Preparation Of Manganese Based Catalyst For Low-temperature SCR Of NO And Its Performance

Nitrogen oxides(NO_x)are one of the main air pollutants in atmospheric environment.With the rapid development of national economy,the NO_xemissions of our country increased year by year,and the pollution is becoming more and more serious.Ammonia selective catalytic reduction(SCR)of NO_x is a more feasible and practical technology in many methods for de NO_x,which has been applied in a fixed source NO_x removal.Catalysts are the key to this technology.V₂O₅-WO₃(Mo O₃)/Ti O₂catalysts are the most effectively and widely used to reduce the NO_x emitted from the station source as the coal-fired power plant.However,there were still several significant drawbacks in these catalysts,such as poor activity below 300 ?,narrow operation temperature window(300-400 ?),and low N₂ selectivity,high conversion of SO₂ to SO₃at high temperature and toxicity of VO_x to the eco-environment and human health.The exhaust temperature of flue gas is lower than 300 ? in cement ceramics and glass and other enterprises of our country,especially after dust removal and desulphurization.More and more researchers were intending to develop novel non-vanadium NH₃-SCR catalysts with high activity,excellent SO₂ resistance and wide reaction temperature windows.In this dissertation,manganese oxide is chosen as the main catalyst,which has excellent redox properties.The nickel,cobalt,cerium and titanium are used for modifying for obtaining the target catalyst,which shows outstanding performance of SCR of NO_x and high N₂ selectivity.Various characterization methods are used for investigating the promotion mechanism of SCR of NO_x and excellent anti-SO₂ performance over modifying manganese-base catalyst.The Ni-Mn oxides were synthesized as the catalysts for SCR,which were investigated by different preparation,methods,different roasting temperature,different Ni/(Mn+Ni)molar ratios and different GHSV.The results show that the Ni_0.4-Mn O_xprepared by the combustion of citric acid and calcined at 400 ? has the best activity in the condition of 40,000 h^-1,which obtained more than 90%the de NO_x efficiency in90-240 ?.Ni_0.4-Mn O_x catalyst was evaluated accompanying with a certain amount of SO₂ and H₂O in exhaust fumes;the purpose was to modify the surface properties of Ni_0.4-Mn O_x catalyst.The used catalyst Ni_0.4-Mn O_x-SH exhibited NO conversion of100%and about N₂ selectivity of 98%in a wide reaction temperature range of 90-360?.The characterization results suggested that the resistance tests of SO₂ and H₂O leaded to the change of Ni_0.4-Mn O_x surface structure.The enhancement of NH₃adsorption,more content of Ni³⁺species,structural defects and less Mn⁴⁺,Mn³⁺species were formed on the surface of Ni_0.4-Mn O_x-SH,the modification of SO₂vulcanization can promote the formation of Br?nsted acid level at the same time,which is beneficial for NH₃-SCR reaction.The Ni-Mn-Ti oxides were synthesized as the catalysts for SCR,which were investigated by different preparation methods,different roasting temperature,different Ti/Mn+Ni and Ni/Mn mole ratio and GHSV.The results show that the Ni_0.4Mn_0.6Ti₁₀prepared by sol-gel method and calcined at 500 ? has the best activity in the condition of 40,000 h^-1,which obtained nearly 100%the denitration efficiency in 190-300 ?.The characterization results suggested that the moderate amount of Ni doping is conducive to the interaction between different metals and increased the Lewis acid on the surface of the catalyst with appropriate oxidation-reduction quality.It is beneficial for broadening the operating temperature window,enhancing N₂ selectivity and SO₂resistance.At the same time,the SCR reaction of Ni_0.4Mn_0.6Ti₁₀ catalyst mainly obeys the E-R mechanism.The Co-Ce-Mn-Ti oxides were synthesized.The effect of Co and/or Ce doping on the SCR activity of MnTi₁₀catalyst was studied,the Co_0.2Ce_0.35Mn_0.45Ti₁₀ catalyst showed the excellent activity for NH₃-SCR.The study indicates that the Co and Ce doping can improve the NO conversion and N₂ selectivity,widen the operating temperature window at the same time.The highly dispersed Ce,Co,Mn and Ti can cause strong interaction among these metals,which can lead to more NH₃/NO_xadsorbed species and reduce the redox property.