| Selective catalytic reduction（SCR）of NOxby NH3 has been commercially applied in denitration from stationary sources.The typical vanadium-based catalysts show efficient activity in the temperature window from 300℃to 400℃,but poor performance for treating low-temperature exhausts（<200℃）,such as flue gases from steel works,cement plants,and glass plants.Cost-effective construction of NH3-SCR catalytic systems to realize NOx removal in low temperature range has become urgent given the increasingly stringent environmental requirements.The perovskite-type catalyst was extracted from Ti-bearing blast furnace slag by in-situ doping.Under the condition of photoexcitation,nearly 100%of the catalyst can be removed at 140°C,and the reaction temperature of 140°C was nitrogen oxide.It not only opens a wide space for the utilization of Ti-bearing blast furnace slag with high added value,but also provides a new economic way for the preparation of low-temperature denitration catalyst.However,the migration path of active elements in the process of phase reconstruction of Ti-bearing blast furnace slag is still unclear,and the relationship between the structure of perovskite-type photocatalyst doped with lanthanide or transition group elements and denitration activity is still unclear,and the micro-mechanism of perovskite a-site doping enhancing activity needs to be elucidated.In view of the above problems,this thesis prepared a series of perovskite-type SCR catalysts through a one-step roasting process,and carried out a systematic study.Thermogravimetry and Differential Thermal Analysis（TG-DSC）showed that Mn O2 changed to Mn3O4 at 500℃and reconverted to Mn O2 at 900℃during mineral phase reconstruction.The simulated in-situ X-Ray Diffraction（XRD）analysis shows that Mn diffuses into the perovskite phase from oxide at 1000℃and Ce enters into the perovskite phase from oxide at 1200℃.The results show that the oxidation atmosphere is very important for the migration of Mn from oxide to perovskite phase,and Mn is distributed in spinel and silicate phase in low valence state in reductive or protective atmosphere,can not be enriched in perovskite phase.The atmosphere has little effect on the doping of lanthanide.The results of SIRS show that the transition elements Fe and Mn replace Ti at B site and lanthanide element Ce replace Ca at A site in perovskite phase.The Ti-bearing blast furnace slag was in-situ doped with lanthanide elements Ce,La,Pr,Sm and Eu respectively.It was found that the above elements were enriched in perovskite phase and exhibited different photocatalytic denitration activities,at the same doping content（5wt%）,La-doped Ca Ti O3 shows the best denitrification activity,50%NOx can be removed at 300°C,the selectivity of N2 is 100%,but the activity of Sm-doped Ca Ti O3is relatively poor.The in-situ doping of Ti-bearing blast furnace slag with transition group elements Ni,Co and Sc shows that Sc can partly enter into perovskite phase,but Ni and Co mainly segregate in silicate phase,and the yield is low,it is difficult to realize the doping of Ni and Co in perovskite phase by mineral phase reconstruction.The adsorption of NO on the surface of the original perovskite was studied by first-principles calculation.It was found that the exposed Ca ion could not chemically adsorb NO（adsorption energy-0.19 e V）,（Ca,Ce）Ti O3 can adsorb NO up to-1.53 e V.The in-situ FTIR results showed that the concentration of nitrate on the surface of（Ca,Ce）Ti O3 was significantly higher than that of the original Ca Ti O3 in NO+O2atmosphere,which indicated that the main mechanism of A-site Ce doping in Ca Ti O3was the formation of new active sites,promoted the activation of NO molecule.One the other hand,the impurity levels formed by doping Ce and Mn at the same time narrow the perovskite gap and endow the catalyst with visible light responsiveness;the doping of Fe and Mn at the same time changes the activation center of O2,shortens the standard SCR reaction path,and improves the catalytic activity of the catalyst. |
PDF Full Text Request