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Catalytic Oxidation of NO over Co3O4/MPS

Author: GaoDongMei
Tutor: HuangZuo
School: Xiangtan University
Course: Environmental Engineering
Keywords: Nitrogen Oxides Catalytic oxidation Mesoporous silica (MPS) Co3O4
CLC: X701
Type: Master's thesis
Year: 2009
Downloads: 36
Quote: 0
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Abstract


Nitrogen oxides are atmosphere pollutants which come from the burning of fossil fuels. NO can not be absorbed either in water or alkali solution except generating complexes. In order to absorb the nitric oxides effectively, NO should be oxidized to NO2 which can easily be absorbed. The strong oxidizer such as O3 and KMnO4 were seldom applied due to their high cost. Researchers focus on the catalytic oxidation of nitrogen oxides. When 50%60% NO is oxidized into NO2 by catalyst, the highest absorption efficiency was gained. Then, nitrogen oxides are absorbed by desulfurizer agent （Ca（OH）2, NaOH, Na2CO3 and ammonia etc.）. By this processing technique, desulfurization and denitration can be realized simultaneously. The key problem of this method is aimed at searching for a catalyst with optimal oxidation activity at low temperature and good resistance to SO2 and H2O.The catalyst of cobalt-based catalyst （Co3O4/MPS） was prepared and applied for catalytic oxidation. Meanwhile, effects of H2O and SO2 on NO oxidation over Co3O4/MPS were investigated. In order to improve the low temperature activity and the ability of SO2 and H2O resistances, the pre-treatment and doped catalysts were studied. The results showed that Co3O4/MPS catalyst with 25% Co3O4 and calcined at 300℃has the optimuim oxidation activity. When the volume fraction of NO is 500×10-6, O2 10%, space velocity 12000 h-1, the oxidation rate of NO over Co3O4/MPS reached 50%60% at 250℃. At 300℃, the oxidation rate reached 82%, being approximate to the thermodynamic equilibrium value.Although the conversion rate of NO decreased with the introduction of H2O, the conversion rate could recover completely after removing residual H2O on Co3O4/MPS catalyst at 300℃. In the presence of SO2 and H2O, the oxidation activity could not recover completely after cutting off H2O and SO2, which is caused by the formation of cobalt sulfate species. The ability of SO2 oxidation over the catalyst determines its performance against SO2 poisoning. The activity of catalyst is greatly affected by the acidity in existence of H2O. Hence, the key to solve SO2 deactivation was to inhibit SO2 oxidation by adjusting the acidity and redox property based on good oxidation performance.The catalysts of Co-M/MPS（M=Mn, Fe, Cr）and two kinds of sulfured Co3O4/MPS were studied. Manganese can improve the activity of Co3O4/MPS at low temperature. The oxidation activity of Co-Mn/MPS reaches 52.6% at 200℃. In the presence of SO2 and H2O, the activities of sulfured Co3O4/MPS catalysts were all better than that of Co3O4/MPS. However, the problem of catalyst poisoning still not be settled completely.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Exhaust gas processing and utilization
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