Preparation And Application Of Rare Earth Modified TiO₂-based Anti-sulfur Denitration Catalyst

In recent years,the rapid development of industry has brought about huge energy consumption,and the dominant energy structure in China is coal consumption,and its combustion and emission of flue gas have caused serious air pollution.NH₃ selective catalytic reduction of NO?NH₃–SCR?is one of the most important technologies for flue gas denitrification,among which the low-temperature NH₃–SCR is emerging and promising.The catalyst requires a low reaction temperature and is placed downstream of a fixed source desulfurization and dedusting device,thereby effectively avoiding the effect of high sulfur and high dust on the catalyst life.It is normal to use wet desulfurization in China,the flue gas after desulfurization contains a certain amount of water and a small amount of untreated SO_x,thus it determined that the resistance to water and sulfur is an important indicator of low temperature NH₃–SCR catalyst.This paper focuses on the study of SO₂ resistance on rare-earth element samarium-doped TiO₂-based mixed-oxide catalysts,providing theoretical guidance for the design of high-performance Ti O₂-based catalysts for SO₂ resistance.The specific research contents are as follows:?1?A series of Sm-and/or Zr-doped MnO_x-TiO₂ catalysts were prepared,and the catalysts exhibited better N₂ selectivity and SO₂ resistance than the undoped MnO_x-TiO₂ catalyst in the NH₃-SCR reaction.The reasons for the good N₂ selectivity and SO₂ resistance of the catalysts were proposed.XPS combined with DFT calculations suggested that electron transfer between the manganese and samarium species by Mn⁴⁺+Sm²⁺?Mn³⁺+Sm³⁺redox cycles occurred in the Sm-containing catalysts.Furthermore,the electron transfer from Sm²⁺to Mn⁴⁺suppressed the electron transfer from NH₃ to Mn⁴⁺,inhibiting the formation of NH₂ or NH.Thus,the pathway for NH generation was removed,and the reaction of 2NH+4NO?3N₂O+H₂O was prevented.Consequently,the N₂ selectivity of the NH₃-SCR reaction was enhanced.In situ DRIFTS combined with TG-DSC-MS results revealed that the deposition rate of sulfate species decreased after Sm doping,which was also attributed to the suppression of the electron transfer from SO₂ to Mn⁴⁺,i.e.,the oxidation of SO₂ to SO₃.Thus,the catalysts exhibited better SO₂ resistance.?2?A Sm-decorated CeTi mixed oxide catalyst for selective catalytic reduction of NO with NH₃?NH₃-SCR?was prepared by inverse co-precipitation method,which exhibited the excellent catalytic activity and a high tolerance to H₂O and SO₂ in a broadened temperature window.A series of characterization results suggested that electron transferring between the cerium and samarium species by Ce⁴⁺+Sm²⁺?Ce³⁺+Sm³⁺redox cycles occurred in the Sm CeTi catalyst,which would improve redox properties and surface acidity and influence the Ce-O-Ti active sites of the catalyst,further changed the mechanisms of SCR reaction pathway.The reason for the better SO₂ tolerance of the SmCeTi catalyst was proposed.Through in situ DRIFTS and other experimental methods,we believe that the electron transfer from SO₂ to Ce⁴⁺after Sm doping is inhibited.Consequently,the SmCeTi catalysts exhibited better SO₂ tolerance.?3?The effects of Sm doping on the NH₃-SCR reaction performance of TiO₂/CeSmOx?Ce:Sm molar ratio of 80:1,40:1,20:1,10:1,5:1?catalysts were investigated.It was found that a small amount of Sm₂O₃ doping was more conducive to the increase of NH₃-SCR activity of TiO₂/CeO₂ catalysts.The physical and chemical properties of the catalysts were characterized by XRD,Raman,UV-vis,H₂-TPR,NH₃-TPD and other techniques.The in situ DRIFTS technique was used to investigate the reaction mechanism and the surface.The relationship between changes in properties and changes in catalyst activity was elucidated.The following conclusions are drawn:The successful incorporation of Sm into the lattice of CeO₂leads to more oxygen vacancies,which improves the redox properties of TiO₂/CeO₂catalysts,and further adjusts the surface acidity of the catalysts,making the catalysts suitable for redox and surface acidity.The incorporation of Sm does not change the catalytic reaction of TiO₂/CeO₂ catalysts,but it improves the adsorption of NH₃ and NO_x,which is beneficial to the catalytic reaction.