Structure–Activity Relationship of NH3–Treated Spherical KNbO3 in Catalytic Carbonyl Sulfide Hydrolysis: Oxygen Vacancy Engineering vs. Nitrogen Doping

Hydrolysis catalyzed by metal oxides is an effective approach for removing carbonyl sulfide (COS) from blast furnace gas, but constructing highly active catalytic sites that function efficiently under low–temperature conditions remains a fundamental challenge. In this work, perovskite–type niobate catalysts (KNbO 3 , NaNbO 3 , and LiNbO 3 ) are synthesized via a sol–gel method and subsequently modified under a strongly reducing NH 3 atmosphere at elevated temperatures to simultaneously generate oxygen vacancies and nitrogen dopants (both substitutional and interstitial), thereby significantly enhancing their catalytic performance and H 2 S selectivity for COS hydrolysis. Among them, NH 3– treated N–KNbO 3 achieves 100% COS conversion and 100% H 2 S selectivity at 100 °C. Comprehensive physicochemical characterizations and density functional theory (DFT) calculations indicate that NH 3 treatment achieves a “four–in–one” effect: oxygen vacancy engineering, nitrogen doping, morphology engineering, and modulation of surface active sites. This study systematically elucidates the structure–activity relationship underlying the synergistic interplay between nitrogen doping and oxygen vacancies in KNbO 3 , demonstrates the cooperative promotional role of oxygen vacancies and interstitial nitrogen during hydrolysis, and underscores the critical importance of surface reactive oxygen species and weakly basic sites. These findings provide both a theoretical foundation and practical design strategies for developing high–performance catalysts for low–temperature COS hydrolysis.