Preparation Of Low-temperature SCR Denitration Catalysts Based On Titanium-bearing Blast Furnace Slag-mineral Phase Reconstruction Mechanism And Structure-activity Relationship Of Perovskite-based Catalysts

Although the research of low-temperature SCR catalysts has made great progress,the cost of the current preparation process is still high.In recent years,photo-thermal coupled selective catalytic reduction（Photo-SCR）denitrification based on perovskite-based catalysts has shown great application prospects,but it has not yet got rid of the dilemma of high production costs.Therefore,exploring efficient activity improvement strategies and low-cost processes has significant practical significance for the commercial application of low-temperature SCR denitration catalysts.As a kind of solid waste,titanium-bearing blast furnace slag has been stored in the open air for a long time,not only the titanium resources couldn’t be effectively used,but also serious ecological environmental problems were caused.In previous research,our group found that perovskite-based catalysts showed good potential in the direction of denitration,and successfully prepared SCR denitration catalysts from titanium-bearing blast furnace slag.However,the existing process flow is long,which limits its low-cost large-scale production.Moreover,the low-temperature denitrification activity still needs to be improved,and the denitrification mechanism is still unclear.Based on this,this study achieved the low-cost,short-process preparation of high-activity perovskite-based SCR catalysts based on titanium-bearing blast furnace slag through preparation process optimization and multiple doping strategies.The phase evolution law and segregation behavior of different elements in the process of mineral phase reconstruction were studied.The improvement mechanism of SCR activity by doping of different elements was clarified,and the action mechanism of visible light on SCR denitration process was revealed for the first time.The specific research content and conclusions are as follows.（1）Based on the optimization of reconfiguring agent and roasting process,a"one-step roasting-acid leaching"process was proposed and verified.The study found that the use of Na OH instead of Na₂CO₃ could effectively avoid the splash problem in the process of mineral phase reconstruction.At the same time,the products obtained by the one-step roasting process had the same mineral composition as the product of the two-step method,and the catalyst obtained after the chemical acid leaching treatment had the same phase and composition,which indicated that one-step roasting instead of two-step roasting process was completely feasible.（2）Based on the"one-step roasting-acid leaching"process,Mn O₂,Fe₂O₃ and Ce O₂were respectively used to doping titanium-bearing blast furnace slag to study the mechanism of mineral phase reconstruction and the segregation behavior of different elements in the reconstruction process.It was found that the mineral phase reconstruction process could be divided into three stages:pyroxene phase dissociation,perovskite enrichment and solid solution homogenization.During the process of reconstruction,Mn,Fe and Ce elements could be incorporated into the perovskite structure of the titanium slag with good interaction.Among them,Fe had no obvious segregation behavior between aluminosilicate and perovskite.Mn and Ce were segregated in the perovskite,especially the segregation of Ce was the most obvious.（3）Under dark field conditions,the SCR denitration activity of catalysts doped with different elements were studied,and the mechanism of activity improvement under Mn doping conditions was explored.It was found that doping of Mn could significantly improve the SCR denitration performance of perovskite catalyst compared with Ce and Fe under the same doping amount of oxides.Among them,the NO_x conversion rate of L-Mn（10）（the sample prepared by doping 10%Mn O₂）at 250°C was as high as 98%,while the NO_xconversion rate of pure Ca Ti O₃ was almost zero at this temperature.In-situ DRIFTS and first-principles calculation results showed that doping Mn could transform the adsorption of NO by Ca Ti O₃ from physical adsorption to chemical adsorption,thus providing new active sites for SCR reaction.（4）Based on the above research,the effects of Fe-Mn and Fe-Ce-Mn multi-element doping on the activity of perovskite-based catalysts were studied,and the optimization mechanism of Fe-Mn doping on the catalyst activity was clarified.Studies had found that Fe,Ce,and Mn can be uniformly distributed at the atomic level in the perovskite at the same time.Under the doping of Fe-Mn,the strong interaction between Fe and Mn made the catalysts exhibit excellent denitration activity at low temperature.Compared with L-Mn（10）,the reaction temperature required for L-Fe（5）Mn（10）to achieve a NO_x conversion rate of above 98%under dark field decreased from 250°C to 175°C.H₂-TPR and first-principles calculations showed that the incorporation of Fe would cause the formation of holes,which could increase the oxidation ability of lattice oxygen,and reduce the energy barrier of the SCR reaction path.However,under dark field conditions,Ce-Fe-Mn ternary doping did not obtain additional activity improvement compared to Fe-Mn binary doping.（5）Under visible light conditions,the SCR denitration performance of different catalysts was studied,and the optimization mechanism of visible light on the catalytic denitration activity was revealed.It was found that the activities of Mn-containing perovskite-based catalysts were significantly improved under visible light conditions.Among them,the complete conversion temperature of L-Fe（5）Ce（5）Mn（10）was further reduced from 175℃to 140℃.It was also found that although the introduction of Ce did not increase the activity of the Fe-Mn doped perovskite catalysts under dark field,it significantly enhanced its activity under visible light conditions.More importantly,through in-situ DRIFTS experiments in the excited state,we found for the first time that the mechanism of photocatalysis for improving the activity of perovskite-based catalysts was not due to the dissociation of the N-H bond of adsorbed NH₃ on the surface,but from the oxidation of NO adsorbed on the surface.Through process improvement,and with the help of two improvement strategies of visible light excitation and multi-element doping,titanium-bearing blast furnace slag can be used as raw material to prepare low-temperature and high-efficiency SCR catalysts on a large scale at low cost.On the one hand,the related work provides a new way for the high value-added utilization of titanium-bearing blast furnace slag,and on the other hand,it provides a theoretical and technological basis for low-cost preparation of high-activity SCR denitration catalysts.