Selective Catalytic Reduction Of NO_x With NH₃ Over Transition Metal Promoted Catalysts

Nitrogen oxides?NO_x?are major atmospheric pollutants,which destroy the ecological environment and do harm to human health.Thus,it is urgent to effectively reduce emission of NO_x.In this work,the metal oxides supported catalysts were prepared by impregnation method with H?-zeolites or TiO₂ as carriers.Effects of various factors on the selective catalytic reduction of NO_x by ammonia?NH₃-SCR?were explored by orthogonal design experiments.The physical and chemical properties of the catalysts were characterized by XRD,BET,H₂-TPR,NO-TPD,CO-TPR and NH₃-TPD and et al.The in situ diffuse reflectance infrared fourier transform spectroscopy?in situ DRIFTS?was used to study the mechanism of the SCR of NO with NH₃.The conclusions were obtained as the following:1.With the H?as the carrier,the orthogonal design experiments which contain four factors and three levels were carried to determine the effect of Cu?W?P?Br on catalysts for NH₃-SCR of NO_x by observing the T₅₀ and T₉₀.The results show that the increase of Cu and Ce loading is beneficial to improve the denitrification performance of the catalysts.In these experiments,the Ce-CWPB-H?-3-8 catalyst is the best for NH₃-SCR of NO_x,which has lower reduction temperature,showing the T₅₀,T₈₀ and T₉₀0 are 181,206 and 217?respectively.2.With the TiO₂ as the carrier,the orthogonal design experiments which contain seven factors and three levels were carried to investigate the effects of Mo,Ce,Cu,Fe,W,P,Zr on catalysts for NH₃-SCR of NO_x and SO₂ oxidation.Also the visual analysis and variance under the indexes of T₅₀ and T₉₀ indicate that:?1?Mo has the most significant effect on NH₃-SCR of NO_x and its contribution rates for activity under the T₅₀and T₉₀ indexes are 30.57%and 40.93%respectively.The activity of T-19catalyst which is improved by the orthogonal design is higher than previous results and its T₅₀?T₈₀ and T₉₀ are 197,235,250?respectively.?2?the results of SO₂ oxidation in orthogonal design catalysts show that the effects of Cu,Fe and Zr on SO₂ oxidation are significant at low temperature?150??and their contribution rates are 20.19%,25.03%and 30.92%respectively,while the effects of Mo,Cu and P on SO₂oxidation are significant at high temperature?300??and the contribution rates are 47.17%,26.85%and 16.87%respectively.The results would be provided as theoretical basis for designing strong anti-sulfur poisoning catalyst.?3?the effects of Mo loading and calcination temperature on the denitrification performance of T-19catalyst are systematically studied,and the results indicate that the catalyst activity is better with 1.5 wt.%Mo loading when the catalyst is calcined at 400?.3.The results of catalysts characterization show that the redox and the NO adsorption-desorption performance of the catalysts are important factors which affect the catalytic activities.The high NO conversion is related to better adsorption and desorption capacity of NO and acidity distribution,as well as the appropriate amount of the adsorbed oxygen,the surface oxygen and the lattice oxygen,which are more favorable for the formation of stable intermediate species.4.The in situ diffuse reflectance infrared fourier transform spectroscopy?in situ DRIFTS?was used to study the mechanism of the SCR of NO by NH₃ on T-19 and Ce-CWPB-H?-3-8 catalysts.The results show that both of T-19 and Ce-CWPB-H?-3-8 catalysts have the acidity site of L acid and B acid with the stronger intensity of L acid than which of B acid.The bridged nitrates and bidentate or monodentate nitrates species are formed when NO and O₂ co-adsorb on the surface of catalysts.The reaction mechanisms about SCR of NO with NH₃ on T-19 and Ce-CWPB-H?-3-8 catalysts follow the E-R?Eley-Rideal?mechanism,which the NH₃ is first adsorbed and formed NH₄⁺ion,then the nitrogen oxides transforme into N₂ and H₂O with interaction with NH₄⁺and the active components.