The Study Of Kinetics And Mechanism Of Removal NO From Flue Gas On V₂O₅/SiC Catalyst

Selective catalytic reduction (SCR) is a method widely used in the field of removal NO from flue gas, which has high efficiency and small secondary pollution. At present, the traditional V2O5/TiO2 and ViO5-WO3/TiO2 catalyst is widely used in the industry SCR due to their good denitration activity. However, operating temperature should be at least 350℃ in order to avoid the poisoning of SO2 which results in the increasing of the energy consumption and running costs. Many references suggested carbon-based catalysts, such as activated carbon(AC), activated coke(ACF) and carbon nanotubes(CNTs), have a high denitration activity. Moreover, these catalysts could not be poisoned by SO2 because the carbon element in these catalysts. However, the above-mentioned carbon-based carrier are easily to be ablated in SCR reaction due to the complex surface composition in AC, ACF and so on. Silicon carbide is a covalent compounds formed by carbon and silicon. Its structure is similar to the tetrahedron of diamond. It has the advantages of stable chemical property, good thermal stability and acid and alkali corrosion and so on. Therefore silicon carbide is an ideal support material.The silicon carbide is used for carrier in this paper. V2O5/SiC catalyst was prepared by impregnation method. The structure and morphology of the catalyst were characterized though SEM, TEM, XRD, XPS and NH3-TPD. The catalyst denitration performances over different reaction conditions, reaction kinetics and the effect of SO2 on the catalyst was studied in this paper. The obtained conclusions are listed below:1. Vanadium oxide existed on the surface of catalyst in the form of V2O5.2. V2O5/SiC catalyst has the best denitration effection when the V2O5 loading is 15%. In the reaction range of 150℃-300 ℃, denitration activity gradually increases with the increasing of reaction temperature. And conversion rate of NO can acheive 100% when the temperature is 300 ℃. Experimental results show that SCR catalyst reaction follows the reaction mechanism of Eley-Rideal. That is, the reaction occurs between the adsorbed NH3 and gaseous or weakly adsorbed NO.3. V2O5/SiC catalyst are unaffected by diffusion rate when the reaction temperature within 150 ℃-300 ℃. The rate of NO conversion on V2O5/SiC is one level with respect to NO, zero level with respect to NH3 and nearly half level with respect to O2. The catalyst apparent activation energy are 38 kJ·mol-1.4. SO2 has a promotion effect on denitration activity when the reaction temperature higher than 200 ℃. And the lower loading of V2O5, the more obvious promoting. The catalyst has good stability. Denitration activity can be maintained more than 90% within 100 h in the experiment. The performance of deNOx over different carriers catalysts is indicated that the promotion of SO2 to the denitration activity of catalyst is more obvious when carbon content is higher than 15%. The possible reason is that SO2 increases the NH3 adsorption performance, while the carbon carrier can effectively promote the reaction of ammonium sulfate salt and NO on the surface of catalyst.