Structure-guided control of Al sites in MFI zeolites: Toward rational catalyst design for efficient methane dehydroaromatization

This work introduces a rational approach to enhance methane dehydroaromatization (MDA) by precisely tuning the location of aluminum atoms within the MFI zeolite framework. By employing combinations of tetrapropylammonium cation (TPA + ), pentaerythritol (PET), and Na + ions as structure-directing agents (SDAs), Al atoms were selectively positioned at channel intersections, within straight/sinusoidal channels, or across both environments in the MFI framework. Comprehensive analysis of aluminum site distribution was conducted using 27 Al MQ MAS NMR, ion-exchange measurements, and ethylene aromatization as a probe reaction. Following Mo impregnation, the dispersion behavior and reduction characteristics of Mo species were elucidated via XPS, H 2 -TPR, TEM, and XANES. In particular, the zeolite synthesized with the [PET, Na + ] combination exhibited a predominant location of Al atoms within the channels, which generated stronger acid sites and led to highly uniform Mo dispersion and a ten-fold higher surface concentration compared to the intersection-dominant Al catalyst. DFT simulations confirmed that such environments enable stronger anchoring of Mo 2 C 2 species and reduced benzene adsorption energies, promoting faster product desorption. As a result, the Mo/[PET, Na + ] catalyst exhibited the highest initial BTX yield of 9.2 % and the lowest coke formation (9.9 %), demonstrating superior catalytic activity and stability. In addition, analysis of coke characteristics indicated that the Mo/[PET, Na + ] catalyst favored the formation of graphitic carbon, which could be readily removed at lower oxidation temperatures. Through combined experimental and theoretical analyses, we reveal that the spatial configuration of Al sites critically influences metal dispersion, product desorption, and coke suppression, thereby establishing a structural blueprint for the rational design of zeolite catalysts. • Efficient methane dehydroaromatization requires coke-resistant and selective catalysts governed by zeolite structure. • Al site locations in MFI zeolites were precisely controlled using different structure-directing agents (TPA, PET, Na + ). • PET, Na⁺]-derived zeolite maximized Mo dispersion in channels, delivering peak BTX yield with minimal coke. • DFT calculations showed Mo 2 C 2 in sinusoidal channels facilitates benzene desorption and suppresses coke formation.