Low temperature selective catalytic oxidation of H₂S: Influencing factors, mechanisms and regeneration

H2S has become a significant environmental problem because of its high toxicity, corrosiveness, and low olfactory threshold. Therefore, the high-performance removal of H2S has become a research focus. Low-temperature (<180 degrees C) H2S selective catalytic oxidation (H2S-SCO) technology has the advantages of high desulfurization accuracy and no secondary pollution. This technology is especially suitable for effectively removing H2S, and the catalysts play a critical role. Metal oxide (MO)-based catalysts (single metal oxides catalysts, mixed metal oxides catalysts, oxide-supported catalysts), and carbon-based catalysts (activated carbon, carbon nanofibers, carbon nanotubes, graphene-based materials, and alkaline mesoporous carbon) used for H2S removal are comprehensively discussed. This review summarizes the research progress of various catalysts for H2S-SCO, and compares their advantages and disadvantages. The influencing factors including internal factors such as basic surface/groups, structural defects, sulfur storage space, and external factors such as humidity, temperature, O-2, GHSV of catalysts performance, and possible catalytic oxidation mechanisms of catalysts are systematically expounded. Out of all the catalysts reviewed, oxide-supported catalysts have shown desirable effects in H2S removal. The regeneration methods for different catalysts are also reviewed and it was found that the high porosity of catalysts with large specific surface areas is crucial for maintaining good regeneration capacity. Compared with thermal regeneration, CS2, and ammonium hydroxide solution washing regeneration are more cost-effective and worthy of further research as regeneration methods. Finally, it is recommended that additional investigation is required to understand the mechanism of interaction between H2S, and catalysts and to identify the effects of H2S, organic sulfur, ammonium hydroxide, and CO2 on catalyst activity.