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.