Roles of the Comproportionation Reaction in SO₂ Reduction Using Methane for the Flexible Recovery of Elemental Sulfur or Sulfides

Abstract

SO 2 reduction with CH 4 to produce elemental sulfur (S 8 ) or other sulfides is typically challenging due to high energy barriers and catalyst poisoning by SO 2 . Herein, we report that a comproportionation reaction (CR) induced by H 2 S recirculating significantly accelerates the reactions, altering reaction pathways and enabling flexible adjustment of the products from S 8 to sulfides. Results show that SO 2 can be fully reduced to H 2 S at a lower temperature of 650 °C, compared to the 800 °C required for the direct reduction (DR), effectively eliminating catalyst poisoning. The kinetic rate constant is significantly improved, with CR at 650 °C exhibiting about 3-fold higher value than DR at 750 °C. Additionally, the apparent activation energy decreases from 128 to 37 kJ/mol with H 2 S, altering the reaction route. This CR resolves the challenges related to robust sulfur−oxygen bond activation and enhances CH 4 dissociation. During the process, the well-dispersed lamellar MoS 2 crystallites with Co promoters (CoMoS) act as active species. H 2 S facilitates the comproportionation reaction, reducing SO 2 to a nascent sulfur (S x *). Subsequently, CH 4 efficiently activates CoMoS in the absence of SO 2 , forming H 2 S. This shifts the mechanism from Mars−van Krevelen (MvK) in DR to sequential Langmuir−Hinshelwood (L-H) and MvK in CR. Additionally, it mitigates sulfation poisoning through this rapid activation reaction pathway. This unique comproportionation reaction provides a novel strategy for efficient sulfur resource utilization.