Influences On The Ratio Of V^4+?3+?/V⁵⁺ And The Redox Rate In Mutual Transformation And SCR DeNO_x Activity

NH₃-SCR method is an effective method to denitration from NO_x emissions from stationary sources.Develop the high-performance SCR catalyst has become the key point of SCR technology.V₂O₅-WO₃/TiO₂ catalyst has been applicated for fixed source denitration in commercial.But in terms of moving source denitration,its denitration performance at low temperatures is worse than at high temperatures,To improve the low temperature denitration activity has been the main purpose at this stage.The study has found that the ratio of V^4+?3+?/V⁵⁺and NH₃-SCR denitration performance exists certain connection,the higher ratio of V^4+?3+?/V⁵⁺the higher low temperature denitration activity of the catalyst has.V-W/Ti catalysts were prepatated by changing the loading amount of V and roasting temperature with impregnation method.The results showed that the V?3%?W/Ti catalyst exhibited the high denitration activity.based on the study of V?3%?W/Ti catalyst,the pH of the precursor solution and roasting process of oxygen were changed to prepare different series of catalysts,to explore the relationship between the ratio of V^4+?3+?/V⁵⁺and the denitration activity.the experimental results showed that the pH value of 0.70 catalyst(V3W8Ti?0.70?and 15%O₂/N₂ calcined catalyst?V3W8Ti?b??exhibited the excellent activity which owned the highest ratio of V^4+?3+?/V⁵⁺.XPS,Raman,NH₃-TPD and NH₃-DRIFT test results showed that the vanadium oxide dispersion state,the valence state and surface acidic strength were influenced by the acidic the pH of the precursor solution and oxygen content in the process of roasting.with enhancing the solution acidity?decreasing the pH?,the aggregation state of vanadium species increased,the surface of the acid increased,the ratio of V^4+?3+?/V⁵⁺and O_?/?O_?+O_b?increased and denitration activity enhanced,various factors were acted each other and exhibited the same trend of denitration activity.In the experiment of the oxygen content in the roasting process,the catalyst calcined with 15%O₂/N₂?V3W8Ti?b??owned the highest ratio of V^4+?3+?/V⁵⁺(V⁴⁺/V⁵⁺was 1.03,(V⁴⁺+V³⁺)/V⁵⁺was 1.35),also exhibited the highest denitration activity.The catalyst which calcined without atmosphere?V3W8Ti?a??owned the highest ratioof V^4+?3+?/V⁵⁺(V⁴⁺/V⁵⁺was 3.54,(V⁴⁺+V³⁺)/V⁵⁺was 6.48),but denitration activity was the worst.The catalyst calcined in the air and pure oxygen(?V3W8Ti?c?and V3W8Ti?d??,the ratio of V^4+?3+?/V⁵⁺descreased(V⁴⁺/V⁵⁺was 0.80 and 0.76,(V⁴⁺+V³⁺)/V⁵⁺was 1.05 and 0.94),the denitration activity is dereased,which indicated that increasing the ratio of V^4+?3+?/V⁵⁺could improve the activity of denitration in a certain range,ratio is too large or too small would lower the denitration activity.oxidation reduction rate was calculated by TPR-TPO test,to explore how the ratio of V^4+?3+?/V⁵⁺influenced denitration activity.the experimental results showed that the reduction rate is larger than the oxidation rate with the same sample of catalyst,oxidation rate is the contral rate.In the process of mutual transformation between V^4+?3+?and V⁵⁺,the number of electrons in oxidation reaction increased,oxidation rate increased,electron transfer in the process of mutual transformation between V^4+?3+?and V⁵⁺match was ensured with moderate ratio of V^4+?3+?/V⁵⁺.The conversion effciency of between V⁵⁺and V^4+?3+?was enhanced,activation energy of the reaction was decreased,so the activity of denitration was increased.If the tatio of V^4+?3+?/V⁵⁺is too high or too low,the total amount of transfer electron would not match and denitration activity would be reduced.