Synthesis of silicalite-1 using fluoride media under microwave irradiation

• Silicalite-1 was synthesized under microwave irradiation in short synthesis time.
• Silicalite-1 was synthesized in fluoride media, hydroxide media and mixture of them.
• Increasing the content of sodium hydroxide favored irregular morphology.

Robust hydrophobic zeolites are targeted for biomass and heavy oil upgrading, which involve large content of water. Silicalite-1 (Si-MFI) zeolite has been synthesized successfully with short synthesis time under microwave irradiation using two different sources of mineralizer agents at 180 °C. The effects of mineralizer agents on the synthesis of silicalite-1 and their effects on the phase produced, particle size and morphology were studied carefully. Eight new formulations were investigated to synthesize silicalite-1 with different strategies: (i) in the presence of both fluoride and hydroxide sources or (ii) in the presence of fluoride only or (iii) in the presence of hydroxide only. In addition, it was confirmed from our synthesis results that the synthesis of silicalite-1 in the absence of both fluoride and sodium hydroxide was possible. It was also noticed that the flexibility of adding ammonium fluoride to the synthetic gel was limited as compared to both sodium and potassium fluoride. It was observed that an addition of fluoride to the synthesis mixture led to an increase of particle size. In opposite, when only sodium hydroxide was added as a mineralizer agent, an increase of sodium hydroxide concentration led to a decrease in the particle size and favored the irregularity of silicalite-1 morphology.

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