Pd-based zeolite passive NOx adsorbers (PNAs) can mitigate diesel cold-start emissions; however, their NOx storage capacity and stability are severely limited by hydrocarbon poisoning. Here, we engineer PdCu/SSZ-13 with Pd cations confined in six-membered rings and Cu cations located in adjacent eight-membered rings in the CHA framework. Relative to Pd/SSZ-13, PdCu/SSZ-13 achieves an NOx uptake of 145.8 μmol·g-1 under the NO+CO atmosphere and retains 113.8 μmol·g-1 in the presence of C3H6, corresponding to an NOx storage efficiency of >83% after 5 min. Cu incorporation further increases C3H6 uptake from 314.2 to 454.8 μmol·g-1 under 2000 ppm of C3H6 and enhances the hydrophobicity of PdCu/SSZ-13. Spectroscopic characterization and density functional theory calculations identify Pd-O-Cu as the key structural configuration that stabilizes Pd electronically and spatially, suppresses C3H6-induced reduction of Pd and its detachment from framework charge-compensation sites, and thereby inhibits subsequent Pd agglomeration during heating. By preserving isolated Pd adsorption centers while promoting hydrocarbon capture, the Pd-O-Cu configuration resolves the central trade-off between NOx storage and hydrocarbon tolerance. This work provides a design principle for hydrocarbon-resistant Pd-based PNAs for diesel exhaust aftertreatment.
Gao et al. (Mon,) studied this question.