Guest-host interactions in As-made Al-ZSM-12: Implications for the synthesis of zeolite catalysts

Al-ZSM-12 samples have been prepared with selectively deuterated benzyltrimethylammonium cations as structure-directing agents (SDAs) to study the motion of the SDA and the spatial relationships between the SDA and the zeolite framework. H-2 NMR shows the methyl groups of the structure-directing agent undergo at least two rapid rotations while the benzyl segment is essentially immobile, undergoing only small angle wobbling motions, Cross-polarization and rotational echo double resonance NMR experiments were performed to study the spatial relationships between the SDA and the framework silicon and aluminum. The results from the CPMAS and REDOR experiments show the methylene protons of the structure-directing agent are preferentially located near the silicon atoms adjacent to the framework aluminum. As a consequence there is relative charge ordering between the SDA and the framework aluminum, suggesting that the framework aluminum is directly associated with the charge center of the SDA. Given the reduced number of configurations accessible to the SDAs in the as-made material, we believe the results suggest a possible route to tailoring the spatial arrangement of trivalent framework atoms through selection of SDAs with appropriate charge distributions.