Research Of Catalytic Performance Of CuSO₄ -CeO₂/TiO₂-SiO₂ And Cr₂(SO₄)₃ /TiO₂ Catalysts In Catalytic Oxidation Of NO

NOx is one of the most important pollutants, generated mainly from the burning of fossil fuel, with NO accounting for over 90% of the fuel gas. However, due to its incapacity of being dissolved in the water, a direct absorption of NO is always a problem. In the removal of NOx from flue gas by catalytic oxidation, 50%⁶0% of NO must be oxidized to NO2 which will be absorbed in a further step, and a relatively higher absorption efficiency of NOx is consequently obtained. By this technique, a simultaneously desulfurization and denitration is realized. Thus the research on the catalysts for the oxidation of NO to NO2 has drawn much attention because of the high price of general oxidant (O3/KMnO4). Such research will lead to a significant decrease in the running cost. In the present paper, catalysts of CuSO4-CeO2/TS and Cr2(SO4)3/TiO₂ were prepared and applied for catalytic oxidation of NO in the presence of excessive oxygen.The effects of loading, calcining temperature, Cu/Ce molar rate, space velocity, volume fractions of NO and O2 on CuSO4-CeO2/TS catalytic oxidation of nitric oxide were studied, and the resistance to poisoning of H2O and SO2 was also investigated. The results showed that the optimum catalyst could be obtained, yielding to an oxidation efficiency of 67.5% at the following conditions: the volume fraction of NO 500×10-6(?), O2 8% (?), space velocity 10 000 h-1and reaction temperature 350℃. When the space velocity was 10 000 h-1 and 20 000 h-1, the oxidation rate was about 67% and 53%, respectively, for 40 h stability test. The NO conversion rate was depressed with 300×10-6 SO2(?) feeding, and stabilized around 24% after reaction for 3 h. When the feeding of SO2 was cut off, the activity was increased a little, and it finally reached to 31%. It was indicated that this catalyst could not resist to the poisoning of SO2. The activity was also decreased with 10% H2O(?) feeding, and was stabilized to around 45.4%. The activity was much worse in the presence of H2O and SO2, and the catalyst was deactivated.The effect of prepared methods, operation factors on Cr2(SO4)3/TiO₂ catalytic oxidation of NO were studied, and the resistance to poisoning of SO2 was also investigated. The results showed that the optimum catalyst could be obtained, yielding to an oxidation efficiency of 65% at the following conditions: the volume fraction of NO 500×10-6(?), O2 8% (?), space velocity 10 000 h-1and reaction temperature 350℃. In order to investigate its performance of anti-poison and adsorption of NO, and SO2, a comparison would be made between this catalyst (Cr2(SO4)3/TiO₂) and Cr2O3/TiO₂. The NO conversion rate by Cr2(SO4)3/TiO₂ was depressed immediately with 300×10-6 SO2(?) feeding, followed by a worse performance, but oxidation rate by Cr2O3/TiO₂ was increased suddenly, and it was then slowly decreased. When SO2 was cut off, their activities were increased a little. The catalysts of Cr2(SO4)3/TiO₂ and Cr2O3/TiO₂ adsorb the amount of SO2 more than that of NO with higher stability. Because of the competition between SO2 and NO, the amount of NO molecules on the surface of the catalyst was sharply decreased, leading to the penetration of NO molecules through the catalyst bed directly without reaction. And the activity was thus decreased. The catalyst Cr2O3/TiO₂ adsorbed SO2 and NO stronger than Cr2(SO4)3/TiO₂. The result of NH3-TPD characteristic showed the reason was that the catalyst surface of Cr2(SO4)3/TiO₂ was more acidic, which had adverse effect on the absorption of acidic gases.