Improvement on Fluorine Migration from SF₆ to SiF₄ by an Efficient Mediator of Fe₂O₃/Cr₂O₃ Composites

An economic and facile method was urgently required for the degradation of SF₆ to replace the high-energy excitation treatment. Both theoretical calculations and experimental observations were conducted to reveal the synergy of Cr/Fe/Si composites on a new technique of SF₆ degradation through reacting silicon dioxide. Density functional theory (DFT) calculations show that strong adsorption of SF₆ on Cr₂O₃, and then the fast F/O exchange between CrF₃ and Fe₂O₃ (energy barrier was 1.45 eV) as well as FeF₃ and SiO₂ (energy barrier was 1.69 eV) enhanced mediated efficiency from SF₆ to SiF₄. The fluorine (F) migration between solid interfaces in Cr₂O₃&Fe₂O₃@SBA15 was responsible for efficient SF₆ removal. The F migration route was composed of SF₆ to CrF₃, CrF₃ to FeF₃, and FeF₃ to SiF₄ with the lowest thermodynamic driving. Enhanced specific accumulative converted amount (SACA) of SF₆ on Cr₂O₃&Fe₂O₃@SBA15 was achieved and the highest SACA was 13.98 mmol/g within 7 h, significantly higher than that on Fe₂O₃@SBA15 (5.74 mmol/g) and Cr₂O₃@SBA15 (2.71 mmol/g). Moreover, X-ray diffractometry and X-ray photoelectron spectroscopy were performed to support DFT calculations, including ion intensities detected using mass spectroscopy and composition analysis of the mediator during the reaction. Therefore, our work put forward a novel approach for economic and efficient SF₆ decomposition through reacting with silicon dioxide under the mediation of Cr₂O₃&Fe₂O₃. This method was also potentially used in effective degradation of refractory non-metal halides.