Decomposition Of Nitrogen Oxides Catalyzed By Supported Metal Catalysts

Nitrogen oxides?NO_x?is one of the major pollutants in the atmosphere,and its excessive emissions will not only cause environmental problems such as acid rain,photochemical smog,haze and so on,which will seriously endanger human health and ecological environment.Therefore,how to efficiently and cost-effectively remove nitrogen oxides from industrial flue gas is of great significance to the prevention and control of atmospheric pollution.Among the many nitrogen oxide removal methods,the catalytic removal method is the most promising and economical method,which the catalyst is the core of the method.Since the flue gas discharged from industrial coal-fired boilers has the characteristics of high temperature,high concentration of dust and SO₂,it is easy to cause catalyst deactivation.To reduce the influence of these factors on the catalyst,the denitration reactor can be placed after the dust removal and desulfurization,but the flue gas temperature is below 300?,it is difficult to meet the reaction temperature of traditional catalyst V2O5-WO3/TiO₂,if the flue gas heated to 350? or more,will undoubtedly increase operating costs.Therefore,the development of low temperature and efficient denitration catalyst is the key to nitrogen oxide catalytic removal method.In this paper,a series of supported metal oxide catalysts are prepared by impregnation method.The activated carbon is pretreated with nitric acid as the surppotor,Ni,Cu and Mn as the active components,and supplemented with rare earth cerium oxide.The effects of catalyst preparation conditions and the flue gas conditions on the decomposition activity of the catalyst are investigated.The reaction mechanism of catalyst catalytic decomposition of NO is analyzed by means of BET,FTIR,XRD and TEM.In the direct catalytic decomposition of NO reaction system,the activity of three different metal oxides is NiO>CuO>MnO₂,and the doping of CeO₂ can further improve the activity of NiO/AC,in which Ce4+/Ce3+ and Ni2+/Ni3+ have strong redox ability to speed up the reduction and oxidation cycle,thereby increasing the NO conversion rate.The results of XRD and TEM show that NiO and CeO₂ are uniformly dispersed on the surface of activated carbon by co-impregnation method,and the NiO and CeO₂ are in the form of amorphous state.When the loading of NiO and CeO₂ is 5% and 3% respectively,the catalyst has the optimum activity,when the temperature is at 300 ?,the NO concentration is between 200⁶00ppm,the space velocity is between 3900⁵850h-1,O₂% is between 1⁸%,the NO conversion can be maintained at 90⁹9%.This catalyst is used for direct catalytic decomposition of NO,with the advantages of high operational flexibility,strong antioxidant activity and high denitrification rate.The process does not require the use of NH3 and other toxic flammable and explosive gases as a reducing agent,which can avoid secondary pollution and reduce the risk of denitrification process.In this paper,the low temperature SCR performance of catalysts MO_x/AC and MO_x-CeO₂/AC are studied.The results show that the order of low temperature SCR activity of three different metal oxides is MnO₂>CuO>NiO.In the low temperature SCR reaction system,MnO₂ has a good low temperature SCR activity.XPS indicates that the Mn element in MnO₂-CeO₂/AC is mainly in the form of Mn4+.And the Ce element mainly coexists with Ce4+ and Ce3+,which can enhance the transfer between electrons and facilitate the regeneration of the active sites,which makes MnO₂-CeO₂/AC show good low temperature SCR activity.When the loading of MnO₂ and CeO₂ is 5% and 3%,respectively,the activity of this catalyst is the best,when the reaction temperature is 75 ?,the n?NH3/NO?=1,the space velocity is between 3900⁹749h-1 and O₂% is between 3⁷%,the NO conversion of the this catalyst can be maintained at about 90⁹9%.This catalyst can be placed in the dust and desulfurization device,which without reheating,can effectively reduce operating costs,and the required reaction temperature is as low as 75?,can avoid the danger of high temperature SCR reactor and steam to the human body.