Coaxial 3D Printing Enabling Mn/CHA@Pd/CHA Zeolite‐Based Core–Shell Monoliths for Efficient Passive NOx Adsorbers

Abstract

AbstractPd‐based zeolites are extensively used as passive NOx adsorbers (PNA) for cold‐start NOx emissions to meet stringent emission regulations. However, optimizing adsorber design to reduce Pd usage with substitution by non‐noble metals that are prone to suffer from H2O remains a significant challenge. Herein, the core–shell Mn/CHA@Pd/CHA zeolite monoliths based on non‐noble metal/zeolite core are constructed using coaxial 3D printing technology and identified as efficient passive NOx adsorbers for the first time. In the Mn/CHA@Pd/CHA monolith, the Pd/CHA shell effectively protected the Mn active sites in the core from H2O, while the integration of the Mn/CHA core not only introduced efficient storage sites but also facilitated NOx desorption, thereby achieving comparable adsorption properties and increased the NOx desorption efficiency by 35% at 350 °C compared with that of Pd/CHA monolith. Furthermore, some non‐noble metal‐based zeolites (e.g., Co/CHA, Mn/MFI, Mn/BEA) and Pd‐based zeolites (e.g., Pd/AEI) are also employed as cores and shells respectively to fabricate a series of core–shell zeolite monoliths via coaxial 3D printing, highlighting the benefits of incorporating non‐noble metals into Pd‐based zeolites for improving adsorption and desorption behaviors. This work provides a promising strategy for designing cost‐effective PNA materials and contributes to improving the exhaust after‐treatment technology.