In Situ Generation by Cyclisation of an Organic Structure Directing Agent for the Synthesis of High Silica Zeolite ERS-7.

Abstract

Zeolites with high framework Si/Al ratios are of interest for industrial applications due to their hydrothermal stability. They are usually synthesised in the presence of pre-prepared organic structure directing agents (OSDAs). The high silica ERS-7 zeolite (topology type ESV) can be crystallised using N,N'-dimethylpyrrolidinium (dmpyrr) that is formed in situ via cyclisation of N,N,N',N'-tetramethyldiaminobutane (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 crystallisation of mordenite, which is otherwise observed to be the favoured product. The ERS-7 prepared via in situ dmpyrr synthesis (Si/Al = 14) is characterised by PXRD and solid-state NMR spectroscopy. The CO2 adsorption seen for the H- and Na-forms indicate 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.