Organotemplate-free synthesis of Al-rich ZSM-35 and ZSM-22 zeolites with the addition of ZSM-57 zeolite seeds

Abstract

Organotemplate-free synthesis of zeolites assisted with zeolite seeds has been a hot topic in the past decade. Herein, we for the first time show an organotemplate-free synthesis of Al-rich S-ZSM-35 and S-ZSM-22 zeolites with the addition of ZSM-57 zeolite seeds. Notably, the adjustment of SiO₂/Al₂O₃ and Na₂O/SiO₂ ratios in the starting gel to suitable values is an important factor in preparing the pure Al-rich S-ZSM-35 (Si/Al ratio at about 5) and S-ZSM-22 (Si/Al ratio at about 20) zeolites. The key to success is that the targeted ZSM-35 and ZSM-22 zeolite products have partly the same composite building units as the ZSM-57 zeolite seeds. The obtained Al-rich S-ZSM-35 and S-ZSM-22 zeolites show good crystallinity, typical crystal morphology, large BET surface area, and fully 4-coordinated aluminum species. In addition, as a typical example, the Al-rich S-ZSM-22 zeolite was evaluated by n-dodecane hydroisomerization reaction, which exhibits outstanding performance due to its Al-rich features (Si/Al ratio at about 20) compared with the conventional ZSM-22 zeolite (Si/Al ratio at about 30).