Nanozeolite-Driven Gear-Catalysis Enabling Sequential Methanol-to-Aromatics Conversion.

Abstract

Controlling diffusion and elementary reaction pathways to achieve high selectivity and stability has been a long-standing challenge in heterogeneous catalysis. Here, we develop a "gear-catalyst" system that spatially and kinetically decouples the methanol-to-aromatics (MTA) reaction into two sequential steps: methanol-to-olefins and olefins-to-aromatics. We show that nanoZSM-5 (high Si/Al ratio, ∼100 nm particle size) serves as a highly efficient smaller "gear" for rapid olefin generation and accelerated mass transfer, while micrometer-sized Zn-exchanged ZSM-5 (Zn/Z5) acts as the larger "gear" to promote aromatization. This gear-like synergy enables precise control of both reaction kinetics and diffusion pathways, reducing undesired overalkylation and coke formation. Consequently, our catalyst delivers a remarkable increase in aromatic yield with an 85% selectivity for benzene, toluene, and xylene in a single pass. In situ spectroscopic studies reveal that the smaller nanoZSM-5 particles modulate local olefin concentrations and prevent early aromatic buildup, thereby extending catalyst lifetimes by suppressing hard-coke formation. The resulting "two-center" mechanism, in which olefins shuttle between adjacent acid and metal sites, demonstrates how a simple physical mixing strategy can decouple complex multistep pathways. Our findings underscore the potential of gear-catalysis concepts to tackle similar diffusion-reaction mismatches in high-value chemical transformations, from syngas-to-aromatics to CO₂-based fuel synthesis.