Study Of The Tuning Role Of Li⁺ In The NH₃-SCR Performance Over Supported And Bulk-doped Mn Based Catalysts

At present,China is a major consumer of petrochemical energy.However,with the increasing demand of people for a better environment,how to deal with the burning waste gas and reduce air pollution is an urgent problem to be solved.NO_x is one of the main pollutants in the atmosphere.Currently,NH₃selective catalytic reduction of NO_x?NH₃-SCR?is considered to be an effective method to eliminate NO_x.In this paper,three types of catalysts were synthesized,including single metal Mn-base supported catalyst,Li-Mn oxides bulk catalyst,and Li-Mn composite oxides supported catalyst,with Ti O₂,Zr O₂,Al₂O₃,and Si O₂ as carrier for supported catalysts.For single manganese oxide supported catalysts,the study found that catalysts with Zr O₂ as support have excellent activity,catalysts with Ti O₂ as support have relatively good selectivity.Based on the characterization results,it can be deduced that factors infulencing the catalytic performance mainly includes Mn O_xdispersion,reduction capacity and the temperature of reduction,oxides state of Mn,and concentration of surface adsorption oxygen and hydroxyl oxygen species.The conversion of NO_x reaches 100%over all Li-Mn bulk catalysts in the testing temperature range,at the space velocity being 80 000 m L g^-1 h^-1.At 400 000 m L g^-1 h^-1,the Li inhibits the activity of catalyst,but when the doping amount of Li reaches 10%,the inhibition is the lowest,the activity and selectivity is the best.By characterizations,it is found that moderate amounts of Li can make the catalyst body generated Mn₅O₈ and Li Mn₂O₄,improve catalyst reduction capability to enhance the catalytic performance.In addition,moderate Li also enhances the catalytic performance by adjusting the concentration of Mn ion,hydroxyl oxygen and adsorption oxygen on the catalyst surface.For the Li-Mn oxides supported catalysts,the addition of Li has different influence on the catalyst of different supports.On catalysts with Ti O₂ as support,Li improves the SCR activity at low temperature and decreases the selectivity.On catalysts with Zr O₂ as support,the selectivity of catalysts is improved due to the doping of Li,and catalysts with Al₂O₃ as support is the opposite of it.On catalysts with Si O₂ as support,the doping of Li improved the activity of catalysts,and the selectivity is also improved.Related characterizations indicated that catalytic performance can be promoted with the doping of Li through the changing in dispersion of active components,formation of new phase,reduction capacity,and the concentration of surface Mn ions,hydroxyl oxygen,and surface adsorption oxygen.Such above trends are different on catalysts containg different supports.