柴油车用钒基催化剂水热老化性能研究

Study on the Hydrothermal Aging Performance of V-based Catalysts for Diesel Vehicles

针对钒系SCR催化剂高温水热稳定性差的问题,通过分析老化前后理化性质与催化性能变化,剖析失活本质。与新鲜样品相比,水热老化后,催化剂活性出现不同程度的降低。催化材料的理化表征测试结果表明,催化剂失活很大程度上是由于催化剂涂层中活性元素钒挥发,导致低温催化活性严重衰减。550℃水热老化后的催化剂样品,NO_(x)起燃温度由199℃升高至220℃。同时,催化剂氨存储量(200℃时)由新鲜态的409.52 mg/L降至137.08 mg/L(550℃水热老化后)。说明较高的排气温度与水汽可能会导致催化剂涂层氨吸附能力衰减,削弱其催化反应的本征活性。此外,水热老化后,材料微观表面结构更为致密,比表面积由新鲜态的29.51 m^(2)/g降至11.95 m^(2)/g(550℃水热老化后),导致污染物气体与催化材料的接触面积减小,一定程度降低了催化效率,导致催化活性降低。

In view of the poor high temperature hydrothermal stability of vanadium-based SCR catalyst,the deactivation essence was analyzed by analyzing the changes of physicochemical properties and catalytic performance before and after aging.Compared with the fresh samples,the activities of catalysts after hydrothermal aging decrease to various degrees.The physical and chemical characterization results of the catalytic materials show that the catalyst deactivation is largely due to the volatilization of the active element vanadium in the catalyst coating,resulting in a severe degradation of low temperature catalytic activity,and the NO_(x) light-off temperature of the catalyst sample after hydrothermal aging at 550℃increased from 199℃to 220℃.Meanwhile,the ammonia storage capacity(at 200℃)of catalyst decreased from 409.52 mg/L in the fresh state to 137.08 mg/L(after hydrothermal aging at 550℃),indicating that the relatively high exhaust temperature and moisture may cause the attenuation of the ammonia adsorption capacity of the catalyst coating,and weaken the intrinsic activity of the catalytic reaction.In addition,the microscopic surface structures of the materials are denser after hydrothermal aging,and their specific surface areas decreased from 29.51 m^(2)/g in the fresh state to 11.95 m^(2)/g(after hydrothermal aging at 550℃),causing a reduced contact area between the pollutant gas and the catalytic materials,which reduce the catalytic efficiency to a certain extent,resulting in a decrease in the activity of the materials.