Effect of extra-framework Ga2O3 species in Ga/ZSM-5 catalysts on methanol-to-aromatics reaction

HZSM-5 zeolite is extensively used in methanol-to-aromatics (MTA) reactions; however, its low aromatics selectivity limits its performance due to weak intrinsic aromatization ability. In this study, a series of bifunctional x -Ga 2 O 3 /HZSM-5 were synthesized by mechanically mixing different Ga 2 O 3 isomers with HZSM-5 to systematically investigate the influence of the crystal structure on methanol aromatization. Among them, β-Ga 2 O 3 /HZSM-5 catalyst exhibited the highest aromatic selectivity, reaching 40 mol%. Structural characterization by XRD, N 2 adsorption, XPS, H 2 -TPR, XANES, and EXAFS analyses revealed that the dispersion and reducibility of extra-framework Ga 3+ species varied with the Ga 2 O 3 structure. In particular, the monoclinic β-Ga 2 O 3 exhibited a pronounced interaction with Brønsted acid sites of HZSM-5, promoting the formation of highly active and stable four-coordinated [Ga 2 O 2 ] 2+ dimers. These species functioned as efficient dehydrogenation and cyclization centers, thereby markedly promoting aromatics production.