柴油机排气的O_(2)-NO_(2)对碳烟氧化的协同效应

Synergistic Effect of O_(2)-NO_(2) on Soot Oxidation from Diesel Engine Exhaust

柴油机排气温度低于873 K时难以直接氧化碳烟,使得柴油机颗粒捕集器(DPF)要实现低温、高效率的再生面临严峻考验.为了明确DPF内O_(2)-NO_(2)快速氧化碳烟的反应机制,基于量子化学与化学动力学,采用微观机理结合宏观分析的手段,探究了O_(2)-NO_(2)协同氧化碳烟的机理,并对碳烟的氧化进行定性与定量分析.研究表明:O_(2)-NO_(2)对碳烟的活性位有竞争吸附作用,NO_(2)的吸附能明显高于O_(2),但O_(2)与碳烟更易形成C(O)及活性O^(*).NO_(2)易与O_(2)产生的C(O)反应,生成的NO3-可有效氧化活性C*,实现O_(2)-NO_(2)对碳烟氧化的协同效应;中等温度为742 K时,O_(2)与芘基(A4-)反应生成A4O的量保持最多,且O_(2)与NO_(2)摩尔分数比为1/2时,A4-的10 s再生效率最高可达78.1%,NO_(2)摩尔分数越大,则更易于触发协同反应机制,A4-的氧化速率也越快.

It is a severe challenge for the diesel particulate filter(DPF)to achieve low-temperature and high-efficiency regeneration because soot is difficult to be oxidized when the diesel engine exhaust temperature is below 873 K.In order to determine the reaction mechanism of O_(2)-NO_(2)rapidly oxidizing soot in the DPF,the mechanism of O_(2)-NO_(2)synergistic oxidation of soot was explored and the soot oxidation was analyzed qualitatively and quantita-tively based on quantum chemistry and chemical kinetics using microscopic mechanism combined with macroscopic analysis.Results show that the O_(2)and NO_(2)have a competitive adsorption effect on active sites of soot.The adsorp-tion energy of NO_(2)is significantly higher than that of O_(2),but O_(2)is more likely to form C(O)compounds and active O^(*).NO_(2)easily reacts with C(O)produced by O_(2)to generate NO3-which effectively oxidizes active C*atoms,realizing synergistic effect of O_(2)-NO_(2)on soot oxidation.When the medium temperature is 742 K,the amount of A4O produced by the reaction between O_(2)and A4-remains the largest,and when the O_(2)/NO_(2)ratio is 1/2,the maximum 10 s regeneration efficiency of A4-is 78.1%.The larger the proportion of NO_(2),the greater the reaction prone to synergistic reaction mechanism,the faster the oxidation rate of A4-.