Na co-cations promoted stability and activity of Pd/SSZ-13 for low-temperature NO adsorption

The abatement of harmful nitrogen oxides (NOx) emission during vehicle cold start is challenging. Passive NOx adsorbers (PNAs) have proven to effectively alleviate NOx emission at low temperatures. In this work, Pd-based Na-SSZ-13 (Pd/Na-13) was synthesized and hydrothermally aged to investigate the effect of Na co-cations on the structure and activity of Pd/SSZ-13 for low-temperature NO adsorption. Compared to Pd-based NH4-SSZ-13 (Pd/NH4-13), Pd/Na-13 exhibited superior stability and activity promoted by Na co-cations in SSZ-13. DRIFTS and Al-27 MAS NMR demonstrated that Na co-cations protected Si-O(H)-Al bonds and thus helping to mitigate dealumination during hydrothermal aging. NO- and CO-DRIFTS studies proved that Pd2+ sites existed in aged Pd/Na-13 dominantly. Strikingly, the aged Pd/Na-13 exhibited excellent adsorption capacity with additional NO adsorption at above 100 degrees C. Our work reveals the co-cation effects on the local environments of Pd/SSZ-13, expecting to provide guidance on the catalyst modification or optimization for low-temperature NO adsorption.