Host-Guest Interactions in Zeolites with Different Framework Topologies Containing Choline Ion as a Guest Molecule

Abstract

Eight zeolites with different framework topologies (i.e., MEI, BPH, FER, OFF, LEV, CHA, LTL, and FAU) are synthesized using choline ion as an organic structure-directing agent. Elemental and thermal analyses, 1H, 13C MAS, 1H-13C CP MAS NMR, and IR spectroscopies are employed to investigate the host-guest interactions in the as-made form of this series of zeolites. The strength of intramolecular hydrogen bonding of the choline ions encapsulated within channels and/or cavities of eight zeolites was found to differ according to the type of their host zeolite structures. Interestingly, the 13C MAS NMR spectra of levyne and L zeolites clearly show the splitting of two methyl 13C resonances with two crystallographically different tetrahedral sites. This suggests that the interactions of choline cations with framework AlO4- tetrahedra could vary with the type of tetrahedral sites in which Al atoms are located. Unexpectedly, the 1H MAS NMR spectra of some zeolites reveal that the intramolecular hydrogen bonding character of choline ions become weak, and in some cases, no hydrogen bonds are present anymore, when the zeolites prepared here are heated at 200 oC or lower.