Seeded growth of urea-promoted ZSM-5 nanoplates with short b-axis thickness for enhanced methanol-to-olefin reactions

Abstract

Catalytic efficiency in zeolite-based reactions critically depends on molecular diffusion kinetics within the confined channels. Nanosized ZSM-5 zeolites with a reduced b-axis thickness shorten the diffusion path and maximize the pore-opening configuration of the straight channels, enhancing mass transfer to active sites. However, achieving precise control over such nanostructures remains challenging. Herein, we report a urea-nanoseed-assisted synthesis of ZSM-5 nanoplates with low b-axis thickness in a sustainable, fluoride-free system. Comprehensive optimization of the synthesis yielded uniform crystals with a short b-axis (30–80 nm), a-axis (75–115 nm), and c-axis (130–210 nm). Mechanistic studies revealed a reversed crystal growth pathway: crystallization initiates at amorphous aggregate surfaces and propagates inward, critically directed by the organic template in the presence of urea. In methanol-to-olefin (MTO) reactions, these nanoplates outperformed commercial ZSM-5, delivering a 30% higher propylene/ethylene ratio and doubling the catalyst's lifespan. This work provides a rational strategy for synthesizing diffusion-optimized zeolites for applications where diffusion plays a critical role.