SCR催化剂铂中毒对DeNOx性能影响的研究

随着排放法规日趋严格,DOC-DPF-SCR后处理系统越来越广泛地应用于柴油机。位于SCR催化剂上游的DOC催化剂,其主要活性组分为贵金属铂、钯,氧化态贵金属在高温时可以气化,并能随排气迁移至SCR催化剂表面,在SCR催化剂上沉积,造成SCR催化剂贵金属中毒。将台架试验后中毒的催化剂制备成小样,并对催化剂进行了性能探究,发现贵金属中毒主要影响DeNO_x的高温阶段(300℃以上)效率;同时在试验室制备两种模拟中毒样件:掺杂涂覆样件和表面涂覆样件,研究了SCR催化剂Pt中毒的现象并分析中毒后的反应机理。掺杂涂覆500×10^-6样件试验结果表明,贵金属中毒后催化剂氧化能力显著提升,氨气泄漏量在350℃降低至0;而选择性还原能力大幅下降,NO_x转化效率在450℃下降至56.3%。表面涂覆50×10^-6样件试验结果与掺杂涂覆500×10^-6相当。两种涂覆方法研究结果表明,中毒主要发生在表层,导致内层催化剂利用率低,吸附的氨气很难传递进催化剂内层,被直接氧化为NO_x和N₂O,导致NO_x转化效率降低。

Effect of Platinum Poisoning on DeNO_x Performance of SCR Catalyst

With the increasingly stringent emission regulations,the DOC-DPF-SCR aftertreatment system is more widely used in diesel engine.The main active components of DOC catalyst located upstream of SCR catalyst are noble metals of platinum and palladium.The oxidized noble metals can be gasified at high temperature and can migrate and deposit on the SCR catalyst with the flow of exhaust gas,which results in noble metal poisoning of SCR catalyst.The poisoned catalyst after the bench test was prepared into small samples and the performance of catalyst was investigated.It was found that the poisoning of noble metal mainly affected the efficiency of DeNO_xin the high temperature stage of above 300℃.At the same time,two simulated poisoning samples were prepared in the laboratory,namely inner coating sample and surface coating sample.The Pt poisoning phenomenon of SCR catalyst was studied and the reaction mechanism after poisoning was analyzed.The experimental results of inner coated with 500×10^-6sample showed that the oxidation capacity of catalyst increased significantly and the ammonia leakage reduced to 0 at 350℃after the noble metal poisoning occurred.However,the selective reduction ability decreased significantly and the NO_xconversion efficiency decreased to 56.3%at 450℃.The surface coated with 50×10^-6sample had the similar experimental results with 500×10^-6sample.The two different coating methods showed that the poisoning mainly occurred in the surface layer and hence the utilization rate of inner catalyst was low.The adsorbed ammonia was difficult to enter the inner catalyst layer and was directly oxidized to NO_xand N₂O,which resulted in reduction of NO_xconversion efficiency.