Evolution of D6R units in the interzeolite transformation from FAU, MFI or *BEA into AEI: transfer or reassembly?

Abstract

The formation and evolution of building units for zeolites play an important role during crystallization. Interzeolite transformation offers a better platform for investigating the conversion behaviors of such building units and the specific crystallization mechanism of zeolites. Herein, we show the different evolution of double six-membered rings (D6R) during the interzeolite transformation from FAU, MFI and *BEA into AEI zeolites based on UV Raman spectroscopy in combination with X-ray powder diffraction (XRD) and DFT calculations. It is found that a direct transfer of D6R occurs from the FAU into AEI zeolite since they share the same structural units (D6R), while towards the newly expanded synthetic strategy from pentasil-type zeolites MFI and *BEA into AEI zeolites, the formation of D6R units in the AEI framework results from the reassembly of single four-membered rings (S4R) and single six-membered rings (S6R) generated by breaking a large number of single five-membered rings (S5R) that are very fragile and easy to decompose under hydrothermal transformation conditions. Such results provide a clear and direct spectroscopic characterization at the molecular level, which will be of great significance in accomplishing a deep understanding of the interzeolite transformation mechanism.