Bolaform Molecules Directing Intergrown Zeolites

Understanding of epitaxial and rotational intergrowth is particularly important for the design and synthesis of hierarchically structured zeolites. Herein, we propose a new route for fabricating hierarchical MTW- and MFI-type zeolites with intergrown structures by tuning the methylene chain lengths between the two N-heterocycles in bolaform quaternary ammonium structure-directing agents (SDAs). MTW-type zeolites with 66.4° rotational intergrowth and MFI-type zeolites with 90° rotational intergrowth were synthesized with methylene chain lengths of 4-6 and 7-9, respectively. A possible theoretical evidence of the geometrical match between SDAs and zeolite structures was proposed by the binding energy obtained by molecular mechanics calculations. It is speculated that the bolaform SDAs are located in the straight 12-membered ring (MR) channels along the b direction of MTW topology, directing the intergrown structure by sharing the (310) plane. The bolaform SDAs located in the intersections of straight 10-MR channels and sinusoidal 10-MR channels of MFI topology directed the intergrown structure by sharing the (010) plane. The hierarchical zeolite catalysts prepared using this strategy, characteristic of hybrid micro- and mesoporosities, proved to be useful for tandem cracking reactions involving bulky molecules.