Generating assembled MFI nanocrystals with reduced b-axis through structure-directing agent exchange induced recrystallization.

Controlling crystal size and shape of zeolitic materials is an effective way to promote their mass transport and catalytic properties.  Herein, we report a single step, Na + - and porogen- free crystallization of MFI hierarchical architecture made up of aligned nanocrystals with reduced b -axis thickness (5-23 nm) and adjustable Si/Al ratios between 35 to 120, employing the commonly used tetrapropylammonium hydroxide (TPAOH) and tetrabutylammonium hydroxide (TBAOH) as structure-directing agents (SDAs). Homogeneous nucleation driven by both SDAs and subsequent SDA-exchange induced dissolution-recrystallization are responsible for the formation of such structure. The enhanced textural and diffusion properties account for a notable  exaggeration of propene selectivity and catalyst lifetime in dimethyl in dimethyl ether-to-olefins (DTO) conversion.  This protocol is extendable to the rational synthesis of other hierarchical zeolites through crystallization process control.