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

The extra-large-pore germanosilicates with UTL topology have been synthesized using a large variety of spiroazocompounds as structure-directing agents. Synthesis conditions were optimized and zeolites with a high crystallinity degree were obtained with 13 different organic structure-directing agents. The influence of the composition of the reaction mixture and template nature (structure, hydrophilicity/hydrophobicity balance, rigidity, pK a) on the phase selectivity, crystallinity degree, and adsorption properties of zeolites with UTL structure was investigated. Selection criteria of organic molecules as potential structure-directing agents (SDAs) in the synthesis of large-pore and extra-large-pore zeolites from silicate and germanosilicate media are proposed. The optimum synthesis time was determined to be 4−9 days for different SDA and (Si + Ge)/SDA molar ratios. Clear synergism between the optimum structure of organic template and the presence of critical amount of inorganic component (GeO2) was evidenced. The UTL zeolite crystallizes as tiny sheets ∼10 μm thick. The effect of the organic template on the size and shape of the crystals was found. The micropore volume of the best crystals is 0.22−0.24 cm3/g, with a micropore diameter of 1.05 nm, based on density functional theory (DFT), and Saito−Foley analyses of adsorption isotherms.

Ge-containing ITQ-22 zeolites have been almost completely degermanated under strong acidic conditions without modifications of the framework topology. Simultaneous to Ge extraction, the framework was partially dissolved; mesopores were formed but the structure was maintained through the re-incorporation of some of silicon species at vacant sites. The presence of many defects in the degermanated framework enabled the incorporation of tetrahedral aluminum, opening the way to the preparation of new and stable acid catalysts with original topologies.

The investigation of the critical synthesis parameters of germanosilicate of UTL topology, possessing 14- and 12-rings, has been carried out in detail. (6R,10S)-6,10-Dimethyl-5-azoniaspiro[4.5]decane hydroxide was used as the structure-directing agent (SDA). The kinetics of the synthesis, the role of the Si/Ge ratio in the synthesis mixture, and the effect of the calcination procedure were investigated in relation to the crystallinity and textural properties of the synthesized material. The optimum synthesis time was found to be six days for Si/Ge and (Si+Ge)/SDA molar ratios of 2 and 1.7, respectively. The UTL zeolite crystallizes as small sheets of 10 mum in size. The micropore volume of the best crystals is 0.22 cm(3) g(-1) with a micropore diameter of 1.05 nm, based on DFT and Saito-Foley analyses of adsorption data.

Pyridine adsorption monitored by FTIR spectroscopy revealed germanosilicate UTL type zeolite to contain intrinsic Brønsted acidity required for catalytic activity. Germanosilicate UTL type zeolite was converted into a bifunctional catalyst and evaluated in n-decane isomerization and hydrocracking. To assess the stability of the framework during catalyst preparation and use, three different strategies of converting the zeolite into bifunctional catalyst were followed: incipient wetness impregnation with Pt(NH 3 ) 4 Cl 2 solution before and after evacuation of the template by calcination, and physical mixing of calcined UTL with Pt-containing amorphous silica. All three samples showed catalytic activity but to very different degrees. The possibility of structure degradation during catalyst preparation and catalysis was investigated by XRD and 29 Si MAS NMR. The impregnation of as-made germanosilicate UTL zeolite with platinum and pretreatment in the reactor led to superior stability and activity. The n-decane test previously was used to probe zeolite micropore architectures with 8-, 10-and 12-membered rings. Its validity is now extended to the extra-large pore zeolites. The linear trend of increasing ethyloctane vs. methylnonane selectivity with increasing pore size has now been confirmed also for UTL with 14 membered rings.

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