Pd基分子筛用于柴油车冷启动排放尾气中被动NOx吸附的研究

氮氧化物被动吸附 (passive NOx adsorber, PNA)是削减柴油车尾气冷启动NOx排放的新兴技术，即通过PNA催化材料吸附存储低温工况（<200oC）NOx，然后在中高温释放后通过NH3-SCR反应净化。Pd基分子筛具有较高的NOx吸附能力和优良的水热稳定性，是最受关注的PNA催化材料。本项目拟通过研究Pd基分子筛的分子筛构型、Pd物种分布和化学状态与其NOx吸附/脱附性能的关系， 结合催化性能和表征数据以及理论计算，明确影响Pd基分子筛的NOx吸附/脱附等催化性能和水热稳定性的关键因素；研究水、CO、碳氢、硫等共存气体对Pd基分子筛的NOx吸附/脱附性能影响，尤其是共存气氛对NOx吸附过程中催化剂表面物种的形成情况。本项目将为设计合成高效的Pd基分子筛PNA催化材料用于削减柴油车低温工况NOx排放提供技术思路和理论依据。

Passive NOx adsorber (PNA) is one of the most promising technologies for cold start NOx emission control for diesel engines. In this method, NOx in exhaust temperature below 200oC can be stored by PNA catalyst materials and released at the normal high temperature and then reduced by NH3-SCR system. Pd/zeolites have received much attention as PNA catalyst materials due to their considerable NO adsorption ability and outstanding hydrothermal stability. In this project, the effects of framework structures of the zeolite support as well as chemical state of Pd species on the NOx adsorption/desorption performance of Pd/zeolites will be studied. Moreover, the stability of Pd in Pd/zeolites with different framework structures during hydrothermal aging will be investigated. Based on the results of catalytic performance and characterizations, as well as theory calculations, the factors which are critical to the NO storage capacity/desorption temperatures of Pd/zeolites and their hydrothermal stability will be revealed. Furthermore, the effect of H2O, hydrocarbons, CO, SO2 on the NOx adsorption/desorption performance of Pd/zeolites will be investigated, especially formation of surface intermediates during NOx adsorption process. The results of this project should lead to a deeper understanding of the Pd/zeolites as PNA catalysts and the principles for designing PNA catalysts with high performance to meet the demanding requirements of diesel exhaust purification.