Study On Sulfur Poisoning And Online Regeneration Of Catalyst For Low-temperature SCR Denitration

Mn-based catalyst has excellent low-temperature activity but is easy to be poisoned in the presence of SO₂ and H₂O.Thermal reduction regeneration can change the regeneration temperature,regeneration atmosphere and regeneration time without moving the catalyst,realize the online regeneration of the catalyst and guarantee the continuous operation of SCR system.It can also effectively reduce the raw material cost and transportation cost.As a result,thermal reduction regeneration is significant for the industrial application of low temperature catalyst regeneration.In this paper,Mn-Ce-Fe/TiO₂ catalyst was prepared and its macroscopic sulfur poisoning process were analyzed.Online regeneration experiment was followed next.Changes in physical and chemical properties before and after catalyst poisoning were analyzed by the characterization methods of TG?H2-TPR?XRD?XPS?BET?XRF?SEM?in situ DRIFTS.Particle Mn_0.4Ce_0.07Fe_0.1/TiO₂ catalyst was prepared by impregnation method.The denitrification efficiency was above 80%in the temperature range of 120°C³20°C.Low concentration of SO₂ had a little effect on the catalyst.The low temperature?under 200??efficiency of the catalyst which was poisoned for 6 hours under the atmosphere of 400ppm SO₂ was less than20%,but still near the fresh level when above 280?.In situ DRIFTS experiments were followed to investigate the active species and intermediate products during SCR process.The results showed that the existence of SO₂ would increase the Br?nsted acidity,but it would also lead to a significant weakening of the Lewis acidity of the catalyst,which affected the adsorption of coordination NH₃.Introduction of SO₂ also produced a large amount of sulfate on the surface of the catalyst.These sulfate will compete with NO for adsorption and seize active sites.In the process of SO₂ poisoning,ammonium sulfate like?NH₄?₂SO₄ and NH₄HSO₄ were produced,a large portion of Mn oxides were sulfated and MnSO₄ was produced,resulting the decrease of specific surface area and the increase of the surface S content.Transition metal was doped into the TiO₂ lattice during the reaction and influenced the crystal structure of TiO_2.Part of Mn elements changed from Mn⁴⁺,Mn³⁺to Mn²⁺.The loss of the amount of surface-active oxygen directly led to the decrease of the ability of the catalyst to reduce NO_X.Online regeneration experiments of the particle catalyst after sulfur poisoning were followed in this study.The influence of temperature,atmosphere and time on the recovery of particle catalyst activity was investigated.Thermal regeneration of air had a better activity of catalyst in the three regeneration atmospheres.The efficiency at 180?after regeneration at 450°C in air could recover to70%of the fresh level.The regeneration time has little effect on various regeneration atmospheres,and a regeneration time of 1h or more is sufficient to enable the complete decomposition of the material.The result of NH₃ regeneration had little difference from the air.The catalyst during120?³20?performed poorly after regeneration in H₂ atmosphere.The result of characterization showed that fine particles attached to the surface of the air-regenerated catalyst are significantly reduced,the surface tends to be smooth,the degree of dispersion is improved,and the degree of agglomeration is reduced.NH₃ regeneration could only decompose ammonium sulfate at 550°C.H₂generation could reduce the generated MnSO4,which led to the decrease of S element in catalyst.But MnTiO3 solid solution was formed during the reduction process,sintering and hole collapse was accompanied at the same time,leading to a great reduction of specific surface area and pore volume.The large decrease in Lewis acid sites is also one of the reasons for the low temperature efficiency of poisoned catalysts.