Formation pathway of stable ZnOH+ species on ion-exchanged Zn/ZSM-5 catalysts for ethylene aromatization

Ethylene aromatization over Zn/ZSM-5 catalysts provides an effective route for upgrading light olefins into aromatics. However, the specific Al sites involved in Zn exchange and the pathway for ZnOH + formation and stabilization remain unclear. In this study, Zn/ZSM-5 catalysts were prepared by varying Zn(NO 3 ) 2 concentration (0.05–0.2 mol/L) and exchange cycles (1–3). The local environment of Zn species was analyzed using Co(II) UV–Vis, 27 Al MAS NMR, IR, ToF-SIMS, XPS, and XAFS. IE-Zn/Z5-0.05-1 and IE-Zn/Z5-0.1-1 exhibit the highest density of six-coordinated ZnOH + species, achieving BTX selectivity of 60% and stable operation for more than 100 h, with low Zn loss and coke deposition. Zn 2+ selectively exchanges with Brønsted acid sites at isolated Al F located at channel intersections of HZSM-5, forming octahedral ZnOH + species strongly anchored to the zeolite framework. This ZnOH + species acts as the likely active center, promoting dehydrogenation and maintaining structural stability.