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

The abatement of harmful nitrogen oxides (NO x ) emission during vehicle cold start is challenging. Passive NO x adsorbers (PNAs) have proven to effectively alleviate NO x 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 NH 4 -SSZ-13 (Pd/NH 4 -13), Pd/Na-13 exhibited superior stability and activity promoted by Na co-cations in SSZ-13. DRIFTS and 27 Al 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 Pd 2+ 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 °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. The hydrothermally aged Pd/Na-13 showed superior stability and activity with an additional adsorption, as well as satisfactory desorption behaviors for the majority of NO x desorption below 350 °C compared with aged Pd/NH 4 -13. • The Pd/Na-13–750A showed higher hydrothermal stability than Pd/NH 4 -13–750A. • The Pd/Na-13–750A possessed higher storage capacity than Pd/NH 4 -13–750A. • More Pd 2+ balanced by two near Al sites was observed in Pd/Na-13–750A. • The Pd/Na-13–750A exhibited an additional NO x adsorption. • The majority of NO x desorbed below 350 °C for Pd/Na-13–750A.