Al-ZSM-5 Nanocrystal Catalysts Grown from Silicalite-1 Seeds for Methane Conversion

This study evaluated Al-ZSM-5 nanocrystals grown from silicalite-1 seed crystals as catalysts for the methane dehydroaromatization (MDA) reaction. Silicalite-1 seed crystals sized between 30 and 40 nm were used to grow Al-ZSM-5 under various synthesis conditions. The size of Al-ZSM-5 was significantly affected by the Si/Al ratio (SAR), synthesis time, and silica nutrients/seed crystal ratio (NSR). Larger crystals were obtained with an increased SAR in the synthesis sols. Gradual growth of Al-ZSM-5 occurred with synthesis time, although the growth in crystal size ceased at 5 h of synthesis at 120 degrees C, indicating the rapid growth of Al-ZSM-5 aided by the silicalite-1 seeds. Precise tuning of Al-ZSM-5 size was possible by changing the nutrient/silicalite-1 seed ratio; a higher NSR led to larger crystals. Two representative Al-ZSM-5 crystals with SARs of 35 and 140 were prepared for catalyst testing, and the crystal sizes were tailored to <100 nm by controlling NSR. The MDA reaction was conducted in the presence of the prepared Al-ZSM-5. The catalyst size exhibited distinct differences in catalyst stability, while the SAR of catalysts did not produce noticeable changes in the catalyst stability of the Al-ZSM-5 crystals and commercial zeolites in this reaction system.

Automated summary

This study evaluated the size control of Al-ZSM-5 nanocrystals by manipulating the Si/Al ratio, synthesis time, and silica nutrients/seed crystal ratio, and tested their catalytic performance in the MDA reaction. Both synthesis conditions and crystal size significantly influenced the growth of Al-ZSM-5, with an increased Si/Al ratio leading to larger crystals in the synthesis sols. The catalyst size showed distinct differences in catalyst stability during the MDA reaction, while changes in the SAR of catalysts did not produce noticeable impacts on the catalyst stability of the Al-ZSM-5 crystals.