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Study of template interactions in MFI and MEL zeolites using quantum methods

Abstract:

The interactions between zeolites and templates in MFI and MEL (MEL1 and MEL2) structures combined with different conformations of tetrapropylammonium (TPA) and tetrabutylammonium (TBA) templates were investigated using DFT type methods. Molecular dynamics (MD) simulations were carried out with a tight binding code with London dispersion (DFTB-LD) approach to investigate the conformational space of templates before zeolite formation. Conformational preferences are in agreement with experimental results observed in zeolite using TPA and TBA templates when the temperature of synthesis changes. Zeolite-templates interactions were calculated by using both DFT-D and DFTB-LD methods. Analysis of intrinsic zeolite-template interactions and energy changes in zeolites and templates may explain experimental findings. Template distortion energies were evaluated at channel interception distances and anion-cation electrostatic effects were also included to account for template aggregation. A model of cation and anion distribution for MFI zeolite is presented.