Hierarchical Fe/ZSM-5 zeolites for efficient Hg0 removal from coal-fired flue gas

• Hierarchical Fe/ZSM-5 with extremely low Fe dosage exhibits superior DeHg ability. • Hierarchical porosity facilitates the dispersion and accessibility of Fe sites. • Fe sites are modulated by Bronsted acid, inducing shielding effect to SO 2 . • First attempt to employ hierarchical ZSM-5 for DeHg application. Coal-fired induced mercury pollution is an increasing threat to both human health and ecological environment. Herein, to boost Hg 0 removal from coal-fired flue gas, we report hierarchically porous Fe/ZSM-5 zeolites through facile chemical treatment (NaOH and HNO 3 etching) and FeCl 3 post-impregnation. Despite being impregnated with extremely low Fe dosage (0.4 w.t.%), Fe/ZSM-5 by acid-etching shows desirable demercuration (DeHg) ability (> 90% under N 2 + O 2 ), which largely surpasses the parent ZSM-5 as well as state-of-the-art zeolite-based and carbon-based materials with significantly higher FeCl 3 impregnation dosage. Besides, acid-etched Fe/ZSM-5 exhibits good SO 2 resistance and long-term DeHg stability under 1200 ppm SO 2 and 10% H 2 O flue gas condition. Comprehensive characterizations and density functional theory (DFT) calculations are further employed to interpret DeHg mechanism. Hierarchical Fe/ZSM-5 produced by acid etching highlights two essential merits: (1) hierarchical porosity significantly facilitates the dispersion of Fe sites and their accessibility to Hg 0 ; (2) reactivity of Fe sites is largely modulated by Bronsted acid, leading to a shielding effect to SO 2 as well as the enhanced Hg 0 bonding and oxidation performance. The promise of hierarchical zeolites demonstrated in this work would advance the development of low-cost and carbon-free materials for the DeHg application in real-world flue gas.