Effects of Si/Al Ratio on Passive NO x Adsorption Performance over Pd/Beta Zeolites.

In the current article, the effect of Si/Al ratio on the NO x adsorption and storage capacity over Pd/Beta with 1 wt% Pd loading was investigated. The XRD, 27 Al NMR and 29 Si NMR measurements were used to determine the structure of Pd/Beta zeolites. XAFS, XPS, CO-DRIFT, TEM and H 2 -TPR were used to identify the Pd species. The results showed that the NO x 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 NO x adsorption and storage capacity, while Pd/Beta-Al (Al-rich, Si/Al~6) and Pd/Beta-C (Common, Si/Al~25) exhibit excellent NO x adsorption and storage capacity and suitable desorption temperature. Pd/Beta-C has slightly lower desorption temperature compared to Pd/Beta-Al. The NO x adsorption and storage capacity increased for Pd/Beta-Al and Pd/Beta-C by hydrothermal aging treatment, while the NO x adsorption and storage capacity on Pd/Beta-Si had no change.