Conformation of intrazeolitic choline ions and the framework topology of zeolite hosts

摘要

The host–guest interactions in as-made zeolites Y, UZM-4, UZM-22, offretite, ferrierite, phillipsite, EU-12 and levyne, all of which were synthesized using choline as an organic structure-directing agent, have been investigated by a combination of different experimental techniques, including Raman, ¹H-¹³C CP MAS NMR and variable-temperature IR spectroscopies, together with theoretical calculations. The conformation of this asymmetric quaternary ammonium cation was shown to differ significantly according to the pore topology of the zeolite host and the intrazeolitic location of the organic guest molecule. Theoretical calculations using the pure-silica zeolite model reveal that among its three representative conformers (i.e., gauche, trans and trans′ forms), the conformer, which was experimentally found to dominantly or exclusively exist in zeolite structures studied, always has a lower interaction energy with the surrounding zeolite framework. Our work provides the first example in which the conformation of organic structure-directing agents plays an important kinetic role in governing the phase selectivity during zeolite nucleation.