柴油机LNT再生过程中铑表面H2还原NOx的详细反应机理

摘要

考虑到柴油机稀燃NOx捕集技术(LNT)浓燃再生阶段会产生较多的H2,研究了H2在Rh催化剂表面还原NOx的反应.建立了Rh表面H2-NO反应体系的详细化学反应机理模型,该模型包括6种气相组分、10种表面组分及19步基元反应,其中包括NH3及N2O等重要中间产物的生成反应.对该反应体系进行了数值模拟,其结果与文献中的试验数据吻合良好,并进一步对表面组分覆盖度、NO反应路径和各基元反应的敏感性系数进行了分析.结果表明,在H2体积分数相对较低的条件下((O)(NO)/(O)(H2)=1.95),150～310℃温度内,NO还原过程中有大量N2O生成,且最终产物N2主要是通过Rh表面吸附态N2O解离生成.同时,敏感性分析表明,N2O的相关基元反应对NO还原有着重要影响.%As non-negligible amount of H2 is generated during rich regeneration period of diesel lean NOx trap (LNT),the abatement of nitrogen oxides by H2 over rhodium catalyst was investigated in this study.A detailed mechanism model of H2-NO reaction over Rh was proposed and used to simulate the NO reduction.The model consists of 6 gas phase species,10 surface species,and 19 elementary reaction steps,including the formation of several important intermediates,such as NH3 and N2O.The proposed mechanism is capable of predicting the experimental results from the literature.The coverages of the surface species,NO reduction pathway,and sensitivity of several typical elementary reactions were studied for better understanding of the reaction.Results show that under relatively low H2 condition ((O)(NO)/(O)(H2) =1.95)and temperature range of 150-310 ℃,large amount of N2O is produced during the H2-NO reaction,and the desired product N2 is mostly generated through the dissociation of adsorbed N2O.Sensitivity analysis shows that N2O related elementary reactions play a crucial role in the reduction of NO over rhodium.