Study On DeNo_x Performance And Mechanism Of Low Temperature SCR Of Vanadium Modified HPMo/TiO₂ Catalysts

Industrial flue gas such as coke oven and sintering is another major source of NO_x emissions in addition to coal-fired flue gas.Selective catalytic reduction（SCR）technology is widely used to control NO_x emissions from stationary sources,and the key is catalysts.The optimal active temperature of the V-W（Mo）/TiO₂ catalyst is300⁴00°C while the temperatures of industrial flue gas emission is generally lower than 250°C.In addition,catalyst is susceptible to the inhibition or poisoning of SO₂and H₂O under the low-temperature.Therefore,it is of great significance to develop a catalyst with high activity and sulfur and water resistance which able to adapt to denitrify under low-temperature.In this research,TiO₂ is used as the carrier,and the mixture of vanadium pentoxide（V₂O₅）and phosphomolybdic acid（HPMo）,is supported as an active component on this carrier.The specific surface and microstructure of the catalyst are further regulated by the surfactant polyethylene glycol（PEG）.Finally HPMo-V-PEG/TiO₂ catalyst was obtained.The low temperature denitrification activity was studied experimentally.The catalyst process parameters and sulfur and water resistance were also investigated.The density functional theory（DFT）and in situ diffuse reflection fourier transform infrared spectroscopy（in situ DRIFT）was used to study the mechanism of denitrification.In the low-temperature denitration activity test of catalyst,the effects of V/Mo molar ratio and the active component loading and other factors on the denitration rate were investigated through experiments.The results show that when the V/Mo molar ratio was 1,the PEG addition amount was 0.5%,the calcination temperature was350°C,and the active component loading amount was 10%,the catalyst activity is the best.The NO_x removal rate is about 71.5%at a reactor temperature of 150°C,and then the denitration efficiency of the catalyst is higher than 99%when the reactor temperature is 200³50°C.The HPMo-V-PEG/TiO₂ catalysts were studied by methods of characterization such as BET,XRD,XPS and NO-TPD and so on.The characterization results show that the catalysts doped with V and PEG can reduce the crystal size of this catalyst,enhance the dispersion of the active components and the ability to adsorb and analyze NO.At the same time,it can promote the redox performance and the acidity of the catalyst,and enhance the denitration activity of the catalyst from the aspects of increasing the specific surface area and the content of adsorbed oxygen.The effects of process parameters such as reaction space velocity,ammonia-nitrogen ratio and oxygen content on denitration efficiency were investigated through experiments.The results show that the space velocity has little effect on the denitration efficiency when the reaction space velocity is lower than15000h^-1.When NH₃/NO≥1,the catalytic activity is above 99%.The catalyst has low active in the absence of oxygen,but the oxygen content above 2%satisfies the reaction conditions.The results of sulfur and water resistance test showed that when the concentration of SO₂ was 200ppm,the effect on denitration rate was not significant.When the water vapor was 2vol.%,the denitration rate was about 98.7%,and when it continued to increase to 10vol.%,the activity decreased slightly.In addition,after the introduction of 200 ppm SO₂ and 4vol.%water vapor for 5h,the denitration activity was maintained at about 85%,the flow of sulfur was stopped,the activity was basically restored,and the peak of SO₄^2-ion was not found by FTIR characterization.The results of DFT and in situ DRIFT indicated that the catalysts followed the two mechanisms of L-H and E-R,in which the L-H mechanism dominated and the active components had synergistic effects.NH₃ can be adsorbed on the L acid and B acid sites of the catalyst,and NO can also adsorb on the surface of the catalyst to form corresponding adsorbed substances.The symmetric absorption peak N-O,and the asymmetric absorption peak of NO₂,and the presence of bidentate nitrate and monodentate nitrate are evidences of the production of reactive intermediate in the L-H mechanism.