| Popis: |
Publisher Summary The chapter explores the ability of alkyltrimethylammonium surfactants of the type C n H 2n+I (CH 3 ) 3 NBr to serve as structure directing agents, or templates, for the formation of microporous or mesoporous molecular sieves frameworks. At equivalent gel compositions and reaction conditions, it was observed that the alkyl chain length of the surfactant molecule dictated the nature of the silicate product obtained as indicated by the X-ray diffraction patterns. Over the entire range of synthesis temperatures examined (100–200°C) the shortest alkyl chain length surfactant (n=6), produced amorphous or microporous zeolitic materials, such as ZSM-5. The zeolite contained the intact surfactant cation consistent with a commonly observed molecular templating effect. At 100°C as the surfactant chain length was increased (n=8, 10, 12, 14, and 16), the formation of mesoporous molecular sieves (MCM-41) was observed. In these cases, a combination of surfactant chain length and reaction conditions favor surfactant aggregation (micelles), and hence, the formation and utilization of supramolecular templates. |
