Valence State Control And Low Temperature Catalytic Activity Of MnO_x/TiO₂ Catalyst

Selective catalytic reduction（SCR）technology is to selectively reduce the NO_x in flue gas to N₂ and water by using NH₃ or other reducing agents under the action of catalyst.It has the advantages of high denitrification efficiency rate,high selectivity and low operation cost.It is a widely used NO_x emission reduction technology in the world.It has also been popularized in China’s thermal power industry.However,the flue gas temperature of industrial furnace in non-power industry such as cement kiln,iron and steel sintering furnace,coking equipment,etc.is too low to use existing catalyst.Therefore,the research and development of low temperature SCR catalysts has become a research hotspot in recent years.Among many low temperature SCR catalysts,manganese based catalysts have attracted wide attention due to their good low temperature activity,selectivity and economy.Manganese in the manganese catalyst exists in the form of manganese oxides of different valence.The combined state of multivalent states makes the oxygen atoms on the sample surface more active,which is one of the reasons for the low temperature activity of MnO_x.However,few reports on the valence state and content of MnO_x in manganese catalysts are reported.At the same time,the relationship between the valence state of MnO_x and the activity of SCR at low temperature is still controversial.In order to solve this problem,this paper uses TiO₂powder as the carrier,Mn as active component,to study the valence state of MnO_x in MnO_x/TiO₂ catalyst、the relationship between valence state and denitrification efficiency,to develop a new SCR catalyst at low temperature and efficiency.In the analysis of the valence state of Mn,it is difficult to accurately divide the peak by using XPS.In order to study the distribution of valence states of Mn ions in catalysts,chemical titration is used.In this chapter,the accuracy is verified by XPS analysis and pure valence MnO_x,and the valence distribution of Mn ions in MnO_x/TiO₂ catalyst prepared by rheological phase method is analyzed.The denitrification efficiency of the MnO_x/TiO₂ catalyst was improved by changing the precursor solution and changing the pH value of the precursor solution to adjust the Mn valence state of the catalyst.The results show that the valence of Mn ion is the highest and the denitrification efficiency is the best in the MnO_x/TiO₂ catalyst prepared with pH as the basic self-made manganese salt（MX）as precursorIn order to further analyze the performance of pure valence MnO_x/TiO₂ catalyst,MnO_x/TiO₂ catalyst was prepared by ball milling and different valence manganese oxides.The effects of ball milling,mixing and ball milling MnO₂-mixing on the performance of the catalyst were compared.The results showed that the MnO₂/TiO₂catalyst prepared by ball milling has the best denitrification efficiency.The best ball milling time is 180min.The catalysts of Mn O/TiO₂,MnO₂/TiO₂,Mn₂O₃/TiO₂,Mn₃O₄/TiO₂ and MnO₂+Mn₂O₃/TiO₂ were compared by XRD,TPR and TPD.The results showed that the MnO₂/TiO₂ catalyst has the best denitrification efficiency.The denitrification efficiency of Mn⁴⁺is better than that of other Mn^x+.On the basis of previous studies,Ce and Fe elements were doped in MnO₂/TiO₂catalyst.CeO₂/TiO₂ catalyst,CeO₂+MnO₂/TiO₂ catalyst,CeO₂+2MnO₂/TiO₂ catalyst and CeO₂+4MnO₂/TiO₂ catalyst were prepared by adjusting the proportion of Mn and Ce,as well as Fe₂O₃/TiO₂ catalyst,Fe₂O₃+MnO₂/TiO₂ catalyst,Fe₂O₃+2MnO₂/TiO₂catalyst and Fe₂O₃+4MnO₂/TiO₂ catalyst.The results showed that the CeO₂+2MnO₂/TiO₂ catalyst had the best denitrification efficiency the best pore structure parameters,the most acidic sites on the surface,and the best reducibility.The Fe₂O₃+2MnO₂/TiO₂ catalyst and Fe₂O₃+4MnO₂/TiO₂ catalyst had the best denitrification efficiency,the best pore structure parameters,the most acidic sites and the best reducibility.