Preparation And Modification Of Low-temperature Denitration Catalyst For Manganese Dioxide

The combustion of coal will emit a lot of nitrogen oxides（NO_x）and other pollutants as a result of which NO_x is one of the main culprits of air pollution.Selective catalytic reduction（SCR）technology is the most mature NO_x treatment technology.At present,the NH₃-SCR technology is widely used in coal-fired power plants at home and abroad which not only needs to be above 350℃ but also the catalytic reactor needs to be installed before the dedusting and desulfurization equipment.As a result,the toxic effect of dust and SO₂ in the flue gas is significantly enhanced,and the service life of the catalyst is greatly reduced.However,the low-temperature SCR technology can arrange the catalytic reactor behind the dust removal and desulfurization equipment,which greatly reduces the toxic effect of SO₂ on the catalyst.The research of denitration catalyst in low-temperature SCR technology is of great practical significance to the treatment of NO_x pollution.In this paper,a series of MnO₂ catalysts under different conditions were prepared from common and cheap manganese salt by hydrothermal method,and the performance of low-temperature NH₃-SCR was studied in depth.The results showed that under the conditions of water-solid mass ratio was 20,the hydrothermal temperature was 150℃,the hydrothermal time was 6h,and the molar ratio of Mn²⁺/Mn⁷⁺was 1.5,the catalyst samples has excellent low-temperature NH₃-SCR activity and optimal economy.The NO conversion rate of MnO₂catalyst samples reached over 75%at 100℃ and the rate maintained above 90%within the range of 150-250℃.Secondly,the NH₃-SCR with the participation of vapor and SO₂ was tested for the catalyst samples under the above optimal conditions.The test temperature was 200℃.It was found that the addition of vapor and SO₂ had a great impact on the performance of the low-temperature NH₃-SCR of MnO₂ catalyst.When only vapor（8%volume fraction）was introduced,the NO conversion rate decreased from 90%to 75%,then slowly recovered to about 85%,and then recovers to around 90%after stopping vapor injection.When only SO₂（100ppm）is introduced,the NO conversion rate reduced from 90%to 53%and the rate restored to about 61%after SO₂ is stopped.when vapor and SO₂ are introduced simultaneously,the NO conversion rate dropped from 90% to 48% and the rate recovered to about 49%after the two gases stopped.Finally,in order to improve the poor water and sulfur resistance of MnO₂ catalyst,the element doping modification was studied.Cu and Ce elements were doped by impregnation calcination.It was found that the introduction of Cu can inhibit the low-temperature NH₃-SCR performance of MnO₂ but improve its poor sulfur and water resistance.In addition,the introduction of Ce not only promote the low-temperature NH₃-SCR performance of MnO₂ but also improve the sulfur and water resistance of the catalysts.When vapor and SO₂ were involved in the simulated flue gas,the NO conversion rate is maintained at about 75%in the range of 200-300℃ when molar ratio Cu/Mn=0.5,and the rate remains above 95%in the range of 150-300℃ when molar ratio Ce/Mn=0.3.