Abstract: Carbonyl sulfide (COS) is commonly found in conventional fossil fuels, such as nature gas, oil-associated gas, and blast-furnace gas, and its untreated emission not only corrodes pipelines and poisons catalysts but will also inevitably pollute the environment and endanger human health. Catalytic hydrolysis is recognized as the most promising strategy to eliminate COS because it can be performed under mild reaction conditions with a high removal efficiency. Notably, alkali metals promote catalytic COS hydrolysis over Al₂O₃ owing to their electron donor properties, basicity, and electrostatic adsorption. However, despite the significant attraction of using potassium-promoted Al₂O₃ (K₂CO₃/Al₂O₃) as conventional catalysts for COS hydrolysis, the mechanism of COS hydrolysis over K₂CO₃/Al₂O₃ remains unclear and is controversial owing to the complex composition of the K species. In this study, commercial Al₂O₃ modified with potassium and sodium salts were synthesized using the wet impregnation method and characterized by various techniques. Based on the results of the activity measurements, the K₂CO₃-, K₂C₂O₄-, NaHCO₃-, Na₂CO₃-, and NaC₂O₄-modified catalysts had a positive effect on COS hydrolysis. Among them, the K₂CO₃/Al₂O₃ catalyst exhibited the highest COS conversion. Notably, the K₂CO₃/Al₂O₃ catalyst exhibited an excellent catalytic performance (~93%, 20 h), which is significantly better than that of pristine Al₂O₃ (~58%). Furthermore, this study provides strong evidence for the role of H₂O during catalytic hydrolysis over K₂CO₃/Al₂O₃ using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray photoelectron spectroscopy (XPS). The in situ DRIFTS analysis revealed that hydrogen thiocarbonate formed as an intermediate during COS hydrolysis over K₂CO₃/Al₂O₃. Meanwhile, the XPS findings suggested that sulfates and elemental sulfur accumulated on the catalyst surface, which may have contributed to catalyst poisoning. Additionally, the effect of water vapor content in the reaction pathway of COS hydrolysis over K₂CO₃/Al₂O₃ was investigated. The presence of excess water resulted in a reduction in catalytic activity owing to competitive adsorption between H₂O and COS molecules on the catalyst surface. The enhancement in the catalytic activity over K₂CO₃/Al₂O₃ may be attributed to the formation of HO-Al-O-K interfacial sites. More importantly, all the catalysts were used under industrially relevant conditions, which provides valuable theoretical guidance for practical applications in the future. Thus, this detailed mechanistic study reveals new insights into the roles of the interfacial K co-catalyst, which provides a new opportunity for the rational design of stable and efficient catalysts for COS hydrolysis.

Key words: Carbonyl sulfide, Catalytic hydrolysis, HO-Al-O-K interface site, Deactivation mechanism, Industrial-relevant condition