Study On Mechanism Of SO₂ Poisoning Of Manganese-based Denitration Catalyst

Selective Catalytic Reduction?NH₃-SCR?is considered to be the most widely used technology for removing fixed source flue gas.The core of this technology is catalysts.However,commercial catalysts are susceptible to dust and high concentrations of SO₂under high temperature conditions,so low temperature SCR technology has attracted widespread attention.However,the low temperature SCR catalyst is very sensitive in low concentration of SO₂,which is easy to cause poisoning and deactivation of the catalyst.Aiming at this problem,this paper takes Mn-based low temperature SCR catalyst as the research object to explore the mechanism of poisoning caused by SO₂.Firstly,the effect of SO₂ on the activity of SCR under ammonia-free conditions was investigated by using manganese oxide-supported palygorskite?Mn₈/PG?catalyst.In this study,the effect of SO₂ on SCR activity of the catalysts under ammonia-free conditions was explored,and the mechanism of the catalyst's deactivation by SO₂ was proposed.The catalysts were characterized by elemental analysis?EA?,specific surface area and pore size determination?BET?,X-ray diffraction?XRD?,and temperature programmed reduction?TPR?etc.It was found that the MnO_x/PG catalyst tends to be seriously deactivated by SO₂ in the absence of ammonia.This result obviously stands against the widely believed consideration which regards the formation of ammonia-sulphate as the main reason for the SO₂-deactivation of SCR catalysts.The SCR activity of the deactivated catalyst was found to be completely recovered after simple washing by water.The results of analysis on either catalyst or liquid after washing showed that metal loss of the catalyst is negligible implying that the formation of soluble MnSO₄ can be neglected.On the other side,the filtrate after washing was detected to be acidic with a pH 5.30.Bases on these results,a reasonable mechanism for the deactivation of MnO_x/PG catalyst by SO₂ was proposed in this study.Gaseous SO₂is easily oxidized to SO₃ on the active surface of the catalyst leading to the formation of polysulphuric acid,wrapping the active component and blocking the micro-pores of catalyst.In other words,the deactivation of MnO_x/PG catalyst is initially caused by the formation of polysulphric rather than the deposition of ammonia sulphate which takes place later.In the SCR process,the adsorption of NH₃ and NO was found to be remarkably inhibited,implying that the pore blocking happens.Secondly,themanganeseoxide-supportedvanadium-tungsten-titanium?Mn₅-V-W/TiO₂?catalyst was used to investigate the effect of SO₂ on the catalyst under ammonia-free conditions,and the effect of simple water-washing regeneration on catalyst activity recovery.Based on a series of simultaneous characterizations,the obtained conclusions are consistent with Mn₈/PG.The main cause of catalyst deactivation is the blocking of pores of polysulfate,that inhibiting the adsorption of NH₃ and NO,and thus affecting SCR activity.Finally,the influence of SO₂ on the unsupported catalyst MnO₂ and the oxidation rate of SO₂ on MnO₂ were studied to simulate the active component of Mn-based catalysts affected by SO₂.