Study On Simultaneous Catalytic Reduction Of Sulfur Dioxide And Nitric Oxide By Carbon Dioxide

Sulfur dioxide(SO₂) and nitric oxide(NO) resulting from the combustion process of coal, are two major air pollutants causing acid rain. For a long time, great attention has been paid on the simultaneous removal of SO₂ and NO. There are various processes under operation or research to remove SO₂ and NO simultaneously, such as absorption, adsorption, plasma generated by pulsed discharge, catalytic removal and so on. Above all, the catalytic reduction of SO₂ and NO is desirable for its great value in theory and practicality by CO, because that CO is easy to be obtained and it can simultaneously reduce SO₂ to sulfur as well as NO to nitrogen.Preparation of catalysts is an important factor which affects the performance for desulfurization or denitrification over rare earth oxides catalysts. After comparison, CeO₂/γ-Al₂O₃, La₂O₃/γ-Al₂O₃, CeO₂-La₂O₃/γ-Al₂O₃ and CeO₂-La₂O₃ were prepared by impregnating in certain ratio. Separate or simultaneous removal of SO₂ and NO over La₂O₃/γ-Al₂O₃, CeO₂/γ-Al₂O₃, CeO₂-La₂O₃/γ-Al₂O₃ and simultaneous removal of SO₂ and NO over CeO₂-La₂O₃ were investigated. The phase characteristics of catalysts were also analyzed by X-ray diffraction. Results are as follows.In SO₂-CO-N₂ system, SO₂ conversions is above 99% over CeO₂- La₂O₃/γ-Al₂O₃ and 98% over La₂O₃/γ-Al₂O₃ as well as that above 80% over 5%CeO₂/γ-Al₂O₃. In NO-CO-N₂ system, the conversion of NO is above 99% both over CeO₂- La₂O₃/γ-Al₂O₃ and CeO₂/γ-Al₂O₃, while sulfide of La₂O₃/γ-Al₂O₃ after the CO-SO₂ reaction is with very high activity for denitrification. CeO₂-La₂O₃/γ-Al₂O₃ has high activity for simultaneous reduction of SO₂ and NO. The SO₂ and NO conversions are all above 98% in SO₂-CO-N₂, NO-CO-N₂ and SO₂-NO-CO-N₂ system. It means that CeO₂-La₂O₃/γ-Al₂O₃ can reduce SO₂ to elemental sulfur as well as NO to nitrogen. At the same time, for the simultaneous removal of SO₂ and NO over CeO₂-La₂O₃/γ-Al₂O₃ catalyst with certain ratio of SO₂:NO:CO, NO has no remarkable effect on the reduction of SO₂ while NO conversion increases, and the influences of solid solutions on the activity for simultaneous reduction of SO₂ and NO vary with the ratio of CeO₂-La₂O₃. The solid solutions and carrier can increase the crystal stability and strengthen the antitoxic resisting sulfur of catalysts. Reaction mechanism is also concluded both according to the experimental results and XRD (XPS) analysis. The reactions may be carried out by COS intermediate phase and redox of CeO₂.