Synthesis of high-silica EU-1 zeolite in the presence of hexamethonium ions: A seeded approach for inhibiting ZSM-48

Synthesis of EU‐1/ZSM‐48 Co‐Crystalline Zeolites from High‐Silica EU‐1 Seeds: Tailoring Phase Proportions and Promoting Long Crystalline‐Phase Stability

“…We previously reported that Al‐rich EU‐1 seeds (i.e., SiO 2 /Al 2 O 3 ratio of 55) are required for the synthesis of high‐silica EU‐1 zeolite (SiO 2 /Al 2 O 3 ratio >120), because it could facilitate the nucleation/growth of EU‐1 and inhibit the formation of the ZSM‐48 phase . In contrast, we decided now to choose high‐silica seeds to examine the influence on the co‐growth behavior of EU‐1 and ZSM‐48 phases.…”

“…Figure illustrates the seed content as a function of EU‐1 phase proportion in EU‐1/ZSM‐48 co‐crystalline zeolites. In the absence of EU‐1 seed in the initial gel, only the ZSM‐48 phase was detected in the resulting sample due to the presence of the high‐silica mixture gel, which is consistent with previous work . After addition of EU‐1‐300 seeds, with the seeds accounting for 1.5 wt % to 6.0 wt % of SiO 2 in the initial gel, the mass fraction of EU‐1 phase in co‐crystalline zeolite increases from 40 % to 80 %.…”

“…Interestingly, when using high‐silica EU‐1‐300 as seeds in the high‐silica gel with an SiO 2 /Al 2 O 3 ratio of 300 and an Na 2 O/SiO 2 ratio of 0.12, EU‐1/ZSM‐48 co‐crystalline zeolite was steadily produced. In contrast, with the addition of Al‐rich seeds (EU‐1‐55), only the EU‐1 phase was produced without formation of ZSM‐48 . This suggests that the Al content in the EU‐1 seeds could play a crucial role in the balance of formation of EU‐1 and ZSM‐48 crystalline phase during the crystallization process.…”

“…Table shows the synthesis parameters and corresponding proportion of EU‐1 phase in the co‐crystalline zeolite. At the same Na 2 O/SiO 2 ratio and 2.5 wt % EU‐1‐300 seeds, the proportion of EU‐1 phase remarkably increases with the HM/SiO 2 ratio, which is in perfect accordance with the result that HM‐rich system favors the synthesis of EU‐1 phase . The length of HM ion is around 14.5 Å, so it can be accommodated in a perpendicular position to the a ‐axis between the channel and a side‐pocket in the framework of EU‐1 zeolite, but can only fill the channel of the ZSM‐48 zeolite .…”

“…In our previous work, by using Al‐rich EU‐1 seeds, pure EU‐1 zeolites with a wide range of SiO 2 /Al 2 O 3 ratios (55–1500) have been successfully prepared in the optimized HM system. The results indicate that Al‐rich EU‐1 seeds (SiO 2 /Al 2 O 3 ratio of ca.55) can reduce the activation energy for EU‐1 nucleation, and hence inhibit the crystal transformation from EU‐1 into ZSM‐48 during the long crystallization process, and finally leads to the formation of high‐silica EU‐1 zeolite …”