Research Of Catalytic Oxidation Of NO Over MnO_x -TiO₂

Combining Wet FGD technology with catalytic oxidation of NO is the most economical technology of desulfurization and denitration simultaneously.This technology has a broad application prospect. But about 90% of NO_x in combustion flue gas is NO, which is hardly to be absorbed, so we need to oxidize NO to NO₂,whice is easily to be absorbed. There has three ways ,one is high energy plasma,the second is chemical oxidation and the third is catalytic oxidation.Among these, catalytic oxidation is the most economical one.Because of this, searching for a catalyst which has optimal oxidation activity and good resistance to SO₂ and H₂O becomes the key to this method. In this thesis, the catalyst of single active component MnO_x was prepared and applied for catalytic oxidation. Meanwhile, effects of H₂O and SO₂ on NO oxidation over the catalyst were investigated.(1)The effects of different precursor of Manganese and along with the nature of supports on the performance of the catalytic oxidation of NO were examined. The result shows that the catalyst which was made by manganese acetate is more activity than the catalyst made by manganese nitrate. And the catalyst supported on TiO₂ has a better catalytic activity than which supported on MPS or TS. The catalyst which was made by manganese nitrate with 50% manganese loading and supported on TiO₂ has optimal oxidation activity. The high NO conversion of 83.2% was observed over it at 300 oC and space velocity 10,000 h^-1。(2)By optimizing the preparation conditions of MnO_x-TiO₂, we got the best preparation conditions. The MnO_x-TiO₂ which was calcined at 300 oC with manganese loading 20%(wt%) showed perfect oxidation activity. The high NO conversion of 89% was observed over it at 300 oC and space velocity 10,000 h^-1.(3)The effects of operating condition on the catalytic oxidation of NO were also investigated. It was found that NO conversion increased with the enhancement of O₂ concentration and decreased with the rise of NO concentration and GHSV. The reaction kinetic equation was expressed as:(4)The effects of H₂O and SO₂ on the catalytic oxidation of NO were studied The 10% H₂O had little negative effect on catalytic activity, and the NO conversion was kept at level of 68%. When SO₂ or both SO₂ and H₂O were present, the NO conversion decreased significantly, and when H₂O and SO₂ were off, the catalytic activity could not recover.(5)FT-IR theory technical analysis was used to analyze poisoning mechanism of MnO_x-TiO₂ by H₂O and SO₂. The catalytic activity decreased in the presence of H₂O due to the formation of manganese nitrate. The catalyst was deactivated irreversiblly in the presence of SO₂ due to the formation of sulfate salts, which is very stable in the reaction temperature. The high decomposition temperature of manganese sulfate also led to difficulties in catalyst regeneration The presence of water exacerbated the formation of sulfate.(6)The oxidation-absorption synthesis experiment was researched under the optimized conditions. The result showed that De-NO_x efficiency of the catalyst was 70% when the temperature of the NO catalytic oxidation reaction is 230℃²60℃. The catalyst is expected to be applied in the removal of NO_x from flue gas without SO₂.