The Structure Of CrMnO_x Compound Based Catalysts And Their Application For NH₃-SCR At Low Temperature

It is an important issue about how to deal with the NO_x degradation in industry emission in China,a country with abundant of coal and lack of oil and natural gas.At present,SCR process is widely used for NO_x removal in the power plant.In this paper,a series of CrMnO_x and its modified Co-CrMnO_x materials synthesized by citric acid method has been explored.CrMnO_x materials prepared at 300 ^oC and 400 ^oC,with large amorphous structures,possess higher NO_x conversion efficiency than those prepared at450 ^oC and 650 ^oC.The optimized sample,300-10,can reach 95%NO_x removal at 100 ^oC when the dosage is 1.5 g and the GHSV is 40000 mL g^-1 h^-1.According to characterization data,annealing at 300 ^oC for 10 hours facilitates the formation of catalysts possessing the largest surface area,reducibility and acidity.While areal activity is measured at 3.8 nmol s^-1m^-2 and is lower than 300-5 material(11.5 nmol s^-1 m^-2).Further,NH₃-TPD and in situ-DRIFT demonstrates a near-linear correlation between areal activity and Lewis acid site density,indicating its dominance in controlling surface reaction rates.After Co is doped in the CrMn system,the conversion results reveal that 10%Co doping can generate a best material in low operation temperature range?80-140 ^oC?,of which,the NO_x removal efficiency is double than the material without any Co doping,when the dosage is 0.75 g and the GHSV is 80000 mL g^-1 h^-1.While the operation temperature range is increased to 160-240 ^oC,20%Co doping seems to be more beneficial and 0.1 g sample can obtain 80%NO_x conversion at 240 ^oC.It is demonstrated from the characterization that most of the Co element in these material is Co²⁺.During Co doping process,Mn²⁺concentration is decreased and the average valence state of Mnⁿ⁺is increasing,which results into a reducibility increment and thusly improve the catalytic activity to some extent.