Nature of the interactions between Fe and Zr for the methane dehydroaromatization reaction in ZSM-5

Methane is an abundant feedstock with steadily increasing availability due to recent technological developments. The methane dehydroaromatization reaction is a possible chemical route to convert methane into benzene, which has a higher energy density. This reaction presents thermodynamic limitations on benzene production, while coke formation is favored. In a previous work, the combination of Fe and Zr in ZSM-5 catalysts showed promising results regarding selective prevention of coke deposition, favoring benzene production. In this work, Fe–Zr/ZSM-5 catalysts were synthesized with varying Zr/Fe ratios and characterized with XRD, BET, TPR-H2, TPD-NH3, Raman and TEM in order to better understand the effects of Zr over Fe. DFT calculations were used to investigate the interactions between Zr and Fe within the ZSM-5 structure. Experimental and computational results show that mixed Fe–Zr oxides were not formed, and ZrO2 and Fe2O3 oxides were deposited on the ZSM-5. The Zr was found to promote Fe2O3 reduction to Fe0 and deposit in the Brønsted acid sites of the zeolite, which could explain the decreased induction period and coke deposition in Fe–Zr/ZSM-5 catalysts for methane dehydroaromatization observed in previous works. [Display omitted] •Zr promotes the reduction of Fe to Fe0 under H2 atmosphere.•Zr oxides deposit in the Brønsted acid sites of ZSM-5.•The d-band center of catalysts might be used as criteria for reduction properties.•Deposition of Zr and Fe in ZSM-5 do not form mixed oxides.