Influence of the distance between Brønsted acid sites and Mo sites in Mo/HZSM-5 on the mechanism of methane dehydroaromatization performance

Methane dehydroaromatization (MDA) presents a promising carbon-neutral pathway for benzene, toluene, and xylene (BTX) production, alternative to petroleum-derived routes. Elucidating the regulatory mechanisms of Brønsted acid site (BAS) strength on reaction pathways, alongside the spatial proximity effects between BAS and Mo active sites in bifunctional synergy, remains a critical scientific challenge in catalyst design. This study systematically tunes both BAS strength (via isomorphous metal substitution) and Mo-BAS spatial proximity in zeolites, integrating MDA catalytic evaluations with density functional theory (DFT) calculations to dissect their individual contributions. Strongly acidic BAS catalysts (compared to moderately acidic Fe/Ga-substituted counterparts) exhibit superior performance, evidenced by enhanced aromatic yields. Conversely, weakly acidic B-substituted zeolites demonstrate optimal mono-/bifunctional synergy, outperforming moderate-acid systems. DFT results reveal that acid strength dictates C−H activation mechanisms by modulating the energy barriers of rate-determining steps. While Al-zeolites deliver the highest activity, B-substituted systems display unique potential for mechanistic investigations. Spatial proximity analysis indicates that micrometer-scale Mo-BAS distances hinder effective synergy due to exceeding electron interaction and mass transfer limits, whereas nanometer-scale proximity enhances activity (via accelerated intermediate transport) and suppresses coke formation. These findings establish a theoretical framework for rationalizing zeolite catalyst optimization through BAS property engineering and spatial control of Mo-BAS cooperation, providing actionable guidelines for designing next-generation MDA catalysts.