Hydrothermal synthesis of an ITH-type germanosilicate zeolite in a non-concentrated gel system

A germanosilicate zeolite with the ITH framework type (designated JLG-18) has been hydrothermally synthesized. Compared with other ITH-type materials synthesized in concentrated systems, JLG-18 was the first one synthesized in a non-concentrated system. In addition, the organic structure-directing agent (OSDA) for the synthesis of JLG-18 was N,N,N′,N′-tetramethyl-1,6- hexanediamine (TMHDA), which was less expensive than those used for the synthesis of other ITH-type materials. The optimal molar ratio of the initial gel was 0.5 SiO₂: 0.5 GeO₂: 7 TMHDA: 1.4 HF: 42 H ₂O. The effects of various synthetic parameters on the formation of final products, such as source materials, GeO₂:SiO₂ ratio, H₂O:(SiO₂ + GeO₂) ratio, TMHDA:(SiO ₂ + GeO₂) ratio, crystallization temperature, and reaction time, were investigated. The as-synthesized samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma (ICP), elemental analysis, thermogravimetric analysis (TG), and N₂ adsorption. JLG-18 with a Si:Ge ratio of 2:1 exhibited excellent thermal stability, even after calcination at 700 C in air. The microporous surface area of JLG-18 was 317.07 m²/g.