In the present work, we report on two passive NO x adsorber (PNA) material candidates: the novel support CeSnO x with and without Pd loading. The NO x adsorption and storage capacities of fresh and hydrothermally aged CeSnO x and Pd/CeSnO x were investigated. The results show that CeSnO x exhibits a rather large NO x uptake and storage capacity (28.9 μmol/g), while the loading of Pd on CeSnO x can further increase the storage capacity to 37.6 μmol/g and affect the desorption temperature of NO x . It was found that the NO x desorption temperature of Pd/CeSnO x was compatible with the efficient operating window of selective catalytic reduction (SCR) catalysts. After a hydrothermal aging treatment at 800 °C for 12 h, the NO x adsorption and storage capacities of CeSnO x and Pd/CeSnO x increased, indicating excellent hydrothermal stability. The interaction of Pd with CeSnO x , the state of Pd species, and the structure of CeSnO x and Pd/CeSnO x are studied by combination of the characterization results.

In the current article, the effect of Si/Al ratio on the NOx adsorption and storage capacity over Pd/Beta with 1 wt% Pd loading was investigated. The XRD, 27Al NMR and 29Si NMR measurements were used to determine the structure of Pd/Beta zeolites. XAFS, XPS, CO-DRIFT, TEM and H2-TPR were used to identify the Pd species. The results showed that the NOx adsorption and storage capacity on Pd/Beta zeolites gradually decreased with the increase of Si/Al ratio. Pd/Beta-Si (Si-rich, Si/Al~260) rarely has NOx adsorption and storage capacity, while Pd/Beta-Al (Al-rich, Si/Al~6) and Pd/Beta-C (Common, Si/Al~25) exhibit excellent NOx adsorption and storage capacity and suitable desorption temperature. Pd/Beta-C has slightly lower desorption temperature compared to Pd/Beta-Al. The NOx adsorption and storage capacity increased for Pd/Beta-Al and Pd/Beta-C by hydrothermal aging treatment, while the NOx adsorption and storage capacity on Pd/Beta-Si had no change.