Carbonyl Sulfide Hydrolysis over FAU Zeolite: Performance and Mechanism

Carbonyl sulfide (COS), a prevalent organic sulfur contaminant in industrial exhaust gases, poses serious threats to both human health and the environment. Catalytic hydrolysis offers an effective strategy for COS removal, as the resulting H2S can be readily eliminated. However, the widespread application of this technology is limited by the poor stability of existing catalysts. In this study, four FAU-type zeolites─LSX, NaX with low and high Si/Al ratios (SARs), and NaY─were synthesized and evaluated for COS hydrolysis. To the best of our knowledge, this is the first report on zeolite-catalyzed COS hydrolysis. Among the four zeolites, LSX exhibited the highest catalytic activity, attributed to its lowest SAR and the highest concentration of alkaline sites. LSX also demonstrated excellent stability, maintaining over 85% COS conversion and H2S selectivity for more than 50 h. The presence of O2 was found to inhibit catalytic performance due to the accumulation of sulfur, sulfite, and sulfate species on the catalyst surface. In situ DRIFTS analysis revealed that COS hydrolysis over LSX proceeds via the activation of COS by surface hydroxyl groups and K+/Na+ ions to form HSCO2– intermediates, which subsequently decompose into CO2 and H2S. The alkali cations play a predominant role in facilitating this process. Water vapor plays a dual role in regenerating hydroxyl sites and promoting intermediate transformation, while elevated temperatures and oxygen exposure lead to intermediate decomposition and the buildup of sulfur-containing byproducts. This work provides valuable insights into the reaction mechanism and offers guidance for the development of robust zeolite catalysts for efficient COS hydrolysis.