Looping upcycling SO2 into value-added H2S by fast-induced reduction process for heavy metals treatment in nonferrous smelting industry

Reversing the pollution to a value-added product can simultaneously alleviate environmental problems and achieve a circular economy. In nonferrous smelting industries, SO2 is hazardous pollution that should be disposed, but H2S is usually required for heavy metals (HMs) treatment. Herein, we developed a field SO2 looping upcycling technology for value-added H2S production to meet the HMs treatment. Results demonstrated that the H2 could accelerate the kinetic rate and decrease the energy barriers of the SO2 and CH4 reaction by a fast -induced reduction process (fast-IRP). Thus, the H2S production rate in fast-IRP was three times higher than the direct reaction between SO2 and CH4. Meanwhile, the T90 temperature (690 degrees C) was significantly lower than SO2 and CH4 reaction about 90 degrees C. Fast-IRP also can resist the SO2 poison effect and prevent sulfation, enhancing the activity, long-term stability (no visible efficiency loss in 50 h), and selectivity (nearly 100 %). Integrated the characterizations and DFT results, we found that the H2 would firstly attack the uncoordinated sulfur species with a hydrodesulfurization process to form the HS-/H2S intermediate species with a lower energy barrier (1.57 eV) than the CH4 (2.83 eV), which can facilely protect the Mo-terminated to avoid sulfation poison. Subse-quently, the HS-/H2S* species would react with the adsorbed SO2 to Sx* to support the deep-reduction reaction for H2S production. This work proposes an actual SO2 field utilization route and also will enlighten an induced redox cycle in the sulfur reduction over the pre-sulfurized catalysts.