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

Ying Li, Dongdong Chen, Xin Xu, Xinyu Wang, Running Kang, Mingli Fu, Yanbing Guo, Peirong Chen*, Yongdan Li, Daiqi Ye

*Corresponding author for this work

Research output: Contribution to journalReview Articlepeer-review

12 Citations (Scopus)
16 Downloads (Pure)

Abstract

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.

Original languageEnglish
Pages (from-to)3467–3485
Number of pages19
JournalEnvironmental Science and Technology
Volume57
Issue number9
Early online date21 Feb 2023
DOIs
Publication statusPublished - 7 Mar 2023
MoE publication typeA2 Review article, Literature review, Systematic review

Keywords

  • cold-start
  • mechanism
  • NO mitigation
  • passive NO adsorber
  • Pd-zeolite

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