Cold-Start NOx Mitigation by Passive Adsorption Using Pd-Exchanged Zeolites: From Material Design to Mechanism Understanding and System Integration

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A2 Katsausartikkeli tieteellisessä aikakauslehdessä
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Environmental Science and Technology, Volume 57, issue 9
It remains a major challenge to abate efficiently the harmful nitrogen oxides (NOx) in low-temperature diesel exhausts emitted during the cold-start period of engine operation. Passive NOx adsorbers (PNA), which could temporarily capture NOx at low temperatures (below 200 °C) and release the stored NOx at higher temperatures (normally 250-450 °C) to downstream selective catalytic reduction unit for complete abatement, hold promise to mitigate cold-start NOx 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 NOx 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 NOx mitigation.
Funding Information: This work was supported by the National Natural Science Foundation of China (21976058), the Science and Technology Program of Guangzhou (202102080490), the Fundamental Research Funds for the Central Universities (2022ZYGXZR018), and the National Engineering Laboratory for Mobile Source Emission Control Technology (NELMS2020A10). P.C. appreciates the funding from the Pearl River Talent Recruitment Program of Guangdong Province (2019QN01L170) and the Innovation & Entrepreneurship Talent Program of Shaoguan City. The authors appreciate the fruitful discussions and helpful suggestions from Dr. Kunpeng Xie (Volvo Group Trucks Technology). Publisher Copyright: © 2023 American Chemical Society.
cold-start, mechanism, NO mitigation, passive NO adsorber, Pd-zeolite
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Li, Y, Chen, D, Xu, X, Wang, X, Kang, R, Fu, M, Guo, Y, Chen, P, Li, Y & Ye, D 2023, ' Cold-Start NO x Mitigation by Passive Adsorption Using Pd-Exchanged Zeolites: From Material Design to Mechanism Understanding and System Integration ', Environmental Science and Technology, vol. 57, no. 9, pp. 3467–3485 .