National Engineering Laboratory for VOCs Pollution Control Technology and Equipment, Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy, South China University of Technology, 510006 Guangzhou, China.
Department of Chemical and Metallurgical Engineering, School of Chemical Engineering, Aalto University, 02150 Espoo, Finland.
Environ Sci Technol. 2023 Mar 7;57(9):3467-3485. doi: 10.1021/acs.est.2c06207. Epub 2023 Feb 20.
It remains a major challenge to abate efficiently the harmful nitrogen oxides (NO) in low-temperature diesel exhausts emitted during the cold-start period of engine operation. Passive NO adsorbers (PNA), which could temporarily capture NO at low temperatures (below 200 °C) and release the stored NO at higher temperatures (normally 250-450 °C) to downstream selective catalytic reduction unit for complete abatement, hold promise to mitigate cold-start NO emissions. In this review, recent advances in material design, mechanism understanding, and system integration are summarized for PNA based on palladium-exchanged zeolites. First, we discuss the choices of parent zeolite, Pd precursor, and synthetic method for the synthesis of Pd-zeolites with atomic Pd dispersions, and review the effect of hydrothermal aging on the properties and PNA performance of Pd-zeolites. Then, we show how different experimental and theoretical methodologies can be integrated to gain mechanistic insights into the nature of Pd active sites, the NO storage/release chemistry, as well as the interactions between Pd and typical components/poisons in engine exhausts. This review also gathers several novel designs of PNA integration into modern exhaust after-treatment systems for practical application. At the end, we discuss the major challenges, as well as important implications, for the further development and real application of Pd-zeolite-based PNA in cold-start NO mitigation.
在发动机运行的冷启动期间，有效减少有害氮氧化物（NO）仍然是一个主要挑战。被动氮吸附剂（PNA）可以在低温（低于 200°C）下暂时捕获 NO，并在较高温度（通常为 250-450°C）下将存储的 NO 释放到下游选择性催化还原单元中以完全消除，有望减轻冷启动 NO 排放。在本综述中，总结了基于钯交换沸石的 PNA 在材料设计、机理理解和系统集成方面的最新进展。首先，我们讨论了用于合成具有原子 Pd 分散度的 Pd-沸石的母体沸石、Pd 前体和合成方法的选择，并回顾了水热老化对 Pd-沸石性能和 PNA 性能的影响。然后，我们展示了如何整合不同的实验和理论方法，以深入了解 Pd 活性位的性质、NO 存储/释放化学以及 Pd 与发动机废气中典型成分/毒物之间的相互作用。本综述还汇集了几种将 PNA 集成到现代排气后处理系统中的新颖设计，以实现实际应用。最后，我们讨论了在冷启动 NO 减排中进一步开发和实际应用基于 Pd-沸石的 PNA 所面临的主要挑战和重要意义。
