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In IGCC systems,sulfur compounds such as hydrogen sulfide and carbonyl sulfide can be produced,due to the sulfur component in coal,and the resulting hydrogen sulfide can be treated using the hot gas absorptive desulfurization process with an absorbent.An SO2 removal process is necessary for IGCC systems,because SO2 is produced in the regeneration process of sulfide sorbent.Sulfur dioxide is also a toxic and corrosive sulfur compound,which damages the health,corrodes equipment,generates acid rain,and pollutes and acidifies the soil.In order to regenerate the sulfidated desulfurization sorbent,oxygen has been used as the oxidant agent on the regeneration process.The small amount of oxygen un-reacted in regeneration process is flowed into direct sulfur recovery process.However,the reactivity for SO2 reduction can be deteriorated with the un-reacted oxygen by various reasons.In this study,the deactivation effects of un-reacted oxygen contained in the off-gas of regeneration process flowed into direct sulfur recovery process of hot gas desulfurization system were investigated.Sn-Zr based catalysts were used as the catalyst for SO2 reduction.The contents of SO2 and O2 contained in the off-gas used as the reactants were fixed to 5.0 vol% and 4.0 vol%,respectively.SO2 reduction over Sn-Zr based catalyst was carried out at the ranges of 200 – 550 ℃ and 0 – 20 atm.The un-reacted oxygen oxidized the elemental sulfur produced by SO2 catalytic reduction and the conversion of SO2 was reduced due to the production of SO2.However,the temperature for the oxidation of elemental sulfur increased with increasing pressure in the catalytic reactor.Therefore,it was concluded that the decrease of reactivity at high pressure is occurred by catalytic deactivation,which is the re-oxidation of lattice oxygen vacancy in Sn-Zr based catalyst with the un-reacted oxygen on the catalysis by redox mechanism.Meanwhile the un-reacted oxygen oxidized CO supplied as the reducing agent and the temperature in the catalyst packed bed also increased due to the combustion of CO.It was concluded that the rapidly increasing temperature in the packed bed can be induced the catalytic deactivation such as the sintering of active components.