Isomorphously Substituted [Fe,Al]ZSM-5 Catalysts for Methane Dehydroaromatization

Dehydroaromatization of methane (MDA) under non-oxidative conditions is a promising reaction for direct valorization natural gas and biogas. Typically, Fe-modified ZSM-5 catalysts display low aromatic productivity high coke selectivity in the MDA reaction. Herein, we show benefit starting from isomorphously substituted Fe-sites [Fe,Al]ZSM-5 zeolites prepared by hydrothermal synthesis. Upon calcination, these samples contain predominantly isolated Fe3+ species, either atomically dispersed within zeolite framework or anchored at exchange sites inside channels. In terms integral hydrocarbon productivity, outperform Fe/ZSM-5, impregnation, as well Mo/ZSM-5 with same Si/Al ratio molar metal loading. Operando X-ray absorption spectroscopy coupled mass spectrometry (XANES-MS) demonstrates that initial tetrahedral are transformed into octahedral extraframework Fe2+ active during form small Fe2O3 clusters oxidative regeneration. Combining activity measurements operando thermogravimetry shows duration induction period, related to formation pool intermediates, strongly depends on Fe dispersion loading can be used suitable descriptor [Fe,Al]ZSM-5. The shorter period comparison impregnated Fe/ZSM-5 linked higher conversion rate over highly faster intermediates.