Preparation And Performance Study Of New Iron-based Catalysts For NH₃-SCR Of NO_x

With the rapid economic development,the missue of nitrogen oxide pollution emitted by stationary sources represented by fossil fuel combustion and mobile sources represented by motor vehicles has become more serious.Currently,ammonia selective catalytic reduction technology is the most effective and economical nitrogen oxide control technology.The core of this technology is the design and synthesis of denitration catalysts.Up to data,V₂O₅-WO₃?Mo O₃?/Ti O₂ series have widely applied as the commercial denitration catalysts,but it still has the disadvantages of high activation temperature,narrow operation window and poor selectivity.In addition,the deactivation of catalysts caused by the SO₂ and alkali metal present in the flue gas is also a problem that need to be addressed to prolong the life span of de-NO_x catalysts.Therefore,it is of great research significance to design new type of de-NO_x catalyst with excellent low temperature activity,wide activity window,and high resistance,and to deeply explore its reaction mechanism,poisoning mechanism and resistance mechanism.Inspired by those motivations,this paper first designed a new de-NO_xcatalyst with specific morphology and excellent low temperature activity from the structure-activity relationship and explored its reaction mechanism through in-situ infrared testing.Then,we explored the effect of different interfaces between active species in the catalyst on the potassium resistance of the catalyst.Finally,we studied the effect of different interactions between the carrier and the active components on the catalyst performance.The main work of this article is as follows:?1?We designed and synthesized a new type of Mn-Fe composite oxide-based monolithic de-NO_x catalyst with metal organic framework?MOF?as precursor and systematically compared it with other Mn-Fe catalysts which prepared by traditional urea-assisted method.The results show that the catalyst prepared with MOF as precursor has better low-temperature de-NO_x activity.The fundamental reason is that MOF derived Mn-Fe solid solution,could results stronger interaction between the active species?manganese oxides and ferric oxides?and promotes the formation of Mn⁴⁺and O_?.At the same time,the enhanced redox of the catalyst promotes the formation of NO₂,thereby realizing the“Fast-SCR process”.In addition,the increase of weak acid sites and Fe³⁺-OH on the surface of catalyst promote the adsorption of NH₃ and the generation of active intermediate species NH₂ during the reaction.In view of the richness of MOF materials and the generality of synthesis methods,this work can provide new ideas for the design of new low-temperature de-NO_x catalysts in the later stage.?2?We prepared three de-NO_x catalysts with different interfaces of Fe₂O₃-Fe VO₄ by co-precipitation,impregnation and physical mixing methods.Studies have shown that different preparation methods have little effect on the catalytic activity of the catalyst,but have a great impact on the alkali metal?use potassium as an example?resistance of the catalyst.The catalyst prepared by impregnation method and physical mixing method showed obvious deactivation after 1%potassium poisoning.But the catalyst prepared by co-precipitation still shown excellent operation window?180-360°C,NO_x conversion>90%?after 1%potassium loading.NH₃-TPD,H₂-TPR,Raman,in situ DRIFTs and other technologies wee used to reveal the reaction mechanism and potassium-resistant mechanism of the target catalyst.The study found that the catalyst prepared by co-precipitation has more acid sites and stronger redox properties.More importantly,it was found that the target catalyst has alkali metal trapping site,which could restrain deterioration of the catalytic behaviors lead by the merge of the alkali metal with the catalytic active sites.This work provides a new idea for the design of high alkali resistance de-NO_x catalysts in the later stage by studying the effect of the interface effect between active components on the potassium resistance of the catalyst.?3?We prepared Fe VO₄/M?M=Ti O₂,Al₂O₃,Ti O₂ and Si O₂?de-NO_x catalysts using four different supports.By systematically comparing the differences in activity,acidity and redox properties of the four catalysts,the effect of different interfaces between the active component and the carrier on the catalyst performance was studied.The results show that when the loading of active component is 10%,the catalyst using Ti O₂ as the carrier has the best activity.It can reach 90%NO conversion rate at 210°C.At the same time,the NO conversion rate of more than 90%can be maintained in the temperature window of 210-360°C.Studies have shown that its excellent catalytic activity comes from its abundant acid sites and stronger redox.This work can provide new ideas for the later design of new de-NO_x catalysts by exploring the effect of the interaction between the active component and the carrier in the catalyst on the catalyst activity...