不同分子筛负载锰铈催化剂的低温NH_3-SCR脱硝性能

分别以β、ZSM-5和USY分子筛为载体,采用浸渍法制备了锰铈催化剂,对其低温NH_3-SCR反应性能进行了评价,并采用XRD、BET、NH_3-TPD、H_2-TPR以及XPS对催化剂进行了表征。结果表明,三种分子筛负载的锰铈催化剂均具有较好的低温NH_3-SCR反应活性,其中,Mn-Ce/USY的催化性能最好,在107℃时NOx转化率可达到90%。负载锰铈后催化剂的比表面积和孔体积均有所下降;活性组分MnOx主要以无定型态分布于催化剂表面,且在ZSM-5上检测到聚集的CeO_2。催化剂表面弱酸对低温NH3-SCR反应起主要作用,催化剂表面上活性组分的表面浓度和氧化态明显不同,较高的Mn~(4+)/Mn~(3+)原子比和吸附氧表面浓度对提高催化剂的低温NH3-SCR反应活性有利。

Performance of Mn-Ce catalysts supported on different zeolites in the NH3-SCR of NOx

With various zeolites such as β, ZSM-5 and USY as the support, a series of Mn-Ce catalysts were prepared by impregnation method and characterized by XRD, BET, NH₃-TPD, H₂-TPR and XPS; their catalytic performance in the NH₃-SCR of NO_x at low temperature was investigated. The results show that all these catalysts are highly active in the NH₃-SCR reaction at low temperature; especially, over the Mn-Ce/USY catalyst, the conversion of NO_x reaches 90% at 107℃. After loaded of manganese and cerium, the specific surface area and pore volume of supported catalysts are decreased. Amorphous MnO_x as the active component and crystalline CeO₂ are detected on the surface of ZSM-5 zeolite. The weak acid sites on the catalyst surface probably play an important role in the NH₃-SCR at low temperature. Meanwhile, a high atomic ratio of Mn⁴⁺/Mn³⁺ and concentration of adsorbed oxygen may also promote the NH₃-SCR reaction at low temperature.