Catalytic Reduction Of NO By NH₃ Over Modified Vanadia-titania Catalyst At Low Temperature

Selective Catalytic Reduction (SCR) method is most widely used in actual flue gas processing and of the highest denitration efficiency currently. Catalyst is important component in SCR system. In recent years, catalyst with high efficiency under low temperature, and high sulfur and water resistance has become the study object of domestic and foreign experts and scholars.Catalyst V₂O₅-Sb₂O₃-TiO₂ was prepared by impregnation method, and the effects of V₂O₅, Sb₂O₃ load, pH and calcination temperature on V₂O₅-Sb₂O₃-TiO₂ low temperature ammonia Selective Catalytic reduction (SCR) NO. Results indicated that catalyst obtained the best SCR activity when V₂O₅ and Sb₂O₃ load were 5% 2% respectively, calcination temperature 400℃, pH=4. NO removal rate reached 97% when reaction temperature was 220℃. The effects of operation conditions on catalyst SCR activity by changing operation factors such as reaction temperature, NH3/NO_x molar rate, volume fractions of import NO_x, space velocity and O₂ content, which provided the right parameters for practical engineering design and operation. Study on transient response experiments of reaction gases on catalyst offered the reactive gas status and the adsorption ability of catalyst to the response gas, which provided basis for reaction mechanism analysis. TiO₂-SiO₂ (TS) support was prepared by the co-precipitation method.V₂O₅-Sb₂O₃-TS catalyst was prepared by impregnation method, and its active component and calcination temperature were optimized. Results showed that when V₂O₅ and Sb₂O₃ load were 7% and 2% respectively, calcination temperature 400℃, catalyst had the best SCR activity. Denitration efficiency reached 90.4% when reaction temperature was 220℃.Performance of catalyst V₂O₅-Sb₂O₃-TiO₂ and V₂O₅-Sb₂O₃-TS against SO₂ and H₂O poisoning was also investigated. Add of Sb₂O₃ not only enhanced V₂O₅-TiO₂ low temperature catalytic activity, but also could greatly improve the catalytic performance of anti-H₂O and SO₂ poisoning. SO₂, NO adsorption transient response and TG-DTG tests showed that, the promotion mechanism of Sb₂O₃ was mainly promoting the catalyst adsorption to NO in existence of SO₂, while reducing the interaction between ammonium sulfate and the catalyst, which made ammonium sulfate more likely to break down. After support was replaced with TS, the catalyst activity decreased. NO removal rate decreased from 97% to 90.4% when the reaction temperature was 220℃. But SO₂ had little effect on activity of catalyst V₂O₅-Sb₂O₃-TS. NO removal rate fell 3 percentage points within 29h. Its resistance to sulfur and water simultaneously had also been enhanced compared to catalyst V₂O₅-Sb₂O₃-TiO₂. FT-IR characterization on the poisoned catalysts indicated that the main reason for decrease of catalyst activity was the presence of ammonium sulfate on catalyst surface. The improvement of Catalyst V₂O₅-Sb₂O₃-TS resistance to sulfur and to sulfur and water simultaneously might contribute to the inhibition of TS support to SO₂ oxidation by catalyst, and thereby the reduction of ammonium sulfate formation.Finally, two different carriers after resistance to sulfur and water simultaneously were regenerated by calcination at 400℃for 8h , and their activity were tested. Results showed that the activity of two catalysts had significantly increased, but the catalytic activity of regenerated catalyst V₂O₅-Sb₂O₃-TS was closer to fresh catalyst. It can be obtained by FT-IR characterization that the active component of poisoned catalyst V₂O₅-Sb₂O₃-TiO₂ was sulfated, but catalyst V₂O₅-Sb₂O₃-TS was not.