Research On Low-temperature SCR Catalysts For Nitrogen Oxides Removal From Waste Incineration Power Plant Flue Gases

With the continuous development of the economy,the output of domestic waste is increasing rapidly.The waste incineration technology has a wide range of application prospects.However,secondary pollutants such as nitrogen oxides would be generated in the incineration process.Selective catalytic reduction（SCR）is widely used in waste incineration plants to remove nitrogen oxides.Among them,the ammonia selective catalytic reduction method（NH₃-SCR）has the high denitration efficiency and mature technology.The core of this technology is a high-performance catalyst.Considering the service life of the SCR catalyst,in practical applications,waste incineration plants usually adopt different heating methods to adjust the temperature of the flue gas before entering the SCR denitrification unit to 160～240°C.However,the acid gases HCl and other substances produced in the waste incineration process could easily cause catalyst deactivation and reduce the denitrification efficiency.Therefore,it is necessary to develop catalysts that have good low-temperature denitrification activity and excellent resistance to the acid gas and water.In recent years,Ce-based catalysts have been widely used in SCR reactions due to the excellent oxygen storage capacity and excellent redox performance.Mo O₃ is usually used as structure and chemical additives to improve the surface acidity of the catalyst.The Sb species can increase the mobility of chemically adsorbed oxygen on the catalyst surface,thereby increasing the SCR reaction activity.Therefore,this article focused on the cerium oxide catalyst,prepared MoCe and SbCe catalysts by adding Mo and Sb,and conducted research on them.The major work and conclusions are as follows:（1）MoCe catalyst was prepared by the co-precipitation method.The low-temperature SCR activity,resistance to HCl,SO₂ and H₂O poisoning performance were studied.The test results showed that the Mo:Ce=0.1:1 catalyst had excellent HCl resistance,and could achieve 85%NO removal rate at 180°C.The NO removal rate could be maintained above 85%after 10 hours of reaction with 50 ppm SO₂ at 200°C.The NO conversion rate could be stabilized at 80%after 13 hours of reaction with 5%H₂O.The characterization results showed that the concentration ofCe³⁺and chemisorption oxygen species on the surface of the catalyst increased after the HCl treatment.In addition,the increase in the acidity of the catalyst surface promotes the adsorption of NH₃,which is conducive to the SCR reaction.（2）In order to further improve the catalyst’s nitrogen selectivity and resistance to HCl poisoning,the SbCe oxide catalyst has been studied in depth,and on this basis,a more suitable SbCe/TiO₂ catalyst for industrial applications has been designed.The test found that the Sb:Ce=1.3:1 catalyst could achieve 92%NO removal rate at 180°C.After HCl treatment,the low-temperature activity and N₂ selectivity of the catalyst were significantly improved.The main reason was that HCl was oxidized into chlorate species.This species could promote the formation of oxygen vacancies and increased the exchange capacity of surface oxygen,thereby promoting the low-temperature activity of the SCR reaction.In addition,HCl treatment promoted the formation of Sb³⁺-OH species.This species could react with NH₃ to produce Sb³⁺-O-NH₄⁺and enhanced the acidity of Br（?）nsted acid sites on the catalyst surface.It would promote the reaction between the coordination of Br（?）nsted acid sites NH₄⁺species and NO₂ to produces N₂ and H₂O.Therefore,the N₂ selectivity of the SbCe catalyst had been significantly improved.The NO conversion rate of SbCe/TiO₂ catalyst is more than 80%at 190～405°C,and the N₂ selectivity can be maintained above 70%.