layers. The differences of Si and Ge atom siting in D4R units in the three zeolites were probed using F-19 MAS NMR after post synthetic incorporation of fluoride and H-1-Si-29 CP/MAS NMR. In IM-12, NMR suggests that Ge atoms are all located in one of the faces of D4R units and form 4Rs that connect Si-rich layers together. In the degermanation process, the 4 Ge atoms of the Ge 4Rs are dislodged simultaneously, in excellent agreement with earlier EXAFS data. In ITQ-13 and ITQ-22 zeolites, Ge distributions are more complex, leading a progressive degermanation of the framework and to the presence of Si-O-Si bridges that prevents the structure from collapsing upon Ge extraction. Data suggest that IM-12 is unique in the family of Ge-containing zeolites

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The hydrothermal crystallizations of two zeolite topologies (FAU and LTA) have been studied by simultaneous UV-Raman spectroscopy and X-ray diffraction in a home built setup. A wide angle X-ray diffractometer has been redesigned and combined with Raman components. The results revealed, despite similar structures of the starting gels, different aluminosilicate species evolved in the two systems, prior to emerging Bragg scattering. Based on this the sodalite cage could be ruled out as a common building unit for both frameworks.

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Tetrahedral framework aluminium was introduced in all-silica zeolite -COK-14 using Atomic Layer Deposition (ALD) involving alternating exposure to trimethylaluminium and water vapour. The modification causes permanent conversion of the originally interrupted framework of -COK-14 to a fully connected OKO type framework, and generates catalytic activity in the acid catalysed hydrocarbon conversion reaction.

All silica COK-14/-COK-14 with OKO topology is the first case of a zeolite which reversibly transforms from a systematically interrupted to a fully connected state and back. Analysis of the opening/closing behavior allowed the study of entropy and framework flexibility as determinants for the stability of zeolite topologies, which, until now, has been experimentally inaccessible. Interconversion of the all-silica COK-14 zeolite with fully connected OKO topology and its -COK-14 variant with systematic framework interruption was investigated using high-temperature XRD, thermogravimetric analysis, ²⁹ Si MAS NMR, nitrogen adsorption and a range of modelling techniques. Specific framework bonds in the OKO framework can be reversibly hydrolyzed and condensed. Structural silanols of the parent -COK-14, prepared by degermanation of the IM-12 zeolite, were condensed by heating at 923 K, and hydrolyzed again to the initial state by contacting the zeolite with warm water. Molecular modelling revealed an inversion of the relative stabilities for both variants depending on temperature and hydration. Condensation of the structural silanols in -COK-14 to COK-14 is entropy driven, mainly resulting from the release of water molecules. Framework reopening in the presence of water is spontaneous due to the high rigidity of the fully connected OKO framework. Isomorphous substitution was demonstrated as a viable option for stabilization of the fully connected OKO framework as this renders the closed framework flexible

EU-7 zeolite with Si/Al ratio of 15 is identified as a BIK type zeolite. The framework charge is compensated with Cs+ cations located in 8-ring channels at regular distances. Even partially exchanged, Cu-loaded EU-7 is active in NH3-SCR and withstands hydrothermal aging at 900 °C needed for application in diesel particulate filters.