Influence of the hydrophobic character of structure-directing agents for the synthesis of pure-silica zeolites

✍ Scribed by Alex V Goretsky; Larry W Beck; Stacey I Zones; Mark E Davis

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 140 KB
• Volume: 28
• Category: Article
• ISSN: 1387-1811
• DOI: 10.1016/s1387-1811(98)00307-2

✦ Synopsis

Tetrapropylammonium, ethanoltripropylammonium and diethanoldipropylammonium cations were used as structure-directing agents for the synthesis of pure-silica, MFI-type zeolites. These molecules are employed to investigate the influence of the organic hydrophobicity/hydrophilicity on zeolite formation. Ethanoltripropylammonium cation can direct the formation of Si-ZSM-5 but at a much slower rate than tetrapropylammonium cation. Diethanoldipropylammonium alone is unable to influence the formation of Si-ZSM-5 but is able to do so with the addition of either seeds or a small amount of tetrapropylammonium. Thus diethanoldipropylammonium cannot elicit nucleation but can support crystal growth. Solid-state nuclear magnetic resonance results show that ethanolalkylammonium molecules are occluded intact within the zeolite pores; however, tetrapropylammonium (more hydrophobic) is preferentially occluded. The results show that control of the hydrophobicity of the organic structure-directing agent is necessary for the synthesis of pure-silica zeolites.