The Passive NOx Adsorber (PNA) is an emerging technology to abate cold-start NOx emissions from lean combustion vehicles. Binding sites on Pd-exchanged zeolites adsorb NO at low temperature (< 150 °C) and release NO and NO₂ at higher temperature, enabling their downstream reduction. The impacts of other exhaust components such as H₂O, hydrocarbons (HCs) and CO, along with operating conditions including temperature and flowrate must be quantified and understood in order to develop effective PNA materials. We have conducted a systematic set of experiments of the NOx uptake and release features on Pd-exchanged SSZ-13 in the absence and presence of several diesel exhaust components. The NO uptake approaches NO/Pd ∼ 1 for a range of conditions, and along with the generation of NO₂ during NO feed and CO₂ (CH₃CHO) during NO + CO (NO + C₂H₄) co-feed, suggests the reduction of well-dispersed Pd cations. The total NO uptake between 50 and 150 °C is nearly constant but occurs in both lower temperature (< ∼120 °C) and higher temperature (>120 °C) regimes, indicating competition of NO uptake with H₂O. The additions of CO and C₂H₄ increase the lower temperature uptake and higher temperature release of NO, both features desirable for application. In contrast, H₂, dodecane, and toluene have a negligible effect on the NO uptake. During NO uptake the co-generation of NO₂, CO₂ and CH₃CHO, respectively with reductants NO, CO, and C₂H₄, provides evidence for the reduction of Pd²⁺ in the form of [Pd(OH)]⁺ bound to zeolitic anionic sites [Al-O-Si]⁻ and/or PdO₂ clusters. Supporting DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) measurements identify several potential surface species that are linked to the multiple NO + NO₂ desorption peaks. Two prospective mechanistic schemes are proposed that are consistent with the uptake/release and DRIFTS data.

被动式NOx吸附器（PNA）是一种新兴技术，可减少稀燃汽车的冷启动NOx排放。Pd交换沸石上的结合位点在低温（<150°C）下吸附NO，并在高温下释放NO和NO ₂，从而使其下游还原。为了开发有效的PNA材料，必须量化和理解其他排气成分（例如H ₂ O，碳氢化合物（HCs）和CO）的影响以及包括温度和流量在内的运行条件。在不存在多种柴油机废气成分的情况下，我们对钯交换的SSZ-13上的NOx吸收和释放特性进行了系统的实验。在一定条件下，随着NO的生成，NO的吸收接近NO / Pd〜1₂ NO进料和CO时₂（CH ₃ NO + CO期间CHO）（NO + C ₂ H ^ ₄）共同进料，建议充分分散的钯阳离子的还原。在50至150°C之间的总NO吸收几乎恒定，但在较低温度（<〜120°C）和较高温度（> 120°C）两种情况下均发生，表明NO吸收与H ₂ O竞争。 CO和C ₂ H ₄增加了低温下NO的吸收和高温释放的能力，这两个特性都是应用所希望的。相反，H ₂，十二烷和甲苯对NO吸收的影响可忽略不计。在NO吸收过程中，NO ₂，CO₂和CH ₃ CHO分别与还原剂NO，CO和C ₂ H _4一起提供了以键合于沸石阴离子位点[Al-O-Si ]的[Pd（OH）] ⁺形式还原Pd ^2+的证据。] ^-和/或PdO ₂簇。支持的DRIFTS（漫反射红外傅里叶变换光谱）测量可识别与多个NO + NO ₂解吸峰相关的几种潜在表面物质。提出了两种与吸收/释放和DRIFTS数据一致的预期机制。