Synthesis and characterization of pure STW-zeotype germanosilicate, Cu- and Co-substituted STW-zeotype materials

•Pure STW-type germanosilicate materials were hydrothermally synthesized.•The STW-type germanosilicate has high thermal stability up to 800 °C.•Co and Cu have been introduced for the first time in the STW-zeotype materials.

Pure STW-type germanosilicate (denoted as GeSi-STW), Cu- and Co-containing STW-zeotype (denoted as Cu-STW and Co-STW) materials were synthesized by the hydrothermal method in the presence of an organic structure-directing agent (OSDA), N,N-diethylethylenediamine (DEEDA). The effects of the reaction mixture ratio and the incorporation of transition metals M (M=Cu and Co) on the synthesis of the pure product was investigated. The synthesized samples were characterized by powder and single-crystal X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma analysis (ICP), thermogravimetric and differential scanning calorimetry (TG–DSC) analysis and UV–vis diffuse reflectance spectra (DRS). The results reveal that the crystallization time, the concentration of H2O in the reaction mixture and the addition of HF all have an important impact on the synthesis of pure STW-type zeolite. GeSi-STW is stable up to 800 °C, and has much higher thermal stability than SU-32 (stable to 400 °C). Co and Cu have been introduced for the first time into STW-zeotype materials.

Graphical abstractSEM images of GeSi-STW (A and B), Co-STW (C and D) and Cu-STW (E and F).Figure optionsDownload full-size imageDownload as PowerPoint slide