Studies on low-temperature degradation for sulfur hexafluoride over sulfidated nanoscale zero-valent iron supported on zeolite ZSM-5: heterostructures, interfacial activation and fluorine migration

Owing to its strong chemical inertness, sulfur hexafluoride (SF 6 ) is intrinsically resistant to degradation. Accordingly, a composite material was developed by coupling sulfidated nanoscale zero-valent iron (S-nZVI) with fly ash-derived zeolite ZSM-5, forming a multi-level heterostructure for efficient SF 6 degradation. Experimental results confirmed that the composite exhibited exceptional low-temperature degradation performance, achieving complete removal of 2 vol% SF 6 at 600 °C with a specific degradation amount of 206.1 mL/g. Remarkably, effective degradation was still maintained at 300 °C, surpassing the previously reported minimum temperature limit (∼450 °C) for SF 6 degradation. Kinetic analysis revealed a near-zero-order reaction behavior with an apparent activation energy of only 27.61 kJ/mol, indicating that the initial stage was dominated by adsorption, diffusion, or interfacial electron transfer rather than S F bond cleavage. Comprehensive characterization showed that the composite possessed Fe 0 /FeS and FeS/ZSM-5 dual heterointerfaces, serving simultaneously as adsorption carriers, electron donors and acceptors. Specifically, the microporous framework of ZSM-5 physically confines nonpolar SF 6 molecules through van der Waals and confinement effects, enriching their local concentration and forming a favorable adsorption-activation interface. Electrons released by Fe 0 migrate directionally to these enrichment sites under the drive of the multi-level heterostructure, enabling concurrent adsorption and electron-induced activation of SF 6 , and thereby facilitating S F bond cleavage. The resulting fluoride ions initially react with Fe 0 to generate FeF 3 , which subsequently interacts with the silicate framework to produce SiF 4 , establishing a mediated fluorine migration pathway from SF 6 to SiF 4 and enabling deep degradation with sustained reactivity.