In Situ Generation by Cyclization of an Organic Structure Directing Agent for the Synthesis of High Silica Zeolite...

Zeolites with high framework Si/Al ratios are of interest for industrial applications due to their hydrothermal stability. They are usually synthesized in the presence of pre-prepared organic structure directing agents (OSDAs). The high silica ERS-7 zeolite (topology type ESV) can be crystallized using N,N-dimethylpyrrolidinium (dmpyrr) that is formed in situ via cyclization of N,N,N',N'-tetramethyl-1,4-diaminobutane (tmdab) when a cationic polymer is also present. The in situ generation of dmpyrr is demonstrated by solid-state ¹³C NMR spectroscopy and supported by both chemical analyses and comparative syntheses using pre-prepared dmpyrr. The cationic polymer inhibits the crystallization of mordenite, which is otherwise observed to be the favored product. The ERS-7 prepared via in situ dmpyrr synthesis (Si/Al = 14) is characterized by PXRD and solid-state NMR spectroscopy. The CO₂ adsorption seen for the H- and Na-forms indicates interactions with accessible Na⁺ cations. The synthetic studies indicate the potential for in situ generation of OSDAs to reduce the need for extended OSDA syntheses.