Low-Temperature SCR DeNO_x Performance Of Activated Coke-Supported Fe-Based Catalysts

As a common atmospheric pollutant,nitrogen oxides?NOx?bring serious harm to the environment and human health.In recent years,selective catalytic reduction?SCR?with ammonia as reducing agent is the main method to reduce NO_X emission.Low-temperature SCR catalysts have become a hot spot of research on denitration catalysts,which was due to placing in the desulfurization and dust removal process,so as to avoid reheating of flue gas and other issues.Fe-based catalyst is a kind of low-temperature SCR catalyst with relatively good activity.However,the main problems which restrict its industrial application are narrow temperature window and poor SO₂ resistance.In this paper,a series of catalysts?Fe/AC,Cr-Fe/AC,Ce-Cr-Fe/AC catalysts?were prepared by impregnating,such as.The low-temperature SCR denitrification performance,physical and chemical properties.and anti-poisoning performance of the catalysts were systematically studied.A series of Fe-based active coke catalysts were prepared by impregnation method.The effects of calcination temperature and Fe loading on the denitrification performance of NH₃-SCR of Fe/AC catalysts were studied at low temperature.The results show the catalyst calcined at 250?and loaded 8%Fe obtain the highest NO_X conversion.The NO_X conversion of Fe/AC?250?catalyst can reach 50%at 140?,and the highest NO_X conversion rate can reach more than 90%at the effective working temperature window?the temperature of the denitration efficiency higher than 90%?of200-240?.The 8Fe/AC catalyst calcined at 250?exists both Lewis acid sites and Br?nsted acid sites and the mechanisms of L-H and the mechanism of E-R coexist.To further improve the SCR activity of the catalyst,the second active component of Cr was added and the Cr-Fe/AC catalyst was prepared by impregnation method.The effects of Cr doping amount,active coke particle size and flue gas flow rate on the NOx conversion of the catalyst were studied,and the catalyst was characterized.The results showed that the catalyst with 6%Cr doping obtain the highest denitration catalyst activity,and NO_X conversion is more than 90%at 160-240?.The characterization results showed that Cr doping could effectively improve the specific surface area of Fe/AC catalyst.In addition,higher Fe³⁺,Cr³⁺,O_?contents and more acid sites in8Fe6Cr/AC were the reasons for its good denitration activity at high and low temperatures.NH₃-TPD experiment confirmed the existence of Bronsted acid sites and Lewis acid sites in 8Fe6Cr/AC catalyst,and both E-R mechanism and L-H mechanism may contribute to the NOx reduction of 8Mn6Fe/AC catalyst.When the testing temperature below 200?,the particle size of 8Fe6Cr/AC catalyst has a certain influence to it's denitration performance at low temperature.At this temperature,the catalyst of 40-60mm obtained the highest denitration efficiency.When the testing temperature over 200?,the particle size of the catalysts has little impact on the denitration efficiency.The anti-alkali metal,anti-heavy metal,anti-sulfur and anti-water properties of Cr-Fe/AC catalyst were also studied.The results showed that 6Cr8Fe/AC catalyst could resist trace?0.1-0.3%?alkali metal?K,Na?poisoning,but when the alkali metal content exceeded 1%,the catalyst poisoning is more serious with the increase of the alkali metal content.In high concentration of alkali metals,6Cr8Fe/AC catalyst deactivation is serious.The 6Cr8Fe/AC catalyst has good resistance to Pb and Zn poisoning.Even if the heavy metal contents reach 2%,The NO_X conversions of 2Pb/Fresh and 2Zn/Fresh catalysts can reache 50%at 160?.The NO_X conversions of 8Fe6Cr/AC catalyst is 70%in the presence of 5%H₂O,but only 45%NO_X conversion was obtained with 100 ppm SO₂ in the reaction gas.Ce-Cr-Fe/AC catalyst was prepared by impregnation method.Ce doping could effectively improve the resistance alkali metal K,Na of the 8Fe6Cr/AC catalyst,and the optimal amount of Ce is 8%.8Ce1k/Fresh achieved 53%NO_X conversion at 120?,87%NO_X conversion was obtained at 200?;8Ce1Na/Fresh catalyst obtained over 50%NO_X conversion at 120?.Its NO_X conversion was higher 15%than the 1Na/Fresh catalyst at 120-200?.The specific surface area,Fe³⁺and Cr³⁺concentrations and the reductivity of Fresh catalyst were decreased by 1%K/Na poisoning.After Ce modification,specific surface area,Fe³⁺and Cr³⁺concentrations and reductivity reduction were improved to some extent.The Ce modified Fresh catalyst has good sulfur and water resistance in a certain time.The 8Ce/Fresh catalyst was completely water-resistant and sulfur-resistant within 260 min and 400 min,respectively.