We have applied transient response methods to study Pd-CHA systems as Passive NOx Adsorbers (PNA) for the low-temperature NOx removal from Diesel exhausts. NO adsorption/TPD experiments were carried out at different temperatures in gaseous mixtures containing the main exhausts components (O₂, CO, H₂O) with the aim to clarify the mechanism determining the capability of Pd-CHA to trap and desorb NO. Pd^I was identified as the main NO storage site, both in mixtures containing a strong reductant like CO and in the presence of O₂ only. When the oxidizing capability of the environment was enhanced, the Pd utilization, i.e. NO _stored/Pd_tot, dropped significantly: this loss is attributed to the competition between the NO storage on the reduced Pd sites and their re-oxidation. Pd oxidation played an important role also in the desorption phase: TPD experiments performed in gaseous mixtures with greater oxidizing strength enabled NO desorption at lower temperatures. The present data emphasize therefore the impact of the Pd redox state on the NO storage/release performances of Pd-CHA based PNAs.

我们已经应用瞬态响应方法来研究Pd-CHA系统作为被动NOx吸附剂（PNA），以从柴油机废气中去除低温NOx。在含有主要排气成分（O ₂，CO，H ₂ O）的气体混合物中，在不同温度下进行了NO吸附/ TPD实验，目的是阐明确定Pd-CHA捕集和解吸NO能力的机理。在含有强还原剂（如CO）的混合物中以及仅在O ₂的存在下，Pd ^I被确定为主要的NO储存位点。当环境的氧化能力得到提高，钯利用率，即NO_存储/钯_TOT，大大降低：这种损失归因于还原的Pd位点上的NO储存与其再氧化之间的竞争。钯的氧化在解吸阶段也起着重要作用：在具有更高氧化强度的气体混合物中进行的TPD实验使得NO在较低的温度下解吸。因此，本数据强调了Pd氧化还原状态对基于Pd-CHA的PNA的NO储存/释放性能的影响。