Elucidating the Role of Ce in Enhancing Phosphorus Poisoning Resistance of Pd-SSZ-13 for Passive NOx Adsorber

Passive NOx adsorber (PNA) based on palladium-loaded small-pore SSZ-13 zeolite (Pd-SSZ-13) is attractive for mitigating cold-start NOx emissions from lean-burn engines, but its practical deployment is hampered by susceptibility to chemical poisons—most notably phosphorus (P) poisoning present in vehicle exhaust. In this work, cerium (Ce) is introduced for the first time as a promoter to enhance the P-tolerance of Pd-SSZ-13. Activity measurements show that, after exposure to P-containing conditions, the Ce-doped catalyst adsorbs ~47.9 µmol/g of NOx, which is markedly higher than that of the unmodified counterpart (~39.9 µmol/g). Comprehensive characterization (in situ DRIFTS, in situ UV-Vis, XPS, HAADF-STEM, and H2-TPR) reveals that Ce incorporation stabilizes the framework aluminum associated with Brønsted acid sites and markedly suppresses the deleterious interaction between P and active Pd2+ species, thereby attenuating P-induced deactivation. These findings demonstrate that Ce not only improves resistance of Pd-SSZ-13 to P poisoning but also extends its robustness toward other common poisons (e.g., alkali metals, sulfur species). Consequently, Ce-modified Pd-SSZ-13 emerges as a promising strategy for durable PNA catalysts in real-world exhaust after-treatment systems.