Synthesis Of SmMn₂O₅ And Its Catalytic Oxidation Of NO

Mullite SmMn2O5 material is expected to be used in diesel vehicle exhaust purification,for which has good NO oxidation performance.In this paper,the effects of morphology and Sm doping on the NO oxidation performance of SmMn2Os were studied,providing a basis for the practical application of this material.Using NaCl and Na2SO4 as eutectic salts and Sm2O3 and MnO2 as raw materials,rod SmMn2O5 with a length of about 2-5 um and a diameter of about 150-500 nm was synthesized by molten salt method.The synthesis temperature(700?1000?)and the proportion of molten salt had little effect on the morphology of the sample.When the ratio of raw material to molten salt was 1:5?1:10?1:15,the highest conversion rate of NO oxidation was 58.9%,64.5%and 52.4%,respectively.XPS test proved that the higher the content of Mn and Mn4+ions in the sample,the higher the NO conversion efficiency of the catalyst.SmMn2O5 samples were synthesized by hydrothermal method.When PH=8,particles with a sample length of 10?50 nm,and when PH=12,nanorods with a length of 300?600 nm and a diameter of 20?30 nm.When PH=8,10 and 12,the highest conversion rate of NO oxidation was 83.8%,86.7%and 89.9%,respectively.The corresponding temperature of the highest conversion rate was reduced from 300? to 275?.Compared with the granular samples,the surface of the rod-shaped samples has more Mn and Mn4+,as well as better adsorption capacity of NO,improving its NO oxidation performance.In situ infrared diffuse reflectance spectra showed that NO oxidation mainly occurred at the Mn site,and Mn bidentate nitrate and monodentate nitrite were the main intermediate products.The sample Sm1-xSrxMn2O5(x=0?0.5)was hydrothermally synthesized.The samples gradually changed from 30?50 nm granule to 30?50 nm diameter and 150?200 nm length nanorods.The highest conversion rate of NO oxidation increased from 69%to 83%,and the corresponding temperature decreased from 325? to 275?.When x=0.1?0.4,Sr doping improves the hydrothermal aging stability of the sample.With the increase of Sr doping amount,the ratio of Mn/Sm Mn4+/Mn3+on the surface of the sample increases,and the stability of Mn bidentate nitrate and monodentate nitrite decreases,so the sample has better NO oxidation performance.