Plasma-assisted catalytic reduction of SO₂ to elemental sulfur: Influence of nonthermal plasma and temperature on iron sulfide catalyst

Herein, we report on low-temperature sulfur dioxide (SO₂) reduction to elemental sulfur via the coupling of nonthermal plasma (NTP) with supported transition metal sulfide catalysts in a dielectric barrier discharge (DBD) reactor. The transition metals include Mo, Fe, Co, Ni, Cu, and Zn. Combining NTP with supported metal sulfide catalysts significantly promotes low-temperature reduction of SO₂ by 148–200%, with over 98% selectivity to elemental sulfur. Over FeS₂/Al₂O₃ catalyst at low temperatures (<250 °C), temperature does not influence SO₂ conversion in the plasma catalytic process, whereas at higher temperatures, the reaction follows a similar trend as thermal catalysis. Strong synergistic effects are attained, as the sulfur yield is about 47–82% higher than the sum of the yield when using DBD-plasma and thermal catalysis separately. The physico−chemical properties of fresh and spent FeS₂/Al₂O₃ catalysts after thermal and plasma reactions are evaluated by N₂ physisorption, FESEM, XPS, XRD, HRTEM, STEM/EDS, and EELS to understand plasma and thermal effects on the catalyst. Our investigations reveal that running the reaction under plasma preserves the surface FeS₂ active phase, preventing its oxidation that otherwise occurs in the thermal catalysis process. Furthermore, plasma inhibits the thermal agglomeration of iron sulfide nanoparticles under reaction conditions.