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 ether-to-olefins (DTO) conversion. This protocol is extendable to the rational synthesis of other hierarchical zeolites through crystallization process control.

Automated summary

Controlling crystal size and shape is crucial for the synthesis of hierarchical zeolites with improved mass transport and catalytic properties. The reported single-step crystallization method using structure-directing agents resulted in aligned nanocrystals with enhanced propene selectivity and catalyst lifetime in dimethyl ether-to-olefins conversion, demonstrating the potential for rational synthesis of hierarchical zeolitic materials.